Lecture No. 5 Morphology and systematics of microorganisms. Prokaryotes (bacteria and actinomycetes).
1 Morphology and systematics of microorganisms. The morphology of microorganisms studies their appearance, shape and structural features, ability to move, spore formation, and methods of reproduction. Morphological characteristics play an important role in the recognition and classification of microorganisms. Since ancient times, the living world has been divided into two kingdoms: the plant kingdom and the animal kingdom. When the world of microorganisms was discovered, they were separated into a separate kingdom. Thus, until the 19th century, the entire world of living organisms was divided into three kingdoms. At first, the classification of microorganisms was based on morphological characteristics, since people knew nothing more about them. By the end of the 19th century, many species had been described; Various scientists, mostly botanists, divided microorganisms into groups adopted for the classification of plants. In 1897, physiological characteristics began to be used, along with morphological ones, for the taxonomy of microbes. As it turned out later, for a scientifically based classification, any signs alone are not enough. Therefore, a set of signs is used:
Morphological (cell shape, size, motility, reproduction, sporulation, Gram stain);
Cultural (growth pattern on liquid and solid nutrient media);
Physiological-biochemical (nature of accumulated products);
Genotypic (physico-chemical properties of DNA).
Genosystematics makes it possible to determine the type of microorganisms not by similarity, but by relatedness. It has been established that the nucleotide composition of total DNA does not change during the development of microorganisms under different conditions. The S- and R-forms are identical in DNA composition. Microorganisms have also been discovered that have a similar nucleotide composition of DNA, although they belong to different systematic groups: Escherichia coli and some corynebacteria. This indicates that when systematically (taxonomy) of microbes, different characteristics should be taken into account.
Until recently, all living beings with a cellular structure, depending on the relationship of the nucleus and organelles with the cytoplasm, the composition of the cell wall and other characteristics, were divided into two groups (kingdoms):
1.1 Prokaryotes-prenuclear (classified as organisms that do not have a clearly defined nucleus, represented by a ring-shaped DNA molecule; the cell wall includes peptidoglycan (murein) and teichoic acids; ribosomes have a sedimentation constant of 70; the energy centers of the cell are located in mesosomes and there are no organelles ).
1.2 Nuclear eukaryotes (with a clearly defined nucleus separated from the cytoplasm by a membrane; the cell wall lacks peptidoglycan and teichoic acids; the ribosomes of the cytoplasm are larger; sedimentation constant is 80; energy processes are carried out in mitochondria; organelles contain the Golgi complex, etc.).
Later it turned out that among microorganisms there are also non-cellular forms - viruses, and therefore a third group (kingdom) was identified - vira.
To designate microorganisms, a double (binary) nomenclature has been adopted, which includes the name of the genus and species. The generic name is written with a capital letter (capital), while the specific name (even coming from a surname) is written with a lowercase letter (small). For example, the anthrax bacillus is called Bacillus anthracis, Escherichia coli is called Escherichia coli, and black aspergillus is Aspergillus niger.
The basic (lowest) taxonomic unit is the species. Species are united into genera, genera into families, families into orders, orders into classes, classes into divisions, divisions into kingdoms.
A species is a collection of individuals of the same genotype with pronounced phenotypic similarity.
Culture - microorganisms obtained from an animal, human, plant or environmental substrate and grown on a nutrient medium. Pure cultures consist of individuals of one species (offspring obtained from one cell - a clone).
Strain is a culture of the same species, isolated from different habitats and characterized by minor changes in properties. For example, E. coli isolated from the human body, cattle, water bodies, and soil can be of different strains.
2 Prokaryotes (bacteria and actinomycetes). Bacteria (prokaryotes) are a large group of microorganisms (about 1600 species), most of which are unicellular. Shape and size of bacteria. The main forms of bacteria are spherical, rod-shaped and convoluted. Globular bacteria - cocci have the usual spherical shape; they are also flattened, oval or bean-shaped. Cocci can be in the form of single cells - monococci (micrococci) or connected in various combinations: in pairs - diplococci, four cells - tetracocci, in the form of more or less long chains - streptococci, and also in the form of cubic-shaped clusters (in the form of bags) of eight cells located in two tiers one above the other - sarcins. There are irregularly shaped clusters resembling bunches of grapes - staphylococci. Rod-shaped bacteria can be single or connected in pairs - diplobacteria, in chains of three to four or more cells - streptobacteria. The relationship between the length and thickness of the sticks can be very different. Crinkled, or curved, bacteria vary in length, thickness, and degree of curvature. Rods slightly curved in the shape of a comma are called vibrios, rods with one or more corkscrew curls are called spirilla, and thin rods with numerous curls are called spirochetes. Thanks to the use of an electron microscope to study microorganisms in natural substrates, bacteria were discovered that have a special cell shape: closed or open ring (toroids); with outgrowths (prosteks); worm-shaped - long with curved very thin ends; and also in the form of a hexagonal star.
The sizes of bacteria are very small: from tenths of a micrometer (μm) to several micrometers. On average, the body size of most bacteria is 0.5-1 microns, and the average length of rod-shaped bacteria is 2-5 microns. There are bacteria whose sizes are significantly larger than the average, and some are on the verge of being visible in conventional optical microscopes. The body shape of bacteria, as well as their size, can change depending on age and growth conditions. However, under certain, relatively stable conditions, bacteria retain their characteristic size and shape. The mass of a bacterial cell is very small, approximately 4-10-1:! G.
Structure of a bacterial cell . The cell of prokaryotic organisms, which include bacteria, has fundamental ultrastructural features. The cell wall (shell) is an important structural element of most bacteria. The cell wall accounts for 5 to 20% of cell dry matter. It has elasticity, serves as a mechanical barrier between the protoplast and the environment, and gives the cell a certain shape. The composition of the cell wall includes a heteropolymer compound specific for prokaryotic cells - peptidoglycan (murein), which is absent in the cell walls of eukaryotic organisms. According to the staining method proposed by the Danish physicist H. Gram (1884), bacteria are divided into two groups: gram-positive and gram-negative. Gram-positive cells retain dye, while gram-negative cells do not, due to differences in the chemical composition and ultrastructure of their cell walls. Gram-positive bacteria have thicker, amorphous cell walls, which contain large amounts of murein (50 to 90% of the dry mass of the cell wall) and teichoic acids. The cell walls of gram-negative bacteria are thinner, layered, contain a lot of lipids, little murein (5-10%) and lack teichoic acids.
The cell wall of bacteria is often covered with mucus. The mucous layer can be thin, barely visible, but it can also be significant and can form a capsule. Often the capsule is much larger in size than the bacterial cell. The sliming of cell walls is sometimes so strong that the capsules of individual cells merge into mucous masses (zoogels), in which bacterial cells are embedded. The mucous substances produced by some bacteria are not retained as a compact mass around the cell wall, but diffuse into the environment. When rapidly multiplying in liquid substrates, mucus-forming bacteria can turn them into a continuous mucous mass. This phenomenon is sometimes observed in sugary extracts from beets during sugar production. In a short time, sugar syrup can turn into a viscous mucous mass. Meat, sausages, and cottage cheese are subject to mucus; The viscousness of milk, pickles, pickled vegetables, beer, and wine is observed. The intensity of mucus formation and the chemical composition of mucus depend on the type of bacteria and cultivation conditions. The capsule has beneficial properties; mucus protects cells from unfavorable conditions - in many bacteria, mucus formation increases under such conditions. The capsule protects the cell from mechanical damage and drying out, creates an additional osmotic barrier, serves as an obstacle to the penetration of phages and antibodies, and sometimes it is a source of reserve nutrients. The cytoplasmic membrane separates the cell contents from the cell wall. This is an essential structure of any cell. When the integrity of the cytoplasmic membrane is violated, the cell loses its viability. The cytoplasmic membrane accounts for 8-15% of the dry matter of the cell. The membrane contains up to 70-90% of cell lipids, its thickness is 7-10 nm 1. On sections of cells in an electron microscope, it is visible in the form of a three-layer structure - one lipid layer and two protein layers adjacent to it on both sides. The cytoplasmic membrane is invaginated into the cell in places, forming all kinds of membrane structures. It contains various enzymes; it is semi-permeable and plays an important role in the metabolism between the cell and the environment. The cytoplasm of a bacterial cell is a semi-liquid, viscous, colloidal system. In some places it is permeated with membrane structures - mesosomes, which originated from the cytoplasmic membrane and have retained connection with it. Mesosomes perform various functions; they and the associated cytoplasmic membrane contain enzymes involved in energy processes - in supplying the cell with energy. Well-developed mesosomes are found only in gram-positive bacteria; in gram-negative bacteria they are poorly developed and have a simpler structure. The cytoplasm contains ribosomes, the nuclear apparatus and various inclusions. Ribosomes are scattered in the cytoplasm in the form of granules 20-30 nm in size; ribosomes are composed of approximately 60% ribonucleic acid (RNA) and 40% protein. Ribosomes are responsible for the synthesis of cell proteins. A bacterial cell, depending on its age and living conditions, may have 5-50 thousand ribosomes. The nuclear apparatus of bacteria is called a nucleoid. Electron microscopy of ultrathin sections of bacterial cells has revealed that the carrier of the cell's genetic information is a deoxyribonucleic acid (DNA) molecule. DNA has the form of a double helical strand closed in a ring; it is also called the “bacterial chromosome”. It is located in a certain area of the cytoplasm, but is not separated from it by its own membrane.
Cytoplasmic inclusion bacterial cells are diverse, mainly these are reserve nutrients that are deposited in cells when they develop in conditions of excess nutrients in the environment, and are consumed when the cells are starved. Polysaccharides are deposited in bacterial cells: glycogen, starch-like substance granulosa, which are used as a source of carbon and energy. Lipids are found in cells in the form of granules and droplets. Fat serves as a good source of carbon and energy. Many bacteria accumulate polyphosphates; they are contained in volutin granules and are used by cells as a source of phosphorus and energy. Molecular sulfur is deposited in the cells of sulfur bacteria.
Motility of bacteria . Spherical bacteria are usually nonmotile. Rod-shaped bacteria are either motile or immobile. Curved and spiral-shaped bacteria are motile. Some bacteria move by sliding. The movement of most bacteria is carried out using flagella. Flagella are thin, spirally twisted filaments of a protein nature that can carry out rotational movements. The length of the flagella varies, and the thickness is so small (10-20 nm) that they can be seen in a light microscope only after special treatment of the cell. The presence, number and location of flagella are constant characteristics for the species and have diagnostic value. Bacteria with one flagellum at the end of the cell are called monotrichous; with a bunch of flagella - lophotrichs", with a bunch of flagella at both ends of the cell - amphitrichs; bacteria in which flagella are located on the entire surface of the cell are called peritrichs. The speed of movement of bacteria is high: in a second, a cell with flagella can cover a distance of 20-50 times more than the length of its body. Under unfavorable living conditions, with cell aging, and mechanical stress, mobility can be lost. In addition to flagella, on the surface of some bacteria there are a large number of thread-like formations, much thinner and shorter than flagella - fimbriae (or pili). .
Reproduction of bacteria. Prokaryotic cells are characterized by simple cell division in two. Cell division begins, as a rule, some time after the division of the nucleoid. Rod-shaped bacteria are divided transversely, spherical in different planes. Depending on the orientation of the division plane and their number, various forms arise: single cocci, paired, chains, in the form of packets, clusters. A feature of bacterial growth is the speed of the process. The rate of division depends on the type of bacteria and cultivation conditions: some species divide every 15-20 minutes, others - every 5-10 hours. With this division, the number of bacterial cells per day reaches a huge number. This is often observed in food products: rapid souring of milk due to the development of lactic acid bacteria, rapid spoilage of meat and fish due to the development of putrefactive bacteria, etc.
Sporulation. Spores in bacteria are usually formed under unfavorable development conditions: with a lack of nutrients, changes in temperature, pH, and with the accumulation of metabolic products above a certain level. Mostly rod-shaped bacteria have the ability to form spores. Each cell produces only one spore (endospore).
Sporulation is a complex process; several stages are distinguished in it: first, a restructuring of the genetic apparatus of the cell is observed, and the morphology of the nucleoid changes. DNA synthesis stops in the cell. Nuclear DNA is pulled out into a strand, which then splits; part of it is concentrated at one of the poles of the cell. This part of the cell is called the sporogenic zone. In the sporogenic zone, the cytoplasm is compacted, then this area is separated from the rest of the cellular contents by a septum. The cut-off area is covered with the membrane of the mother cell, and a so-called prospore is formed. A prospore is a structure located inside the mother cell, from which it is separated by two membranes: outer and inner. A cortical layer (cortex) is formed between the membranes, similar in chemical composition to the cell wall of a vegetative cell. In addition to peptidoglycan, the cortex contains dipicolinic acid (C 7 H 8 O 4 Mg), which is absent in vegetative cells. Subsequently, a spore shell consisting of several layers is formed on top of the prospore. The number, thickness and structure of layers vary among different types of bacteria. The surface of the outer shell can be smooth or with projections of different lengths and shapes. On top of the spore shell, a thin cover is often formed, surrounding the spore in the form of a sheath - an exosporium.
The spores are usually round or oval in shape. The diameter of the spores of some bacteria exceeds the width of the cell, as a result of which the shape of the spore-bearing cells changes. The cell takes on a spindle shape (clostridium) , if the spore is located in its center, or the shape of a drumstick (plectridium) when the spore is close to the end of the cell.
After the spore matures, the mother cell dies, its shell is destroyed, and the spore is released. The process of spore formation occurs over several hours.
The presence of a dense, impenetrable shell in bacterial spores, a low water content in it, a large amount of lipids, as well as the presence calcium And dipicolinic acid cause high resistance of spores to environmental factors. Spores can remain viable for hundreds or even thousands of years. For example, viable spores have been isolated from the corpses of mammoths and Egyptian mummies, which are thousands of years old. The spores are resistant to high temperatures: in a dry state they die after heating at 165-170°C for 1.5-2 hours, and with superheated steam (in an autoclave) - at 121°C for 15-30 minutes.
Under favorable conditions, the spore germinates into a vegetative cell; this process usually lasts several hours.
The germinating spore begins to actively absorb water, its enzymes are activated, and the biochemical processes leading to growth are enhanced. During spore germination, the cortex turns into the cell wall of a young vegetative cell; Dipicolinic acid and calcium are released into the external environment. The outer shell of the spore breaks, and through the breaks a “sprout” of a new cell comes out, from which a vegetative bacterial cell is then formed.
Only vegetative cells cause food spoilage. Knowledge of the factors that promote the formation of spores in bacteria and the factors that cause their germination into vegetative cells is important in choosing a method for processing products in order to prevent their microbial spoilage.
The information presented above mainly characterizes the so-called true bacteria. There are others more or less different from them, which include the following.
Filamentous (filamentous bacteria). These are multicellular organisms in the form of filaments of various lengths, with a diameter from 1 to 7 microns, mobile or attached to the substrate. Mostly threads with a mucous sheath. They may contain magnesium oxide or iron oxides. They live in bodies of water and are found in soil.
Myxobacteria. These are rod-shaped bacteria that move by sliding. They form fruiting bodies - clusters of cells enclosed in mucus. The cells in the fruiting bodies enter a dormant state - myxospores. These bacteria live in the soil and on various plant debris.
Budding and stalked bacteria reproduce by budding, forming stalks, or both. There are species with outgrowths - prosteks. They live in soil and water bodies.
Actinomycetes. Bacteria have a branched shape. Some are slightly branched rods (see Fig. 2, e), others are in the form of thin branching threads forming a unicellular mycelium. Mycelial actinomycetes, called "ray fungi", reproduce by spores developing on the aerial branches of the mycelium. Actinomycetes are colored; they are widespread in nature. They are also found on food products and can cause spoilage. The product acquires a characteristic earthy odor. Many actinomycetes produce antibiotics. There are species that are pathogenic to humans and animals.
Mycoplasmas. Organisms without a cell wall, covered only with a three-layer membrane. The cells are very small, sometimes ultramicroscopic in size (about 200 nm), pleomorphic (various shapes) - from coccoid to filamentous. Some cause diseases in humans, animals, and plants.
Basics of bacterial taxonomy Modern classification systems for bacteria are essentially artificial; they unite bacteria into certain groups based on their similarity in a set of morphological, physiological, biochemical and genotypic characteristics. For these purposes, Bergi’s manual for identifying bacteria is used (1974, 8th edition and 1984). - 9th edition). According to the 8th edition, all prokaryotes are divided into two divisions - cyanobacteria and bacteria. The first section - cyanobacteria (blue-green algae) - are phototrophic microorganisms. The second section is bacteria. This department is divided into 19 groups. The 17th group includes actinomycetes. According to the 9th edition, the kingdom of prokaryotes is divided into four divisions depending on the presence or absence of a cell wall and its chemical composition: the first division - thin-skinned, includes groups of bacteria, gram-negative, phototrophic and cyanobacteria; the 2nd section includes hard-skinned bacteria, including groups of bacteria that are positive for Gram staining; the third section includes mycoplasmas - bacteria that do not have a cell wall; The fourth section includes methane-forming and archaebacteria (a special group of bacteria that lives in extreme environmental conditions and is one of the oldest forms of life).
The morphology of microorganisms studies the shape and structure of their cells, methods of movement and reproduction. Microorganisms vary in appearance and size. The structure of microbial cells is also different, and therefore they belong to different systematic groups.
All living organisms on Earth that have a cellular structure are divided into two superkingdoms: prokaryotes and eukaryotes. This division of living organisms is based mainly on the structural features of the nuclear apparatus. Prokaryotic cells lack a nucleus. Their nuclear apparatus is represented by a DNA molecule located in the nuclear zone directly in the cytoplasm. Eukaryotic cells have a nucleus separated from the cytoplasm by a double nuclear membrane.
BACTERIA
About 4000 species of bacteria are known. Their diversity is especially pronounced in relation to physiological and biochemical properties. To a certain extent, it is also manifested in morphology.
The size of the cells of different bacteria varies greatly. The sizes of many bacterial forms are in the range of 0.5-10 microns. However, the size of a number of bacteria does not fit within these boundaries. Among them there are many relatively large forms, and there are also extremely small forms. For example, filamentous bacteria of the genus Beggiatoa reach significant lengths - up to 60 µm or more and Saprospira - up to 500 µm. These are one of the largest bacteria. Giant forms are found among spirochetes: some reach 500 microns in length. The smallest known organisms with a cellular structure are mycoplasmas. The sizes of individual forms of mycoplasmas do not exceed 0.1-0.2 microns, which lies on the border or even beyond the resolution of a light microscope. In the same species of bacteria, cell sizes may vary to a greater or lesser extent depending on the age of the cultures and (or) the cultivation conditions. In many bacteria, cell length changes particularly noticeably. Cell diameter is a more stable feature.
The bulk of bacteria are single-celled organisms. But often cells do not separate after division and form combinations of various shapes, which are determined by the location of the dividing septum. These combinations are not equivalent to multicellular organisms, since each cell in them is autonomous and can exist independently after being separated from other cells.
Bacteria, with the exception of mycoplasmas, have a definite cell shape. In most bacteria it is supported by a strong (rigid) cell wall. The cell wall of spirochetes is elastic, and their convoluted shape is maintained by axial fibrils located under the cell wall. The cell shape of many bacteria is constant and remains throughout life. But there are bacteria that exhibit more or less pronounced pleomorphism. Often it reflects the stages of the development cycle of a microorganism. In this case, an orderly, regular alternation of certain forms is revealed. Changes in morphology can also occur under the influence of cultivation conditions. The polymorphism of mycoplasmas is associated with their lack of a cell wall.
Morphological types of bacteria are few in number compared to higher organisms. The cells of a significant part of bacteria have a spherical, cylindrical or spiral shape. There is an extensive group of branching bacteria, a relatively small number of filamentous forms and bacteria that form outgrowths (prostecs).
Spherical bacteria - cocci. Under a microscope they are spherical in shape. Many cocci are characterized by the formation of various combinations (Fig. 2). Cocci dividing in the same plane and in the same direction can form pairs (diplococci) or chains (streptococci) of cells. When division occurs uniformly in two mutually perpendicular planes, groups arise
Figure 2. Combinations of cocci: 1 - diplococci; 2 - streptococci; 3 - tetracocci and sarcina; 4 - staphylococci and micrococci
from four cells - tetracocci, and if in three, they form packets of the correct shape - sarcinae. With uneven division in several planes, clusters of irregular shape are observed, resembling a bunch of grapes. They are characteristic of representatives of staphylococci and micrococci. Micrococci are also often called single spherical cells.
Under the influence of various environmental factors, some cocci can turn into oval, conical and ellipsoidal cells.
Cylindrical (rod-shaped) bacteria under a microscope they look like rods. This is one of the most numerous groups of bacteria. Different species may differ markedly from each other in cell sizes. One of the largest rod-shaped bacteria is Vasillus megaterium. Its length is 5-10 microns, diameter is about 1 micron. The shortest include rickettsia, the size of which can be only 0.3 X 1.0 microns. In cases where the length is only slightly greater than the diameter of the cell, rods are difficult to distinguish from cocci. The ends of the sticks are straight, rounded or pointed (Fig. 3).
Figure 3. Rod-shaped bacteria: 1 - Pseudomonas aeruginosa; 2 - Bacillus mycoides; 3 - Basillus megaterium; 4 - Cytophaga
Rod-shaped bacteria often form pairs or chains of cells. Paired combinations of cells are observed, for example, in certain species of the genus Pseudomonas, long chains can be seen in culture Bacillus mucoides. A number of rod-shaped bacteria are characterized by pronounced pleomorphism.
Shape changes associated with bacterial development have been observed in species Azotobacter And Rhizobium; in myxobacteria and rickettsia. Thus, already in a young culture of Azotobacter one can see cells not only rod-shaped, but also oval or coccoid in shape. They are often connected in pairs or form clusters, and sometimes chains of 4 or more cells. In old cultures, large round, irregularly shaped resting cyst cells predominate. Rickettsia, in addition to short rods 1-1.5 µm long, can be represented by cocci with a diameter of less than 0.5 µm, long rods - 3-4 µm, or intricately curved filaments, the length of which reaches 40 or more micrometers. There are bacteria in which a change in cell shape is associated with sporulation.
Under unfavorable conditions, various degenerative forms appear in cultures of many rod-shaped bacteria with signs of lysis, granulation of contents, large vacuoles, etc. This can be observed, for example, in culture Bacillus megaterium(Fig. 3).
Figure 4 Twisted forms: 1 - vibrios; 2 - spirilla; 3 - spirochetes
Bacteria that form outgrowths (prosteks). The main part of this group consists of bacteria, in which prosthecas are protrusions of cellular contents, surrounded by a cell wall with a cytoplasmic membrane and not separated from the cell by a septum. In some bacteria, for example in species of the genus Hyphomicrobium, the formation of outgrowths is associated with reproduction. Cells of representatives of this genus most often have the form of rods with pointed ends, but they are also oval, ovoid or bean-shaped. Filamentous outgrowths are formed at one or both poles of the cell. The outgrowths can branch, giving rise to hyphal-like structures. At the end of each branch a bud is formed, which is a daughter cell. Sometimes mature buds do not separate from the mother cell and also form outgrowths and buds. Then an accumulation of hyphae and cells occurs (Fig. 5).
Figure 5 Bacteria forming outgrowths: 1 - Caulobacter; 2 - Hyphomicrobium; 3 - Ancalomicrobium; 4 - Gallionella
In other bacteria, prosteks are not related to reproduction. Such bacteria include, for example, species of the genus Caulobacter And Ancalomicrobium. Cells Caulobacter- These are slightly curved rods with one polar flagellum. A relatively short outgrowth - a stalk - appears at one pole of the cell. At the end of the stem there is a small thickening of sticky material - a retainer. With its help, cells attach to some substrate, and sometimes to each other. In the latter case, characteristic clusters are formed. In species Ancalomicrobium Several streaks appear on an irregularly shaped cell - from 2 to 8. The cell takes on a bizarre star-shaped appearance.
Sometimes stalked bacteria are classified as bacteria that form mucous appendages that are not associated with the cytoplasm of the cell. These are, for example, Gallionella species, the bean-shaped cells of which secrete mucus in the form of a thin thread on the concave side. Under a microscope, such a thread looks like a spirally curved ribbon.
Figure 6. Filamentous bacteria: 1 - Beggiatoa; 2 - Thiothrix; 3 - Saprospira; 4 - Simonsiella; 5 - Caryophanon; 6 - class cyanobacteria Hormogoneae; 7 - Leptothrix; 8 - Sphaerotilus; 9 - Crenothrix
This is a relatively small group of multicellular organisms. They are chains (trichomes) of cylindrical, oval or disc-shaped cells. Typical representatives of filamentous forms are bacteria of the genera Beggiatoa And Thiothrix(Fig. 6). Their threads are of equal thickness throughout. Trichome species Thiothrix collected in bundles and attached at the base to the substrate. Threads Leucothrix, similar Thiothrix, for the most part also grow in a bunch, attaching to a solid surface, but, unlike Thiothrix, they taper towards the end.
Trichome species Saprospira twisted in the form of a spiral, and in species Simonsiella they are flattened and ribbon-like. In species Caryophan The transverse cell walls of most of the cells that make up the filament are not continuous, since their formation lags behind the growth of the trichome. Filamentous bacteria are large microorganisms. Thus, the length of the threads of some representatives of the genus Caryophanon reaches 40 microns, and the thickness is 4 microns. Strands of green bacteria group Chloroflexus can have a length of 300 microns. Particularly long trichomes form, as already noted, species Beggiatoa And Saprospira(up to 500 microns).
Branching bacteria. This large group includes true actinomycetes, nocardia, mycobacteria, coryne-like bacteria and a number of other organisms. True actinomycetes have highly branched mycelium that persists throughout life, which makes them externally similar to filamentous fungi (Fig. 7). However, the total length of actinomycete filaments usually does not exceed a few millimeters, and the thickness is only 0.5-1.5 microns, while the length of fungal mycelium reaches several centimeters, and the diameter can be about 50 microns. Among representatives of the genus Streptomyces partitions are formed in the mycelium, but there are few of them, so the cells that make it up are mostly multinucleated. The mycelium of most actinomycetes is devoid of septa, and in this way it resembles the multinucleate nonseptate mycelium of phycomycetes.
Figure 7. Mycelium of actinomycete (1) and fungus (2) at the same magnification
In nocardia and mycobacteria, the mycelial type of development is temporary and often limited. Species of the genus Nocardia form abundant, undifferentiated mycelium in the initial stages of development. Subsequently, it breaks up into rod-shaped or spherical fragments.
Mycoplasmas. This is a fairly large group of bacteria that do not have a cell wall. Therefore they are very polymorphic. In the culture of one species, one can simultaneously detect small granular formations, coccoid, ellipsoid, pear-shaped, disc-shaped, rod-shaped and even branched and unbranched filamentous forms (Fig. 8). The size of large mycoplasma cells reaches 10 µm, and the size of small structures does not exceed 0.1 µm.
Figure 8.
Most bacteria reproduce by binary transverse isomorphic fission. This method of reproduction is characteristic of cocci, many rod-shaped forms and vibrios, spirilla, spirochetes, and some filamentous bacteria. The cells of the bulk of bacteria divide in one plane. In many cocci, division occurs in several planes. The cells of most bacteria diverging after division are located one after another or randomly, and in species Arthrobacter And Corynebacteriut at an angle to each other. If after division the cells do not diverge, then the formation of various clusters of cells is observed - pairs, chains, packets and others. In some cases, uneven division occurs. By fragmentation of the mycelium or its rudiments into rods and cocci, for example, species Nocardia And Mycobacteriu. Reproduction by disintegration of threads into sections is observed in Beggiatoa And Saprospira. Two unequal cells - one mobile with a flagellum, but without a stalk, and the other immobile without a flagellum, but with a stalk - are formed during cell division Caulobacter(Fig. 9). Only immobile cells with prosteca are capable of dividing.
Some bacteria (species Hyphoticrobiot And Rhodopseudoтona s, Ancalo-ticrobiot etc.) reproduce by budding. U Rhodopseudotopas And Apcaloticgobiut buds form directly on the surface of cells, and in Hyphoticrobiot- at the ends of the hyphae.
Figure 9. Diagram of Caulobacter cell growth and division
Figure 10. Gonidia (1) and hormogonium (2) of filamentous bacteria
Bacteria also have more complex methods of reproduction. Filamentous cyanobacteria class Chataesiphoneae and bacteria of the genera Thiothrix, Caryophanon, Sphaerotilus, Leptothrix, Leucothrix reproduce with the help of special reproductive single mobile cells - gonidia (Fig. 10), which are formed as a result of repeated division of the end cells of the thread. The motility of gonidia is associated with the presence of flagella. For filamentous cyanobacteria class Hortogopeae Reproduction by hormogonies is typical. These are short chains that arise, like gonidia, during filament cell division. They do not have flagella and move by sliding due to the secretion of mucus. Reproduction by hormogonies is also observed in species Leucothrix.
Actinomycetes reproduce mainly by motile or immobile spores (conidia). Conidia are located singly or in chains, directly on the mycelium, at the ends of spore-bearing hyphae - sporangiophores (sporangiophores) or in special sporulation organs - sporangia. Sporangiophores (and, accordingly, chains of spores) of different species differ from each other. They can be long or short, straight, wavy or spiral; have a consistent, opposite or whorled arrangement (Fig. 11). Sporangia are spherical or irregular in shape (Fig. 12), endogenous spores are formed in them.
There are many bacteria that can reproduce in several ways. For example, representatives of the genus Rhizobiut They reproduce by division and budding; actinomycetes reproduce by spores and pieces of vegetative mycelium. Filamentous cyanobacteria reproduce by gonidia or hormogonium, as well as by the breakdown of trichomes into separate sections, bacteria of the genus Chloroflexus- binary fission and thread sections. Caryophanon And Sphaerotilus- with the help of gonidia and transverse isomorphic division of the trichome, Leucothrix gonidia and hormogonium. In mycoplasmas, one can observe binary fission, fragmentation of filaments and large cells to cocci, as well as a process resembling budding.
Figure 11 Shape of aerial spore carriers in actinomycetes
Figure 12. Sporangia of actinomycetes: 1 - Actinoplanes; 2 - Amorphosporangium; 3 - Spirillospora
Many bacteria are immobile. Almost all cocci, more than 50% of rod-shaped bacteria, budding and branching bacteria, a significant part of filamentous forms, rickettsia, and mycoplasma are immobile. About 1/5 of the bacteria have the ability to move. The mobility of most of them is due to the presence of special locomotor structures - flagella. Flagella are found in some cocci (certain representatives of the genus Methylococcus), a number of rod-shaped bacteria (species Bacillus, Clostridium, Pseudotopas, Rhizobium, Azotobacter, Escherichia etc.), in vibrios and spirilla, in filamentous bacteria of the genus Caryophanon. In some groups of bacteria, special reproductive cells with flagella appear only at a certain stage of development. These are motile cells of Caulobacteria, gonidia of most filamentous organisms, spores (conidia) of some actinomycetes (species Actinoplapes And Geodertatopftilus).
Figure 13. Types of flagellation in bacteria: 1 - monotrichial; 2 - lophotrichial; 3 - lateral; 4 - amphitrichyal; 5 - peritrichial; 6 - “mixed” polar - peritrichial
Flagella originate under the cytoplasmic membrane and exit through the pores of the membrane and cell wall. In different bacteria, the length of the flagella varies from 3 to 20 microns, the thickness - from 10 to 20 microns, and their number - from 1 to 100. Flagella can be located monopolarly, bipolarly, along the side or along the entire surface of the cell (Fig. 13). The cells of some bacteria simultaneously have two different sets of flagella: polar and peritrichous, differing in length and thickness.
The presence, number, size and location of flagella are of diagnostic value. For example, species of the genus Vibrio equipped with one polar flagellum, Selenotonas one flagellum is attached to the side. For representatives of the family Pseudotonas characteristically monotrichial or lophotrichial monopolar flagellation, and for spirilla lophotrichial mono- and bipolar. The peritrichous arrangement of flagella is characteristic of the species Clostridium, Escherichia, Rhizobium, Caryophanon etc. Often, within the same genus of bacteria, motile and immobile species are found, and motile forms may have different types of flagellation. Thus, among mobile representatives of the genus Bacillus flagella are located laterally or peritrichally.
Active movement of most bacteria with flagella is possible only in a liquid medium. However, some bacteria - peritrichous bacteria - can also move on solid substrates. These include, for example, Proteus vulgaris, which spreads quite quickly over the surface. moist agar medium, forming an extensive thin coating. The movement of flagellated bacteria is observed mainly in young cultures. With age, cells gradually lose their flagella and become immobile, although they remain viable.
Motile forms include spirochetes, myxobacteria, many filamentous cyanobacteria and flexibacteria that do not have flagella.
They are able to move on solid or semi-solid substrates
by sliding. Spirochetes can also move in a liquid environment
rotational, light wave-like movements. sliding
the movement is possibly due to uneven mucus secretion
through the pores of the cell wall. Motility of spirochetes and some myxobacteria (species Myxococcus) is also associated with contraction of axial microfibrils located under the cell wall (in spirochetes) or under the cytoplasmic membrane (in myxobacteria).
Resting forms of bacteria include endospores, cysts, and akinetes. They allow the cell to endure unfavorable conditions for a more or less long time. Under conditions suitable for growth, the resting forms develop into an ordinary vegetative cell.
Endospores. The ability to form endospores is possessed by rod-shaped bacteria belonging to the genera Bacillus, Clostridium And
Desulfototaculut, as well as some cocci (genus Sporosarcina) and thermophilic actinomycetes of the genus Thertoactinotyces. Sporulation is a complex differentiation process that begins in a culture when it enters the stationary phase of growth and when the conditions inducing it are created. These conditions are very diverse: deficiency of nutrients in the environment, accumulation of metabolic products, changes in the acidity of the environment, temperature, etc. As a result, a new cell is formed inside the vegetative cell - an endospore, completely different from the mother one in structure, chemical composition and physiological properties. Endospores are covered with thick multi-layered, impenetrable covers and have a very low water content, so upon microscopic examination they are easily recognized by their high light refractive ability.
The shape of the cells of many bacteria does not change during sporulation. The endospore is localized in the center of the cell, eccentrically and/or terminally, which depends on the type of bacteria. This is the so-called bacillary type of sporulation (Fig. 14, 1 ). In a number of bacteria, the middle of the cell expands somewhat during the formation of a spore, and the cell takes on the appearance of a shuttle or spindle. The spore is located in the thickened part - in the center of the cell or eccentrically (Fig. 14, 2 ). This is a clostridial type of sporulation. In some bacteria, during sporulation, the cell greatly expands and is rounded at one end, becoming similar to a drumstick. The spore is localized at the expanded end (Fig. 14, 3 ). This type of sporulation is called plectridial. The bacillary type of sporulation is characteristic of many representatives of the genus Bacillus, clostridial and plectridial - mainly to species of the genus Clostridium. Often, in the culture of one species of this genus, both clostridial and plectridial forms are found simultaneously.
Figure 14. Types of endospore formation in bacteria: 1 - bacillary; 2 - clostridial; 3 - plectridial
Endospores are round, oval or ellipsoid in shape. Their shell can be smooth or with projections. The diameter of the endospores of some bacteria significantly exceeds the diameter of the cell. The type of sporulation, as well as the shape, size and location of the endospore in the vegetative cell are used to diagnose bacteria.
As a rule, only one endospore is formed in each vegetative cell. After maturation, endospores are released due to lysis of mother cells and enter the resting stage. Endospores are extremely resistant to various unfavorable factors and can remain viable for many years until they are exposed to conditions conducive to their germination.
Sporulation is not an obligatory stage of bacterial development. It is possible to create conditions in which cells will not proceed to form spores.
Cysts found in myxobacteria, rickettsia, representatives of the genera Azotobacter, Bdellovibrio, Arthrobacter. Their formation usually occurs in the late stages of bacterial development and is associated with unfavorable cultivation conditions - depletion of the nutrient substrate, contamination of the environment with harmful metabolic products, drying, etc. Cysts can only be seen in old cultures.
Cysts can be spherical, oval, irregularly rounded, or in the form of very shortened rods. Most often they are larger than vegetative cells. Sometimes the cysts are almost the same in shape and size. In most bacteria, cysts have a thickened cell wall and dense cytoplasm, so they refract light more strongly than vegetative cells. Cysts are more resistant to unfavorable factors than vegetative cells, but are inferior to endospores in this regard.
Akinetes characteristic of certain types of filamentous cyanobacteria. These are large, thick-walled cells (Fig. 15), arising either from a single vegetative cell or by the fusion of many cells. In some cyanobacteria, akinetes are always found and are probably an obligatory stage of development, while in others they are formed only under unfavorable conditions.
Figure 15. Akinetes (a) and heterocysts (D) of the filamentous cyanobacterium Cylindrospermum
The cells of all bacteria, with the exception of mycoplasmas, are covered on the outside with a cell wall, the thickness of which varies from 0.01 to 0.04 microns in different species. In accordance with the differences in the chemical composition of cell walls and their ultrastructure, expressed in the unequal ability of cell walls to retain triphenylmethane dyes with iodine, prokaryotic microorganisms are divided into two groups. One category includes bacteria, in whose cells the complex formed by crystalline or gentian violet and iodine does not become discolored upon subsequent treatment with alcohol. Another group includes bacteria that do not have the ability to retain dye and become discolored when treated with alcohol. This method of differential staining of bacteria was proposed in 1884 by the Danish physicist Christian Gram. Bacteria that can stain with Gram are called gram-positive, and those that cannot stain are called gram-negative. The first group includes most coccal forms, spore-forming rod-shaped bacteria of the genera Bacillus And Clostridium, filamentous bacteria Saguorhanon, branching bacteria. The second group includes various rod-shaped bacteria that do not form endospores (genus Pseudotonas, Escherichia etc.), prostecobacteria, myxobacteria, rickettsia, many filamentous forms, spirilla, spirochetes, some cocci, etc. The chemical composition and structure of the cell walls of gram-negative microorganisms is much more complex than that of gram-positive ones.
The acid resistance of mycobacteria is also associated with the peculiarities of the chemical composition of cell walls. It is expressed in the ability of cells, fixed and stained when heated with carbol fuchsin, to firmly retain the color after treatment with a solution of mineral acid or acidified alcohol.
By certain means, for example, under the influence of lysozyme, bacterial cells can be deprived of cell walls. In this form, they are able to exist only in an isotonic nutrient medium.
The cell wall of many bacteria can be surrounded on the outside by a mucous layer - a capsule. Capsules are of a polysaccharide, sometimes glycoprotein or polypeptide nature. Capsules less than 0.2 microns thick, indistinguishable under a light microscope, are called microcapsules. The capsule and cell wall are the surface structures of the bacterial cell, which also include flagella and villi (fimbriae, pili) found in many motile and immobile bacteria. The villi are shorter and thinner than most flagella - their length is 3-4 µm, diameter 4-35 nm. The number of villi in different bacteria varies from a few units to many thousands. They apparently have nothing to do with the mobility of bacteria. Capsules and villi are not necessary cellular structures. Bacteria function normally without them.
An essential structure of any cell is the cytoplasmic membrane, which separates the cytoplasm from the cell wall. Membrane thickness. 5-10 nm. If its integrity is violated, cells lose viability. The cytoplasm of a number of bacteria is permeated with membrane structures that are derivatives of the cytoplasmic membrane. In heterotrophic bacteria they are called mesosomes. They look like plates (lamellae), bubbles (vesicles) or tubes. Mesosomes can be located in the zone of cell division, near the nucleotide and on the periphery of the cell, near the cytoplasmic membrane. In Gram-positive bacteria, mesosomal structures are more developed than in Gram-negative bacteria. In phototrophic bacteria, membrane formations in the form of vesicles are called chromatophores, and those with a flattened shape are called thylakoids. There are bacteria in which the membrane system is not detected.
A certain area in the cytoplasm of a bacterial cell is occupied by a nucleoid. It consists of one double helical strand of DNA closed in a ring. The nuclear apparatus of prokaryotes does not have a nucleolus and is not separated from the cytoplasm by a membrane. Through mesosomes, the nucleoid is connected to the cytoplasmic membrane. During the period of intensive division in the cells of a number of bacteria ( Escherichia coli, Oscillatoria atoena) several nucleoids can be detected.
Ribosomes are found in the cytoplasm of bacteria in free form or in connection with membrane structures. They have a sedimentation constant of 70S, their sizes range from 15 to 30 nm. The number of ribosomes can be from 5 to 50 thousand, which depends on the age of the cell and culture conditions. There are more ribosomes in young cells.
Inclusions are often found in the cells of various bacteria
spare substances. These are polysaccharides, lipids, polyphosphates, sulfur. They accumulate when there is an excess of certain nutrients in the environment, and are consumed during starvation. Of the reserve polysaccharides, glucans are especially common: glycogen, starch and a starch-like substance - granulosa. They are detected in the cells of spore-forming bacteria of the genera Bacillus And Clostgidium, as well as in purple bacteria, etc. Polysaccharides are deposited in the cytoplasm evenly or in the form of granules. Reserve lipids of 6 bacteria are represented by polyester - hydroxybutyric acid and waxes. Polyhydroxybutyrate accumulates in environments with excess carbon in many
bacteria: species Bacillus, Pseudotanas, Spirillut, Azotobacter, Sphaerotilus etc. It is found only in prokaryotes. Wax - esters of high molecular weight fatty acids and alcohols are characteristic of mycobacteria. Polysaccharides and lipids serve as a good source of carbon and energy for the cell.
Under conditions that prevent the synthesis of nucleic acids, many bacteria create a phosphorus reserve in the form of polyphosphate granules. They were first described in Spirillit volutans, so they were called volutin. These formations are also called metachromatic grains, as they exhibit a metachromatic effect: they acquire a red color when treated with a blue dye.
Certain types of spore-forming bacteria ( Bacillus thuringiensis, Bacillus c ereus, Bacillus popilliae etc.) under certain conditions form crystals of a protein nature in cells, which have a regular bipyramidal shape and are located directly near the spore. They are called parasporal bodies.
Some bacterial structures and inclusions that strongly refract light (endospores, aerosomes, deposits of polyhydroxybutyrate and sulfur) are clearly visible in a light microscope without special treatment. Some structures (flagella, cell wall, nucleoid, volutin, etc.) can be identified using a light optical microscope only after staining with appropriate dyes. A number of structural elements of bacteria - microcapsules, villi, mesosomes, ribosomes, etc. are visible only in an electron microscope (Fig. 16).
Figure 16. Diagram of the structure of a bacterial cell: 1 - ribosomes, 2 - the beginning of the formation of a transverse septum, 3 and 4 - reserve deposits, 5 - nuclear region, 6 - capsule, 7 - cell walls, 8 - protoplasmic membrane, 9 - grain from which the flagellum begins
Chapter 1. MORPHOLOGY AND CLASSIFICATION OF MICROORGANISMS
Morphology microorganisms studies the shape and structural features of cells, the ability to move, form spores, methods of reproduction, etc. According to modern concepts, all living organisms with a cellular structure are divided into two superkingdoms: prokaryotes and eukaryotes (Greek “karyon” - nucleus) . Organisms that do not have a cellular structure constitute the third superkingdom - akaryotes (for example, viruses). Prokaryotes include only one kingdom - bacteria, including cyanobacteria (blue-green algae). Eukaryotes include three kingdoms: animals, plants and fungi.
Rice. 1. Forms of bacteria:
A- spherical; b - rod-shaped; V- crimped; 4- filamentous; d- new forms- 1 - micrococci; 2 - streptococci; 3 - diplococci and tetracocci;... 4 - staphylococci; 5 - sardines; b - rods without spores; 7 - sticks with spores; 8"-vibrios; 9 - spirilla; 10 - spirochetes; //- toroids; 12 - bacteria that form stains; 13 - vermiform"; 14 - hexagonal
The division of living organisms into prokaryotes and eukaryotes is based primarily on the structural features of their nuclear apparatus. Using an electron microscope, it was determined that bacteria lack a true nucleus, so they were called prokaryotes, that is, “prenuclear” organisms. It is known that the basis of the nuclear apparatus is deoxyribonucleic acid (DNA), the molecule of which has the form of a double helical strand. The nuclear apparatus of prokaryotes includes a DNA molecule in the form of a strand closed in a ring, located directly in the cytoplasm. The nuclear apparatus of prokaryotes is called a nucleoid, which in Latin means “like a nucleus.” Eukaryotes have a true nucleus with a nucleolus surrounded by a nuclear membrane. DNA is contained within the nucleus. Along with this main feature, there are many specific features in the structure and metabolism of prokaryotes.
The main objects of technical microbiology are bacteria, filamentous fungi, and yeast, which mainly constitute both beneficial and undesirable microflora of food production.
PROKARYOTES (BACTERIA]
In the world of microorganisms, bacteria occupy a leading place in terms of numbers (about 4000 species) and the variety of chemical transformations they carry out. Most bacteria are unicellular organisms, but there are also multicellular ones.
Shape and size of bacteria. Single-celled bacteria are divided into three main groups according to their appearance: spherical, rod-shaped and convoluted (Fig. 1).
Spherical bacteria - cocci (Fig. \,A) can be single - micrococci or connected in pairs - diplococci. Often, when dividing, cells for one reason or another do not diverge and form various combinations, which depend on the location of the dividing septum. When dividing partitions are located in two mutually perpendicular planes, groups consisting of four cells are formed - Tetracocci. When dividing in three mutually perpendicular planes, packet-like clusters are formed, consisting of eight to sixteen cocci, called Sarcins. When cocci divide in different directions, clusters of cells are formed that resemble bunches of grapes - staphylococci. If the division of cocci occurs in one direction and they do not separate, then chains of cells are formed - streptococci. These combinations are not equivalent to multicellular microorganisms, since each cell in them is a separate organism capable of independent existence after separation from other cells.
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Rice. 2. Actinomycetes:
A- mycelium; b - spore-bearing
Rod-shaped bacteria (Fig. 1, b) have the shape of an elongated cylinder, can be single or connected in pairs, as well as in the form of chains of three or more cells. The ratio of cell length to its diameter varies greatly among them. The short rods are only slightly longer than the cross section and are sometimes quite difficult to distinguish from cocci. Rod-shaped bacteria are the most numerous group of bacteria.
Twisted (Fig. 1, V) There are three types of bacteria: vibrios- sticks curved in the shape of a comma; spirilla, having several regular curls, and spirochetes, having the appearance of small spirals with numerous curls.
In addition to these most common forms of bacteria in nature, there are a small number of filamentous forms (Fig. 1, G). They are multicellular organisms in the form of filaments consisting of identical cylindrical or disc-shaped cells.
Relatively recently, new forms of bacteria were discovered in soil and water bodies, the cells of which have the form of an open or closed ring (toroids), a hexagonal star, a rosette, as well as cells with outgrowths (simples) and a worm-like shape (Fig. 1, d).
Rice. 3. Scheme of the structure of a bacterial cell: 1 - capsule; 2 - cell wall; 3 - cytoplasmic membrane; 4 - cytoplasm; 5 - mesosomes; 6 - ribosomes; 7 - polysaccharide granules; 8 - nucleoid; 9 - sulfur inclusions; 10 - fat drops; 11 - polyphosphate granules; 12 - intraplasmic membrane formations; 13 - basal body; 14 - flagella
Bacteria include another, special group of microorganisms - actinomycetes. Their cells mainly look like very thin, long, straight, branching filaments (Fig. 2).
The size of bacteria is negligible, the cross section of the cells of most bacteria does not exceed 0.5-0.8 microns, the average length of rod-shaped bacteria is from 0.5 to 3 microns. Filamentous bacteria are much larger - non-
which are 15-125 microns in length and 5-35 microns in diameter. The length of spirochete cells can reach 500 microns. The smallest of microorganisms - mycoplasmas, which do not have a cell wall, have a size of 0.1-0.15 microns.
The average volume of a bacterial cell is 0.07 μm 3, its weight is 5-10 ~ 12 g. 1 mm 3 can contain up to 10 9 bacterial cells.
In food production, spherical and rod-shaped bacteria are of primary importance.
Structure, chemical composition and functions of cellular structures of bacterial (prokaryotic) cells. The essential cellular structures in the vast majority of bacteria are: the cell wall, the cytoplasmic membrane (CP*M), the nuclear apparatus (nucleoid) and ribosomes (Fig. 3).
The outside of the cell is covered with tough cell wall. It gives shape to the cell, protects it from adverse external thermal and mechanical influences, and protects the cell from the penetration of excess water into it. In some bacteria, on the outer surface of the cell wall, capsules or mucous layer. The capsule most often consists of polysaccharides (dextran, levan), less often of polypeptides. A capsule is an optional structure of a bacterial cell. Sometimes capsules serve as a source of reserve nutrients. For example, capsules of polysaccharides are formed in leuconostoc cells on media with a significant amount of carbohydrates.
Based on the chemical composition and structure of the cell wall, bacteria are divided into 2 large groups: gram-positive And gram negative bacteria(Tram+ and Gram -).
gis. *. part of the problem buildings cell walls of gram-positive and gram-negative bacteria
They are named after the Danish scientist Christian Gram, who proposed a special method for staining bacteria (Gram stain). After staining, the bacterial preparation is treated with alcohol or acetone, as a result of which the Gram - bacteria become discolored, while the Gram + bacteria retain a dark purple color. Gram stain is important for classifying bacteria.
Both Gram + and Gram - bacteria have rigidity
- CELL WALL Due to the presence of a polymer compound
opinions peptidoglycan(murei-na), but in Gram+ bacteria its amount is much greater (up to 90-95% of the cell wall substances), and in Gram - 5-10%. The peptidoglycan layer of Gram+ bacteria is tightly adjacent to the CPM (Fig. 4).
In addition, the cell walls of Gram+ bacteria contain other polymers - teichoic acids, which, like peptidoglycan, are found only in prokaryotes and are not found in eukaryotes. The cell wall of Gram+ bacteria contains small amounts of polysaccharides. In Gram+ bacteria, the cell wall has a thickness of 20-80 nm, it is single-layered and dense.
The cell wall of Gram bacteria is much thinner - 10-13 nm, but it is multilayered. Peptidoglycan forms only the inner layer, loosely adjacent to the CPM. Adjacent to the inner layer is an outer membrane consisting of lipoproteins And lipopolysaccharides. There are no teichoic acids in the cell wall of Gram bacteria.
The outer membrane of Gram bacteria prevents the penetration of toxic substances into the cell, therefore Gram bacteria are much more resistant to the action of antibiotics, toxic chemicals and other substances compared to Gram+ bacteria. Therefore, in food production, the fight against Gram bacteria using disinfectants is not always effective.
Cytoplasmic membrane(CPM) is located under the cell wall, limits the contents of the cell and plays a very important role in the life of the cell. Violation of its integrity leads to cell death. Chemically, CPM is a protein-lipid complex consisting of proteins (50-75% of the mass of CPM), lipids (mainly phospholipids - 15-45%) and a small amount of carbohydrates. The CPM has pores through which nutrients enter the cell and the end products of metabolism are excreted.
Since in prokaryotes the CPM is the only membrane structure in the cell, unlike eukaryotes, it performs many functions: transports nutrients from the external environment into the cell using specific carrier proteins; on the inner side of the CPM there are redox enzymes involved in supplying the cell with energy, and hydrolytic enzymes that break down high-molecular compounds. In some bacteria, the CPM forms invaginations into the cell - mesosomes, having different shapes and sizes and performing different functions (participation in energy processes, cell division processes, reproduction process, etc.).
Cytoplasm- this is the internal contents of the cell, surrounded by the CPM, which is a semi-liquid colloidal system. It contains water up to 70-80% of the cell mass, enzymes, amino acids, a set of RNA, substrates and metabolic products of the cell. The cytoplasm contains the remaining vital structures of the cell - the nucleoid, ribosomes, as well as storage substances of various natures.
Nucleoid is the nuclear apparatus of prokaryotes. This is a compact formation occupying a central region in the cytoplasm, consisting of a double helical strand of DNA closed in a ring, which is also called the bacterial chromosome. The bacterial chromosome comes into contact with the mesosome at one point. When unfolded, a DNA strand can be more than 1 mm long, i.e. almost 1000 times the length of a bacterial cell. All genetic information in prokaryotes, as well as in eukaryotes, is contained in DNA, therefore the function of the nucleoid is to transmit hereditary properties. Before cell division, the nucleoid is divided in half. The nuclear apparatus of prokaryotes does not have a nucleolus and is not separated from the cytoplasm by a nuclear membrane, as is the case in eukaryotes.
Ribosomes- small granules scattered in the cytoplasm, consisting of RNA (60%) and protein (40%). They play a very important physiological role, since protein synthesis occurs on them. In young cells, an increased content of ribosomes is observed.
In bacterial cells, in addition to the obligatory cellular structures, there are inclusion of spare substances. They accumulate when there is an excess of certain nutrients in the environment, and are consumed when the cell starves. The storage substances of bacterial cells include polysaccharides, including glycogen, starch and granulosa; fat drops, containing lipids (fats) in the form of poly-p-hydroxybutyric acid, which is synthesized in media rich in carbohydrates. Poly-p-hydroxybutyric acid is found only in prokaryotes and its amount can reach 50% of the dry mass of cells. Granulose and lipids serve as a good source of carbon and energy for the cell. In many prokaryotes, polyphosphates accumulate in their cells in the form of granules, also called currency or meta-chromatin grains. They are used by cells as a source of phosphorus.
Rice. 5. Attachment diagram
1 - cell wall; 2 - cyto-
plasma membrane; 3 -
flagella membrane; 4 -discs
grounds; 5 - flagella
In the cells of some bacteria involved in sulfur transformations, molecular sulfur is deposited in the form of special inclusions.
Motility of bacteria. Capable
Approximately 50% of the bacteria are capable of movement. These are mainly many rod-shaped and all convoluted forms of bacteria. Almost all spherical bacteria (cocci), more than 50% of rod-shaped bacteria and a number of others are immobile.
Most often, movement is carried out using flagella(see Fig. 3) - thin threads 10-20 nm thick, consisting of a special protein flagellina. The length of the flagella can be many times greater than the length of the cell. Flagella (Fig. 5.) are attached to the membrane using two pairs base discs and through the pores in it and the cell wall they come out. Speed of movement of bacteria With using flagella is high (20-60 µm/s).
The nature of the arrangement of flagella on the cell surface is one of the signs of the classification of bacteria (Fig. 6). Their number can be from 1 to 100. Bacteria that have one flagellum at the end of the cell are called monotrichs; with a bundle of flagella at one or both ends of the cell - lofotri*hami; one flagellum on both ends - amphitrichs. Bacteria in which flagella cover the entire surface of the cell are called peritrichs. Flagella provide active cell movement only in a liquid medium, and when flagella are lost due to aging or mechanical stress, cells lose the ability to move, but retain viability.
Motile forms also include spirochetes, some filamentous (multicellular) and other bacteria that do not. flagella. Spirochetes can move both in a liquid medium and on a solid substrate as a result of wave-like contractions of the cell. Filamentous bacteria, cyanobacteria and others have a sliding type of movement along solid and semi-solid substrates.
The ability to move allows bacteria to move to that area of the environment in which the conditions for their growth and reproduction (concentration of nutrients and oxygen in the environment, light, etc.) are most optimal.
Rice. 6. Location of flagella in motile forms of bacteria: A- monotrich; b - amphitrichus; V- lophotrichus; G - peritrichus
Growth and reproduction of bacteria. The main distinguishing feature of living organisms from inanimate nature is growth and reproduction. Height is a physiological process during which the size and mass of a cell increase. The growth of a bacterial cell is limited, and, having reached a certain size, it stops growing. The process begins reproduction, i.e., an increase in the number of individuals (cells) when a daughter cell is separated from the mother cell.
Most bacteria reproduce by simply dividing into two parts. This method of reproduction is called binary transverse division. In the vast majority of Gram+ bacteria, cells divide exactly in half using septa(transverse septum). On opposite sides of the inner part of the cell wall, two protrusions are formed, growing towards each other (from the periphery to the center), in the same places the CPM forms mesosomes (invaginations). Enzymes located in mesosomes synthesize cell wall material. The transverse septum is initially formed from CPM and peptidoglycan; the outer layers are synthesized later.
The cells of most Gram bacteria divide by forming a constriction. In the center of the cell on one side of the CPM And the cell wall gradually bends until it merges with the opposite cell surface. The formation of a transverse septum or constriction is preceded by DNA division, as a result of which one nucleoid enters each daughter cell.
Actinomycetes reproduce mainly exospores(external spores), which are formed singly or in chains at the ends of the spore-bearing gif- spore bearers, having the most varied shapes (see Fig. 2). There are other methods of reproduction.
Endospore formation. Ability to educate endospore(internal spores) are possessed only by some rod-shaped Gram+ bacteria. Since only one spore is formed in each cell, sporulation is not possible.
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Rice. 7. Types of sporulation in bacteria:
A- bacillary; b- clostridial; c - plectridial
reproduction, and the resting stage of the cell to endure unfavorable conditions. Spores are formed during starvation, when there is an excess of metabolic products or when temperature, humidity and pH do not correspond to their optimal values for the development of this type of bacteria.
There are three types of sporulation (Fig. 7). If, when a spore forms in the center of a cell, its shape does not change, then this type of sporulation is called bacillary; it is characteristic of representatives of the Vaschis genus. If the cell in the middle thickens and takes on the appearance of a spindle, then this type of sporulation is called clostridial. Sometimes a spore is formed closer to the end of the cell and then the cell takes on the appearance of a tennis racket - this type of sporulation is called plectridial(Fig. 7). Clostridial and plectridial types of sporulation are characteristic of bacteria of the genus Cloz1:ps1st.
Sporulation is a complex process as a result of which an endospore is formed in a cell, which differs from a vegetative cell in structure and chemical composition (Fig. 8). The endospore has an outer and inner membrane, between which is located cortex(bark), similar in chemical composition to the cell wall of a vegetative cell. Multilayered spore covers are formed on top of the outer membrane, consisting mainly of proteins. Some bacteria form another layer on the outside of the spore - exosporium, consisting of lipids and proteins.
During sporulation, accumulation of a specific substance occurs - dipicolinic acid, which is absent in the vegetative cell, as well as calcium ions. The process of spore formation takes * several hours. Once the spore has formed, the membrane and other parts of the cell are destroyed and the spore is released.
Rice. 8. Scheme of the structure of a bacterial spore:
/ - nucleoid; 2 - cytoplasm; 3 - internal membrane; 4 - cortex; 5 - outer membrane; 6 - covers consisting of several layers; 7 - exosporium
The spores are unusually resistant to temperature, for example, spores of the causative agent of severe food poisoning - botulism - can withstand heating up to 100 ° C for 5-6 hours. The spores can withstand drying, exposure to ultraviolet rays, toxic substances, etc. The resistance of the spores is due to the fact that that their integuments are difficult to permeate and contain a lot of lipids, as well as dipicolinic acid and calcium. The activity of enzymes in them is suppressed. The high heat resistance of spores is due to their low water content, which protects proteins from denaturation at high temperatures.
Bacterial spores can remain viable for tens or even hundreds of years. Once in favorable conditions, the spore absorbs water and swells, its thermal stability decreases, the activity of enzymes increases, under the influence of which the membranes dissolve, and the spore grows into a vegetative cell.
Food spoilage is caused only by vegetative bacterial cells. Therefore, it is necessary to know the conditions that promote the formation of spores and their germination into vegetative cells in order to correctly choose the method of processing food products in order to prevent their spoilage under the influence of bacteria.
Principles of classification of bacteria. Currently, there is no typical classification of bacteria, although work on its creation is ongoing. The classification of all living beings is based almost entirely on directly observable and easily determined morphological characteristics of organisms. In bacteria, due to the small number of their morphological characteristics, it is impossible to create a generally accepted classification and additional characteristics are required.
In addition, organisms, in accordance with the basic principles of classification of living beings, should be arranged in rows from the simplest to the most complex, i.e., how their gradual development (evolution) proceeded. This classification of organisms is natural. The smallest unit of classification is view- a group of organisms endowed with common stable characteristics and descending from a common ancestor. Closely related species are grouped into a higher systematic unit - genus; close births - in families, families - in orders or squads, orders - in classes, and classes - in types.
However, microbiologists currently do not have sufficient knowledge about the evolution of bacteria. Therefore, most existing classifications of bacteria are artificial. Artificial classifications are intended to determine a particular group of microorganisms that is of practical interest to the researcher.
The scientific names of microorganisms consist of two Latin words: the first is written with a capital letter and means the genus, the second is written with a lowercase letter and means the species of that genus. For example: Vaschis zymshis (bacillus hay) is a bacterium belonging to the genus Vaschis, rod-shaped, forming endospores of the bacillary type, constantly living on hay.
To classify bacteria, the following characteristics are mainly used: morphological(cell shape, presence and location of flagella, method of reproduction, Gram stain, presence of endospores); physiological(attitude to the effects of temperature, pH, oxygen, type of nutrition, method of obtaining energy, nature of the products formed); cultural(the nature of growth on various nutrient media of bacterial cultures in the mass, and not in the form of individual cells: on liquid media this is the presence of film, turbidity, sediment; on solid media - the type of colonies and their features).
In recent years, the classification of bacteria proposed by R. Murray in 1978 has gained recognition. This is an artificial classification based on the structure of the cell wall. All bacteria that are characterized by a cell wall structure similar to that of Gram+ bacteria are classified in the division Tchmtaci1.ez*. Another division, Ogastiles, unites all bacteria that have a cell wall characteristic of Gram bacteria. The third division unites special forms of bacteria that lack a true cell wall; they do not play a role in food production and therefore will not be considered. Bacteria that are important in food production belong to the first two sections.
Department of r1gtaci1es. It includes 4 groups; The division into groups is based on the shape of the cells and the ability to form endospores and exospores. These are cocci, two groups of rod-shaped bacteria, actinomycetes and related organisms.
Cocci are characterized by a round shape; cell division occurs in one or more planes, and various combinations of cells are formed; cocci are immobile and do not form endospores. Many micrococci are causative agents of food spoilage; leuconostoc is a pest in sugar production; some staphylococci, developing in food products, produce poisonous substances
* From Lat. “cuticle” - skin, “firma” - solid, “gratia” - graceful.
substances (toxins) and cause food poisoning. This* also includes lactic acid streptococci, used in the production of fermented milk products, margarine, butter, etc.
The second group are rods that form endospores. These include one family, whose representatives are very widespread in nature. These are single rods connected in chains, many of them are mobile and have peritrichous flagellation. The rods form endospores of the bacillary type (genus Bacchis) and clostridial or plectridial type (genus ClosxrMst). Many are causative agents of food spoilage (for example, putrefactive, butyric acid bacteria). There are many causative agents of infectious diseases (anthrax, tetanus) and food poisoning - botulism.
The third group is rods that do not form endospores. These include only one family, which includes the genus Lactobacus. These are rod-shaped, non-spore-forming lactic acid bacteria*. More often they are single long and thin sticks, sometimes short sticks in chains. They are pests in fermentation processes. They are used in the production of fermented milk products, cheese making, pickling vegetables, and bakery.
The fourth group is actinomycetes and related organisms. Actinomycetes are a peculiar group of bacteria, which are long thin branching filaments without partitions, called hyphae, the interweaving of which forms mycelium. The lower part of the mycelium, growing into the substrate, is called substrate mycelium and serves to provide the body with nutrition, the upper part of the mycelium rises above the substrate and is called aerial mycelium. Actinomycetes reproduce by exospores formed in spore carriers. Some of the actinomycetes are short, branching rods. Found on food products, they can cause spoilage, in which the food acquires a distinct earthy odor. There are also pathogenic species (tuberculosis and diphtheria bacilli). Actinomycetes are the main producers of antibiotics produced on an industrial scale, as well as B vitamins (B b 2, B 3, B 6, B 1 2).
Division (3g achischesis. All representatives of Gram bacteria do not form spores and differ sharply in their ability to develop in light and without it. Bacteria found in food production are indifferent to light. They differ in the shape of cells and the method of movement. In the number of representatives
* Despite the fact that representatives of this genus are rods that do not form spores, in the scientific literature they retain the old name Lacto-Lacchis.
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lords And significance in nature and human life, the most interesting of them are pseudomonads and enterobacteria.
Of the pseudomonads, the most important for food production is the extensive genus Pseudomonas. These are single mobile rods with one or a bunch of polar flagella (monotrichs and lophotrichs). Pseudomonas are very widespread V nature, actively participate in the cycle of substances, are often found in water bodies and soil contaminated with various compounds, such as pesticides, and also participate in their decomposition. Many of the pseudomonads form fluorescent pigments that are released into the environment and cause spoilage of food products (some putrefactive, fat-oxidizing and other bacteria).
Gram rods also include acetic acid bacteria of the genera Acetobae (er (peritrichs) and Dicopobaciler (mono-trichs), used in the production of vinegar. Many of them are pests in fermentation industries.
In food production, the most important group of intestinal bacteria is Enterobacteriaceae. These are single mobile rods, peritrichs, but there are also stationary forms. Some of them constantly inhabit the intestines of humans and animals (for example, E. coli), others are causative agents of infectious gastrointestinal diseases (dysentery, typhoid fever, paratyphoid fever) transmitted through food products, as well as causative agents of food poisoning.
The classification of bacteria that are important in food production and discussed in this course is given on p. 20.
EUKARYOTES (MYCELIAL FUNGI AND YEAST)
One of the three kingdoms belonging to the superkingdom, eukaryotes, are fungi. Previously, it was believed that fungi occupy an intermediate position between the plant and animal kingdoms, since a number of characteristics bring them closer to both animals and plants. But at present, fungi are classified into a separate kingdom Myco1a. This large and diverse group of organisms includes up to 100 thousand species.
Mushrooms are widespread in nature. They live in various climatic zones from the tropics to the Arctic, and are especially numerous in soils, including high-mountain ones, on plants; They are found in fresh and salt water bodies, in places with high humidity, etc. Mushrooms need organic substances for their development.
Among fungi there are organisms that develop from the organic substances of dead organisms; they participate in the cycle of substances in nature. But there are also those
Rice. 9. Mushroom mycelium:
A- unseptate; b - septate
which can only exist in living organisms and cause their diseases. Some of the mushrooms produce toxic substances - mycotoxins. Many fungi cause food spoilage and damage to a variety of products and materials, some can even grow on optical surfaces where there is a minute amount of lubricant. They utilize lubricant and cause clouding of the lenses. But mushrooms also have important practical significance; many of them are eaten, used in the production of ethyl alcohol, organic acids, enzymes, antibiotics, vitamins, some types of cheese, etc.
Filamentous fungi. The kingdom of fungi is divided into seven classes, but the objects of study of microbiology are mainly three, including filamentous fungi - zygomycetes (formerly called molds), ascomycetes and deuterium.
Shape and dimensions. The cells of filamentous fungi have an elongated shape in the form of filaments (hyphae), the dimensions of which reach up to 5-30 microns in diameter, which significantly exceeds the size of a bacterial cell.
The interweaving of hyphae forms the body of the mushroom - mycelium, or mycelium(Fig. 9). Most of the hyphae develop above the surface of the substrate (aerial mycelium), on which the reproductive organs are located, and some - in the thickness of the substrate (substrate mycelium). The hyphae of most filamentous fungi are multicellular; their cells have transverse partitions - septa Such mycelium is called septate, it is found in ascomycetes and deuteromycetes. The mycelium of zygomycetes is nonseptate and consists of one giant cell with several nuclei. Hyphae grow by apical cells, and hyphal cells are not uniform in length.
Some fungi at a certain stage of development form fruiting bodies, inside which there are organs of various
Rice. 10. Mushroom structure diagram
1 - cell wall; 2 - core; 3 - nuclear membrane; 4 - ribosomes; 5 - Golgi apparatus; 6 - cytoplasmic membrane; 7 - lysosomes; 8 - endoplasmic reticulum; 9 - mitochondria; 10 - cytoplasm
multiplications covered on top with a dense interweaving of hyphae. In other types of fungi, dense interlacings of highly branched hyphae form sclerotssh, rich in reserve nutrients. They serve to endure unfavorable conditions and are the resting form of the fungus.
Filamentous fungi do not have flagella and are nonmotile organisms.
Cell structure. In filamentous fungi, cells
have a structure characteristic
for cells of eukaryotic microorganisms (Fig. 10). They have a well-developed system of intracellular elementary biological membranes (unlike prokaryotes, which have only one membrane structure inside their cells - the cytoplasmic membrane). The intracellular structures of eukaryotes, completely limited from the cytoplasm by such membranes, are called organelles. In addition to the CPM, organelles include the nucleus, mitochondria, endoplasmic reticulum, Golgi apparatus and lysosomes.
Outside, the cell of filamentous fungi is covered with a multilayered rigid cell wall, consisting of 80-90% polysaccharides. The main one is the nitrogen-containing polysaccharide chitin. Polysaccharides are associated with proteins, lipids, and polyphosphates. Below the cell wall is the CPM, which surrounds the cytoplasm. Located in the cytoplasm core; it contains nucleolus, chromosomes and is surrounded by a nuclear membrane with pores. Ribosome precursors are synthesized and accumulated in the nucleolus, which are then transported through the pores of the nucleus into the cytoplasm. Mushrooms have from one to 20-30 nuclei in their flies. Scattered in the cytoplasm ribosomes.
Mitochondria- membrane structures that play a very important role. They are multi-chamber sacs or tubes with elastic walls that form invaginations - cristas(Fig. 11). They contain oxidative- 
Rice. 11. Scheme of the structure of mitochondria:
A- general structure diagram; b - longitudinal section of a mitochondria; / - outer mitochondrial membrane; 2 - inner mitochondrial membrane; 3 - cristae; 4 - matrix
reducing enzymes (in prokaryotes, these enzymes are localized in the CPM) involved in energy metabolism. Therefore, mitochondria are called “power stations of the cell”, “energy ensembles”, etc.
Endoplasmic reticulum--membrane system consisting of tubules, vesicles or cisterns that do not have a strictly defined localization, but are located either along the periphery of the cell, or around the nucleus, or permeate the entire cytoplasm
plasma. They contain various enzymes responsible for the synthesis of lipids, carbohydrates, and the transport of substances within the cell. Golgi apparatus- a system of membranes associated with the nuclear membrane and membranes of the endoplasmic reticulum. It is located in a region of the cytoplasm where there are no ribosomes. The role of the Golgi apparatus is not fully understood. It is assumed that the Golgi apparatus synthesizes cell wall material and new membranes, and also with its help transports substances synthesized in the endoplasmic reticulum and removes metabolic products from the cell.
Lysosomes They are membrane structures of round shape. They contain hydrolytic enzymes (in prokaryotes they are localized in the CPM), which break down proteins, polysaccharides, and lipids.
In the cells of filamentous fungi are clearly visible vacuoles- cavities surrounded by a membrane and filled with cell sap. They are usually located near the cell wall, and their number increases as cells age. The main reserve nutrients of filamentous fungi are glycogen, which is formed on media with excess sugar; metachromatin, which is in the form of granules in the vacuoles themselves, and lipids accumulate in the cytoplasm near the vacuoles in the form of fat droplets.
Reproduction and classification. Filamentous fungi reproduce asexually and sexually. Both methods of reproduction are associated with the formation of spores - external (exo-spores) and internal (endospores). The formation of spores during sexual reproduction is preceded by the process of fusion of the contents of two cells and their nuclei. The newly formed nucleus is divided into several parts - a spore. In addition, all mushrooms
Rice. 12. Zygomycetes:
1 - Kb12oriz; b - Misog - sporangium with endospores; V - successive stages of zygospore formation during sexual reproduction; G- germinated zygospore with sporangium
can reproduce vegetatively - by apical growth
hyphae, as well as with the help of pieces of hyphae and mycelium. Mushrooms, spo
capable of sexual reproduction, belong to perfect
(ascomycetes, zygomycetes), and those that do not have sexual
reproduction refers to imperfect mushrooms (deutero-
mycetes). Fungi have a wide variety of ways
and reproductive organs. \
Class Zygomycetes (zygomycetes). These are the most simply organized mushrooms. Their mycelium is nonseptate, multinucleate, and looks like one giant branched cell. Zygomycetes include mucor fungi. They are widespread in nature. Representatives of the genera Misog and KYgoriz are of greatest importance.
Zygomycetes reproduce asexually and sexually (Fig. 12). With asexual reproduction^ in special spherical swellings - sporangia, formed at the ends of long fruiting hyphae - sporangiophores, endospores are formed, called sporangiospores. Sporangiophores can be solitary (in fungi of the genus Misog) or collected in bunches with root-like growths at the base - rhizoids (in fungi of the genus Khoriz).
During sexual reproduction, first there is a fusion of two multinucleated mycelial hyphae, which are usually short formations with a slight thickening at the ends. Then a pairwise fusion of nuclei occurs. Sexual reproduction ends with the formation zygotes(zygospores), which after a period of dormancy germinates and forms a short hypha with a sporangium at the end. During spore germination, nuclear division occurs. The multinuclear cytoplasm of the sporangium breaks up into many sporangiospores, which under favorable conditions can germinate into mycelium.
Rice. 13. Conidiophores of ascomycetes: A - in fungi of the genus Asperidchis; b- in fungi of the genus Regps; / - vegetative mycelium; 2 - conidium-carrier; 3 - phialids; 4 - conidia
Many mushrooms of the genus * Misog cause food spoilage by forming fluffy gray deposits. Fungi of the genus Khoriz cause so-called “soft rot” of berries, fruits and vegetables. Flour fungi form organic acids and enzymes and are capable of causing weak alcoholic fermentation, which is why they are used in some Eastern countries to produce drinks.
Class Az sot u-se1;e5 (and with Komi tse-ty, or marsupial fungi). These include representatives of the widespread fungi of the genera Pestrum and Az-pergum.
Ascomycetes have well-developed multicellular mycelium. Asexual reproduction occurs with the help of exospores called conidia, which are formed at the ends of specialized hyphae - conidiophores. In Aspergillus they are simple, without partitions, swollen at the top in the form of a bubble, on which they are located phialides, separating chains of spherical conidia. In penicillids, the conidiophores are multicellular, in the form of a brush consisting of whorls of phialids (Fig. 13). Conidia come in different colors (green, yellow, black, blue, etc.). Conidia are spread by air currents, insects, drops of dew, rain and, germinating, form a new mycelium.
Sexual reproduction of ascomycetes occurs by fusion of the contents and nuclei of two cells of different hyphae, after which nuclear division occurs; Cytoplasm is concentrated around the new nuclei and a spore membrane is formed. The mother cell becomes covered with a thick membrane and turns into ask(bag), inside of which there are most often 8 ascospores. The top of the bag is covered with an interlacing of hyphae, forming fruiting body.
Rice. 14. Conidiophores and conidia of various genera of imperfect fungi: A- Vo1guIz; b- Rizagsht; V - AIerpaNa; G - C1ac1o5ropit
However, some representatives of marsupial fungi have found practical application. Thus, some representatives of penicillium fungi are used as producers of the antibiotic penicillin on an industrial scale, while others are used in the production of Roquefort and Camembert cheese. Aspergillus produces organic acids, and therefore is used for the industrial production of citric acid (Aspergillus citric acid). Many aspergilli are used for the industrial production of various enzyme preparations used in the food and light industries.
Class Deuteromycetes (deuteromycetes). Deuteromycetes, or imperfect fungi, have multicellular mycelium. They do not have sexual reproduction; they reproduce only asexually, mainly by conidia, which, like conidiophores, have a wide variety of shapes and appearances.
Conidiophores are most often multicellular, but can be solitary - branching or in the form of bundles, with swellings. Conidia can be unicellular, multicellular, sometimes with longitudinal and transverse partitions (Fig. 14). The shape of conidia is spherical, ellipsoidal, filamentous
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prominent, sickle-shaped, star-shaped, etc. Some deuteromycetes (for example, milk mold) reproduce not by conidia, but by special cells - arthrospores, which are formed as a result of fragmentation of the conidiophore or hyphae (Fig. 15).
Imperfect fungi are widespread in nature. Do most of them cause various diseases? plants and food spoilage. Thus, representatives of the genus Rhine are causative agents of diseases of fruits and vegetables (fusarium) and cause spoilage of potatoes (dry rot). Some species of this fungus produce substances that are toxic to humans and cause severe food poisoning. Fungi of the genus Vogguiz cause spoilage of onions, cabbage, carrots, tomatoes, and, together with other fungi, rot of sugar beets. Mushrooms of the genus A1-(ermana) infect root crops during storage (black rot). Heart rot of beets is caused by a fungus of the genus Pbo-ta. Milk mold Deodoshchum sanctilum causes spoilage of pickled vegetables, sour cream, cottage cheese, etc., forming a white velvety film on the surface. Mushrooms from the genus Clacosropyga are often found on food products stored in refrigerators.
Yeast. The yeast group includes unicellular fungal organisms that do not have a true mycelium.
Yeasts are widespread in nature. They live mainly on plants where there are sugary substances that they ferment (nectar of flowers, juicy fruits, berries, especially overripe and damaged ones, leaves, birch trunks during sap flow and oak trunks during mucus flow, soil). Yeast is carried by the wind , rain and insects.
Shape and dimensions. Yeast can have oval, ovoid, round, lemon-shaped, less often cylindrical, triangular, sickle-shaped, arrow-shaped, flask-shaped cells. The size of yeast varies among different species from 1.5 - 2 to 10 microns in diameter and up to 2---20 microns (sometimes up to 50 microns) in length.
Rice. 1.6. Diagram of the structure of a yeast cell:
1 - cytoplasmic membrane; 2 - cell wall; 3 - nucleolus; 4 - core; 5 - fat drops; 6 - mitochondria; 7 - vacuole; 8 - polyphosphate granules; 9 - endoplasmic reticulum; 10 - dictyoso-we; 11 - kidney scar; 12 - ribosomes; 13 - cytoplasm
Some yeasts at a certain stage of development can form mycelial structures - pseudomycelium. Yeast, like all fungi, are nonmotile organisms.
Cell structure. Yeast, like filamentous fungi, belongs to eukaryotes and has a cell structure similar to them, but there are some differences (Fig. 16). The cell wall of yeast, unlike fungi, consists of 60-70% polysaccharides glucan and mannan, associated with proteins." and lipids, and only a small amount (1-3%) is chitin, which is embedded in the wall in the form of granules. In a number of yeasts, under certain conditions, mucous capsules of varying thickness of a polysaccharide nature can be formed.. Cells of such yeast can stick together, form flakes and settle to the bottom of the vessels in which they develop.
Yeast cells, like fungi, have well-developed:; membrane apparatus - CPM, endoplasmic reticulum, Golgi apparatus, lysosomes, mitochondria. The cytoplasm contains a nucleus. Ribosomes in yeast are located in the cytoplasm and on? the outside of the nuclear membrane. There are vacuoles and inclusions of reserve nutrients: lipids (especially in yeast - lipid producers), glycogen, metachromatin. The cellular structures of yeast perform the same functions as those of fungi.
Reproduction and classification. Yeast reproduces vegetatively and by spores produced asexually and sexually. The method of reproduction is an important characteristic for the classification of yeast. Vegetative methods of propagation include: budding, division and budding division (Fig. 17).
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Methods of vegetative propagation of yeast: budding; a - budding, b - division; V - budding division
Budding is the most common method of yeast propagation. During budding, a small tubercle appears on the surface of the mother (dividing) cell - bud, which gradually increases to almost the size of the mother cell and turns into a daughter cell. It separates from the mother, leaving a kidney scar at the site of attachment. The bud no longer forms at this site. One bud may form (polar budding), two buds at different ends of the mother cell (bipolar budding), or in several places on the surface of the mother cell (multiple budding). Daughter cells may not be separated from the mother cell and remain connected to it. Budding is characteristic of oval and round shaped yeasts.
In some yeasts, during budding, daughter cells do not separate from the mother, but stretch out in length and continue to form more and more new buds, which leads to the formation of false mycelium (pseudomycelium). Pseudomyadelic is characteristic of filmy yeasts.
Division cells as a result of the formation of a transverse partition in it - a septum - is characteristic of cylindrical yeast.
Budding division characterized by the fact that the formation of daughter cells begins with budding and ends with the appearance of a clearly visible septum in the area of the isthmus. This method of reproduction is typical for lemon-shaped yeast.
Any vegetative method of reproduction is preceded by nuclear division, in which one of the newly formed nuclei, along with the cytoplasm and part of the cellular structures, becomes V daughter cell and they get the opportunity to exist independently. Some yeasts have a method of asexual reproduction using asexual spores formed without the fusion of yeast cells. Asexual spores - endospores - often appear in indefinite numbers in old: yeast cultures that reproduce by division and form mycelium.
Sexual reproduction in yeast also occurs with the help of spores, but their formation is preceded by the process of copulation (fusion of the contents of two cells and their nuclei). A zygote is formed, in which spores then form: the nucleus divides, the cytoplasm compacts around the new nuclei, and they become covered with a dense membrane. A zygote with spores inside 1 is called an ascus (bag), and the spores are called ascospores. Such yeasts belong to the class of ascomycetes and are called ascomycete yeasts. Ascospores can only be formed by young cells grown on a complete nutrient medium and transferred to conditions of starvation, poor supply of oxygen and moisture. In different types of yeast, 2-4, and sometimes 8 spores are formed in the ascus.
Under favorable conditions, ascospores emerge from the ascus and transform into vegetative cells. In some species of yeast, the nuclei of mother and daughter cells or the nuclei of two sister buds can fuse. Sometimes copulation of germinating spores of neighboring cells occurs.
Yeast ascospores can be oval, round, bean-shaped, needle-shaped, helmet-shaped, cap-shaped. with a smooth, wrinkled surface, with warty or awl-shaped outgrowths, etc. Yeast spores, as well as spores of filamentous fungi, perform a dual function: they serve to endure unfavorable conditions, but most importantly, unlike endospores of bacteria, they serve for reproduction . Yeast spores are more stable than vegetative cells, but* less stable than bacterial spores. Thus, yeast spores withstand heating at a temperature 10° more than a vegetative cell (40-50 °C), and bacterial spores - 50-60 °C more than vegetative cells (60-120 °C).
Since yeasts are essentially single-celled, non-mycelial fungi, they are included in the classification* of fungi. However, they are not separated into a separate systematic unit, but are distributed among three classes of fungi - ascomycetes, basidiomycetes and deuteromycetes. For the microbiology of food production, only ascomycete and imperfect yeasts are important. There is a fundamental difference between these yeasts: ascomycete yeasts have. sexual process and they cause vigorous alcoholic fermentation. .Imperfect yeast does not undergo the sexual process and, as a rule, causes weak alcoholic fermentation or does not cause it at all.
Ascomycete yeast. Includes approximately 2/3 yeast. Among them, Saccharomycetes are of greatest practical importance, uniting more than half of the known yeast genera. A particularly important role belongs to the genus Saccharomyces, all species of which cause vigorous alcoholic fermentation. Yeasts of this genus reproduce asexually (budding) and with the help of ascospores, which form sexually.
In food production, two types of yeast of this genus are most widely used: Saccharomyces cerevisia (large oval cells) in the production of ethyl alcohol, beer, kvass and in baking, and Saccharomyces ellipsoides (large elliptical cells) - they are used mainly in winemaking. Each of these industries uses its own specific race(varieties) of these types of yeast, which have the most valuable production properties.
Ascomycete yeasts also include other genera of yeast. This is the genus of Schizosaccharomycetes, the cells of which are rod-shaped and reproduce by division or with the help of “ascospores formed as a result of sexual reproduction * (their number is 4-8). Yeasts of this genus cause alcoholic fermentation. Type 3 Schizosaccharomyces pombe is used V fermentation industry in countries with hot climates, for example in Africa, where Pombe beer is produced. Yeasts of the genus Saccharomycoda have large lemon-shaped cells. They reproduce by budding division at both ends of the cell (bipolar) and with the help of ascospores (there are 2-4 of them), which are arranged in pairs and are formed sexually. Moreover, with the sexual method, copulation of spores occurs in the ascus, and not the fusion of yeast cells. These yeast causes alcoholic fermentation, and they are pests in winemaking, as they form (products that give wines an unpleasant sour smell.
Some ascomycete yeasts are used in the microbiological industry to produce lipids and vitamins. Thus, yeast of the genus Lipomyces have large round cells, which in old cultures are filled entirely with a large drop of fat. They usually have well-defined capsules. Yeasts of the genus Lipomyces reproduce by budding and ascospores, the number of which in some species can reach up to 30 in one ascus.
Imperfect yeast. They belong to the class of deuteromycetes. They do not form spores, so these yeasts are often called asporogenous. They reproduce by budding. Imperfect yeast causes either weak fermentation or no fermentation at all, which is why they are often called non-saccharomycetes.
Many of them cause food spoilage and are pests in a number of food industries. However, some of the imperfect yeasts have found useful practical applications. Among the imperfect yeasts, the most important genera are Candida, Torulopsis and Rhodotorula.
Yeasts of the genus Candida have elongated cells, the combinations of which form a primitive pseudomycelium. Many of them do not cause alcoholic fermentation and are pests in fermentation industries (for example, Candida mycoderma), since, being aerobes, they oxidize alcohol to di: carbon monoxide (carbon dioxide) and water. Other representatives of the genus Candida are pests in yeast production and reduce the quality of baker's yeast, as they are weak-fermenting species. Some of them cause spoilage of pickled vegetables, soft drinks and a number of other products. Among these yeasts there are pathogenic species that cause candidiasis, affecting the mucous membranes of the oral cavity, nasopharynx and other human organs. Various types of yeast of the genus Candida are used to obtain feed protein and protein-vitamin concentrates (PVC).
Yeasts of the genus Torulopsis have small round or oval cells. Many species are capable of causing weak alcoholic fermentation and are used in the production of kefir and kumiss. Some are used for industrial production of feed protein.
Yeasts of the genus Rhodotorula have round, oval or elongated cells, the latter forming pseudomycelium. Colonies of such yeast are red and yellow due to the presence of carotenoid pigments, which are provitamin A. These yeasts are used for the industrial production of feed protein-carotenoid concentrates, which serve as a source of fat-soluble vitamin A for animals. Other representatives of this genus accumulate a lot of lipids in cells and are used in the microbiological industry as lipid producers, along with representatives of another genus of imperfect yeast - Cryptococcus.
VIRUSES
The invention of the electron microscope made it possible for the first time to observe the smallest organisms - viruses and phages. Viruses are often called filterable for their ability to pass through the pores of bacteriological filters, which retain bacteria during mechanical sterilization. Viruses were discovered in 1892 by the Russian botanist D.I. Ivanovsky while studying a disease of tobacco - tobacco mosaic. Their sizes range from 10-12 nm (foot-and-mouth disease, polio viruses) to 200-350 nm (smallpox, herpes viruses).
Viruses do not have a cellular structure. They are spherical, rod-shaped, filamentous and sperm-shaped. The viral particle is called a virion. It consists of nucleic acid (DNA or RNA) and globulin protein; some viruses also contain lipids and carbohydrates. Characteristics
Rice. 18. Phage structure diagram:
1 - head; 2 - DNA; 3 - process; 4 - rod; 5 - basal plate with spines; 6 - threads of the process
A significant feature of viruses is their ability to form crystals, which has long been the cause of debate about the living or nonliving nature of viruses. Subsequently, it was proven that the crystals are nucleic acid and protein. Then a number of properties were established that confirmed the idea of the living nature of viruses - the ability to self-reproduce (reproduction), variability, adaptability to living conditions, as well as the ability to cause infectious processes. The development and reproduction of viruses is possible only in the cells of a living organism - the host, i.e. they are parasites of humans, causing infectious diseases (influenza, polio, measles, chicken pox, etc.), as well as animals and plants.
To treat some diseases caused by influenza viruses, herpes and adenoviruses, enzyme preparations are used - nucleases, causing the destruction of nucleic acids, which deprives viruses of the ability to reproduce themselves, and therefore eliminates their infectivity.
In 1898, the Russian scientist N.F. Gamaleya, while studying anthrax in cattle, first observed that spore-forming bacilli - the causative agents of the disease - dissolve under the influence of some agent. In 1915, the English microbiologist F. Twort and in 1917, the Canadian microbiologist F. D. Errel, established the nature of this phenomenon. It was called bacteriophagy, and the causative agent was called a bacteriophage (“bacteria eater”).
The sizes of phages range from 40 to 140 nm. Bacteriophages have the appearance of a multifaceted heads with rod, coated on the outside with a protein shell (Fig. 18). There is a channel inside the rod. The phage head is filled with a DNA molecule. At the base of the rod there is basal plate with spikes and threads.
The effect of phage on a bacterial cell occurs in several stages (Fig. 19): adsorption of the phage on the bacterial cell using a basal plate with teeth and threads, penetration of DNA from the phage head through the channel into the bacterial cell, in which then, under the influence of phage DNA
Fig* 19. Scheme of phage development in a bacterial cell:
A - adsorption; b- transfer of DNA into the cell; V- restructuring of metabolism in the cell;
G - formation of new bacteriophage particles; d - cell wall dissolution
a complete restructuring of metabolism occurs, it is no longer bacterial DNA that is synthesized, but phage DNA, which leads to To the formation of new phage particles in the bacterial cell, dissolution of the bacterial cell wall, its death.
Bacteriophages cause great harm in the dairy industry (production of cheese, cottage cheese, sour cream) and in the production of margarine. They mainly infect lactic acid streptococci in the starter cultures used to produce these products. Under the influence of the bacteriophage, streptococcal cells lyse (dissolve) and die. In the antibiotic industry, actinophages lyse the production culture of actinomycetes - antibiotic producers.
In medicine, bacteriophages are used to treat certain diseases, such as dysentery.
Bacteria
Bacteria are single-celled prokaryotic microorganisms. Their size is measured in micrometers (µm). Bacteria do not have a variety of forms. There are three main forms: spherical bacteria - cocci, rod-shaped and convoluted. In addition, there are intermediate forms (Fig. 2).
Cocci(Greek kokkos - grain) have a spherical or slightly elongated shape. They differ from each other depending on how they are located after division. Cocci located singly are micrococci, and cocci located in pairs are diplococci. Pathogenic diplococci include lancet-shaped pneumococci and bean-shaped diplococci - meningococci and gonococci. Streptococci divide in one plane and after division do not diverge, forming chains (Greek streptos - chain). Pathogenic streptococci are the causative agents of purulent-inflammatory diseases, sore throat, erysipelas, and scarlet fever. Tetracocci form combinations of four cocci as a result of division in two mutually perpendicular planes, sarcina (lat. sarcio - to bind) are formed by division in three mutually perpendicular planes and look like clusters of 8-16 cocci. As a result of random division, staphylococci form clusters resembling a bunch of grapes (Greek staphyle - bunch of grapes). Among them there are pathogenic species that cause purulent-inflammatory and septic diseases.
Rod-shaped bacteria (Greek bacteria - stick) capable of forming spores are called bacilli if the spore is not wider than the stick itself, and clostridia if the diameter of the spore exceeds the diameter of the stick. Rods that are incapable of sporulation are called bacteria. Rod-shaped bacteria, unlike cocci, are diverse in size, shape and arrangement of cells: short (1-5 µm), thick, with rounded ends, bacteria of the intestinal group; thin, slightly curved tuberculosis bacilli; thin diphtheria rods located at an angle; large (3-8 microns) anthrax bacilli with “chopped off” ends, forming long chains - streptobacilli. Convoluted forms of bacteria include vibrios, which have a slightly curved comma-shaped shape (Vibrio cholerae) and spirilla, consisting of several curls. Convoluted forms also include Campylobacter, which under a microscope looks like the wings of a flying seagull.
Bacterial cell structure. The structural elements of a bacterial cell can be divided into: a) permanent structural elements - present in each type of bacteria throughout the life of the bacterium; this is the cell wall, cytoplasmic membrane, cytoplasm, nucleoid; b) unstable structural elements that not all types of bacteria are capable of forming, and those bacteria that form them can lose them and acquire them again depending on the conditions of existence. These are the capsule, inclusions, pili, spores, flagella.
Cell wall covers the entire surface of the cell. Gram-positive bacteria have a thicker cell wall: up to 90% is a polymer compound of peptidoglycan associated with teichoic acids and a layer of protein. In gram-negative bacteria, the cell wall is thinner, but more complex in composition: it consists of a thin layer of peptidoglycan, lipopolysaccharides, and proteins; it is covered with an outer membrane. The outer membrane of gram-negative bacteria is a barrier to some antibiotics, including those that have been developed recently. It is possible that this can explain why, recently, gram-negative bacteria, such as Escherichia coli and Pseudomonas aeruginosa, have been playing an increasingly important role in the occurrence of nosocomial infections. Previously, the leadership in this area belonged to staphylococci.
The cell wall plays an important biological role: it gives the bacterium a certain shape, protects it from environmental influences, and participates in the transport of nutrients and metabolic products. At the same time, cell wall peptidoglycan is a target for the action of penicillin and other antibiotics, which disrupt the formation of polymeric peptidoglycan. This makes it clear why penicillins act predominantly on gram-positive bacteria, and on young growing cells.
The importance of the cell wall in maintaining a certain shape and protecting it from the environment is clearly demonstrated by the example of spheroplasts and protoplasts, which are formed when the cell wall is destroyed under the influence of penicillin or lysozyme. Completely or partially lacking a cell wall, they are spherical in shape, can survive only in a hypertonic environment and are unable to reproduce. L-form bacteria are bacteria that have completely or partially lost their cell wall, but have retained the ability to reproduce. They received their name in honor of the Lister Institute in England, where they were first obtained. Having no cell wall, they also acquire a spherical shape. L-forms also occur in natural conditions, persist for a long time in the human body and play an important role in the pathogenesis of some infectious diseases.
Cytoplasmic membrane located directly under the cell wall. It has selective permeability, and thanks to this it regulates the water-salt metabolism of the cell, the transport of nutrients into the cell and the excretion of metabolic products. Permease enzymes are involved in these processes. In addition, there are enzymes that carry out biological oxidation.
The cytoplasmic membrane, by invagination into the cell, forms membrane structures - mesosomes. The cell's genome (DNA) is associated with the mesosome, and from here the process of DNA replication begins during cell division.
Cytoplasm - The internal gel-like contents of the bacterial cell are permeated with membrane structures that create a rigid system. The cytoplasm contains ribosomes (in which protein biosynthesis occurs), enzymes, amino acids, proteins, and ribonucleic acids.
Nucleoid - This is a bacterial chromosome, a double strand of DNA, closed in a ring, associated with the mesosome. Unlike the nucleus of eukaryotes, the DNA strand is freely located in the cytoplasm and does not have a nuclear membrane, nucleolus, or histone proteins. The DNA strand is many times longer than the bacterium itself (for example, E. coli has a chromosome length of more than 1 mm).
In addition to the nucleoid, the cytoplasm may contain extrachromosomal heredity factors called plasmids. These are short, circular strands of DNA attached to mesosomes.
Inclusions are contained in the cytoplasm of some bacteria in the form of grains that can be detected by microscopy. Mostly this is a supply of nutrients. For example, diphtheria bacilli have volutin grains at the ends, and this is an important feature for identifying this type of bacteria. At the same time, these can also be accumulations of inorganic substances, for example, sulfur, and products of bacterial metabolism.
Drank (Latin pili - hairs) otherwise cilia, fimbriae, fimbriae, villi - short thread-like processes on the surface of bacteria. Common pili, several hundred in number, uniformly cover the bacterium. They carry out attachment (adhesion) of bacteria to the host cell and participate in nutrition. Sex pili (sex pili) have a canal inside and are formed only by donor cells. They ensure conjugation in bacteria and the transfer of DNA from one cell to another.
Controversy Among pathogenic bacteria, only rods form - bacilli and clostridia. Bacterial spores are not a method of reproduction, since only one spore is formed from one cell. The biological role of spores is the preservation of the species in unfavorable environmental conditions.
The transformation of a bacterial cell into a spore occurs when the bacterium enters the external environment, most often into the soil. The spore is formed inside the cell, then the vegetative body is lysed. Spore formation occurs within 24 hours. The spores are extremely stable and can remain viable for a long time: spores of the causative agents of anthrax, tetanus, and botulism remain alive in the soil for decades. They do not die at 100°C; they can only be killed by autoclaving, dry heat at 160-170°C for 1-2 hours, or using sporicidal chemicals. When exposed to favorable conditions (optimal temperature, sufficient humidity, availability of nutrients), spores germinate into vegetative forms. Warming the spores at 100°C causes their thermal activation followed by germination. This phenomenon is used in sterilization using fractional methods.
Sporulation is one of the properties characteristic of certain types of bacteria. The shape and location of the spore within the cell are a permanent feature of the species and can be used to identify it. The shape of the spores can be round or oval. The location is central - in anthrax bacilli, subterminal (closer to one of the ends) - in botulinum clostridia and gas anaerobic infection, terminal (at the end) - in tetanus clostridia. For staining spores, the Ozheshka method is used, based on their acid resistance.
Flagella. Many types of bacteria are able to move thanks to the presence of flagella. Of the pathogenic bacteria, only among the rods and convoluted forms there are mobile species. Flagella are thin elastic threads, the length of which in some species is several times greater than the length of the body of the bacterium itself. The number and location of flagella is a characteristic species characteristic of bacteria. Bacteria are distinguished: monotrichs - with one flagellum at the end of the body, lophotrichs - with a bundle of flagella at the end, amphitrichs, which have flagella at both ends, and peritrichs, in which the flagella are located over the entire surface of the body. Monotrichs include Vibrio cholerae, and peritrichs include Salmonella typhoid.
The flagella are so thin that they are not visible under a light microscope. They can be seen in an electron microscope, as well as with special staining methods, when the thickness of the flagellum is artificially increased: with the help of tannin, the flagellar protein is swollen, and then treated with silver nitrate or a dye, which settles on the flagella, increasing their thickness. One can indirectly judge the presence of flagella by observing the mobility of living bacteria in “crushed” or “hanging” drop preparations. Determining the motility of bacteria is an important diagnostic feature, and in everyday practical work it is convenient to use the sowing method. Bacteria are inoculated into a column of semi-liquid nutrient agar by pricking. Immobile bacteria grow along the course of the injection, while mobile bacteria exhibit diffuse growth.
Capsule - the outer mucous layer that many bacteria have. In some species it is so thin that it can only be detected in an electron microscope - this is a microcapsule. In other types of bacteria, the capsule is well defined and visible in a conventional optical microscope - this is a macrocapsule. The capsule usually consists of polysaccharides, and in anthrax bacillus - of polypeptides
Some bacteria form a capsule only in the host’s body, for example, pneumococci, anthrax bacillus, plague bacillus; others permanently retain it - these are capsular bacteria, for example, Klebsiella. The capsule protects bacteria from phagocytosis and antibodies, so in the infectious process it plays the role of one of the pathogenicity factors that ensure the antiphagocytic activity of the pathogen. The presence of a capsule is a differential feature for determining the type of microbes such as pneumococcus, anthrax, Klebsiella pneumoniae, which form a macrocapsule visible in a light microscope. To detect the capsule, the Burri-Gins staining method is used: in this case, fuchsin-stained bacteria surrounded by a colorless capsule are visible against a dark background of ink.
Mycoplasmas
Mycoplasmas are prokaryotes, their sizes are 125-200 nm. These are the smallest of cellular microbes, their size is close to the resolution limit of an optical microscope. They lack a cell wall, and in this respect they are close to the L-forms of bacteria. The absence of a cell wall is associated with the characteristic features of mycoplasmas. They do not have a constant shape, so spherical, oval, and thread-like shapes are found. Since mycoplasmas do not form peptidoglycan, they are insensitive to penicillins and other antibiotics that selectively inhibit the synthesis of this substance.
Mycoplasmas are widespread in nature. They can be isolated from soil, wastewater, animals and humans. There are also pathogenic species: Mycoplasma pneumoniae is the causative agent of respiratory diseases. Opportunistic Mycoplasmas also play a role in the development of diseases: M.hominis - diseases of the genitourinary tract, M.arthritidis - rheumatoid arthritis. Of the genus ureaplasmas, Ureaplasma urealyticum is pathogenic, causing diseases of the genitourinary organs.
Rickettsia
Rickettsia is characterized by pleomorphism, that is, depending on the conditions of existence, their morphology changes. In conditions favorable for reproduction, these are coccoid forms (300-400 nm) or short rods; in conditions when the growth process occurs faster than reproduction, long rods and filamentous forms predominate.
Many species of rickettsia cause human diseases called rickettsioses. These are Rickettsia prowazekii, the causative agent of epidemic typhus, and Coxiella burneti, the causative agent of Q fever.
Chlamydia
Actinomycetes
Actinomycetes are unicellular microorganisms that belong to prokaryotes. Their cells have the same structure as bacteria: a cell wall containing peptidoglycan, a cytoplasmic membrane; the cytoplasm contains the nucleoid, ribosomes, mesosomes, and intracellular inclusions. Therefore, pathogenic actinomycetes are sensitive to antibacterial drugs. At the same time, they have a form of branching intertwining threads similar to mushrooms, and some actinomycetes belonging to the Strentomycetes family reproduce by spores. Other families of actinomycetes reproduce by fragmentation, that is, the disintegration of filaments into separate fragments.
Actinomycetes are widespread in the environment, especially in soil, and participate in the cycle of substances in nature. Among actinomycetes there are producers of antibiotics, vitamins, and hormones. Most antibiotics currently used are produced by actinomycetes. These are streptomycin, tetracycline and others.
Pathogenic representatives of actinomycetes cause actinomycosis and nocardiosis in humans. These are Actinomyces israelli, Nocardia asteroides and others. The causative agents of actinomycosis outside the body, on a nutrient medium, are long branching threads, in places breaking up into fragments. In the human body, pathogenic actinomycetes form drusen - intertwined threads in the center with separate threads extending in the form of rays along the periphery. Hence the name: actinomycetes - radiant fungi. The ends of the threads, immersed in the tissue, are thickened, slimed and have a different chemical composition, and, like a bacterial capsule, protect the microbe from phagocytosis.
Spirochetes.
Spirochetes are prokaryotes. They have characteristics common to both bacteria and protozoan microorganisms. These are single-celled microbes, shaped like long, thin, spirally curved cells, capable of active movement. Under unfavorable conditions, some of them can turn into cysts.
Electron microscope studies made it possible to establish the structure of spirochete cells. These are cytoplasmic cylinders surrounded by a cytoplasmic membrane and a cell wall containing peptidoglycan. The cytoplasm contains the nucleoid, ribosomes, mesosomes, and inclusions. Under the cytoplasmic membrane there are fibrils that provide various movements of spirochetes - translational, rotational, flexion.
Saprophytic spirochetes are present in the environment. Several non-pathogenic species are permanent inhabitants of the human body. Species pathogenic to humans belong to three genera: Treponema, Borrelia, Leptospira. They differ in the shape and arrangement of the curls. Treponemas consist of 8-12 curls of equal size, the position of which does not change during movement. Borrelia form 5-8 curls, changing with movement like the movement of a snake. Leptospires consist of 40-50 very small permanent whorls, the ends are curved in the form of hooks and have thickenings. When moving, the ends of the leptospires bend in different directions, and a shape is formed in the form of the Russian letter C or the Latin S. Spirochetes, with the exception of Borrelia, do not perceive aniline dyes well, so they are stained using the Romanovsky-Giemsa method. It is best to observe live spirochetes in a dark field of view.
Pathogenic representatives of spirochetes: Treponema pallidum - causes syphilis, Borrelia recurrentis - relapsing fever, Borrelia burgdorferi - Lyme disease, Leptospira interrogans - leptospirosis.
Mushrooms.
Fungi (Fungi, Mycetes) are eukaryotes, lower plants, lacking chlorophyll, and therefore they do not synthesize organic carbon compounds, that is, they are heterotrophs, have a differentiated nucleus, and are covered with a shell containing chitin. Unlike bacteria, fungi do not have peptidoglycan in their shell, therefore they are insensitive to penicillins. The cytoplasm of fungi is characterized by the presence of a large number of various inclusions and vacuoles.
Among microscopic fungi (micromycetes) there are unicellular and multicellular microorganisms that differ in morphology and methods of reproduction. Fungi are characterized by a variety of methods of reproduction: division, fragmentation, budding, formation of spores - asexual and sexual.
In microbiological studies, one most often encounters molds, yeasts and representatives of the group of so-called imperfect fungi.
Mold form a typical mycelium spreading along the nutrient substrate. Aerial branches rise upward from the mycelium, ending in fruiting bodies of various shapes carrying spores.
Mucor or capitate molds (Mucor) are unicellular fungi with a spherical fruiting body filled with endospores.
Molds of the genus Aspergillus are multicellular fungi with a fruiting body that, under microscopy, resembles the tip of a watering can spraying streams of water; hence the name "watering mold". Some Aspergillus species are used industrially to produce citric acid and other substances. There are species that cause diseases of the skin and lungs in humans - aspergillosis.
Molds of the genus Penicillum, or racemes, are multicellular fungi with a fruiting body in the form of a brush. The first antibiotic, penicillin, was obtained from certain types of green mold. Among the penicilliums there are species pathogenic for humans that cause penicilliosis. Various types of molds can cause spoilage of food products, medicines, and biological products.
Yeast- yeast fungi (Saccharomycetes, Blastomycetes) have the shape of round or oval cells, many times larger than bacteria. The average size of yeast cells is approximately equal to the diameter of a red blood cell (7-10 microns). A distinctive morphological feature of yeast is the absence of filamentous mycelium and normal reproduction by budding. On the surface of the mother cells, processes appear, which, having then separated from the mother cell, turn into independent new individuals. In addition to budding, true yeast can reproduce sexually, forming asci - sexual spores.
Most yeast species are non-pathogenic. Their ability to cause fermentation is widely used in industry - in baking, winemaking, and in the production of alcohols and vitamins. There are pathogenic yeast fungi that cause diseases, for example, Blastomyces dermatitidis - the causative agent of blastomycosis, Pneumocystis carinii - the causative agent of pulmonary pneumocystis.
Imperfect mushrooms do not have special fruiting organs. These include yeast-like fungi and dermatomycetes.
Yeast-like fungi, like true yeast, are round or oval cells that reproduce by budding. But there are two significant characteristics by which they are distinguished when conducting microbiological studies: yeast-like fungi, unlike true yeast, form pseudomycelium and do not form sexual spores. Yeast-like fungi of the genus Candida can be found on the mucous membranes of healthy people. In newborns and infants, and in weakened patients, they cause candidiasis - damage to the mucous membranes, skin, and internal organs. This disease can occur due to exogenous infection. But more often, candidiasis develops as an endogenous infection during long-term treatment with broad-spectrum antibiotics, which, being directed against bacteria that cause the disease, simultaneously suppress the growth of bacteria - representatives of the normal microflora of the body, which leads to dysbiosis. Being eukaryotes, Candida fungi are insensitive to antibacterial antibiotics. Freed from the antagonistic influence of bacteria, they multiply uncontrollably and cause candidiasis. The most common causative agents of candidiasis in humans are Candida albicans, C.tropicalis and others.
Dermatomycetes are causative agents of diseases of the skin (Greek derma - skin), hair, and nails. This is Trichophyton - the causative agent of trichophytosis, Epidermophyton - the causative agent of epidermophytosis, Microspore - the causative agent of microsporia, Achorion - the causative agent of scab. In hair, skin flakes, and nail scrapings, segments of dermatomyctic mycelium are clearly visible, as they strongly refract light.
Protozoa
Protozoa - Protozoa (Greek proto - beginning, zoa - animal) - eukaryotes, microscopic single-celled animal organisms. Compared to bacteria, they are characterized by a more complex structure. They have primitive organs, such as the mouth and anus, contractile vacuoles, and myonemes. The nucleus is differentiated. Protozoa do not have a shell separate from the protoplasm, although some of them form a pellicle due to the compaction of the outer layer of protoplasm. The movement of protozoa is carried out using different mechanisms: the movement of protoplasm that forms pseudopodia (amoebas), the presence of flagella (flagellates) or cilia (ciliated). During reproduction, they undergo complex developmental cycles, with alternating sexual and asexual cycles, in the body of the main host - the vector of infection and the intermediate host - a person or animal. Moreover, at different stages of development, different forms of the same microorganism can be so different from each other that different chemotherapy drugs are used against them. For example, different drugs act selectively on the sexual and asexual forms of plasmodia of malaria.
The study of the morphology of protozoa can be carried out in a living state, and their movement can be observed. Simple staining is not suitable for stained research, since it does not reveal the complex structure of these microorganisms. The Romanovsky-Giemsa staining method is used to differentiate the individual elements of the cell.
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Morphology of microorganisms
Microorganisms include microscopic living beings that do not form chlorophyll, including bacteria and fungi (molds, yeasts, actinomycetes).
Most microbes are unicellular and only a few are multicellular. The unicellular group includes bacteria, protozoa, yeast, and certain types of molds, and the multicellular group includes filamentous bacteria and most molds. Viruses do not have a cellular structure like other microorganisms.
Bacteria. Shape and size of bacteria. Based on their appearance, there are three main forms of bacteria: spherical (cocci), rod-shaped (cylindrical) and convoluted (Fig. 8).
Rice. 8. Main forms of bacteria: 1 - micrococci; 2 - diplococci; 3 - streptococci; 4 - tetracocci; 5 - sarcins; 6 - staphylococci; 7 - bacilli; 8 - bacteria; 9 - streptobacteria; 10 - vibrios; 11 - spirilla; 12 - spirochetes
The size of bacteria can fluctuate depending on living conditions and the influence of the external environment (nutrition, temperature, humidity, etc.). The size of coccoid forms ranges from 0.75 to 2 microns, rod-shaped from 0.3-1 to 2-10 and convoluted from 0.1-0.15 to 3-20 microns.
Cocci - most of them have a regular ball shape, but some types are elongated and resemble a candle, lancet, or beans. Depending on the relative position of the cells (after division), cocci are divided into micrococci - single, randomly located cocci; diplococci - arranged in pairs; streptococci - form a chain when cocci divide in one plane; tetracocci - combinations of four cocci; Sarcines - cocci, connected in the form of packets, and staphylococci - clusters of cocci, reminiscent of bunches of grapes.
Rod-shaped bacteria - the shape can be in the form of a cylinder, ovoid of various lengths and diameters. The ends of the sticks are rounded, pointed or sharply cut off. Rods that form spores are called bacilli, those that do not form spores are called bacteria. Rods arranged in pairs are called diplobacteria, or diplobacillus, and those arranged in a chain are called streptobacteria, or streptobacilli.
Convoluted bacteria are microorganisms that have the appearance of a spiral. They are divided into vibrios, which resemble a slightly curved comma, spirilla, which have several large curls, and spirochetes, bacteria with thin, numerous curls.
The structure of bacterial cellsAnd. The ultrastructure of bacteria is studied using electron microscopic and microchemical studies, which make it possible to quite accurately determine the structure and components of the microbial cell. A bacterial cell consists of a membrane, cytoplasm, and nuclear substance (Fig. 9).
The shell has significant strength, elasticity, and elasticity, and thanks to this, a rigid frame of the microbial cell is created, protecting it from adverse external influences and giving it a permanent shape (cocci, rods). The shell has tiny pores, it is semi-permeable, and through it the exchange of substances with the external environment occurs.
The chemical composition of the shell is heterogeneous: nitrogenous and nitrogen-free compounds are found in its composition.
The bacterial membrane is represented by three structures: the outer capsular layer, the cell wall and the cytoplasmic membrane.
Rice. 9. Structure of a bacterial cell: 1 - shell; 2 - cytoplasm; 3 - nuclear structure
Cytoplasm is a dispersed mixture of colloids consisting of proteins, water, RNA (ribonucleic acid), lipids, carbohydrates, minerals, etc. The cytoplasm is surrounded by a thin cytoplasmic membrane consisting of lipoprotein and ribonucleic components. Enzyme systems that take part in the exchange of substances with the environment are associated with the cytoplasmic membrane.
The cytoplasm contains various inclusions filled with cell sap, which are a reserve nutrient substrate. Processes of synthesis and breakdown of substances constantly occur in the cytoplasm, i.e. all functions inherent in a living organism are carried out.
The nuclear substance of a bacterial cell, represented by DNA (deoxyribonucleic acid) in the form of oval and fine-grained inclusions, is distributed diffusely in the cytoplasm. Around the DNA nucleoid in the cytoplasm of bacteria there are short double-stranded strands of extrachromosomal DNA, called plasmids. They control the function of drug resistance (R-plasmids), the production of enterotoxins and determine the extrachromosomal transmission of hereditary properties.
Some types of bacteria form spores and capsules (Fig. 10). The capsule is a product of swelling and mucilage of the cell membrane; it protects bacteria from the influence of unfavorable factors. Under unfavorable conditions, round bodies called spores form inside some rod-shaped bacteria.
Spore-forming rods (bacilli) can exist in two forms: vegetative, i.e. capable of growth and reproduction, and spore-bearing, incapable of reproduction. A spore is a microbial cell that has lost a large amount of water and is covered with a dense shell. Only one spore is formed inside the microbial cell, which serves to preserve the species. If the diameter of the spores exceeds the diameter of the microbial cell, it is clostridia (for example, the causative agent of tetanus).
Rice. 10. Spores and capsules of bacteria: A - disputes; b - capsules
Under favorable conditions (presence of moisture, nutrients and optimal temperature), the spore germinates and turns into a vegetative form. The spores are extremely resistant to adverse external factors (drying, high and low temperatures, etc.) and can persist for years.
Motility of bacteria. Many types of bacteria can move independently using special flagella. Flagella are thin long filaments, several times longer than the length of the bacterial body. The diameter of the flagella is about 1/20 the width of the bacterial cell. The convoluted forms of microbes move by contracting the body. Microbes that do not have flagella and are not convoluted are immobile.
Mushrooms. Fungi are a large group of plant organisms. They are characterized by three main properties: they reproduce vegetatively and through spores; have a vegetative body in the form of mycelium; Mushrooms lack chlorophyll (unlike plants). The most widespread in nature are molds, yeasts, and actinomycetes. Some types of molds and yeasts are used in the food industry for technological purposes, while some of the fungi cause spoilage of food and are causative agents of diseases in humans and animals.
Mold. Sometimes they are called microscopic fungi. These are non-motile, non-chlorophyll organisms visible to the naked eye. Molds have a more complex structure than bacteria (Fig. 11). A mold consists of intertwined threads (hyphae) that form the body of the fungus (mycelium). Hyphae can be unicellular or multicellular. Each hyphal cell has a membrane, cytoplasm with inclusions, and several separate nuclei.
Rice. 11. Molds: 1 - brush mold (penicillium); 2 - leech mold (Aspergillus); 3 - capitate mold (mukor); 4 - grape mold; 5 - chocolate mold, 6 - milk mold.
A mold consists of intertwined threads (hyphae) that form the body of the fungus (mycelium). Hyphae can be unicellular or multicellular. Each hyphal cell has a membrane, cytoplasm with inclusions, and several separate nuclei.
One-celled mold fungi include capitate mold (mukor). Its body consists of one branched cell. The fruiting hypha on which the spores are located is called a sporangiophorus. Some types of mucor mushrooms are used in the food industry for the preparation of organic acids and alcohol. Many types of mucor cause food spoilage.
Multicellular molds include penicillium, aspergillus, grape, chocolate and other molds. In these types of molds, the mycelium has partitions (septa), the spores are called conidia, and the fruiting hyphae are called conidiophores. In milk mold, the spores are called oidia.
Some multicellular molds are producers of antibiotics - penicillin, aspergillin, and are used in industry for the preparation of enzyme preparations and citric acid. At the same time, mold such as aspergillus causes aspergillosis - damage to the upper respiratory tract. Many molds cause spoilage in meat and dairy products. Thus, candidium gives the meat an unpleasant odor by breaking down proteins; chocolate mold forms dark, almost black spots on the meat.
Yeast. These are non-motile unicellular organisms of round, oval or rod-shaped shape, ranging in size from 8 to 15 microns. A yeast cell has a membrane, a cytoplasmic membrane, cytoplasm with inclusions, and a round or oval nucleus. In the cytoplasm of a yeast cell there are vacuoles - intracellular formations containing nutrients and various inclusions in the form of grains. In nature, there are spore-forming and non-spore-forming yeasts. Some types of yeast are used in the food industry for the preparation of bread, beer, wine, kumiss, etc. There are yeast organisms that cause defects in dairy and meat products, for example, yeast from the genus Rhodotorula, Mycoderma, Pasterianum. Yeast-like organisms of the genera candida and blastomyces cause diseases: candidomycosis, blastomycosis with damage to the eyes, nails, tendons, joints, oral mucosa, respiratory tract, and digestive tract.
Actinomycetes(radiant mushrooms). Actinomycetes occupy an intermediate position between molds and bacteria. Their body consists of rather long branching thin single-celled filaments (hyphae). The length of actinomycetes can reach several centimeters. Actinomycete cells have a membrane, cytoplasm and nucleus. The plexus of hyphae forms aerial mycelium, which grows above the nutrient medium and forms spore carriers, on which are spores, through which actinomycetes reproduce. Some actinomycetes cause food spoilage; there are pathogenic ones that cause a disease known as actinomycosis. microorganism bacterial cell morphology
Actinomycetes are producers of antibiotics such as streptomycin, tetracycline, biomycin, etc.
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