Bacteria- one of the most ancient organisms on Earth. Despite the simplicity of their structure, they live in all possible habitats. Most of them are found in the soil (up to several billion bacterial cells per 1 gram of soil). There are many bacteria in the air, water, food, inside and on the bodies of living organisms. Bacteria have been found in places where other organisms cannot live (on glaciers, in volcanoes).

Typically a bacterium is a single cell (although there are colonial forms). Moreover, this cell is very small (from fractions of a micron to several tens of microns). But the main feature of a bacterial cell is the absence of a cell nucleus. In other words, bacteria belong prokaryotes.

Bacteria are either mobile or immobile. In the case of non-motile forms, movement is carried out using flagella. There may be several of them, or there may be only one.

Cells of different types of bacteria can differ greatly in shape. There are spherical bacteria ( cocci), rod-shaped ( bacilli), similar to a comma ( vibrios), crimped ( spirochetes, spirilla), etc.

Structure of a bacterial cell

Many bacterial cells have mucous capsule. It performs a protective function. In particular, it protects the cell from drying out.

Like plant cells, bacterial cells have cell wall. However, unlike plants, its structure and chemical composition are somewhat different. The cell wall is made up of layers of complex carbohydrates. Its structure is such that it allows various substances to penetrate into the cell.

Under the cell wall is cytoplasmic membranenA.

Bacteria are classified as prokaryotes because their cells do not have a formed nucleus. They do not have chromosomes characteristic of eukaryotic cells. The chromosome contains not only DNA, but also protein. In bacteria, their chromosome consists only of DNA and is a circular molecule. This genetic apparatus of bacteria is called nucleoid. The nucleoid is located directly in the cytoplasm, usually in the center of the cell.

Bacteria do not have true mitochondria and a number of other cellular organelles (Golgi complex, endoplasmic reticulum). Their functions are performed by invaginations of the cell cytoplasmic membrane. Such invaginations are called mesosomes.

In the cytoplasm there is ribosomes, as well as various organic inclusion: proteins, carbohydrates (glycogen), fats. Bacterial cells may also contain various pigments. Depending on the presence or absence of certain pigments, bacteria can be colorless, green, or purple.

Nutrition of bacteria

Bacteria arose at the dawn of life on Earth. They were the ones who “discovered” different ways of eating. Only later, with the complication of organisms, two large kingdoms clearly emerged: Plants and Animals. They differ from each other primarily in the way they feed. Plants are autotrophs, and animals are heterotrophs. Bacteria have both types of nutrition.

Nutrition is the way a cell or body obtains the necessary organic substances. They can be obtained from outside or synthesized independently from inorganic substances.

Autotrophic bacteria

Autotrophic bacteria synthesize organic substances from inorganic ones. The synthesis process requires energy. Depending on where autotrophic bacteria receive this energy from, they are divided into photosynthetic and chemosynthetic.

Photosynthetic bacteria use the energy of the Sun, capturing its radiation. In this they are similar to plants. However, while plants release oxygen during photosynthesis, most photosynthetic bacteria do not release it. That is, bacterial photosynthesis is anaerobic. Also, the green pigment of bacteria differs from the similar pigment of plants and is called bacteriochlorophyll. Bacteria do not have chloroplasts. Mostly photosynthetic bacteria live in bodies of water (fresh and salty).

Chemosynthetic bacteria To synthesize organic substances from inorganic ones, the energy of various chemical reactions is used. Energy is not released in all reactions, but only in exothermic ones. Some of these reactions take place in bacterial cells. So in nitrifying bacteria the oxidation of ammonia into nitrites and nitrates occurs. Iron bacteria oxidize ferrous iron into oxide iron. Hydrogen bacteria oxidize hydrogen molecules.

Heterotrophic bacteria

Heterotrophic bacteria are not capable of synthesizing organic substances from inorganic ones. Therefore, we are forced to obtain them from the environment.

Bacteria that feed on the organic remains of other organisms (including dead bodies) are called saprophytic bacteria. They are otherwise called rotting bacteria. There are many such bacteria in the soil, where they decompose humus into inorganic substances, which are subsequently used by plants. Lactic acid bacteria feed on sugars, converting them into lactic acid. Butyric acid bacteria decompose organic acids, carbohydrates, and alcohols to butyric acid.

Nodule bacteria live in the roots of plants and feed on the organic matter of the living plant. However, they fix nitrogen from the air and provide it to the plant. That is, in this case there is a symbiosis. Other heterotrophic symbiont bacteria live in the digestive system of animals, helping to digest food.

During the process of respiration, organic substances are destroyed and energy is released. This energy is subsequently spent on various life processes (for example, movement).

An effective way to obtain energy is oxygen respiration. However, some bacteria can obtain energy without oxygen. Thus, there are aerobic and anaerobic bacteria.

Aerobic bacteria oxygen is needed, so they live in places where it is available. Oxygen is involved in the oxidation reaction of organic substances to carbon dioxide and water. In the process of such respiration, bacteria receive a relatively large amount of energy. This method of breathing is characteristic of the vast majority of organisms.

Anaerobic bacteria They do not require oxygen to breathe, so they can live in an oxygen-free environment. They receive energy from fermentation reactions. This oxidation method is ineffective.

Bacteria reproduction

In most cases, bacteria reproduce by dividing their cells in two. Before this, the circular DNA molecule doubles. Each daughter cell receives one of these molecules and is therefore a genetic copy of the mother cell (clone). Thus, it is typical for bacteria asexual reproduction.

Under favorable conditions (with sufficient nutrients and favorable environmental conditions), bacterial cells divide very quickly. Thus, one bacterium can produce hundreds of millions of cells per day.

Although bacteria reproduce asexually, in some cases they exhibit the so-called sexual process, which flows in the form conjugation. During conjugation, two different bacterial cells come closer and a connection is established between their cytoplasms. Parts of the DNA of one cell are transferred to the second, and parts of the DNA of the second cell are transferred to the first. Thus, during the sexual process, bacteria exchange genetic information. Sometimes bacteria exchange not sections of DNA, but entire DNA molecules.

Bacterial spores

The vast majority of bacteria form spores under unfavorable conditions. Bacterial spores are mainly a way of surviving unfavorable conditions and a method of dispersal, rather than a method of reproduction.

When a spore is formed, the cytoplasm of the bacterial cell contracts, and the cell itself is covered with a dense, thick protective membrane.

Bacterial spores remain viable for a long time and are able to survive very unfavorable conditions (extremely high and low temperatures, drying out).

When a spore finds itself in favorable conditions, it swells. After this, the protective shell is shed, and an ordinary bacterial cell appears. It happens that cell division occurs and several bacteria are formed. That is, sporulation is combined with reproduction.

The importance of bacteria

The role of bacteria in the cycle of substances in nature is enormous. This primarily applies to rotting bacteria (saprophytes). They are called nature's orderlies. By decomposing the remains of plants and animals, bacteria convert complex organic substances into simple inorganic substances (carbon dioxide, water, ammonia, hydrogen sulfide).

Bacteria increase soil fertility by enriching it with nitrogen. Nitrifying bacteria undergo reactions during which nitrites are formed from ammonia, and nitrates from nitrites. Nodule bacteria are able to assimilate atmospheric nitrogen, synthesizing nitrogen compounds. They live in the roots of plants, forming nodules. Thanks to these bacteria, plants receive the nitrogen compounds they need. Basically, leguminous plants enter into symbiosis with nodule bacteria. After they die, the soil is enriched with nitrogen. This is often used in agriculture.

In the stomach of ruminants, bacteria break down cellulose, which promotes more efficient digestion.

The positive role of bacteria in the food industry is great. Many types of bacteria are used to produce lactic acid products, butter and cheese, pickling vegetables, and also in winemaking.

In the chemical industry, bacteria are used to produce alcohols, acetone, and acetic acid.

In medicine, bacteria are used to produce a number of antibiotics, enzymes, hormones and vitamins.

However, bacteria can also cause harm. They not only spoil food, but with their secretions they make it poisonous.

Features of the structure of a bacterial cell. Main organelles and their functions

Differences between bacteria and other cells

1. Bacteria are prokaryotes, that is, they do not have a separate nucleus.

2. The cell wall of bacteria contains a special peptidoglycan - murein.

3. The bacterial cell lacks the Golgi apparatus, endoplasmic reticulum, and mitochondria.

4. The role of mitochondria is performed by mesosomes - invaginations of the cytoplasmic membrane.

5. There are many ribosomes in a bacterial cell.

6. Bacteria may have special organelles of movement - flagella.

7. The sizes of bacteria range from 0.3-0.5 to 5-10 microns.

Based on the shape of the cells, bacteria are divided into cocci, rods and convoluted.

In a bacterial cell there are:

1) main organelles:

a) nucleoid;

b) cytoplasm;

c) ribosomes;

d) cytoplasmic membrane;

e) cell wall;

2) additional organelles:

a) disputes;

b) capsules;

c) villi;

d) flagella.

Cytoplasm is a complex colloidal system consisting of water (75%), mineral compounds, proteins, RNA and DNA, which are part of the nucleoid organelles, ribosomes, mesosomes, and inclusions.

Nucleoid is a nuclear substance dispersed in the cytoplasm of the cell. It does not have a nuclear membrane or nucleoli. DNA, represented by a double-stranded helix, is localized in it. Usually closed in a ring and attached to the cytoplasmic membrane. Contains about 60 million base pairs. This is pure DNA and does not contain histone proteins. Their protective function is performed by methylated nitrogenous bases. The nucleoid encodes the basic genetic information, i.e., the genome of the cell.

Along with the nucleoid, the cytoplasm may contain autonomous circular DNA molecules with a lower molecular weight - plasmids. They also encode hereditary information, but it is not vital for the bacterial cell.

Ribosomes are ribonucleoprotein particles 20 nm in size, consisting of two subunits - 30 S and 50 S. Ribosomes are responsible for protein synthesis. Before protein synthesis begins, these subunits are combined into one - 70 S. Unlike eukaryotic cells, bacterial ribosomes are not united into the endoplasmic reticulum.

Mesosomes are derivatives of the cytoplasmic membrane. Mesosomes can be in the form of concentric membranes, vesicles, tubes, or in the form of a loop. Mesosomes are associated with the nucleoid. They are involved in cell division and sporulation.

Inclusions are metabolic products of microorganisms, which are located in their cytoplasm and are used as reserve nutrients. These include inclusions of glycogen, starch, sulfur, polyphosphate (volutin), etc.

Modern science has made fantastic progress over the past centuries. However, some mysteries still excite the minds of outstanding scientists.

Nowadays, the answer to the pressing question has not been found - how many varieties of bacteria exist on our huge planet?

Bacterium- an organism with a unique internal organization, which is characterized by all the processes characteristic of living organisms. The bacterial cell has many amazing features, one of which is its variety of shapes.

A bacterial cell can be spherical, rod-shaped, cubic or star-shaped. In addition, the bacteria are slightly bent or form a variety of curls.

Cell shape plays an important role in the proper functioning of a microorganism, as it can influence the ability of a bacterium to attach to other surfaces, obtain necessary substances, and move around.

The minimum cell size is usually 0.5 µm, but in exceptional cases the size of the bacterium can reach 5.0 µm.

The structure of the cell of any bacterium is strictly ordered. Its structure is significantly different from the structure of other cells, such as plants and animals. Cells of all types of bacteria do not have such elements as: a differentiated nucleus, intracellular membranes, mitochondria, lysosomes.

Bacteria have specific structural components - permanent and non-permanent.

The permanent components include: the cytoplasmic membrane (plasmolemma), cell wall, nucleoid, cytoplasm. Non-permanent structures are: capsule, flagella, plasmids, pili, villi, fimbriae, spores.

Cytoplasmic membrane

Any bacterium is surrounded by a cytoplasmic membrane (plasmolemma), which includes 3 layers. The membrane contains globulins, which are responsible for the selective transport of various substances into the cell.

The plasmalemma also performs the following important functions:

• mechanical– ensures the autonomous functioning of the bacterium and all structural elements;
• receptor– proteins located in the plasmalemma act as receptors, that is, they help the cell perceive various signals;
• energy– some proteins are responsible for the energy transfer function.

Disruption of the functioning of the plasmalemma leads to the fact that the bacterium is destroyed and dies.

Cell wall

A structural component unique to bacterial cells is the cell wall. This is a rigid, permeable membrane that acts as an important component of the structural skeleton of the cell. It is located on the outside of the cytoplasmic membrane.

The cell wall provides protection and also gives the cell a permanent shape. Its surface is covered with numerous spores, which allow necessary substances to enter and remove decay products from the microorganism.

Protection of internal components from osmotic and mechanical effects is another function of the wall. It plays an indispensable role in controlling cell division and the distribution of hereditary characteristics within it. It contains peptidoglycan, which is what gives the cell valuable immunobiological characteristics.

The thickness of the cell wall ranges from 0.01 to 0.04 µm. With age, bacteria grow and the amount of material from which it is built increases accordingly.

Nucleoid

Nucleoid is a prokaryote in which all the hereditary information of a bacterial cell is stored. The nucleoid is located in the central part of the bacterium. Its properties are equivalent to the core.

A nucleoid is one DNA molecule closed in a ring. The length of the molecule is 1 mm, and the volume of information is about 1000 features.

The nucleoid is the main carrier of material about the properties of the bacterium and the main factor in the transmission of these properties to the offspring. The nucleoid in bacterial cells does not have a nucleolus, membrane or basic proteins.

Cytoplasm

Cytoplasm– an aqueous solution containing the following components: mineral compounds, nutrients, proteins, carbohydrates and lipids. The ratio of these substances depends on the age and type of bacteria.

The cytoplasm contains various structural components: ribosomes, granules and mesosomes.

• Ribosomes are responsible for protein synthesis. Their chemical composition includes RNA molecules and protein.
• Mesosomes are involved in the formation of spores and cell reproduction. They can take the form of a bubble, loop, or tube.
• The granules serve as an additional energy resource for bacterial cells. These elements come in a variety of forms. They contain polysaccharides, starch, and droplets of fat.

Capsule

Capsule is a mucous structure tightly bound to the cell wall. Examining it under a light microscope, you can see that the capsule envelops the cell and its outer boundaries have a clearly defined contour. In a bacterial cell, the capsule serves as a protective barrier against phages (viruses).

Bacteria form a capsule when environmental conditions become aggressive. The capsule includes mainly polysaccharides, and in certain cases it may contain fiber, glycoproteins, and polypeptides.

Main functions of the capsule:

• • adhesion to cells in the human body. For example, streptococci adhere to tooth enamel and, in alliance with other microbes, provoke the appearance of caries;
  • protection from negative environmental conditions: toxic substances, mechanical damage, increased oxygen levels;
  • participation in water metabolism (protecting the cell from drying out);
  • creation of an additional osmotic barrier.

The capsule forms 2 layers:

• internal – part of the cytoplasm layer;
• external - the result of the excretory function of the bacterium.

The classification is based on the structural features of the capsules. They are:

• normal;
• complex capsules;
• with striated fibrils;
• intermittent capsules.

Some bacteria also form a microcapsule, which is a mucous formation. A microcapsule can only be identified under an electron microscope, since the thickness of this element is only 0.2 microns or even less.

Flagella

Most bacteria have cell surface structures that ensure its motility and movement - flagella. These are long processes in the shape of a left-handed spiral, built from flagellin (a contractile protein).

The main function of flagella is that they allow bacteria to move through a liquid environment in search of more favorable conditions. The number of flagella in one cell can vary: from one to several flagella, flagella on the entire surface of the cell or only on one of its poles.

There are several types of bacteria depending on the number of flagella they contain:

• Monotrichs- they have only one flagellum.
• Lophotrichs– have a certain number of flagella at one end of the bacterium.
• Amphitrichy– characterized by the presence of flagella at polar opposite poles.
• Peritrichous– flagella are located over the entire surface of the bacterium; they are characterized by slow and smooth movement.
• Atriches– flagella are absent.

Flagella perform motor activity by performing rotational movements. If bacteria do not have flagella, they are still able to move, or rather slide, using mucus on the surface of the cell.

Plasmids

Plasmids are small, mobile DNA molecules that are separate from chromosomal factors of heredity. These components usually contain genetic material that makes the bacteria more resistant to antibiotics.

They can transfer their properties from one microorganism to another. Despite all their features, plasmids do not act as important elements for the life of a bacterial cell.

Pili, villi, fimbriae

These structures are localized on the surfaces of bacteria. There are from two units to several thousand per cell. Both the bacterial motile cell and the immobile one have these structural elements, since they do not have any effect on the ability to move.

In quantitative terms, pili reach several hundred per bacterium. There are pili that are responsible for nutrition, water-salt metabolism, as well as conjugative (sexual) pili.

The villi are characterized by a hollow cylindrical shape. It is through these structures that viruses penetrate the bacterium.

Villi are not considered essential components of bacteria, since the process of division and growth can be successfully completed without them.

Fimbriae are located, as a rule, at one end of the cell. These structures allow the microorganism to fixate in the tissues of the body. Some fimbriae have special proteins that contact the receptor ends of cells.

Fimbriae differ from flagella in that they are thicker and shorter, and also do not implement the function of movement.

Controversy

Spores are formed in the event of negative physical or chemical manipulation of the bacterium (as a result of drying out or lack of nutrients). They vary in spore size, since they can be completely different in different cells. The shape of the spores also differs - they are oval or spherical.

Based on their location in the cell, spores are divided into:

• central - their position in the very center, such as in the anthrax bacillus;
• subterminal - located at the end of the stick, giving the shape of a club (for the causative agent of gas gangrene).

In a favorable environment, the spore life cycle includes the following stages:

• preparatory stage;
• activation stage;
• initiation stage;
• germination stage.

The spores are distinguished by their special vitality, which is achieved thanks to their shell. It is multilayered and consists mainly of protein. The increased immunity of spores to negative conditions and external influences is ensured precisely thanks to proteins.

The structure of bacteria has been well studied using electron microscopy of whole cells and their ultrathin sections, as well as other methods. The bacterial cell is surrounded by a membrane consisting of a cell wall and a cytoplasmic membrane. Under the shell there is protoplasm, consisting of cytoplasm with inclusions and a hereditary apparatus - an analogue of the nucleus, called the nucleoid (Fig. 2.2). There are additional structures: capsule, microcapsule, mucus, flagella, pili. Some bacteria are capable of forming spores under unfavorable conditions.

Rice. 2.2. Structure of a bacterial cell: 1 - capsule; 2 - cell wall; 3 - cytoplasmic membrane; 4 - mesosomes; 5 - nucleoid; 6 - plasmid; 7 - ribosomes; 8 - inclusions; 9 - flagellum; 10 - pili (villi)

Cell wall- a strong, elastic structure that gives the bacterium a certain shape and, together with the underlying cytoplasmic membrane, restrains high osmotic pressure in the bacterial cell. It is involved in the process of cell division and transport of metabolites, has receptors for bacteriophages, bacteriocins and various substances. The thickest cell wall is found in gram-positive bacteria (Fig. 2.3). So, if the thickness of the cell wall of gram-negative bacteria is about 15-20 nm, then in gram-positive bacteria it can reach 50 nm or more.

The basis of the bacterial cell wall is peptidoglycan. Peptidoglycan is a polymer. It is represented by parallel polysaccharide glycan chains consisting of repeating N-acetylglucosamine and N-acetylmuramic acid residues connected by a glycosidic bond. This bond is broken by lysozyme, which is an acetylmuramidase.

A tetrapeptide is attached to N-acetylmuramic acid by covalent bonds. The tetrapeptide consists of L-alanine, which is linked to N-acetylmuramic acid; D-glutamine, which in gram-positive bacteria is combined with L-lysine, and in gram-tri-

Rice. 2.3. Scheme of the architecture of the bacterial cell wall

beneficial bacteria - with diaminopimelic acid (DAP), which is a precursor of lysine in the process of bacterial biosynthesis of amino acids and is a unique compound present only in bacteria; The 4th amino acid is D-alanine (Fig. 2.4).

The cell wall of gram-positive bacteria contains small amounts of polysaccharides, lipids and proteins. The main component of the cell wall of these bacteria is multilayer peptidoglycan (murein, mucopeptide), accounting for 40-90% of the mass of the cell wall. Tetrapeptides of different layers of peptidoglycan in gram-positive bacteria are connected to each other by polypeptide chains of 5 glycine residues (pentaglycine), which gives the peptidoglycan a rigid geometric structure (Fig. 2.4, b). Covalently linked to the peptidoglycan of the cell wall of gram-positive bacteria teichoic acids(from Greek tekhos- wall), the molecules of which are chains of 8-50 glycerol and ribitol residues connected by phosphate bridges. The shape and strength of bacteria is given by the rigid fibrous structure of the multilayer peptidoglycan, with cross-links of peptides.

Rice. 2.4. Structure of peptidoglycan: a - gram-negative bacteria; b - gram-positive bacteria

The ability of Gram-positive bacteria to retain gentian violet in combination with iodine when stained using Gram stain (blue-violet color of bacteria) is associated with the property of multilayer peptidoglycan to interact with the dye. In addition, subsequent treatment of a bacterial smear with alcohol causes a narrowing of the pores in the peptidoglycan and thereby retains the dye in the cell wall.

Gram-negative bacteria lose the dye after exposure to alcohol, which is due to a smaller amount of peptidoglycan (5-10% of the cell wall mass); they are discolored with alcohol, and when treated with fuchsin or safranin they become red. This is due to the structural features of the cell wall. Peptidoglycan in the cell wall of gram-negative bacteria is represented by 1-2 layers. The tetrapeptides of the layers are connected to each other by a direct peptide bond between the amino group of DAP of one tetrapeptide and the carboxyl group of D-alanine of the tetrapeptide of another layer (Fig. 2.4, a). Outside the peptidoglycan there is a layer lipoprotein, connected to peptidoglycan through DAP. Followed by outer membrane cell wall.

Outer membrane is a mosaic structure composed of lipopolysaccharides (LPS), phospholipids and proteins. Its inner layer is represented by phospholipids, and the outer layer contains LPS (Fig. 2.5). Thus, the outer mem-

Rice. 2.5. Lipopolysaccharide structure

the brane is asymmetric. The outer membrane LPS consists of three fragments:

Lipid A has a conservative structure, almost the same in gram-negative bacteria. Lipid A consists of phosphorylated glucosamine disaccharide units to which long chains of fatty acids are attached (see Fig. 2.5);

Core, or core, crustal part (from lat. core- core), relatively conservative oligosaccharide structure;

A highly variable O-specific polysaccharide chain formed by repeating identical oligosaccharide sequences.

LPS is anchored in the outer membrane by lipid A, which causes LPS toxicity and is therefore identified with endotoxin. The destruction of bacteria by antibiotics leads to the release of large amounts of endotoxin, which can cause endotoxic shock in the patient. The core, or core part, of LPS extends from lipid A. The most constant part of the LPS core is ketodeoxyoctonic acid. O-specific polysaccharide chain extending from the core of the LPS molecule,

consisting of repeating oligosaccharide units, determines the serogroup, serovar (a type of bacteria detected using immune serum) of a particular strain of bacteria. Thus, the concept of LPS is associated with the concept of O-antigen, by which bacteria can be differentiated. Genetic changes can lead to defects, shortening of bacterial LPS and, as a result, the appearance of rough colonies of R-forms that lose O-antigen specificity.

Not all gram-negative bacteria have a complete O-specific polysaccharide chain, consisting of repeating oligosaccharide units. In particular, bacteria of the genus Neisseria have a short glycolipid called lipooligosaccharide (LOS). It is comparable to the R form, which has lost O-antigen specificity, observed in mutant rough strains E. coli. The structure of VOC resembles the structure of the glycosphingolipid of the human cytoplasmic membrane, so VOC mimics the microbe, allowing it to evade the host's immune response.

The matrix proteins of the outer membrane permeate it in such a way that protein molecules called porinami, border hydrophilic pores through which water and small hydrophilic molecules with a relative mass of up to 700 D pass.

Between the outer and cytoplasmic membrane is periplasmic space, or periplasm containing enzymes (proteases, lipases, phosphatases, nucleases, β-lactamases), as well as components of transport systems.

When the synthesis of the bacterial cell wall is disrupted under the influence of lysozyme, penicillin, protective factors of the body and other compounds, cells with an altered (often spherical) shape are formed: protoplasts- bacteria completely lacking a cell wall; spheroplasts- bacteria with a partially preserved cell wall. After removal of the cell wall inhibitor, such altered bacteria can reverse, i.e. acquire a full cell wall and restore its original shape.

Bacteria of the spheroid or protoplast type, which have lost the ability to synthesize peptidoglycan under the influence of antibiotics or other factors and are able to reproduce, are called L-shapes(from the name of the D. Lister Institute, where they first

have been studied). L-forms can also arise as a result of mutations. They are osmotically sensitive, spherical, flask-shaped cells of various sizes, including those passing through bacterial filters. Some L-forms (unstable), when the factor that led to changes in bacteria is removed, can reverse, returning to the original bacterial cell. L-forms can be produced by many pathogens of infectious diseases.

Cytoplasmic membrane in electron microscopy of ultrathin sections, it is a three-layer membrane (2 dark layers, each 2.5 nm thick, separated by a light intermediate layer). In structure, it is similar to the plasmalemma of animal cells and consists of a double layer of lipids, mainly phospholipids, with embedded surface and integral proteins that seem to penetrate through the structure of the membrane. Some of them are permeases involved in the transport of substances. Unlike eukaryotic cells, the cytoplasmic membrane of a bacterial cell lacks sterols (with the exception of mycoplasmas).

The cytoplasmic membrane is a dynamic structure with mobile components, so it is thought of as a mobile fluid structure. It surrounds the outer part of the cytoplasm of bacteria and is involved in the regulation of osmotic pressure, transport of substances and energy metabolism of the cell (due to enzymes of the electron transport chain, adenosine triphosphatase - ATPase, etc.). With excessive growth (compared to the growth of the cell wall), the cytoplasmic membrane forms invaginates - invaginations in the form of complexly twisted membrane structures, called mesosomes. Less complexly twisted structures are called intracytoplasmic membranes. The role of mesosomes and intracytoplasmic membranes is not fully understood. It is even suggested that they are an artifact that occurs after preparing (fixing) a specimen for electron microscopy. Nevertheless, it is believed that derivatives of the cytoplasmic membrane participate in cell division, providing energy for the synthesis of the cell wall, and take part in the secretion of substances, sporulation, i.e. in processes with high energy consumption. Cytoplasm occupies the main volume of bacteria

cell and consists of soluble proteins, ribonucleic acids, inclusions and numerous small granules - ribosomes, responsible for the synthesis (translation) of proteins.

Ribosomes bacteria have a size of about 20 nm and a sedimentation coefficient of 70S, in contrast to the 80S ribosomes characteristic of eukaryotic cells. Therefore, some antibiotics, by binding to bacterial ribosomes, inhibit bacterial protein synthesis without affecting protein synthesis in eukaryotic cells. Bacterial ribosomes can dissociate into two subunits: 50S and 30S. rRNA is a conserved element of bacteria (“molecular clock” of evolution). 16S rRNA is part of the small ribosomal subunit, and 23S rRNA is part of the large ribosomal subunit. The study of 16S rRNA is the basis of gene systematics, allowing one to assess the degree of relatedness of organisms.

The cytoplasm contains various inclusions in the form of glycogen granules, polysaccharides, β-hydroxybutyric acid and polyphosphates (volutin). They accumulate when there is an excess of nutrients in the environment and act as reserve substances for nutrition and energy needs.

Volyutin has an affinity for basic dyes and is easily detected using special staining methods (for example, according to Neisser) in the form of metachromatic granules. With toluidine blue or methylene blue, volutin is stained red-violet, and the cytoplasm of the bacterium is stained blue. The characteristic arrangement of volutin granules is revealed in the diphtheria bacillus in the form of intensely stained cell poles. The metachromatic coloration of volutin is associated with a high content of polymerized inorganic polyphosphate. Under electron microscopy, they look like electron-dense granules 0.1-1 microns in size.

Nucleoid- equivalent to the nucleus in bacteria. It is located in the central zone of bacteria in the form of double-stranded DNA, tightly packed like a ball. The nucleoid of bacteria, unlike eukaryotes, does not have a nuclear envelope, nucleolus and basic proteins (histones). Most bacteria contain one chromosome, represented by a DNA molecule closed in a ring. But some bacteria have two ring-shaped chromosomes (V. cholerae) and linear chromosomes (see section 5.1.1). The nucleoid is revealed in a light microscope after staining with DNA-specific stains

methods: according to Feulgen or according to Romanovsky-Giemsa. In electron diffraction patterns of ultrathin sections of bacteria, the nucleoid appears as light zones with fibrillar, thread-like structures of DNA bound in certain areas to the cytoplasmic membrane or mesosome involved in chromosome replication.

In addition to the nucleoid, the bacterial cell contains extrachromosomal heredity factors - plasmids (see section 5.1.2), which are covalently closed rings of DNA.

Capsule, microcapsule, mucus.Capsule - a mucous structure more than 0.2 microns thick, firmly associated with the bacterial cell wall and having clearly defined external boundaries. The capsule is visible in imprint smears from pathological material. In pure bacterial cultures, the capsule is formed less frequently. It is detected using special methods of staining a smear according to Burri-Gins, which creates a negative contrast of the substances of the capsule: ink creates a dark background around the capsule. The capsule consists of polysaccharides (exopolysaccharides), sometimes of polypeptides, for example, in the anthrax bacillus it consists of polymers of D-glutamic acid. The capsule is hydrophilic and contains a large amount of water. It prevents the phagocytosis of bacteria. The capsule is antigenic: antibodies to the capsule cause its enlargement (capsule swelling reaction).

Many bacteria form microcapsule- mucous formation less than 0.2 microns thick, detectable only by electron microscopy.

It should be distinguished from a capsule mucus - mucoid exopolysaccharides that do not have clear external boundaries. Mucus is soluble in water.

Mucoid exopolysaccharides are characteristic of mucoid strains of Pseudomonas aeruginosa, often found in the sputum of patients with cystic fibrosis. Bacterial exopolysaccharides are involved in adhesion (sticking to substrates); they are also called glycocalyx.

The capsule and mucus protect bacteria from damage and drying out, since, being hydrophilic, they bind water well and prevent the action of the protective factors of the macroorganism and bacteriophages.

Flagella bacteria determine the mobility of the bacterial cell. Flagella are thin filaments that take on

They originate from the cytoplasmic membrane and are longer than the cell itself. The thickness of the flagella is 12-20 nm, length 3-15 µm. They consist of three parts: a spiral filament, a hook and a basal body containing a rod with special discs (one pair of discs in gram-positive bacteria and two pairs in gram-negative bacteria). Flagella are attached to the cytoplasmic membrane and cell wall by discs. This creates the effect of an electric motor with a rod - a rotor - rotating the flagellum. The proton potential difference on the cytoplasmic membrane is used as an energy source. The rotation mechanism is provided by proton ATP synthetase. The rotation speed of the flagellum can reach 100 rps. If a bacterium has several flagella, they begin to rotate synchronously, intertwining into a single bundle, forming a kind of propeller.

Flagella are made of a protein called flagellin. (flagellum- flagellum), which is an antigen - the so-called H-antigen. Flagellin subunits are twisted in a spiral.

The number of flagella in different species of bacteria varies from one (monotrichus) in Vibrio cholerae to tens and hundreds extending along the perimeter of the bacterium (peritrichus), in Escherichia coli, Proteus, etc. Lophotrichs have a bundle of flagella at one end of the cell. Amphitrichy has one flagellum or a bundle of flagella at opposite ends of the cell.

Flagella are detected using electron microscopy of preparations coated with heavy metals, or in a light microscope after treatment with special methods based on etching and adsorption of various substances leading to an increase in the thickness of the flagella (for example, after silvering).

Villi, or pili (fimbriae)- thread-like formations, thinner and shorter (3-10 nm * 0.3-10 µm) than flagella. The pili extend from the cell surface and are composed of the protein pilin. Several types of pili are known. General type pili are responsible for attachment to the substrate, nutrition, and water-salt metabolism. They are numerous - several hundred per cell. Sex pili (1-3 per cell) create contact between cells, transferring genetic information between them by conjugation (see Chapter 5). Of particular interest are type IV pili, in which the ends are hydrophobic, as a result of which they curl; these pili are also called curls. Location

They are located at the poles of the cell. These pili are found in pathogenic bacteria. They have antigenic properties, bring bacteria into contact with the host cell, and participate in the formation of biofilm (see Chapter 3). Many pili are receptors for bacteriophages.

Disputes - a peculiar form of resting bacteria with a gram-positive type of cell wall structure. Spore-forming bacteria of the genus Bacillus, in which the size of the spore does not exceed the diameter of the cell are called bacilli. Spore-forming bacteria in which the size of the spore exceeds the diameter of the cell, which is why they take the shape of a spindle, are called clostridia, for example bacteria of the genus Clostridium(from lat. Clostridium- spindle). The spores are acid-resistant, therefore they are stained red using the Aujeszky method or the Ziehl-Neelsen method, and the vegetative cell is stained blue.

Sporulation, the shape and location of spores in a cell (vegetative) are a species property of bacteria, which allows them to be distinguished from each other. The shape of the spores can be oval or spherical, the location in the cell is terminal, i.e. at the end of the stick (in the causative agent of tetanus), subterminal - closer to the end of the stick (in the causative agents of botulism, gas gangrene) and central (in the anthrax bacillus).

The process of sporulation (sporulation) goes through a number of stages, during which part of the cytoplasm and chromosome of the bacterial vegetative cell are separated, surrounded by an ingrowing cytoplasmic membrane - a prospore is formed.

The prospore protoplast contains a nucleoid, a protein synthesizing system, and an energy production system based on glycolysis. Cytochromes are absent even in aerobes. Does not contain ATP, energy for germination is stored in the form of 3-glycerol phosphate.

The prospore is surrounded by two cytoplasmic membranes. The layer surrounding the inner membrane of the spore is called wall of spores, it is composed of peptidoglycan and is the main source of cell wall during spore germination.

Between the outer membrane and the spore wall, a thick layer is formed consisting of peptidoglycan, which has many cross-links - cortex.

Located outside the outer cytoplasmic membrane spore shell, consisting of keratin-like proteins, co-

holding multiple intramolecular disulfide bonds. This shell provides resistance to chemical agents. The spores of some bacteria have an additional covering - exosporium lipoprotein nature. In this way, a multilayer, poorly permeable shell is formed.

Sporulation is accompanied by intensive consumption by the prospore and then by the developing spore shell of dipicolinic acid and calcium ions. The spore acquires heat resistance, which is associated with the presence of calcium dipicolinate in it.

The spore can persist for a long time due to the presence of a multilayer shell, calcium dipicolinate, low water content and sluggish metabolic processes. In soil, for example, the pathogens of anthrax and tetanus can persist for decades.

Under favorable conditions, spores germinate, going through three successive stages: activation, initiation, growth. In this case, one bacterium is formed from one spore. Activation is readiness for germination. At a temperature of 60-80 °C, the spore is activated for germination. Germination initiation lasts several minutes. The outgrowth stage is characterized by rapid growth, accompanied by the destruction of the shell and the emergence of a seedling.

Bacteria, despite their apparent simplicity, have a well-developed cell structure that is responsible for many of their unique biological properties. Many structural details are unique to bacteria and not found among archaea or eukaryotes. However, despite the relative simplicity of bacteria and the ease of growing individual strains, many bacteria cannot be grown in the laboratory, and their structures are often too small to study. Therefore, although some principles of bacterial cell structure are well understood and even applied to other organisms, most of the unique features and structures of bacteria are still unknown.

cell morphology

Most bacteria are either spherical in shape, the so-called coci (from the Greek word kokkos- grain or berry), or rod-shaped, the so-called bacilli (from the Latin word bacillus- stick). Some rod-shaped bacteria (vibrios) are somewhat bent, while others form spiral curls (spirochetes). All this diversity of bacterial forms is determined by the structure of their cell wall and cytoskeleton. These forms are important for bacterial function because they can influence the bacteria's ability to obtain nutrients, attach to surfaces, move, and escape from predators.

Bacteria size

Bacteria can have a wide range of shapes and sizes (or morphologies). In size, bacterial cells are typically 10 times smaller than eukaryotic cells, of course being only 0.5-5.0 µm at their largest size, although giant bacteria such as Thiomargarita namibiensis And Epulopiscium fishelsoni, can grow up to 0.5 mm in size and be visible to the naked eye. The smallest free-living bacteria are mycoplasmas, members of the genus Mycoplasma only 0.3 microns in length, approximately equal in size to the largest viruses.

Small size is important for bacteria because it results in a large surface area to volume ratio, aiding rapid transport of nutrients and excretion of waste. A low surface area to volume ratio, on the contrary, limits the metabolic rate of the microbe. The reason for the existence of large cells is unknown, although it appears that the large volume is used primarily to store additional nutrients. However, there is also a smallest size of free-living bacterium. According to theoretical calculations, a spherical cell with a diameter of less than 0.15-0.20 microns becomes incapable of independent reproduction, since it physically does not contain all the necessary biopolymers and structures in sufficient quantities. Recently, nanobacteria (and similar nanobes And ultramicrobacteria), having sizes smaller than the “acceptable” ones, although the existence of such bacteria is still in question. They, unlike viruses, are capable of independent growth and reproduction, but require a number of nutrients that they cannot synthesize from the host cell.

Cell membrane structure

As in other organisms, the bacterial cell wall provides the structural integrity of the cell. In prokaryotes, the primary function of the cell wall is to protect the cell from internal turgor caused by much higher concentrations of proteins and other molecules inside the cell compared to those around it. The bacterial cell wall differs from the wall of all other organisms by the presence of peptidoglycan (role-N-acetylglucosamine and N-acetomuramic acid), which is located directly outside the cytoplasmic membrane. Peptidoglycan is responsible for the rigidity of the bacterial cell wall and, in part, for determining the shape of the cell. It is relatively porous and does not resist the penetration of small molecules. Most bacteria have cell walls (with a few exceptions, such as mycoplasma and related bacteria), but not all cell walls have the same structure. There are two main types of bacterial cell walls, gram-positive and gram-negative bacteria, which are distinguished by Gram staining.

Cell wall of gram-positive bacteria

The cell wall of Gram-positive bacteria is characterized by the presence of a very thick layer of peptidoglycan, which is responsible for the staining of gentian violet dye during the Gram staining procedure. Such a wall is found exclusively in organisms belonging to the phyla Actinobacteria (or gram-positive bacteria with high %G+C) and Firmicutes (or gram-positive bacteria with low%G+C). Bacteria in the Deinococcus-Thermus group can also stain positive for Gram stains, but contain some cell wall structures typical of Gram-negative organisms. The cell walls of Gram-positive bacteria have polyalcohols built into them called techoic acid, some of which are associated with lipids to form lipochoic acids. Because lipochoic acids covalently bind to lipids within the cytoplasmic membrane, they are responsible for linking peptidoglycan to the membrane. Techoic acid provides gram-positive bacteria with a positive electrical benefit due to phosphodiesterate bonds between the monomers of techoic acid.

Cell wall of gram-negative bacteria

Unlike Gram-positive bacteria, Gram-negative bacteria contain a very thin layer of peptidoglycan, which is responsible for the inability of cell walls to contain crystal violet dye during the Gram staining procedure. In addition to the peptidoglycan layer, gram-negative bacteria have a second, so-called outer membrane, located outside the cell wall and assembles phospholipids and lipopolysaccharide on its outer side. Negatively charged lipopolysaccharide also provides the cell with a negative electrical charge. The chemical structure of the outer membrane lipopolysaccharide is often unique to individual strains of bacteria and is often responsible for the reaction of antigens with members of those strains.

outer membrane

Like any phospholipid bilayer, the outer membrane is quite impermeable to all charged molecules. However, protein channels (dip) present in the outer membrane allow the passive transport of many ions, sugars and amino acids across the outer membrane. Thus, these molecules are present in the periplasmic, the layer between the outer and cytoplasmic membranes. The periplasmic contains a layer of peptidoglycan and many proteins that are responsible for hydrolysis and reception of extracellular signals. It is read that periplasma is gel-like, not liquid, due to its high protein and peptidoglycan content. Signals and vital substances from the periplasmic membrane enter the cell cytoplasm using transport proteins in the cytoplasmic membrane.

Bacterial cytoplasmic membrane

The bacterial cytoplasmic membrane is composed of a bilayer of phospholipids, and therefore has all the general functions of the cytoplasmic membrane, acting as a permeability barrier to most molecules and enclosing transport proteins that regulate the transport of molecules into cells. In addition to these functions, energy cycling reactions also occur on bacterial cytoplasmic membranes. Unlike eukaryotes, bacterial membranes (with some exceptions, such as mycoplasmas and methanotrophs) generally do not contain sterols. However, many bacteria contain structurally related compounds, called hopanoids, that presumably perform the same function. Unlike eukaryotes, bacteria can have a wide variety of fatty acids in their membranes. Along with the typical saturated and unsaturated fatty acids, bacteria may contain fatty acids with additional methyl, hydroxy or even cyclic groups. The relative proportions of these fatty acids can be adjusted by the bacterium to maintain optimal membrane fluidity (for example, during changes in temperature).

Surface structures of bacteria

Villi and fimbriae

Villi and fimbriae (pili, fimbriae)— oriental in structure the surface structures of bacteria. At first these terms were introduced separately, but now similar structures are classified as types I, IV and sex villi, but many other types remain unclassified.

Genital villi are very long (5-20 microns) and are present on the bacterial cell in small quantities. They are used to exchange DNA during bacterial conjugation.

Type I villi or fimbriae are short (1-5 microns), extend from the outer membrane in many directions, and are tubular in shape, present in many members of the phylum Proteobacteria. These fibers are usually used to attach to surfaces.

Type IV villi or fimbriae are of medium length (about 5 microns), located at the poles of bacteria. Type IV villi help to attach to surfaces (for example, during the formation of biofilms), or to other cells (for example, animal cells during pathogenesis). Some bacteria (for example, Myxococcus) use type IV villi as a mechanism of movement.

S-layer

On the surface, outside the peptidiglycan layer or outer membrane, there is often a protein S-layer. Although the function of this layer is not fully known, it is believed that this layer provides chemical and physical protection to the cell surface and may serve as a macromolecular barrier. It is also believed that S-layers may have other functions, for example, they can serve as pathogenicity factors in Campylobacter and contain external enzymes in Bacillus stearothermophilus.

Capsules and mucus

Many bacteria secrete extracellular polymers outside their cell walls. These polymers are usually composed of polysaccharides and sometimes proteins. Capsules are relatively impermeable structures that cannot be dyed with many dyes. They are generally used to attach bacteria to other cells or non-living surfaces when forming biofilms. They have a varied structure from a disorganized mucous layer of cellular polymers to highly structured membrane capsules. Sometimes these structures are involved in protecting cells from engulfment by eukaryotic cells, such as macrophages. Also, mucus secretion has a signaling function for slow-moving bacteria and is possibly used directly for the movement of bacteria.

flagella

Perhaps the most easily recognized extracellular structure of a bacterial cell is the flagella. Bacterial flagella are filamentous structures that actively rotate around their axis using a flagellar motor and are responsible for the movement of many bacteria in a liquid environment. The location of the flagella depends on the type of bacteria and there are several types. Cell flagella are complex structures consisting of many proteins. The filament itself is composed of flagellin (FlaA), which forms a tubular-shaped filament. The basal motor is a large protein complex that spans the cell wall and both membranes (if present), forming the rotational motor. This motor moves due to the electrical potential on the cytoplasmic membrane.

secretion systems

In addition, specialized secretion systems are located in the cytoplasmic membrane and cell membrane, the structure of which depends on the type of bacterium.

Internal structure

Compared to eukaryotes, the intracellular structure of a bacterial cell is somewhat simpler. Bacteria contain almost no membrane organelles like eukaryotes. Of course, the chromosome and ribosomes are the only easily visible intracellular structures found in all bacteria. Although some groups of bacteria contain complex, specialized intracellular structures, a few of them are discussed below.

Cytoplasm and cytoskeleton

The entire interior of a bacterial cell within the inner membrane is called the cytoplasm. The homogeneous fraction of the cytoplasm, containing a set of soluble RNA, proteins, products and substrates of metabolic reactions, is called cytosol. The other part of the cytoplasm is represented by various structural elements, including the chromosome, ribosomes, bacterial cytoskeleton and others. Until recently, it was believed that bacteria do not have a cytoskeleton, but now orthologs or even homologs of all types of eukaryotic filaments have been found in bacteria: microtubules (FtsZ), actin (MreB and ParM) and intermediate filaments (Crestentin). The cytoskeleton has many functions, often responsible for cell shape and intracellular transport.

Bacterial chromosome and plasmids

Unlike eukaryotes, the bacterial chromosome is not located in the inner part of the membrane-bounded nucleus, but is located in the cytoplasm. This means that the transfer of cellular information through the processes of translation, transcription and replication occurs within the same compartment and its components can interact with other structures of the cytoplasm, in particular ribosomes. The bacterial chromosome is not packaged using histones like eukaryotes, but instead exists as a compact, supercoiled structure called a nucleoid. Bacterial chromosomes themselves are circular, although there are examples of linear chromosomes (for example, in Borrelia burgdorferi). Along with chromosomal DNA, most bacteria also contain small independent pieces of DNA called plasmids, which often encode individual proteins that are beneficial but of little importance to the host bacterium. Plasmids can be easily acquired or lost by bacteria and can be transferred between bacteria as a form of horizontal gene transfer.

Ribosomes and protein complexes

In most bacteria, numerous intracellular structures are ribosomes, the site of protein synthesis in all living organisms. Bacterial ribosomes are also somewhat different from eukaryotic and archaeal ribosomes and have a sedimentation constant of 70S (as opposed to 80S in eukaryotes). Although the ribosome is the most common intracellular protein complex in bacteria, other large complexes are sometimes observed using electron microscopy, although in most cases their purpose is unknown.

internal membranes

One of the main differences between a bacterial cell and a eukaryotic cell is the absence of a nuclear membrane and, often, the absence of membranes at all within the cytoplism. Many important biochemical reactions, such as energy cycle reactions, occur due to ionic gradients across membranes, creating a potential difference like a battery. The lack of internal membranes in bacteria means that these reactions, such as electron transfer in electron transport chain reactions, occur across the cytoplasmic membrane, between the cytoplasm and the periplasm. However, in some photosynthetic bacteria there is a developed network of cytoplasmic photosynthetic membranes derived from them. In purple bacteria (eg. Rhodobacter) they have retained a connection with the cytoplasmic membrane, which is easily detected on sections under an electron microscope, but in cyanobacteria this connection is either difficult to find or lost in the process of evolution.

granules

Some bacteria form intracellular granules to store nutrients such as glycogen, polyphosphate, sulfur, or polyhydroxyalkanoates, giving the bacteria the ability to store these substances for later use.

gas vesicles

Gas vesicles are spindle-shaped structures found in some floating bacteria that provide buoyancy to the cells of these bacteria, reducing their overall density. They consist of a protein shell that is very impermeable to water but penetrable to most gases. By adjusting the amount of gas present in its gas vesicles, the bacterium can increase or decrease its overall density and thus move up or down within the water column, maintaining itself in an environment optimal for growth.

Carboxysomes

Carboxysomes are intracellular structures found in many autotrophic bacteria, such as Cyanobacteria, nitrous bacteria and Nitrobacteria. These are protein structures that resemble viral particles in morphology, and contain the carbon dioxide fixation enzymes in these organisms (especially ribulose bisphosphate carboxylase/oxygenase, RuBisCO, and carbonic anhydrase). It is believed that the high local concentration of enzymes together with the rapid conversion of bicarbonate to carbonic acid by carbonic anhydrase allows faster and more efficient fixation of carbon dioxide than is possible within the cytoplasm.

Such structures are known to contain coenzyme B12-containing glycerol dehydratase, a key enzyme in the fermentation of glycerol to 1,3-propanediol in some members of the family Enterobacteriaceae (e.g. Salmonella).

Magnetosomes

A well-known class of membrane organelles in bacteria that more closely resemble eukaryotic organelles but may also be associated with the cytoplasmic membrane are magnetosomes, present in magnetotactic bacteria.

Bacteria on the farm

With the participation of bacteria, fermented milk products (kefir, cheese) and otsotic acid are obtained. Certain groups of bacteria are used to produce antibiotics and vitamins. Used for pickling cabbage and tanning leather. And in agriculture, bacteria are used for the production and storage of green animal feed.

It's a pity on the farm

Bacteriaii can spoil food. By settling in products, they produce toxic substances for both humans and animals. If the serum and poisoned drugs are NOT applied in a timely manner, a person may die! Therefore, be sure to wash vegetables and fruits before eating!

Spores and inactive forms of bacteria

Some bacteria of the phylum Firmicutes are capable of forming endospores, allowing them to withstand extreme environmental and chemical conditions (for example, gram-positive Bacillus, Anaerobacter, Heliobacterium And Clostridium). In almost all cases, one endosprora is formed, so this is not a reproductive process, although Anaerobacter can form up to seven endospores per cell. Endospores have a central nucleus composed of cytoplasm containing DNA and ribosomes, surrounded by a layer of plug and protected by an impenetrable and rigid membrane. Endospores do not exhibit any metabolism and can withstand extreme physicochemical pressures, such as high levels of ultraviolet radiation, gamma radiation, detergents, disinfectants, heat, pressure and drying. In this inactive state, these organisms, in some cases, can remain viable for millions of years and survive even in outer space. Endospores can cause diseases, for example anthrax can be caused by inhalation of endospores Bacillus anthracis.

Methane-oxidizing bacteria in the genus Methylosinus also form spores that are resistant to drying, the so-called exospores, because they are formed by budding at the end of the cell. Exospores do not contain diaminopicolinic acid, a characteristic component of endospores. Cysts are other inactive, thick-walled structures formed by members of the genera Azotobacter, Bdellovibrio (bdelocysts), And Myxococcus (myxospores). They are resistant to drying and other harmful effects, but to a lesser extent than endopores. When cysts form, representatives Azotobacter, cell division ends with the formation of a thick multilayered wall and membrane surrounding the cell. Filamentous Actinobacteria form reproductive spores of two categories: conditioniospores, which are chains of spores formed from mycelium-like threads, and sporangiospores, which are formed in specialized sacs, sporangia.

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