Essay on the structure of bacterial cells. Bacteria - a general characteristic. Classification, structure, nutrition and role of bacteria in nature. Pili, villi, fimbriae

General scheme buildings bacterial cell shown in Figure 2. The internal organization of a bacterial cell is complex. Each systematic group microorganisms has its specific features buildings.

Cell wall. The bacterial cell is covered with a dense membrane. This surface layer, located outside the cytoplasmic membrane, is called the cell wall (Fig. 2, 14). The wall performs protective and supporting functions, and also gives the cell a permanent, characteristic shape (for example, the shape of a rod or coccus) and is the outer skeleton of the cell. This dense shell makes bacteria related to plant cells, which distinguishes them from animal cells that have soft shells. Inside the bacterial cell, the osmotic pressure is several times, and sometimes tens of times higher than in the external environment. Therefore, the cell would quickly rupture if it were not protected by such a dense, rigid structure as the cell wall.

The thickness of the cell wall is 0.01-0.04 µm. It is from 10 to 50% of the dry mass of bacteria. The amount of material from which the cell wall is built changes during bacterial growth and usually increases with age.

Murein (glycopeptide, mucopeptide) is the main structural component of the walls, the basis of their rigid structure in almost all bacteria studied so far. This is an organic compound of a complex structure, which includes sugars that carry nitrogen - amino sugars and 4-5 amino acids. Moreover, the amino acids of cell walls have an unusual shape (D-stereoisomers), which is rarely found in nature.

,
,

The constituent parts of the cell wall, its components, form a complex strong structure (Fig. 3, 4 and 5).

Using the method of staining, first proposed in 1884 by Christian Gram, bacteria can be divided into two groups: gram-positive And gram negative. Gram-positive organisms are able to bind certain aniline dyes, such as crystal violet, and retain the iodine-dye complex after treatment with iodine and then alcohol (or acetone). The same bacteria in which this complex is destroyed under the influence of ethyl alcohol (cells become discolored) are gram-negative.

The chemical composition of the cell walls of Gram-positive and Gram-negative bacteria is different.

In gram-positive bacteria, the cell walls include, in addition to mucopeptides, polysaccharides (complex, high-molecular sugars), teichoic acids (complex in composition and structure, compounds consisting of sugars, alcohols, amino acids and phosphoric acid). Polysaccharides and teichoic acids are associated with the framework of the walls - murein. We do not yet know what structure these constituent parts of the cell wall of gram-positive bacteria form. With the help of electronic photographs, thin sections (layering) were not found in the walls of gram-positive bacteria. Probably, all these substances are very closely related to each other.

The walls of gram-negative bacteria are more complex in chemical composition, they contain a significant amount of lipids (fats) associated with proteins and sugars in complex complexes - lipoproteins and lipopolysaccharides. In general, there is less murein in the cell walls of gram-negative bacteria than in gram-positive bacteria. The wall structure of Gram-negative bacteria is also more complex. Using an electron microscope, it was found that the walls of these bacteria are multilayered (Fig. 6).

The inner layer is murein. Above it is a wider layer of loosely packed protein molecules. This layer is in turn covered by a layer of lipopolysaccharide. The top layer is made up of lipoproteins.

The cell wall is permeable: through it, nutrients freely pass into the cell, and metabolic products are released into the environment. Large molecules with high molecular weight do not pass through the shell.

Capsule. The cell wall of many bacteria is surrounded from above by a layer of mucous material - a capsule (Fig. 7). The thickness of the capsule can be many times greater than the diameter of the cell itself, and sometimes it is so thin that it can only be seen through an electron microscope - a microcapsule.

The capsule is not an obligatory part of the cell, it is formed depending on the conditions in which the bacteria enter. It serves as a protective cover of the cell and participates in water exchange, protecting the cell from drying out.

By chemical composition, capsules are most often polysaccharides. Sometimes they consist of glycoproteins (complex complexes of sugars and proteins) and polypeptides (genus Bacillus), in rare cases - of fiber (genus Acetobacter).

Mucous substances secreted into the substrate by some bacteria determine, for example, the mucous-viscous consistency of spoiled milk and beer.

Cytoplasm. The entire contents of a cell, with the exception of the nucleus and cell wall, is called the cytoplasm. The liquid, structureless phase of the cytoplasm (matrix) contains ribosomes, membrane systems, mitochondria, plastids and other structures, as well as reserve nutrients. The cytoplasm has an extremely complex, fine structure (layered, granular). With the help of an electron microscope, many interesting details of the structure of the cell have been revealed.

The outer lipoprotein layer of the protoplast of bacteria, which has special physical and chemical properties, is called cyto plasma membrane(Fig. 2, 15).

Inside the cytoplasm are all vital structures and organelles.

The cytoplasmic membrane plays a very important role - it regulates the flow of substances into the cell and the release of metabolic products to the outside.

Through the membrane, nutrients can enter the cell as a result of an active biochemical process involving enzymes. In addition, the membrane is the synthesis of some of the components of the cell, mainly the components of the cell wall and capsule. Finally, the most important enzymes (biological catalysts) are located in the cytoplasmic membrane. The orderly arrangement of enzymes on membranes makes it possible to regulate their activity and prevent the destruction of some enzymes by others. Ribosomes are attached to the membrane - structural particles on which protein is synthesized. The membrane is made up of lipoproteins. It is strong enough and can provide the temporary existence of a cell without a shell. The cytoplasmic membrane makes up to 20% of the dry mass of the cell.

In electron photographs of thin sections of bacteria, the cytoplasmic membrane appears as a continuous strand about 75 Å thick, consisting of a light layer (lipids) enclosed between two darker ones (proteins). Each layer has a width of 20-30A. Such a membrane is called elementary (Table 30, Fig. 8).

Between the plasma membrane and the cell wall there is a connection in the form of desmoses - bridges. The cytoplasmic membrane often gives invaginations - invaginations into the cell. These invaginations form special membrane structures in the cytoplasm, called mesosomes. Some types of mesosomes are bodies separated from the cytoplasm by their own membrane. Numerous vesicles and tubules are packed inside such membranous sacs (Fig. 2). These structures perform a variety of functions in bacteria. Some of these structures are analogues of mitochondria. Others perform the functions of the endoplasmic reticulum or the Golgi apparatus. By invagination of the cytoplasmic membrane, the photosynthetic apparatus of bacteria is also formed. After invagination of the cytoplasm, the membrane continues to grow and forms stacks (Table 30), which, by analogy with plant chloroplast granules, are called thylakoid stacks. These membranes, which often fill most of the cytoplasm of a bacterial cell, contain pigments (bacteriochlorophyll, carotenoids) and enzymes (cytochromes) that carry out the process of photosynthesis.

The cytoplasm of bacteria contains ribosomes - protein-synthesizing particles with a diameter of 200A. There are more than a thousand of them in a cage. Ribosomes are made up of RNA and protein. In bacteria, many ribosomes are located freely in the cytoplasm, some of them can be associated with membranes.

Ribosomes are the centers of protein synthesis in the cell. At the same time, they often combine with each other, forming aggregates called polyribosomes or polysomes.

In many bacteria, the granules are composed of starch or other polysaccharides - glycogen and granulosa. Some bacteria, when grown on a sugar-rich medium, have droplets of fat inside the cell. Another widespread type of granular inclusions is volutin (metachromatin granules). These granules are composed of polymetaphosphate (reserve substance, including phosphoric acid residues). Polymetaphosphate serves as a source of phosphate groups and energy for the body. Bacteria accumulate volutin more often under unusual nutritional conditions, such as on a medium that does not contain sulfur. Sulfur droplets are found in the cytoplasm of some sulfur bacteria.

In addition to various structural components, the cytoplasm consists of a liquid part - a soluble fraction. It contains proteins, various enzymes, t-RNA, some pigments and low molecular weight compounds - sugars, amino acids.

As a result of the presence of low molecular weight compounds in the cytoplasm, a difference arises in the osmotic pressure of the cellular contents and the external environment, and in different microorganisms this pressure can be different. The highest osmotic pressure was noted in gram-positive bacteria - 30 atm, in gram-negative bacteria it is much lower - 4-8 atm.

Nuclear device. In the central part of the cell, the nuclear substance is localized - deoxyribonucleic acid a (DNA).

Bacteria do not have such a nucleus as in higher organisms (eukaryotes), but there is its analogue - the "nuclear equivalent" - nucleoid(see Fig. 2, 8), which is an evolutionarily more primitive form of organization of nuclear matter. Microorganisms that do not have a real nucleus, but have its analogue, belong to prokaryotes. All bacteria are prokaryotes. In the cells of most bacteria, most of the DNA is concentrated in one or more places. In eukaryotic cells, DNA is located in a specific structure - the nucleus. The nucleus is surrounded by a shell membrane.

Flagella. Some bacteria have adnexal structures on their surface; the most widespread of them are flagella - the organs of movement of bacteria.

The flagellum is anchored under the cytoplasmic membrane by two pairs of discs. Bacteria can have one, two, or many flagella. Their location is different: at one end of the cell, at two, over the entire surface, etc. (Fig. 9). Bacterial flagella have a diameter of 0.01-0.03 microns, their length can be many times greater than the length of the cell. Bacterial flagella Consist of a protein - flagellin - and are twisted helical filaments.

On the surface of some bacterial cells there are thin villi - fimbriae.

Plant life: in 6 volumes. - M.: Enlightenment. Edited by A. L. Takhtadzhyan, Chief Editor Corresponding Member USSR Academy of Sciences, prof. A.A. Fedorov. 1974 .

The structure and chemical composition of the bacterial
cells

The general structure of a bacterial cell is shown in Figure 2. The internal organization of a bacterial cell is complex. Each systematic group of microorganisms has its own specific structural features.
Cell wall. The bacterial cell is covered with a dense membrane. This surface layer, located outside the cytoplasmic membrane, is called the cell wall (Fig. 2, 14). The wall performs protective and supporting functions, and also gives the cell a permanent, characteristic shape (for example, the shape of a rod or coccus) and is the outer skeleton of the cell. This dense shell makes bacteria related to plant cells, which distinguishes them from animal cells that have soft shells.
Inside the bacterial cell, the osmotic pressure is several times, and sometimes tens of times higher than in the external environment. Therefore, the cell would quickly rupture if it were not protected by such a dense, rigid structure as the cell wall.
The thickness of the cell wall is 0.01-0.04 µm. It is from 10 to 50% of the dry mass of bacteria. The amount of material from which the cell wall is built changes during bacterial growth and usually increases with age.
The main structural component of the walls, the basis of their rigid structure in almost all bacteria studied so far is murein

mucopeptide). This is an organic compound of a complex structure, which includes sugars that carry nitrogen - amino sugars and 4-5 amino acids. Moreover, the amino acids of cell walls have an unusual shape (D-stereoisomers), which is rarely found in nature.

The constituent parts of the cell wall, its components, form a complex strong structure (Fig. 3, 4 and 5).
Using the method of staining, first proposed in 1884 by Christian Gram, bacteria can be divided into two groups: gram-positive And
gram negative. Gram-positive organisms are able to bind certain aniline dyes, such as crystal violet, and retain the iodine-dye complex after treatment with iodine and then alcohol (or acetone). The same bacteria in which this complex is destroyed under the influence of ethyl alcohol (cells become discolored) are gram-negative.
The chemical composition of the cell walls of Gram-positive and Gram-negative bacteria is different.
In gram-positive bacteria, the cell walls include, in addition to mucopeptides, polysaccharides (complex, high-molecular sugars), teichoic acids
(complex in composition and structure compounds consisting of sugars, alcohols, amino acids and phosphoric acid). Polysaccharides and teichoic acids are associated with the framework of the walls - murein. We do not yet know what structure these constituent parts of the cell wall of gram-positive bacteria form. With the help of electronic photographs, thin sections (layering) were not found in the walls of gram-positive bacteria.
Probably, all these substances are very closely related to each other.
The walls of gram-negative bacteria are more complex in chemical composition, they contain a significant amount of lipids (fats) associated with proteins and sugars in complex complexes - lipoproteins and lipopolysaccharides. In general, there is less murein in the cell walls of gram-negative bacteria than in gram-positive bacteria.
The wall structure of Gram-negative bacteria is also more complex. Using an electron microscope, it was found that the walls of these bacteria are multilayered (Fig.
6).

The inner layer is murein. Above it is a wider layer of loosely packed protein molecules. This layer is in turn covered by a layer of lipopolysaccharide. The top layer is made up of lipoproteins.
The cell wall is permeable: through it, nutrients freely pass into the cell, and metabolic products are released into the environment. Large molecules with high molecular weight do not pass through the shell.
Capsule. The cell wall of many bacteria is surrounded from above by a layer of mucous material - a capsule (Fig. 7). The thickness of the capsule can be many times greater than the diameter of the cell itself, and sometimes it is so thin that it can only be seen through an electron microscope - a microcapsule.
The capsule is not an obligatory part of the cell, it is formed depending on the conditions in which the bacteria enter. It serves as a protective cover of the cell and participates in water exchange, protecting the cell from drying out.
By chemical composition, capsules are most often polysaccharides.
Sometimes they consist of glycoproteins (complex complexes of sugars and proteins) and polypeptides (genus Bacillus), in rare cases - of fiber (genus Acetobacter).
Mucous substances secreted into the substrate by some bacteria determine, for example, the mucous-viscous consistency of spoiled milk and beer.
Cytoplasm. The entire contents of a cell, with the exception of the nucleus and cell wall, is called the cytoplasm. The liquid, structureless phase of the cytoplasm (matrix) contains ribosomes, membrane systems, mitochondria, plastids and other structures, as well as reserve nutrients. The cytoplasm has an extremely complex, fine structure (layered, granular). With the help of an electron microscope, many interesting details of the structure of the cell have been revealed.

The outer lipoprotein layer of the bacterial protoplast, which has special physical and chemical properties, is called the cytoplasmic membrane (Fig.
2, 15).
Inside the cytoplasm are all vital structures and organelles.
The cytoplasmic membrane plays a very important role - it regulates the flow of substances into the cell and the release of metabolic products to the outside.
Through the membrane, nutrients can enter the cell as a result of an active biochemical process involving enzymes. In addition, the membrane is the synthesis of some of the components of the cell, mainly the components of the cell wall and capsule.
Finally, the most important enzymes (biological catalysts) are located in the cytoplasmic membrane. The orderly arrangement of enzymes on membranes makes it possible to regulate their activity and prevent the destruction of some enzymes by others. Ribosomes are attached to the membrane - structural particles on which protein is synthesized.
The membrane is made up of lipoproteins. It is strong enough and can provide the temporary existence of a cell without a shell. The cytoplasmic membrane makes up to 20% of the dry mass of the cell.
In electron photographs of thin sections of bacteria, the cytoplasmic membrane appears as a continuous strand about 75 Å thick, consisting of a light layer
(lipids) enclosed between two darker ones (proteins). Each layer has a width
20-30A. Such a membrane is called elementary (Table 30, Fig. 8).

Between the plasma membrane and the cell wall there is a connection in the form of desmoses
- bridges. The cytoplasmic membrane often gives invaginations - invaginations into the cell. These invaginations form special membrane structures in the cytoplasm, called
mesosomes. Some types of mesosomes are bodies separated from the cytoplasm by their own membrane. Numerous vesicles and tubules are packed inside such membranous sacs (Fig. 2). These structures perform a variety of functions in bacteria. Some of these structures are analogues of mitochondria. Others perform the functions of the endoplasmic reticulum or the Golgi apparatus. By invagination of the cytoplasmic membrane, the photosynthetic apparatus of bacteria is also formed.
After invagination of the cytoplasm, the membrane continues to grow and forms stacks (Table 30), which, by analogy with plant chloroplast granules, are called thylakoid stacks. Pigments (bacteriochlorophyll, carotenoids) and enzymes are localized in these membranes, which often fill most of the cytoplasm of a bacterial cell.
(cytochromes) that carry out the process of photosynthesis.

,
The cytoplasm of bacteria contains ribosomes - protein-synthesizing particles with a diameter of 200A. There are more than a thousand of them in a cage. Ribosomes are made up of RNA and protein. In bacteria, many ribosomes are located freely in the cytoplasm, some of them can be associated with membranes.
Ribosomes are the centers of protein synthesis in the cell. At the same time, they often combine with each other, forming aggregates called polyribosomes or polysomes.

The cytoplasm of bacterial cells often contains granules of various shapes and sizes.
However, their presence cannot be considered as some kind of permanent feature of the microorganism, usually it is largely associated with the physical and chemical conditions of the environment. Many cytoplasmic inclusions are composed of compounds that serve as a source of energy and carbon. These reserve substances are formed when the body is supplied with a sufficient amount of nutrients, and, conversely, are used when the body enters conditions that are less favorable in terms of nutrition.
In many bacteria, the granules are composed of starch or other polysaccharides - glycogen and granulosa. Some bacteria, when grown on a sugar-rich medium, have droplets of fat inside the cell. Another widespread type of granular inclusions is volutin (metachromatin granules). These granules are composed of polymetaphosphate (reserve substance, including phosphoric acid residues).
Polymetaphosphate serves as a source of phosphate groups and energy for the body. Bacteria accumulate volutin more often under unusual nutritional conditions, such as on a medium that does not contain sulfur. Sulfur droplets are found in the cytoplasm of some sulfur bacteria.
In addition to various structural components, the cytoplasm consists of a liquid part - a soluble fraction. It contains proteins, various enzymes, t-RNA, some pigments and low molecular weight compounds - sugars, amino acids.
As a result of the presence of low molecular weight compounds in the cytoplasm, a difference arises in the osmotic pressure of the cellular contents and the external environment, and this pressure may be different for different microorganisms. The highest osmotic pressure was noted in gram-positive bacteria - 30 atm, in gram-negative bacteria it is much lower - 4-8 atm.
Nuclear device. In the central part of the cell, the nuclear substance is localized - deoxyribonucleic acid a (DNA).

,
Bacteria do not have such a nucleus as higher organisms (eukaryotes), but have its analogue -
"nuclear equivalent" - nucleoid(see Fig. 2, 8), which is an evolutionarily more primitive form of organization of nuclear matter. Microorganisms that do not have a real nucleus, but have its analogue, belong to prokaryotes. All bacteria are prokaryotes. In the cells of most bacteria, most of the DNA is concentrated in one or more places. In eukaryotic cells, DNA is located in a specific structure - the nucleus. The nucleus is surrounded by a shell membrane.

In bacteria, DNA is less densely packed than in true nuclei; A nucleoid does not have a membrane, a nucleolus, or a set of chromosomes. Bacterial DNA is not associated with the main proteins - histones - and is located in the nucleoid in the form of a bundle of fibrils.
Flagella. Some bacteria have adnexal structures on their surface; the most widespread of them are flagella - the organs of movement of bacteria.
The flagellum is anchored under the cytoplasmic membrane by two pairs of discs.
Bacteria can have one, two, or many flagella. Their location is different: at one end of the cell, at two, over the entire surface, etc. (Fig. 9). Bacterial flagella have a diameter
0.01-0.03 microns, their length can be many times greater than the length of the cell. Bacterial flagella Consist of a protein - flagellin - and are twisted helical filaments.

On the surface of some bacterial cells there are thin villi -
fimbriae.
Plant life: in 6 volumes. - M.: Enlightenment. Edited by A. L. Takhtadzhyan, chief
editor USSR Academy of Sciences, prof. A.A. Fedorov. 1974

The structure and chemical composition of a bacterial cell

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CYTOPLASMA (CPU)

Participate in spore formation.

MESOSOME

With excessive growth, in comparison with the growth of the CS, the CPM forms invaginates (invaginations) - mesosomes. Mesosomes are the center of the energy metabolism of the prokaryotic cell. Mesosomes are analogues of eukaryotic mitochondria, but are simpler in structure.

Well-developed and complexly organized mesosomes are characteristic of Gram+ bacteria.

Cell wall of bacteria

In Gram bacteria, mesosomes are less common and are simply organized (in the form of a loop). Mesosome polymorphism is observed even in the same species of bacteria. Rickettsia have no mesosomes.

Mesosomes vary in size, shape, and location within the cell.

Mesosomes are distinguished by shape:

- - lamellar (lamellar),

- - vesicular (having the form of bubbles),

- - tubular (tubular),

- mixed.

According to the location in the cell, mesosomes are distinguished:

- - formed in the zone of cell division and the formation of the transverse septum,

- - to which the nucleoid is attached;

– – formed as a result of invagination of the peripheral parts of the CPM.

Mesosome functions:

1. Strengthen the energy metabolism of cells, as they increase the total "working" surface of the membranes.

2. Participate in secretory processes(in some Gram+ bacteria).

3. Participate in cell division. During reproduction, the nucleoid moves to the mesosome, receives energy, doubles and divides by amitosis.

Detection of mesosomes:

1. Electron microscopy.

Structure. Cytoplasm (protoplasm) is the content of the cell, surrounded by the CPM and occupying the bulk of the bacterial cell. CPU is internal environment cells and is a complex colloidal system consisting of water (about 75%) and various organic compounds (proteins, RNA and DNA, lipids, carbohydrates, minerals).

The layer of protoplasm located under the CPM is denser than the rest of the mass in the center of the cell. The fraction of the cytoplasm, which has a homogeneous consistency and contains a set of soluble RNA, enzyme proteins, products and substrates of metabolic reactions, is called cytosol. Another part of the cytoplasm is represented by a variety of structural elements: nucleoid, plasmids, ribosomes and inclusions.

Functions of the cytoplasm:

1. Contains cell organelles.

Detection of the cytoplasm:

1. Electron microscopy.

Structure. Nucleoid - the equivalent of the eukaryotic nucleus, although it differs from it in its structure and chemical composition. The nucleoid is not separated from the CP by a nuclear membrane, does not have nucleoli and histones, contains one chromosome, has a haploid (single) set of genes, and is not capable of mitotic division.

The nucleoid is located in the center of the bacterial cell, contains a double-stranded DNA molecule, not a large number of RNA and proteins. In most bacteria, a double-stranded DNA molecule about 2 nm in diameter, about 1 m long, with a molecular weight of 1–3x109 Da is closed into a ring and tightly packed like a coil. In mycoplasmas, the molecular weight of DNA is the smallest for cellular organisms (0.4–0.8 × 109 Da).

Prokaryotic DNA is built in the same way as in eukaryotes (Fig. 25).

Rice. 25. DNA structure of prokaryotes:

A- a fragment of a DNA strand formed by alternating residues of deoxyribose and phosphoric acid. A nitrogenous base is attached to the first carbon atom of deoxyribose: 1 - cytosine; 2 - guanine.

B- DNA double helix: D- deoxyribose; F - phosphate; A - adenine; T - thymine; G - guanine; C - cytosine

The DNA molecule carries many negative charges, since each phosphate residue contains an ionized hydroxyl group. In eukaryotes, negative charges are neutralized by the formation of a DNA complex with the main proteins - histones. There are no histones in prokaryotic cells; therefore, charge neutralization is carried out by the interaction of DNA with polyamines and Mg2+ ions.

By analogy with eukaryotic chromosomes, bacterial DNA is often referred to as a chromosome. It is represented in a cell in singular because bacteria are haploid. However, before cell division, the number of nucleoids doubles, and during division it increases to 4 or more. Therefore, the terms "nucleoid" and "chromosome" do not always coincide. When cells are exposed to certain factors (temperature, pH, ionizing radiation, salts of heavy metals, some antibiotics, etc.), many copies of the chromosome are formed. When the influence of these factors is eliminated, as well as after the transition to the stationary phase, one copy of the chromosome is found in the cells.

For a long time, it was believed that no regularity could be traced in the distribution of DNA strands of the bacterial chromosome. Special studies have shown that prokaryotic chromosomes are a highly ordered structure. Part of the DNA in this structure is represented by a system of 20–100 independently supercoiled loops. Supercoiled loops correspond to currently inactive DNA regions and are located in the center of the nucleoid. On the periphery of the nucleoid there are despiralized areas where messenger RNA (mRNA) is synthesized. Since the processes of transcription and translation proceed simultaneously in bacteria, the same mRNA molecule can be simultaneously associated with DNA and ribosomes.

In addition to the nucleoid, the cytoplasm of a bacterial cell can contain plasmids - factors of extrachromosomal heredity in the form of additional autonomous circular molecules of double-stranded DNA with a lower molecular weight. Plasmids also encode hereditary information, but it is not vital for a bacterial cell.

Functions of Nucleiod:

1. Storage and transmission of hereditary information, including the synthesis of pathogenicity factors.

Nucleoid detection:

1. Electron microscopy: on the electron diffraction patterns of ultrathin sections, the nucleoid has the form of light zones of smaller optical density with fibrillar, thread-like structures of DNA (Fig. 26). Despite the absence of a nuclear membrane, the nucleoid is quite clearly separated from the cytoplasm.

2. Phase-contrast microscopy of native preparations.

3. Light microscopy after staining with DNA-specific methods according to Felgen, according to Pashkov or according to Romanovsky-Giemsa:

- the preparation is fixed with methyl alcohol;

- a Romanovsky-Giemsa dye (a mixture of equal parts of three colors - azure, eosin and methylene blue, dissolved in methanol) is poured onto a fixed preparation for 24 hours;

- the paint is drained, the preparation is washed with distilled water, dried and microscoped: the nucleoid stains purple and is diffusely located in the cytoplasm, stained pale pink.

Features of the chemical composition of bacterial cells

The structure of a bacterial cell. Main differences between prokaryotes and eukaryotes. Functions of individual structural elements of a bacterial cell. Features of the chemical composition of the cell walls of gram-positive and gram-negative bacteria.

A bacterial cell consists of a cell wall, cytoplasmic membrane, cytoplasm with inclusions, and a nucleus called a nucleoid. There are additional structures: capsule, microcapsule, mucus, flagella, pili. Some bacteria under adverse conditions are able to form spores.
Differences in the structure of the cell
1) Prokaryotes do not have a nucleus, but eukaryotes do.
2) Prokaryotes from organelles have only ribosomes (small, 70S), while eukaryotes, in addition to ribosomes (large, 80S), have many other organelles: mitochondria, ER, cell center, etc.
3) A prokaryotic cell is much smaller than a eukaryotic cell: 10 times in diameter, 1000 times in volume.
1) DNA is circular in prokaryotes and linear in eukaryotes
2) In prokaryotes, DNA is naked, almost not connected to proteins, while in eukaryotes, DNA is connected to proteins in a 50/50 ratio, a chromosome is formed
3) In prokaryotes, DNA lies in a special region of the cytoplasm called the nucleoid, while in eukaryotes, DNA lies in the nucleus.
Permanent components of a bacterial cell.
Nucleoid - the equivalent of the nucleus of prokaryotes
The cell wall is different in Gr+ and Gr-bacteria. Determines and maintains a constant form, provides communication with the external environment, determines the antigenic specificity of bacteria, and has important immunospecific properties; violation of the synthesis of the cell wall leads to the formation of L-forms of bacteria.
Gr+: this coloration is associated with the content of teichoic and dipoteichoic acids in the CS, which penetrate it through and fix it in the cytoplasm. Peptidoglycan is thick, composed of a plasma membrane bound by beta-glycosidic bonds.
Gr -: a thin layer of peptidoglycans, the outer membrane is represented by lipopolysaccharide glycocoproteins, glycolipids.
CPM - consists of lipoproteins. Perceives all chemical information entering the cell. It is the main barrier. Participates in the process of nucleoid and plasmid replication; contains a large number of enzymes; Participates in the synthesis of cell wall components.
Mesosomes are analogs of mitochondria in a bacterial cell
Ribosomes 70S are numerous small granules located in the cytoplasm.
UNPERMANENT:
Flagella: composed of the protein flagellin, originate from the CMP, the main function is motor.
Pili: due to them, attachment to the host cell occurs
Plasmids. Capsule, Spores, Inclusions.

Main article: Supramembrane complex

The supra-membrane apparatus of bacteria is represented by a cell wall, the specific organization of which serves as the basis for dividing them into two non-taxonomic groups (gram-positive and gram-negative forms) and correlates with a very large number of morphofunctional, metabolic and genetic characters. The cell wall of prokaryotes is essentially a polyfunctional organoid, derived from the protoplast and carrying a significant proportion of the metabolic load of the cell.

Cell wall of Gram-positive bacteria

The structure of the cell wall

In gram-positive bacteria (Fig. 12, A), the cell wall is generally more simple. The outer layers of the cell wall are formed by protein in combination with lipids. In some species of bacteria, a layer of surface protein globules has been relatively recently discovered, the shape, size, and location of which are specific to the species. Inside the cell wall, as well as directly on its surface, enzymes are placed that break down substrates to low molecular weight components, which are subsequently transported through the cytoplasmic membrane into the cell. It also contains enzymes that synthesize extracellular polymers, such as capsular polysaccharides.

Polysaccharide capsule

The polysaccharide capsule, which envelops the cell wall of a number of bacteria from the outside, is mainly of particular adaptive significance, and its presence is not necessary to preserve the vital activity of the cell. So, it provides attachment of cells to the surface of dense substrates, accumulates some minerals and in pathogenic forms prevents their phagocytosis.

Murein

A rigid murein layer adjoins directly to the cytoplasmic membrane.

Murein, or peptidoglycan, is a copolymer of acetylglucosamine and acetylmuramic acid with oligopeptide crosslinks. It is possible that the murein layer is one giant bag molecule that ensures the rigidity of the cell wall and its individual shape.

Teichoic acids

In close contact with the mureic layer is the second polymer of the wall of gram-positive bacteria - teichoic acids. They are credited with the role of an accumulator of cations and a regulator of ion exchange between the cell and the environment.

Cell wall of Gram-negative bacteria

The structure of the cell wall

Compared with gram-positive forms, the cell wall of gram-negative bacteria is more complex and its physiological significance is incomparably wider. In addition to the murein layer, the second protein-lipid membrane is located closer to the surface (Fig. 12, B, C), which includes lipopolysaccharides. It is covalently linked to murein by cross-links from lipoprotein molecules. The main function of this membrane is the role of a molecular sieve; in addition, enzymes are located on its outer and inner surfaces.

3. Structure of a bacterial cell.

The space bounded by the outer and cytoplasmic membranes is called periplasmic and is a unique property of gram-negative bacteria. A whole set of enzymes is localized in its volume - phosphatases, hydrolases, nucleases, etc. They break down relatively high-molecular nutrient substrates, and also destroy their own cellular material released into the environment from the cytoplasm. To a certain extent, the periplasmic space can be likened to the eukaryotic lysosome. In the periplasmic zone, it is possible not only to carry out the most efficient enzymatic reactions, but also to isolate compounds from the cytoplasm that pose a threat to its normal functioning. Material from the site http://wiki-med.com

Functions of the bacterial cell wall

Both in gram-positive and gram-negative forms, the cell wall plays the role of a molecular sieve, selectively carrying out passive transport of ions, substrates and metabolites. In bacteria that have the ability to actively move due to flagella, the cell wall is a component of the locomotor mechanism. Finally, individual sections of the cell wall are closely associated with the cytoplasmic membrane in the zone of nucleoid attachment and play an important role in its replication and segregation.

In one of the bacterial species, the process of destruction of the old cell wall, which occurs during cell division, is ensured by the work of at least four systems of hydrolytic enzymes present in the cell wall in a latent state. During cell division, a regular and strictly sequential activation of these systems occurs, leading to the gradual destruction and desquamation of the old ("mother") shell of the bacterial cell.

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bacterial cell wall functions
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cell wall structure
characterization of the bacterial cell wall

The cell wall of gram-positive bacteria contains a small amount of polysaccharides, lipids, proteins. The main component of the cell wall of these bacteria is a multilayer peptidoglycan (murein, mucopeptide), which makes up 40-90% of the mass of the cell wall. Teichoic acids (from Greek teichos - wall) are covalently bound to the peptidoglycan of the cell wall of gram-positive bacteria.
The cell wall of gram-negative bacteria includes an outer membrane linked by a lipoprotein to the underlying layer of peptidoglycan. On ultrathin sections of bacteria, the outer membrane has the form of a wavy three-layer structure similar to the inner membrane, which is called cytoplasmic. The main component of these membranes is a bimolecular (double) layer of lipids. The inner layer of the outer membrane is represented by phospholipids, and the outer layer contains lipopolysaccharide (LPS). Lipopolysaccharide of the outer membrane consists of three fragments: lipid A - a conservative structure, almost the same in gram-negative bacteria; core, or core, core part (Latin core - core), relatively conservative oligosaccharide structure (most permanent part core of LPS is ketodeoxyoctonic acid); highly variable O-specific polysaccharide chain formed by repeating identical oligosaccharide sequences (O-antigen). Proteins in the matrix of the outer membrane permeate it in such a way that protein molecules called porins border hydrophilic pores through which water and small hydrophilic molecules pass.
In violation of the synthesis of the bacterial cell wall under the influence of lysozyme,
penicillin, protective factors of the body, cells with a modified (often spherical) shape are formed: protoplasts - bacteria completely devoid of a cell wall; spheroplasts are bacteria with a partially preserved cell wall. Sphero- or protoplast-type bacteria that have lost the ability to synthesize peptidoglycan under the influence of antibiotics or other factors and are able to multiply are called L-forms.
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 the bacteria is removed, can reverse, "returning" to the original bacterial cell.
Between the outer and cytoplasmic membranes is the periplasmic space, or periplasm, containing enzymes (proteases, lipases, phosphatases, nucleases, beta-lactomases) and components of transport systems.

The cytoplasmic membrane at electron microscopy ultrathin sections is a three-layer membrane (2 dark layers 2.5 nm thick are separated by a light - intermediate). In structure, it is similar to the plasmalemma of animal cells and consists of a double layer of phospholipids with embedded surface and integral proteins, as if penetrating through the membrane structure. 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 complex twisted structures are called intracytoplasmic membranes.

Cytoplasm

The cytoplasm consists of soluble proteins, ribonucleic acids, inclusions and numerous small granules - ribosomes responsible for the synthesis (translation) of proteins. Bacterial ribosomes are about 20 nm in size and have a sedimentation coefficient of 70S, in contrast to the 80S ribosomes characteristic of eukaryotic cells. Ribosomal RNA (rRNA) are conservative elements of bacteria ("molecular clock" of evolution). 16S rRNA is part of the small subunit of ribosomes, and 23S rRNA is part of the large subunit of ribosomes. The study of 16S rRNA is the basis of gene systematics, making it possible to assess the degree of relatedness of organisms.
In the cytoplasm there are various inclusions in the form of glycogen granules, polysaccharides, beta-hydroxybutyric acid and polyphosphates (volutin).

cell wall

They are reserve substances for the nutrition and energy needs of bacteria. 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. The characteristic arrangement of volutin granules is revealed in diphtheria bacillus in the form of intensely stained poles of the cell.

Nucleoid

Nucleoid is the equivalent of the nucleus in bacteria. It is located in the central zone of bacteria in the form of double-stranded DNA, closed in a ring and tightly packed like a ball. The nucleus of bacteria, unlike eukaryotes, does not have a nuclear membrane, nucleolus and basic proteins (histones). Usually, a bacterial cell contains one chromosome, represented by a DNA molecule closed in a ring.
In addition to the nucleoid, represented by one chromosome, the bacterial cell contains extrachromosomal factors of heredity - plasmids, which are covalently closed DNA rings.

Capsule, microcapsule, mucus

A capsule is a slimy structure more than 0.2 µm thick, firmly attached to the bacterial cell wall and having clearly defined outer boundaries. The capsule is distinguishable in smears-imprints from pathological material. In pure cultures of bacteria, the capsule is formed less frequently. It is detected with special smear staining methods (for example, according to Burri-Gins), which create a negative contrast of the capsule substances: 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 prevents phagocytosis of bacteria. The capsule is antigenic: antibodies against the capsule cause it to enlarge (capsule swelling reaction).
Many bacteria form a microcapsule - a mucous formation less than 0.2 microns thick, which can be detected only with electron microscopy. From the capsule should be distinguished slieb - mucoid exopolysaccharides that do not have clear boundaries. Slime is soluble in water.
Bacterial exopolysaccharides are involved in adhesion (sticking to substrates), they are also called glycocalyx. Beyond synthesis
exopolysaccharides by bacteria, there is another mechanism for their formation: through the action of extracellular bacterial enzymes on disaccharides. As a result, dextrans and levans are formed.

Flagella

Bacterial flagella determine the motility of the bacterial cell. Flagella are thin filaments that originate from the cytoplasmic membrane and are longer than the cell itself. The flagella are 12–20 nm thick and 3–15 µm long. They consist of 3 parts: a spiral thread, a hook and a basal body containing a rod with special discs (1 pair of discs in Gram-positive and 2 pairs of discs in Gram-negative bacteria). The discs of the flagella are attached to the cytoplasmic membrane and cell wall. This creates the effect of an electric motor with a motor rod that rotates the flagellum. Flagella consist of a protein - flagellin (from flagellum - flagellum); is an H antigen. Flagellin subunits are coiled.
The number of flagella in bacteria of different species varies from one (monotrich) in Vibrio cholerae to ten or hundreds of flagella extending along the perimeter of the bacterium (peritrich) in Escherichia coli, Proteus, etc. Lofotrichs have a bundle of flagella at one end of the cell. Amphitrichous have one flagellum or a bundle of flagella at opposite ends of the cell.

drinking

Pili (fimbriae, villi) - filamentous formations, thinner and shorter (3-10 nm x 0.3-10 microns) than flagella. Pili extend from the cell surface and consist of the pilin protein, which has antigenic activity. There are pili responsible for adhesion, that is, for attaching bacteria to the affected cell, as well as pili responsible for nutrition, water-salt metabolism and sexual (F-pili), or conjugation pili. Drinks were plentiful - several hundred per cage. However, sex pili are usually 1-3 per cell: they are formed by so-called "male" donor cells containing transmissible plasmids (F-, R-, Col-plasmids). A distinctive feature of sex pili is interaction with special "male" spherical bacteriophages, which are intensively adsorbed on sex pili.

controversy

Spores are a peculiar form of dormant firmicute bacteria, i.e. bacteria
with a gram-positive type of cell wall structure. Spores are formed under unfavorable conditions for the existence of bacteria (drying, nutrient deficiency, etc.. One spore (endospore) is formed inside the bacterial cell. The formation of spores contributes to the preservation of the species and is not a method of reproduction, like in fungi. Spore-forming bacteria of the genus Bacillus have spores that do not exceeding the diameter of the cell.Bacteria whose spore size exceeds the diameter of the cell are called clostridium, for example, bacteria of the genus Clostridium (lat. Clostridium - spindle).The spores are acid-resistant, therefore, they are stained red according to the Aujeszky method or according to the Ziehl-Neelsen method, and the vegetative cell into blue.

The shape of the dispute can be oval, 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 pathogens of botulism, gas gangrene) and central (in anthrax bacilli). The spore persists for a long time due to the presence of a multi-layered shell, calcium dipicolinate, low water content and sluggish metabolic processes. Under favorable conditions, spores germinate through three successive stages: activation, initiation, germination.

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Diversity of living cells

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1.3 Structural features of the fungal cell

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Modern science has made fantastic progress in recent centuries. However, some mysteries still excite the minds of prominent scientists.

Today, the answer to the urgent question has not been found - how many varieties of bacteria exist on our vast 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 the 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.

The shape of the cell plays an important role in the proper functioning of the microorganism, as it can affect the ability of the bacterium to attach to other surfaces, obtain the necessary substances and move.

The minimum cell size is usually 0.5 µm, however, 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 differs significantly 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.

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

cytoplasmic membrane

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

The plasma membrane 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 to perceive various signals;
energy Some proteins are responsible for the function of energy transfer.

Violation of the functioning of the plasma membrane leads to the fact that the bacterium collapses and dies.

cell wall

The structural component inherent only in bacterial cells is the cell wall. This is a rigid permeable membrane, which 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 performs the function of protection, and in addition gives the cell a permanent shape. Its surface is covered with numerous spores that let in the necessary substances 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 the control of cell division and the distribution of hereditary traits in it. It contains peptidoglycan, which 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, which stores all the hereditary information of a bacterial cell. The nucleoid is located in the central part of the bacterium. Its properties are equivalent to the kernel.

A nucleoid is a single DNA molecule closed in a ring. The length of the molecule is 1 mm, and the amount 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 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 spore formation and cell reproduction. May be in the form of a bubble, loop, tubule.
Granules serve as an additional energy resource for bacterial cells. These elements come in a variety of forms. They contain polysaccharides, starch, fat droplets.

Capsule

Capsule It is a mucous structure tightly bound to the cell wall. Examining it under a light microscope, one 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 conditions external environment become aggressive. The capsule includes in its composition mainly polysaccharides, and in certain cases it may contain fiber, glycoproteins, polypeptides.

The main functions of the capsule:

- adhesion with cells in the human body. For example, streptococci stick together with tooth enamel and, in alliance with other microbes, provoke caries;
- protection from negative environmental conditions: toxic substances, mechanical damage, advanced level oxygen;
- participation in water metabolism (protection of cells 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 was based on the structural features of the capsules. They are:

normal;
complex capsules;
with cross-striped fibrils;
discontinuous capsules.

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

Flagella

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

The main function of flagella is that they allow bacteria to move in 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 in them:

Monotrichous- they have only one flagellum.
lophotrichous- have a certain number of flagella at one end of the bacterium.
amphitriches- characterized by the presence of flagella at polar opposite poles.
Peritrichi- flagella are located over the entire surface of the bacterium, they are characterized by slow and smooth movement.
Atrichi- flagella are absent.

Flagella commit motor activity making rotational movements. If bacteria do not have flagella, it is still able to move, or rather, slide with the help of mucus on the surface of the cell.

Plasmids

Plasmids are small mobile DNA molecules separate from chromosomal heredity factors. These components usually contain genetic material that makes the bacterium 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. They count from two units to several thousand per cell. Both the bacterial mobile cell and the immobile cell have these structural elements, since they do not have any effect on the ability to move.

Quantitatively, pili reach several hundred per bacterium. There are pili that are responsible for nutrition, water-salt metabolism, as well as conjugation (sex) pili.

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

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

Fimbria are located, as a rule, at one end of the cell. These structures allow the microorganism to be fixed in the tissues of the body. Some fimbriae have special proteins that are in contact with the receptor endings of the cells.

Fimbria differ from flagella in that they are thicker and shorter, and also do not realize 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 or lack of nutrients). They are diverse in spore size, since they can be completely different in different cells. The shape of the spores also differs - they are oval or spherical.

By location in the cell, spores are divided into:

central - their position in the very center, as, for example, in anthrax;
subterminal - located at the end of the stick, giving the shape of a club (in 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.

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

From point of view modern science prokaryotes have a primitive structure. But it is this "unpretentiousness" that helps them survive in the most unexpected conditions. For example, in hydrogen sulfide sources or at nuclear test sites. Scientists have calculated that the total mass of all terrestrial microorganisms is 550 billion tons.

Bacteria are unicellular. But this does not mean that bacterial cells give in to animal or plant cells. Microbiology already has knowledge of hundreds of thousands of species of microorganisms. Nevertheless, representatives of science daily discover their new types and features.

It is no wonder that for the complete development of the Earth's surface, microorganisms have to take a variety of forms:

cocci - balls;
streptococci - chains;
bacilli - sticks;
vibrios - curved commas;
spirilla are spirals.

The size of bacteria is measured in nanometers and micrometers. Their average value is 0.8 µm. But among them there are giant prokaryotes reaching 125 microns and more. The real giants among midgets are spirochetes 250 microns long. Now compare with them the size of the smallest prokaryotic cell: mycoplasmas "grow" quite a bit and reach 0.1-0.15 microns in diameter.

It is worth saying that it is not so easy for bacteria giants to survive in the environment. It is difficult for them to find enough nutrients for themselves to successfully perform their function. But on the other hand, they are not easy prey for predator bacteria that feed on their counterparts - single-celled microorganisms, “flowing around” and eating them.

The external structure of bacteria

cell wall

The cell wall of a bacterial cell is its protection and support. It gives the microorganism its specific shape.
The cell wall is permeable. Nutrients pass through it inside and metabolic products (metabolism) out.
Some types of bacteria produce a special mucus that resembles a capsule that protects them from drying out.
Some cells have flagella (one or more) or villi that help them move.
In bacterial cells that turn pink on Gram stain ( gram negative), the cell wall is thinner, multilayered. Enzymes that break down nutrients are released to the outside.
Bacteria that turn purple on Gram stain gram-positive), the cell wall is thick. Nutrients that enter the cell are broken down in the periplasmic space (the space between the cell wall and the cytoplasmic membrane) by hydrolytic enzymes.
There are numerous receptors on the surface of the cell wall. Cell killers are attached to them - phages, colicins and chemical compounds.
Wall lipoproteins in some types of bacteria are antigens, which are called toxins.
With prolonged treatment with antibiotics and for a number of other reasons, some cells lose their membrane, but retain the ability to reproduce. They acquire a rounded shape - L-shape and can be stored in the human body for a long time (cocci or tuberculosis bacilli). Unstable L-forms have the ability to return to their original form (reversion).

Capsule

Under adverse environmental conditions, the bacteria form a capsule. The microcapsule adheres tightly to the wall. It can only be seen in electron microscope. The macrocapsule is often formed by pathogenic microbes (pneumococci). In Klebsiella pneumonia, a macrocapsule is always found.

capsule-like shell

The capsule-like shell is a formation loosely associated with the cell wall. Thanks to bacterial enzymes, the capsule-like shell is covered with carbohydrates (exopolysaccharides) of the external environment, which ensures adhesion of bacteria to different surfaces, even completely smooth ones. For example, streptococci, entering the human body, are able to stick together with teeth and heart valves.

The functions of the capsule are diverse:

protection from aggressive environmental conditions,
ensuring adhesion (adhesion) with human cells,
possessing antigenic properties, the capsule has a toxic effect when introduced into a living organism.

Flagella

Some bacterial cells have flagella (one or more) or villi that help them move. The flagella contain the contractile protein flagelin.
The number of flagella can be different - one, a bunch of flagella, flagella at different ends of the cell or over the entire surface.
Movement (random or rotational) is carried out as a result of the rotational movement of the flagella.
The antigenic properties of flagella have a toxic effect in the disease.
Bacteria that do not have flagella, being covered with mucus, are able to glide. Aquatic bacteria contain vacuoles in the amount of 40 - 60, filled with nitrogen.

They provide diving and ascent. In the soil, the bacterial cell moves through the soil channels.

drinking

Pili (villi, fimbriae) cover the surface of bacterial cells. The villus is a helically twisted thin hollow thread of protein nature.
drinking general type provide adhesion (adhesion) with host cells. Their number is huge and ranges from several hundred to several thousand. From the moment of attachment, any infectious process begins.
sex saws promote the transfer of genetic material from the donor to the recipient. Their number is from 1 to 4 per cell.

cytoplasmic membrane

The cytoplasmic membrane is located under the cell wall and is a lipoprotein (up to 30% lipids and up to 70% proteins).
Different bacterial cells have different lipid composition of membranes.
Membrane proteins perform many functions. Functional proteins are enzymes due to which the synthesis of its various components occurs on the cytoplasmic membrane, etc.
The cytoplasmic membrane consists of 3 layers. The double phospholipid layer is permeated with globulins, which ensure the transport of substances into the bacterial cell. If it fails, the cell dies.
The cytoplasmic membrane is involved in sporulation.

The internal structure of bacteria

Cytoplasm

The entire contents of a cell, with the exception of the nucleus and cell wall, is called the cytoplasm. The liquid, structureless phase of the cytoplasm (matrix) contains ribosomes, membrane systems, mitochondria, plastids and other structures, as well as reserve nutrients. The cytoplasm has an extremely complex, fine structure (layered, granular). With the help of an electron microscope, many interesting details of the structure of the cell have been revealed.

The outer lipoprotein layer of the bacterial protoplast, which has special physical and chemical properties, is called the cytoplasmic membrane. Inside the cytoplasm are all vital structures and organelles. The cytoplasmic membrane plays a very important role - it regulates the flow of substances into the cell and the release of metabolic products to the outside. Through the membrane, nutrients can enter the cell as a result of an active biochemical process involving enzymes.

In addition, the membrane is the synthesis of some of the components of the cell, mainly the components of the cell wall and capsule. Finally, the most important enzymes (biological catalysts) are located in the cytoplasmic membrane. The orderly arrangement of enzymes on membranes makes it possible to regulate their activity and prevent the destruction of some enzymes by others. Ribosomes are attached to the membrane, the building blocks on which protein is synthesized. The membrane is made up of lipoproteins. It is strong enough and can provide the temporary existence of a cell without a shell. The cytoplasmic membrane makes up to 20% of the dry mass of the cell.

Granules

Many cytoplasmic inclusions are composed of compounds that serve as a source of energy and carbon. These reserve substances are formed when the body is supplied with a sufficient amount of nutrients, and, conversely, are used when the body enters conditions that are less favorable in terms of nutrition.

In many bacteria, the granules are composed of starch or other polysaccharides such as glycogen and granulosa. Some bacteria, when grown on a sugar-rich medium, have droplets of fat inside the cell. Another widespread type of granular inclusions is volutin (metachromatin granules). These granules are composed of polymetaphosphate (reserve substance, including phosphoric acid residues). Polymetaphosphate serves as a source of phosphate groups and energy for the body. Bacteria accumulate volutin more often under unusual nutritional conditions, such as on a medium that does not contain sulfur. Sulfur droplets are found in the cytoplasm of some sulfur bacteria.

mesosomes

Between the plasma membrane and the cell wall there is a connection in the form of desmoses - bridges. The cytoplasmic membrane often gives invaginations - protrusions into the cell. These invaginations form special membrane structures in the cytoplasm called mesosomes.

Some types of mesosomes are bodies separated from the cytoplasm by their own membrane. Numerous vesicles and tubules are packed inside such membranous sacs. These structures perform a variety of functions in bacteria. Some of these structures are analogues of mitochondria.

Others perform the functions of the endoplasmic reticulum or the Golgi apparatus. By invagination of the cytoplasmic membrane, the photosynthetic apparatus of bacteria is also formed. After invagination of the cytoplasm, the membrane continues to grow and forms stacks, which, by analogy with plant chloroplast granules, are called thylakoid stacks. These membranes, which often fill most of the cytoplasm of a bacterial cell, contain pigments (bacteriochlorophyll, carotenoids) and enzymes (cytochromes) that carry out the process of photosynthesis.

Nucleoid

Bacteria do not have such a nucleus as higher organisms (eukaryotes), but have its analogue - the "nuclear equivalent" - the nucleoid, which is an evolutionarily more primitive form of organization of nuclear matter. It consists of one double-stranded DNA strand 1.1–1.6 nm long, closed in a ring, which is considered as a single bacterial chromosome, or genophore. The nucleoid in prokaryotes is not delimited from the rest of the cell by a membrane - it lacks a nuclear membrane.

The nucleoid structures include RNA polymerase, basic proteins and no histones; the chromosome is fixed on the cytoplasmic membrane, and in gram-positive bacteria - on the mesosomes. The bacterial chromosome replicates in a polyconservative way: the parent DNA double helix unwinds and a new complementary chain is assembled on the template of each polynucleotide chain. The nucleoid does not have a mitotic apparatus, and the divergence of the daughter nuclei is ensured by the growth of the cytoplasmic membrane.

The bacterial nucleus is a differentiated structure. Depending on the stage of cell development, the nucleoid can be discrete (discontinuous) and consist of separate fragments. This is due to the fact that the division of a bacterial cell in time is carried out after the completion of the replication cycle of the DNA molecule and the formation of daughter chromosomes.

The nucleoid contains the bulk of the genetic information of a bacterial cell. In addition to the nucleoid, extrachromosomal genetic elements, plasmids, are found in the cells of many bacteria, represented by small circular DNA molecules capable of autonomous replication.

Plasmids

Plasmids are autonomous molecules coiled into a ring of double-stranded DNA. Their mass is much less than the mass of a nucleotide. Despite the fact that hereditary information is encoded in the DNA of plasmids, they are not vital and necessary for a bacterial cell.

Ribosomes

Ribosomes are the centers of protein synthesis in the cell. At the same time, they often combine with each other, forming aggregates called polyribosomes or polysomes.

Inclusions

Inclusions are metabolic products of nuclear and non-nuclear cells. They represent a supply of nutrients: glycogen, starch, sulfur, polyphosphate (valutin), etc. When stained, inclusions often take on a different appearance than the color of the dye. According to currency, you can diagnose diphtheria bacillus.

What is missing in bacterial cells?

Since a bacterium is a prokaryotic microorganism, many organelles are always absent in bacterial cells, that are characteristic of eukaryotic organisms:

the Golgi apparatus, which helps the cell by accumulating unnecessary substances, and subsequently removes them from the cell;
plastids, contained only in plant cells, determine their color, and also play a significant role in photosynthesis;
lysosomes, which have special enzymes and help break down proteins;
mitochondria provide cells necessary energy, and also participate in reproduction;
endoplasmic reticulum, which provides transport to the cytoplasm of certain substances;
cell center.

It is also worth remembering that bacteria do not have a cell wall, therefore, processes such as pinocytosis and phagocytosis cannot proceed.

Features of bacterial processes

Being special microorganisms, bacteria are adapted to exist in conditions where oxygen may be absent. And the very same breathing in them occurs due to mesosomes. It is also very interesting that green organisms are able to photosynthesize in exactly the same way as plants. But it is important to take into account the fact that in plants the process of photosynthesis occurs in chloroplasts, while in bacteria on membranes.

Reproduction in a bacterial cell occurs in the most primitive way. The mature cell divides in two, after some time they reach maturity, and this process is repeated. Under favorable conditions, a change of 70-80 generations can occur per day. It is important to remember that bacteria, due to their structure, do not have access to such methods of reproduction as mitosis and meiosis. They are unique to eukaryotic cells.

It is known that the formation of spores is one of several ways that fungi and plants reproduce. But bacteria can also form spores, which few of their species do. They have this ability in order to experience especially unfavourable conditions which may be life threatening.

There are species that are able to survive even in space conditions. This cannot be repeated by any living organisms. Bacteria became the progenitors of life on Earth due to the simplicity of their structure. But the fact that they exist to this day shows how important they are to the world around us. With their help, people can get as close as possible to answering the question of the origin of life on Earth, constantly studying bacteria and learning something new.

The most interesting and fascinating facts about bacteria

Staphylococcus bacteria crave human blood

Staphylococcus aureus (Staphylococcus aureus) is a common bacterial species that infects about 30 percent of all people. In some people, it is part of the microbiome (microflora), and is found both inside the body and on the skin or in the oral cavity. While there are harmless strains of staph, others, such as methicillin-resistant Staphylococcus aureus (Methicillin-resistant Staphylococcus aureus), pose serious health problems, including skin infections, cardiovascular disease, meningitis, and diseases of the digestive system.

Vanderbilt University researchers found that staph bacteria prefer human blood over animal blood. These bacteria are partial to the iron found in the hemoglobin found in red blood cells. Staphylococcus aureus rips apart blood cells to get to the iron inside them. It is believed that genetic variations in hemoglobin may make some people more desirable to staph bacteria than others.

bacteria make it rain

Researchers have found that bacteria in the atmosphere may play a role in the production of rain and other forms of precipitation. This process begins when bacteria from plants are blown into the atmosphere by the wind. At altitude, ice forms around them and they begin to grow. Once the frozen bacteria reach a certain growth threshold, the ice begins to melt and returns to earth as rain. Bacteria of the species Psuedomonas syringae have even been found in the center of large hail particles. They produce a special protein in cell membranes that allows them to bind water in a unique way, promoting ice formation.

Fighting acne causing bacteria

Researchers have found that certain strains of acne-causing bacteria may actually help prevent acne. The bacterium that causes acne, Propionibacterium acnes, lives in the pores of our skin. When these bacteria provoke an immune response, the area on the skin swells and pimples form.

However, certain strains of bacteria have been found to be less likely to cause acne. These strains may be why people with healthy skin rarely get acne. By studying the genes of Propionibacterium acnes strains collected from people with acne and healthy skin, the researchers identified a strain that was common in clear skin and rare in acne-prone skin. Future research will include attempts to develop a drug that only kills acne-causing strains of the bacterium Propionibacterium acnes.

Bacteria on gums can lead to cardiovascular disease

Who would have thought that brushing your teeth regularly could help prevent heart disease? Previous studies have found a link between gum disease and cardiovascular disease. Now scientists have found a specific link between these diseases.

It is hypothesized that both bacteria and humans produce certain types of proteins called stress proteins. These proteins are produced when cells experience various types of stress. When a person has a gum infection, immune system cells begin to attack the bacteria. Bacteria produce stress proteins when attacked, and white blood cells also attack stress proteins.

The problem is that white blood cells cannot distinguish between stress proteins produced by bacteria and those produced by the body. As a result, cells of the immune system also attack stress proteins produced by the body, which causes white blood cells to accumulate in the arteries and lead to atherosclerosis. A calcified heart is the main cause of cardiovascular disease.

Soil bacteria improve learning

Did you know that time spent in the garden or gardening can help you study better? According to researchers, the soil bacterium Mycobacterium vaccae can improve learning in mammals.

It is likely that these bacteria enter our body through ingestion or through breathing. The bacterium Mycobacterium vaccae is thought to improve learning by stimulating the growth of brain neurons, which leads to increased serotonin levels and reduced anxiety.

The study was carried out using mice fed live Mycobacterium vaccae bacteria. The results showed that the bacteria-fed mice navigated the maze much faster and with less anxiety than mice that did not eat the bacteria. Scientists suggest that Mycobacterium vaccae plays a role in improving problem solving and reducing stress levels.

Bacterial Power Machines

Researchers at the Argonne National Laboratory have found that the bacterium Bacillus subtilis has the ability to turn very small gears. These bacteria are aerobic, meaning they need oxygen to grow and develop. When they are placed in a solution with micro air bubbles, the bacteria float in the teeth of the gear and cause it to turn in a certain direction.

It takes several hundred bacteria working in unison to start the gear turning. It has also been found that bacteria can turn several interconnected gears. The researchers were able to control the speed at which the bacteria turned the gears by adjusting the amount of oxygen in the solution. The decrease in the amount of oxygen led to the slowdown of the bacteria. The removal of oxygen causes them to stop moving completely.

The cell of prokaryotic organisms has a complex, strictly ordered structure and has fundamental features ultra structural organization and chemical composition.

Structural components of a bacterial cell are divided into basic and temporary (Fig. 2). The main structures are: cell wall, cytoplasmic membrane with its derivatives, cytoplasm with ribosomes and various inclusions, nucleoid; temporary - capsule, mucous membrane, flagella, villi, endospores, formed only at certain stages life cycle bacteria, in some species they are completely absent.

In a prokaryotic cell, structures located outside the cytoplasmic membrane are called superficial (cell wall, capsule, flagella, villi).

The term "envelope" is currently used to refer to the cell wall and capsule of bacteria or only the cell wall, the cytoplasmic membrane is not part of the envelope and refers to the protoplast.

The cell wall is an important structural element of a bacterial cell, located between the cytoplasmic membrane and the capsule; in non-capsular bacteria, this is the outer shell of the cell. It is obligatory for all prokaryotes, with the exception of mycoplasmas and L-forms of bacteria. Performs a number of functions: protects bacteria from osmotic shock and other damaging factors, determines their shape, participates in metabolism; in many species of pathogenic bacteria, it is toxic, contains surface antigens, and also carries specific receptors for phages on the surface. The bacterial cell wall has pores that are involved in the transport of exotoxins and other bacterial exoproteins. The thickness of the cell wall is 10-100 nm, and it accounts for 5 to 50% of the dry matter of the cell.

The main component of the bacterial cell wall is peptidoglycan, or murein (lat. murus - wall), a supporting polymer that has a network structure and forms a rigid (hard) outer frame of the bacterial cell. Peptidoglycan has a main chain (backbone) consisting of alternating N-acetyl-M-glucosamine and N-acetylmuramic acid residues connected by 1,4-glycosidic bonds, identical tetrapeptide side chains attached to N-acetylmuramic acid molecules, and short transverse peptide chains. bridges linking polysaccharide chains. The two types of bonds (glycosidic and peptide) that connect the peptidoglycan subunits give this heteropolymer the structure of a molecular network. The backbone of the peptidoglycan layer is the same in all types of bacteria; tetrapeptide protein chains and peptide (transverse) chains are different in different species.

According to tinctorial properties, all bacteria are divided into two groups: gram-positive and gram-negative. In 1884, X. Gram proposed a staining method that was used to differentiate bacteria. The essence of the method lies in the fact that gram-positive bacteria firmly fix the complex of gentian violet and iodine, do not undergo discoloration with ethanol and therefore do not perceive the additional dye fuchsin, remaining colored purple. In gram-negative bacteria, this complex is easily washed out of the cell with ethanol, and they turn red upon additional application of fuchsin. In some bacteria positive color according to Gram is observed only in the stage of active growth. The ability of prokaryotes to stain according to the Gram method or to decolorize with ethanol is determined by the specifics of the chemical composition and ultrastructure of their cell wall. Peptidoglycan in gram-positive bacteria is the main component of the cell wall and ranges from 50 to 90%, in gram-negative bacteria - 1-10%. Structural microfibrils of peptidoglycan of Gram-negative bacteria are cross-linked less compactly; therefore, the pores in their peptidoglycan layer are much wider than in the molecular framework of Gram-positive bacteria. With this structural organization of peptidoglycan, the violet complex of gentian violet and iodine in gram-negative bacteria will be washed out faster.

The cell wall of gram-positive bacteria adheres tightly to the cytoplasmic membrane, is massive, its thickness is in the range of 20-100 nm. It is characterized by the presence of teichoic acids, they are associated with peptidoglycan and are polymers of a triatomic alcohol - glycerol or a pentaatomic alcohol - ribitol, the residues of which are connected by phosphodiester bonds. Teichoic acids bind magnesium ions and participate in their transport into the cell. Small amounts of polysaccharides, proteins, and lipids were also found in the cell wall of Gram-positive prokaryotes.

Rice. 2. Scheme of the structure of a prokaryotic cell:

1 - capsule; 2 - cell wall; 3 - cytoplasmic membrane; 4 - nucleoid; 5 - cytoplasm; 6 - chromatophores; 7 - thylakoids; 8 - mesosome; 9 - ribosomes; 10 - flagella; 11 - basal body; 12 - drinking; 13 - inclusion of sulfur; 14 - drops of fat; 15 - polyphosphate granules; 16 - plasmid

The cell wall of gram-negative bacteria is multilayered, its thickness is 14-17 nm. The inner layer is peptidoglycan, which forms a thin (2 nm) continuous mesh surrounding the cell. Peptidoglycan contains only mesodiaminopimelic acid and no lysine. The outer layer of the cell wall - the outer membrane - consists of phospholipids, lipopolysaccharide, lipoprotein and proteins. The outer membrane contains base proteins (matrix), they are firmly associated with the peptidoglycan layer. One of their functions is the formation of hydrophilic pores in the membrane, through which molecules with a mass of up to 600, sometimes 900, diffuse. Matrix proteins, in addition, also play the role of receptors for some phages. The lipopolysaccharide (LPS) of the cell walls of gram-negative bacteria consists of lipid A and a polysaccharide. LPS, which is toxic to animals, is called endotoxin. Teichoic acids have not been found in Gram-negative bacteria.

The structural components of the cell wall of gram-negative bacteria are separated from the cytoplasmic membrane and separated by a gap called the periplasm or periplasmic space.

Protoplasts and spheroplasts. Protoplasts are forms of prokaryotes that are completely devoid of a cell wall, usually formed in gram-positive bacteria. Spheroplasts are bacteria with a partially destroyed cell wall. They retain elements of the outer membrane. They are observed in gram-negative bacteria and much less often in gram-positive ones. They are formed as a result of the destruction of the peptidoglycan layer by lytic enzymes, such as lysozyme, or blocking the biosynthesis of peptidoglycan by the antibiotic penicillin and others in an environment with an appropriate osmotic pressure.

Protoplasts and spheroplasts are spherical or hemispherical and 3–10 times larger than the original cells. Under normal conditions, osmotic lysis occurs and they die. Under conditions of increased osmotic pressure, they are able to survive, grow and even divide for some time. When the factor that destroys peptidoglycan is removed, the protoplasts usually die, but can turn into L-forms; spheroplasts easily revert to the original bacteria, sometimes transform into L-forms, or die.

L-Forms of bacteria. These are phenotypic modifications, or mutants, of bacteria that have partially or completely lost the ability to synthesize cell wall peptidoglycan. Thus, L-forms are bacteria that are defective in the cell wall. They got their name due to the fact that they were isolated and described at the Lister Institute in England in 1935. They are formed when exposed to L-transforming agents - antibiotics (penicillin, polymyxin, bacitracin, vencomycin, streptomycin), amino acids (glycine, methionine, leucine, etc.), the enzyme lysozyme, ultraviolet and x-rays. Unlike protoplasts and spheroplasts, L-forms have a relatively high viability and a pronounced ability to reproduce. In terms of morphological and cultural properties, they differ sharply from the original bacteria, which is due to the loss of the cell wall and changes in metabolic activity.

The L-forms of bacteria are polymorphic. There are elementary bodies 0.2-1 microns in size (minimal reproductive elements), balls - 1-5, large bodies - 5-50, threads - up to 4 microns and more. L-form cells have a well-developed system of intracytoplasmic membranes and myelin-like structures. Due to a defect in the cell wall, they are osmotically unstable and can only be cultivated on special media with high osmotic pressure; they pass through bacterial filters.

There are stable and unstable L-forms of bacteria. The former are completely devoid of a rigid cell wall, which brings them closer to protoplasts; they very rarely reverse to their original bacterial forms. The latter may have elements of the cell wall, in which they show similarities with spheroplasts; in the absence of the factor that caused their formation, they revert to the original cells.

The process of formation of L-forms is called L-transformation or L-induction. Almost all types of bacteria, including pathogens (causative agents of brucellosis, tuberculosis, listeria, etc.), have the ability to L-transformation.

L-forms are of great importance in the development of chronic recurrent infections, the carriage of pathogens, their long-term persistence in the body. The transplacental invasiveness of elementary bodies of L-forms of bacteria has been proven.

The infectious process caused by L-forms of bacteria is characterized by atypicality, duration of the course, severity of the disease, and is difficult to respond to chemotherapy.

A capsule is a mucous layer located above the cell wall of a bacterium. The substance of the capsule is clearly delimited from the environment. Depending on the thickness of the layer and the strength of the connection with the bacterial cell, a macrocapsule is distinguished, with a thickness of more than 0.2 microns, which is clearly visible in light microscope, and a microcapsule, less than 0.2 µm thick, detectable only with an electron microscope or detected by chemical and immunological methods. The macrocapsule (true capsule) is formed by B. anlhracis, C1. perfringens, microcapsule - Escherichia coJi. The capsule is not an obligatory structure of a bacterial cell: its loss does not lead to the death of the bacterium. Capsular mutants of bacteria are known, for example, the anthrax vaccine strain STI-1.

The substance of the capsules consists of highly hydrophilic micelles, while their chemical composition is very diverse. The main components of most prokaryotic capsules are homo- or heteropolysaccharides (Entsrobacteria, etc.). In some species of bacilli, the capsules are built from a polypeptide. Thus, the B. anthracis capsule contains a D-glutamic acid polypeptide (dextrorotatory isomer). The composition of the microcapsule of mycobacterium tuberculosis of mammals includes glycopeptides represented by an ester of trehalose and mycolic acid (cord factor).

Capsule synthesis is a complex process and has its own characteristics in different prokaryotes; It is believed that capsule biopolymers are synthesized on the outer surface of the cytoplasmic membrane and are released onto the surface of the cell wall in certain specific areas.

There are bacteria that synthesize mucus, which is deposited on the surface of the cell wall in the form of a structureless layer of a polysaccharide nature. The mucous substance surrounding the cell often exceeds the diameter of the latter in thickness. In the saprophytic bacterium leuconostoc, the formation of one capsule is observed for many individuals. Such accumulations of bacteria enclosed in a common capsule are called zoogleys.

The capsule is a multifunctional organoid that plays an important biological role. It is the site of localization of capsular antigens that determine the virulence, antigenic specificity, and immunogenicity of bacteria. The loss of the capsule in pathogenic bacteria sharply reduces their virulence, for example, in acapsular strains of the anthrax bacillus. Capsules ensure the survival of bacteria, protecting them from mechanical damage, drying out, infection with phages, toxic substances, and in pathogenic forms - from the action of the protective forces of the macroorganism: encapsulated cells are poorly phagocytosed. In some types of bacteria, including pathogenic ones, it promotes cell attachment to the substrate.

In veterinary microbiology, capsule detection is used as a differential morphological trait pathogen in anthrax testing.

For staining capsules, special methods are used - Romanovsky - Giemsa, Gins - Burri, Olt, Mikhin, etc.

The microcapsule and the mucous layer are determined by serological tests (RA), the antigenic components of the capsule are identified using the immunofluorescent method (IF) and RDD.

Flagella are organelles of bacterial movement, represented by thin, long, filamentous structures of a protein nature. Their length exceeds the bacterial cell by several times and is 10-20 µm, and in some spirilla reaches 80-90 µm. The flagellum filament (fibril) is a complete spiral cylinder with a diameter of 12–20 nm. In Vibrios and Proteus, the filament is surrounded by a sheath 35 nm thick.

The flagellum consists of three parts: a spiral filament, a hook, and a basal body. The hook is a curved protein cylinder that acts as a flexible connecting link between the basal body and the rigid filament of the flagellum. The basal body is a complex structure consisting of a central rod (axis) and rings.

Rice. 3. Flagella:

a - monotrichous; b - amphitriches; c - lophotrichous; g - peritrichous

Flagella are not vital important structures bacterial cell: there are phase variations of bacteria, when they are present in one phase of cell development, and absent in another. So, in the causative agent of tetanus in old cultures, cells without flagella predominate.

The number of flagella (from I to 50 or more) and the places of their localization in bacteria of different species are not the same, but are stable for one species. Depending on this, the following groups of flagellated bacteria are distinguished: moiotrichous bacteria with one polar flagellum; amphitrichous - bacteria with two polar flagella or having a bundle of flagella at both ends; lophotrichous - bacteria that have a bundle of flagella at one end of the cell; peritrichous - bacteria with many flagella located on the sides of the cell or on its entire surface (Fig. 3). Bacteria that do not have flagella are called atrichia.

Being organs of locomotion, flagella are typical of floating rod-shaped and tortuous forms of bacteria and are found only in isolated cases in cocci. They provide efficient movement in a liquid medium and slower movement on the surface of solid substrates. The speed of movement of monotrichs and lophotrichs reaches 50 μm/s, amphitrichs and peritrichs move more slowly and usually cover a distance equal to the size of their cell in 1 s.

Bacteria move randomly, but they are capable of directed forms of movement - taxis, which are determined by external stimuli. In response to various environmental factors, bacteria a short time localized in the optimal habitat area. Taxis can be positive or negative. It is customary to distinguish: chemotaxis, aerotaxis, phototaxis, magnototaxis. Chemotaxis is caused by the difference in the concentration of chemicals in the environment, aerotaxis is caused by oxygen, phototaxis is caused by the intensity of illumination, magnetotaxis is determined by the ability of microorganisms to navigate in a magnetic field.

Identification of motile flagellar forms of bacteria is important for their identification in the laboratory diagnosis of infectious diseases.

Pili (fimbriae, villi) are straight, thin, hollow protein cylinders 3–25 nm thick and up to 12 µm long, extending from the surface of the bacterial cell. They are formed by a specific protein - pilin, originate from the cytoplasmic membrane, are found in mobile and immobile forms of bacteria and are visible only in an electron microscope (Fig. 4). On the cell surface there can be from 1-2, 50-400 or more pili to several thousand.

Rice. 4. Drank

There are two classes of pili: sexual (sekspili) and pili of a general type, which are more often called fimbriae. The same bacterium can have pili different nature. Sex pili appear on the surface of bacteria in the process of conjugation and act as organelles through which the transfer of genetic material (DNA) from a donor to a recipient occurs.

Pili of a general type are located peritrichially (E. coli) or at the poles (pseudomonas); one bacterium can contain hundreds of them. They take part in the adhesion of bacteria into agglomerates, the attachment of microbes to various substrates, including cells (adhesive function), in the transport of metabolites, and also contribute to the formation of films on the surface of liquid media; cause agglutination of erythrocytes.

Cytoplasmic membrane and its derivatives. The cytoplasmic membrane (plasmolemma) is a semi-permeable lipoprotein structure of bacterial cells that separates the cytoplasm from the cell wall. It is an obligatory polyfunctional component of the cell and makes up 8-15% of its dry mass. Destruction of the cytoplasmic membrane leads to the death of the bacterial cell. On ultrathin sections in an electron microscope, its three-layer structure is revealed - two limiting osmiophilic layers, each 2-3 nm thick, and one osmiophobic central layer 4-5 nm thick.

The cytoplasmic membrane is chemically a protein-lipid complex consisting of 50-75% proteins and 15-50% lipids. The main part of membrane lipids (70-90%) is represented by phospholipids. It is built from two monomolecular protein layers, between which there is a lipid layer, consisting of two rows of correctly oriented lipid molecules.

The cytoplasmic membrane serves as an osmotic barrier of the cell, controls the flow of nutrients into the cell and the release of metabolic products to the outside, it contains substrate-specific permease enzymes that actively selectively transfer organic and inorganic molecules.

Cytoplasmic membrane enzymes catalyze the final steps in the synthesis of membrane lipids, cell wall components, capsules, and exoenzymes; the membrane contains enzymes of oxidative phosphorylation and electron transport enzymes responsible for energy synthesis.

In the process of cell growth, the cytoplasmic membrane forms numerous invaginates that form intracytoplasmic membrane structures. Local invaginates of the membrane are called mesosomes. These structures are well expressed in Gram-positive bacteria, worse in Gram-negative bacteria and poorly in Rickettsia and Mycoplasmas.

A connection between mesosomes and the bacterial chromosome has been established; such structures are called nucleoidomeshes. Mesosomes integrated with the nucleoid take part in karyokinesis and cytokinesis of microbial cells, ensuring the distribution of the genome after the end of DNA replication and the subsequent divergence of daughter chromosomes. Mesosomes, like the cytoplasmic membrane, are the centers of bacterial respiratory activity; therefore, they are sometimes called analogues of mitochondria. However, the significance of mesosomes has not yet been finally elucidated. They increase the working surface of the membranes, perhaps they perform only a structural function, dividing the bacterial cell into relatively separate compartments, which creates more favorable conditions for the enzymatic processes to occur. In pathogenic bacteria, they provide the transport of protein molecules of exotoxins.

The cytoplasm is the contents of a bacterial cell, delimited by the cytoplasmic membrane. It consists of cytosol - a homogeneous fraction, including soluble RNA components, substrate substances, enzymes, metabolic products, and structural elements - ribosomes, intracytoplasmic membranes, inclusions and nucleoid.

Ribosomes are organelles that carry out protein synthesis. They consist of protein and RNA connected in a complex by hydrogen and hydrophobic bonds. Bacterial ribosomes are granules 15–20 nm in diameter, have a sedimentation constant of 70S, and are formed from two ribonucleoprotein subunits: 30S and 50S. One bacterial cell can contain from 5,000-50,000 ribosomes; by means of mRNA, they are combined into polysomes-aggregates consisting of 50-55 ribosomes with high protein-synthesizing activity.

In the cytoplasm of bacteria, various types of inclusions are detected. They may be solid, liquid or gaseous, with or without a proteinaceous membrane, and are intermittently present. A significant part of them is reserve nutrients and products of cellular metabolism. Reserve nutrients include: polysaccharides, lipids, polyphosphates, sulfur deposits, etc. Of the inclusions of a polysaccharide nature, glycogen and a starch-like substance granulosa are more often found, which serve as a source of carbon and energy material. Lipids accumulate in cells in the form of fat granules and droplets, these include poly-/3-hydroxybutyric acid granules surrounded by a membrane, which sharply refract light and are clearly visible in a light microscope. Anthrax bacilli and aerobic spore-forming saprophytic bacteria are also detected. Mycobacteria accumulate waxes as reserve substances. The cells of some coryne bacteria, spirilla, and others contain volutin granules formed by polyphosphates. They are characterized by metachromasia: toluidine blue and methylene blue stain them purple-red. Volutin granules play the role of phosphate depots.

Inclusions surrounded by a membrane also include gas vacuoles, or aerosomes, they reduce the specific mass of cells and are found in aquatic prokaryotes.

Nucleoid is the nucleus of prokaryotes. It consists of one double-stranded DNA strand 1.1-1.6 nm long, closed in a ring, which is considered as a single bacterial chromosome, or genophore.

The nucleoid in prokaryotes is not delimited from the rest of the cell by a membrane - it lacks a nuclear membrane.

The nucleoid contains the bulk of the genetic information of a bacterial cell.

In addition to the nucleoid, extrachromosomal genetic elements, plasmids, were found in the cells of many bacteria, represented by small circular DNA molecules capable of autonomous replication.

Cell wall of bacteria

Features of the chemical composition of bacterial cells

The structure of a bacterial cell. Main differences between prokaryotes and eukaryotes. Functions of individual structural elements of a bacterial cell. Features of the chemical composition of the cell walls of gram-positive and gram-negative bacteria.

Cell wall of Gram-positive bacteria

The structure of the cell wall

Polysaccharide capsule

Murein

Teichoic acids

Cell wall of Gram-negative bacteria

The structure of the cell wall

3. Structure of a bacterial cell.

Functions of the bacterial cell wall

.the main component of the cell wall of gram-positive bacteria is

bacterial cell wall functions

features of the structure of the bacterial cell wall

cell wall structure

characterization of the bacterial cell wall

Cytoplasm

cell wall

Nucleoid

Capsule, microcapsule, mucus

Flagella

drinking

controversy

2. b) The structure of a bacterial cell

The structure of a bacterial cell

3. Features of the structure, properties and functions of cell membranes

1.1 The general plan of the structure of eukaryotic cells, which also characterizes the structure of an animal cell

1.2 Structural features of a plant cell

1.3 Structural features of the fungal cell

1.4 The general plan of the structure of prokaryotic cells, which also characterizes the structure of a bacterial cell

Structure of a bacterial cell

1. Describe the structure of a bacterial cell. Draw the cell organelles

13. Simple, complex and supercomplex cells and their functions

1. Cell as an elementary structural unit of the body. The main components of the cell

1.1 Structural features

2. Functions of cell organelles

4.1 Structural features

5.1 Structural features

The energy system of the cell. The general plan of the structure of mitochondria and plastids, their functions. The hypothesis of the symbiotic origin of mitochondria and chloroplasts

cytoplasmic membrane

cell wall

Nucleoid

Cytoplasm

Capsule

Flagella

Plasmids

Pili, villi, fimbriae

controversy

The external structure of bacteria

cell wall

Capsule

capsule-like shell

Flagella

drinking

cytoplasmic membrane

The internal structure of bacteria

Cytoplasm

Granules

mesosomes

Nucleoid

Plasmids

Ribosomes

Inclusions

What is missing in bacterial cells?

Features of bacterial processes

The most interesting and fascinating facts about bacteria

Staphylococcus bacteria crave human blood

bacteria make it rain

Fighting acne causing bacteria

Bacteria on gums can lead to cardiovascular disease

Soil bacteria improve learning

Bacterial Power Machines