Features of the cellular structure of bacteria. The structure of bacteria. bacterial cell wall functions

In addition to the 5 kingdoms of wildlife, there are two more kingdoms: prokaryotes and eukaryotes. Therefore, if we consider systematic position bacteria, it will be as follows:

Why are these organisms singled out as a separate taxon? The whole point is that for bacterial cell characteristic is the presence of some features that leave an imprint on its vital activity and interaction with other creatures and humans.

Discovery of bacteria

Ribosomes are the smallest structures in large numbers scattered in the cytoplasm. Their nature is represented by RNA molecules. These granules are the material by which it is possible to determine the degree of relationship and the systematic position of a particular type of bacterium. Their function is the assembly of protein molecules.

Capsule

A bacterial cell is characterized by the presence of protective mucous membranes, the composition of which is determined by polysaccharides or polypeptides. Such structures are called capsules. There are micro- and macrocapsules. This structure is not formed in all species, but in the vast majority, that is, it is not mandatory.

What does the capsule protect the bacterial cell from? From phagocytosis by host antibodies if the bacterium is pathogenic. Or from drying and exposure to harmful substances, if we talk about other types.

Slime and inclusions

Also optional structures of bacteria. Mucus, or glycocalyx chemical basis is a mucoid polysaccharide. It can be formed both inside the cell and external enzymes. Well soluble in water. Purpose: attachment of bacteria to the substrate - adhesion.

Inclusions are microgranules in the cytoplasm of various chemical nature. These can be proteins, amino acids, nucleic acids, or polysaccharides.

Organelles of movement

Features of a bacterial cell are also manifested in its movement. For this, flagella are present, which can be in different amount(from one to several hundred per cell). The basis of each flagellum is flagellin protein. Due to elastic contractions and rhythmic movements from side to side, the bacterium can move in space. The flagellum is attached to the cytoplasmic membrane. The location can also vary between species.

drinking

Even thinner than flagella, structures involved in:

attachment to the substrate;
water-salt nutrition;
sexual reproduction.

They consist of pilin protein, their number can reach up to several hundred per cell.

Similarity to plant cells

Bacterial and have one undeniable similarity - the presence of a cell wall. However, if in plants it is indisputable, then in bacteria it is not present in all species, that is, it refers to optional structures.

Chemical composition of the bacterial cell wall:

peptidoglycan murein;
polysaccharides;
lipids;
proteins.

Usually this structure has a double layer: outer and inner. Functions performs the same as plants. Supports and defines the permanent shape of the body and provides mechanical protection.

Spore formation

What is the structure of a bacterial cell, we examined in sufficient detail. It remains only to mention how bacteria can survive adverse conditions, very for a long time without losing viability.

They do this by forming a structure called a spore. It has nothing to do with reproduction and only protects bacteria from adverse conditions. The form of disputes can be different. When normal environmental conditions are restored, the spore is initiated and germinates into an active bacterium.

The body of a bacterium is represented by a single cell. The forms of bacteria are varied. The structure of bacteria differs from the structure of animal and plant cells.

The cell lacks a nucleus, mitochondria and plastids. The carrier of hereditary information DNA is located in the center of the cell in a folded form. Microorganisms that do not have a true nucleus are classified as prokaryotes. All bacteria are prokaryotes.

It is assumed that on earth there are over a million species of these amazing organisms. To date, about 10 thousand species have been described.

A bacterial cell has a wall, cytoplasmic membrane, cytoplasm with inclusions, and a nucleotide. Of the additional structures, some cells have flagella, pili (a mechanism for sticking together and holding on to the surface), and a capsule. Under adverse conditions, some bacterial cells are able to form spores. The average size bacteria 0.5-5 microns.

The external structure of bacteria

Rice. 1. The structure of a bacterial cell.

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 - an L-shape and can be stored for a long time in the human body (cocci or tuberculosis bacilli). Unstable L-forms have the ability to return to their original form (reversion).

Rice. 2. In the photo, the structure of the bacterial wall of gram-negative bacteria (left) and gram-positive (right).

Capsule

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

Rice. 3. In the photo, pneumococcus. The arrows indicate the capsule (electron diffraction pattern of an ultrathin section).

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.

Rice. 4. Streptococci are able to stick together with tooth enamel and, together with other microbes, are the cause of caries.

Rice. 5. In the photo, the defeat of the mitral valve in rheumatism. The reason is streptococci.

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.

Rice. 6. Scheme of attachment and operation of the flagellum.

Rice. 7. In the photo different types flagellated microbes.

Rice. 8. The photo shows different types of flagellated microbes.

drinking

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

Rice. 9. The photo shows E. coli. Visible flagella and drinking. The photo was taken using a tunneling microscope (STM).

Rice. 10. The photo shows numerous pili (fimbriae) in cocci.

Rice. 11. The photo shows a bacterial cell with fimbriae.

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.

Rice. 12. The photo clearly shows a thin cell wall (CS), a cytoplasmic membrane (CPM) and a nucleotide in the center (bacterium Neisseria catarrhalis).

The internal structure of bacteria

Rice. 13. The photo shows the structure of a bacterial cell. The structure of a bacterial cell differs from the structure of animal and plant cells - the cell lacks a nucleus, mitochondria and plastids.

Cytoplasm

The cytoplasm is 75% water, the remaining 25% is mineral compounds, proteins, RNA and DNA. The cytoplasm is always dense and motionless. It contains enzymes, some pigments, sugars, amino acids, a supply of nutrients, ribosomes, mesosomes, granules and all sorts of other inclusions. In the center of the cell, a substance is concentrated that carries hereditary information - the nucleoid.

Granules

The granules are made up of compounds that are a source of energy and carbon.

mesosomes

Mesosomes are cell derivatives. Have different shape- concentric membranes, vesicles, tubules, loops, etc. Mesosomes have a connection with the nucleoid. Participation in cell division and spore formation is their main purpose.

Nucleoid

The nucleoid is analogous to the nucleus. It is located in the center of the cell. DNA is localized in it - the carrier of hereditary information in a folded form. The untwisted DNA reaches a length of 1 mm. The nuclear substance of a bacterial cell does not have a membrane, a nucleolus and a set of chromosomes, and is not divided by mitosis. Before division, the nucleotide is doubled. During division, the number of nucleotides increases to 4.

Rice. 14. The photo shows a section of a bacterial cell. A nucleotide is visible in the central part.

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.

Rice. 15. The photo shows a bacterial plasmid. The photo was taken with an electron microscope.

Ribosomes

Ribosomes of a bacterial cell are involved in protein synthesis from amino acids. Ribosomes of bacterial cells are not united in the endoplasmic reticulum, as in cells that have a nucleus. It is ribosomes that often become the "target" for many antibacterial drugs.

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. You can diagnose by currency.

Shapes of bacteria

Bacterial cell shape and size great importance during their identification (recognition). The most common forms are spherical, rod-shaped and convoluted.

Table 1. Main forms of bacteria.

globular bacteria

Spherical bacteria are called cocci (from the Greek coccus - grain). They are arranged one at a time, two at a time (diplococci), in bags, chains and like bunches of grapes. This arrangement depends on the mode of cell division. The most harmful microbes are staphylococci and streptococci.

Rice. 16. The photo shows micrococci. Bacteria are round, smooth, white, yellow and red. Micrococci are ubiquitous in nature. They live in different cavities of the human body.

Rice. 17. In the photo, diplococcus bacteria - Streptococcus pneumoniae.

Rice. 18. Sarcina bacteria in the photo. Coccoid bacteria are combined into packets.

Rice. 19. In the photo, streptococcus bacteria (from the Greek "streptos" - a chain).

Arranged in chains. They are the causative agents of a number of diseases.

Rice. 20. In the photo, the bacteria are "golden" staphylococci. Arranged like "bunch of grapes". The clusters have a golden color. They are the causative agents of a number of diseases.

rod-shaped bacteria

Rod-shaped bacteria that form spores are called bacilli. They are cylindrical in shape. by the most prominent representative of this group is the bacillus. Bacilli include plague and hemophilic rods. The ends of rod-shaped bacteria can be pointed, rounded, truncated, expanded, or split. The shape of the sticks themselves can be correct and incorrect. They can be arranged one at a time, two at a time, or form chains. Some bacilli are called coccobacilli because they are round in shape. But, nevertheless, their length exceeds the width.

Diplobacilli are double rods. Anthrax sticks form long threads (chains).

The formation of spores changes the shape of the bacilli. In the center of the bacilli, spores form in butyric bacteria, giving them the appearance of a spindle. In tetanus sticks - at the ends of the bacilli, giving them the appearance of drumsticks.

Rice. 21. The photo shows a rod-shaped bacterial cell. Multiple flagella are visible. The photo was taken with an electron microscope. Negative.

Rice. 24. In butyric bacilli, spores form in the center, giving them the appearance of a spindle. At tetanus sticks - at the ends, giving them the appearance of drum sticks.

Convoluted bacteria

No more than one turn has a cage bend. Several (two, three or more) - Campylobacter. Spirochetes have a peculiar appearance, which is reflected in their name - "spira" - a bend and "hate" - a mane. Leptospira ("leptos" - narrow and "spera" - gyrus) are long filaments with closely spaced whorls. Bacteria resemble a twisted spiral.

Rice. 27. In the photo, a spiral-shaped bacterial cell is the causative agent of "rat bite disease."

Rice. 28. In the photo, leptospira bacteria are the causative agents of many diseases.

Rice. 29. In the photo, leptospira bacteria are the causative agents of many diseases.

club-shaped

Club-shaped corynebacteria are the causative agents of diphtheria and listeriosis. The arrangement of metachromatic grains at its poles gives this form to the bacterium.

Rice. 30. Photo of Corynebacterium.

Read more about bacteria in the articles:

Bacteria have been living on planet Earth for more than 3.5 billion years. During this time they have learned a lot and adapted to a lot. The total mass of bacteria is enormous. It is about 500 billion tons. Bacteria have mastered almost all known biochemical processes. The forms of bacteria are varied. The structure of bacteria has become quite complicated over millions of years, but even today they are considered the most simply arranged unicellular organisms.

From the point of view of 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 with an electron microscope. The macrocapsule is often formed by pathogenic microbes (pneumococci). In Klebsiella pneumonia, a macrocapsule is always found.

capsule-like shell

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.
General drank 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 lipoprotective layer of the bacterial protoplast, which has special physical and chemical properties is called the cytoplasmic membrane. Inside the cytoplasm are all vital important structures and organelles. The cytoplasmic membrane performs a very important role- 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.

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.

Granules

The cytoplasm of bacterial cells often contains granules 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 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 cyto plasma 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 a nucleus like higher organisms(eukaryotes), but there is 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 main volume is concentrated in the nucleoid genetic information 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

Ribosomes

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.

Inclusions

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 with the 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 survive especially adverse conditions that can 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 distributed to clean skin and rarely seen on 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.

A bacterial cell, despite the external simplicity of its structure, is a very complex organism, which is characterized by processes that are characteristic of all living beings. The bacterial cell is dressed in a dense shell, consisting of a cell wall, a cytoplasmic membrane, and, in some species, a capsule.

cell wall- one of the main elements of the structure of a bacterial cell is a surface layer located outside the cytoplasmic membrane. The wall performs protective and supporting functions, and also gives the cell a permanent, characteristic shape for it (for example, the shape of a rod or coccus); has a certain rigidity (rigidity), and is the outer skeleton of the cell. Inside the bacterial cell, 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. Murein is the main structural component of the walls, the basis of their rigid structure in almost all bacteria studied so far. The surface of the cell wall of some rod-shaped bacteria is covered with outgrowths, spikes or tubercles. Using the method of staining, first proposed in 1884 by Christian Gram, bacteria can be divided into two groups: gram-positive and gram-negative. The cell wall is responsible for Gram staining of bacteria. The ability or inability to stain according to Gram is associated with a difference in the chemical composition of the bacterial cell walls. 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.

Closely adjacent to the cell wall of a bacterial cell is the outer layer of the cytoplasm - cytoplasmic membrane, usually consisting of a double layer of lipids, each of the surfaces of which is covered with a monomolecular layer of protein. The membrane makes up about 8-15% of the cell's lipids. The total thickness of the membrane is approximately 9 nm. The cytoplasmic membrane plays the role of an osmotic barrier that controls the transport of substances into and out of the bacterial cell.

The cell wall of many bacteria is surrounded on top by a layer of mucous material - capsule. 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.

Beneath the cytoplasmic membrane in bacteria is itoplasm, which is the entire contents of the cell, with the exception of the nucleus and cell wall. The cytoplasm of bacteria is a dispersed mixture of colloids, consisting of water, proteins, carbohydrates, lipids, mineral compounds and other substances. The liquid structureless phase of the cytoplasm (matrix) contains ribosomes, membrane systems, plastids and other structures, as well as reserve nutrients.

Bacteria do not have such a nucleus, as in higher organisms, but there is its analogue "nuclear equivalent" - nucleoid, which is an evolutionarily more primitive form of organization of nuclear matter. The nucleoid of a bacterial cell is located in its central part.

A resting bacterial cell usually contains one nucleoid; cells in the phase preceding division have two nucleoids; in the phase of logarithmic growth - reproduction - up to four or more nucleoids. In addition to the nucleoid, the cytoplasm of a bacterial cell can contain hundreds of times shorter DNA strands - the so-called extrachromosomal factors of heredity, called plasmid. As it was found out, plasmids are not necessarily present in bacteria, but they give the body additional, useful properties for it, in particular, those associated with reproduction, resistance to drugs, pathogenicity, etc.

Some bacteria have adnexal structures on their surface; the most widespread of them are flagella - organs of movement of bacteria. Bacteria can have one, two or more flagella. Their location is different: at one end of the cell, at two, over the entire surface, etc.

A bacterium with one flagellum is called monotrichome; a bacterium with a bunch of flagella at one end of the cell lofotrichoma; at both ends - amphitrichous; a bacterium with flagella all over the cell is called peritrichous. The number of flagella is different in different types of bacteria and can reach up to 100. The thickness of the flagella varies from 10 to 20 nm, the length is from 3 to 15 microns, and in the same bacterial cell, the length can vary depending on the state of the culture and environmental factors .

Bacteria are prokaryotes (Fig. 1.2) and differ significantly from plant and animal cells (eukaryotes). They belong to unicellular organisms and consist of a cell wall, cytoplasmic membrane, cytoplasm, nucleoid ( required components bacterial cell). Some bacteria may have flagella, capsules, spores (optional components of a bacterial cell).

Rice. 1.2. Combined schematic representation of a prokaryotic (bacterial) cell with flagella.
1 - granules of polyhydroxybutyric acid; 2 - fat droplets; 3 - sulfur inclusions; 4 - tubular thylakoids; 5 - lamellar thylakoids; 6 - bubbles; 7 - chromatophores; 8 - nucleus (nucleoid); 9 - ribosomes; 10 - cytoplasm; 11 - basal body; 12 - flagella; 13 - capsule; 14 - cell wall; 15 - cytoplasmic membrane; 16 - mesosome; 17 - gas vacuoles; 18 - lamellar structures; 19 - polysaccharide granules; 20 - polyphosphate granules

cell wall

The cell wall is the outer structure of bacteria with a thickness of 30-35 nm, the main component of which is peptidoglycan (murein). Peptidoglycan is a structural polymer composed of alternating N-acetylglucosamine and N-acetylmuramic acid subunits linked by glycosidic bonds (Fig.
1.3).

Rice. 1.3. Schematic representation of the single layer structure of peptidoglycan

Parallelly located polysaccharide (glycan) chains are fastened together by transverse peptide bridges (Fig. 1.4).

Rice. 1.4. Detailed structure of the peptidoglycan structure Light and black short arrows indicate bonds cleaved respectively by lysozyme (muramidase) and specific muroendopeptidase

The polysaccharide backbone is easily destroyed by lysozyme, an antibiotic of animal origin. Peptide bonds are a target for penicillin, which inhibits their synthesis and prevents the formation of the cell wall. The quantitative content of peptidoglycan affects the ability of bacteria to stain according to Gram. Bacteria with a significant thickness of the murein layer (90-95%) are steadfastly stained with gentian violet in blue- purple and are called Gram-positive bacteria.

Gram-negative bacteria with a thin layer of peptidoglycan (5-10%) in the cell wall after the action of alcohol lose gentian violet and are additionally stained with magenta in pink color. The cell walls of Gram-positive and Gram-negative prokaryotes differ sharply in both chemical composition(Table 1.1), and by ultrastructure (Fig. 1.5).

Rice. 1.5. Schematic representation of the cell wall in gram-positive (a) and gram-negative (b) prokaryotes: 1 - cytoplasmic membrane; 2 - peptidoglycan; 3 - periplasmic space; 4 - outer membrane; 5 - DNA

In addition to peptidoglycan, the cell wall of gram-positive bacteria contains teichoic acids (polyphosphate compounds), in a smaller amount - lipids, polysaccharides, proteins.

Table 1.1. Chemical composition of cell walls of Gram-positive and Gram-negative prokaryotes

Gram-negative prokaryotes have an outer membrane that includes lipids (22%), proteins, polysaccharides, and lipoproteins.

The cell wall in bacteria performs mainly shaping and protective functions, provides rigidity, forms a capsule, and determines the ability of cells to adsorb phages.

All bacteria, depending on their relationship to Gram stain, are divided into Gram-positive and Gram-negative.

Gram stain technique

1. Put filter paper on the smear and pour a carbolic solution of gentian violet for 1-2 minutes.
2. Remove the paper, drain the dye and, without washing the smear with water, pour Lugol's solution for 1 minute.
3. Drain Lugol's solution and decolorize the preparation in 96% alcohol for 30 seconds.
4. Washed with water.
5. Paint for 1-2 minutes with an aqueous solution of fuchsin.
6. Washed with water and dried.

As a result of staining, gram-positive bacteria are stained in purple, gram-negative - in red.

The reason for the different attitude of bacteria to Gram stain is explained by the fact that after treatment with Lugol's solution, an alcohol-insoluble complex of iodine with gentian violet is formed. This complex in gram-positive bacteria, due to the weak permeability of their walls, cannot diffuse, while in gram-negative bacteria it is easily removed by washing them with ethanol and then with water.

Bacteria completely devoid of a cell wall are called protoplasts, they have a spherical shape, have the ability to divide, respire, synthesize proteins, nucleic acids, enzymes. Protoplasts are unstable structures that are very sensitive to changes in osmotic pressure, mechanical influences, and aeration; they do not have the ability to synthesize the constituent parts of the cell wall;

If, under the influence of lysozyme and other factors, a partial dissolution of the cell wall occurs, then bacterial cells turn into spherical bodies, called spheroplasts.

Under the influence of some external factors bacteria are able to lose their cell wall, forming L-forms (named after the D. Lister Institute, where they were first isolated); such transformation may be spontaneous (eg, in chlamydia) or induced, eg, under the influence of antibiotics. There are stable and unstable L-forms. The former are not capable of reversion, while the latter reverse to their original forms after the removal of the causative factor.

cytoplasmic membrane

The cytoplasm of a bacterial cell is limited from the cell wall by a thin semi-permeable structure 5–10 nm thick, called the cytoplasmic membrane (CPM). The CPM consists of a double layer of phospholipids permeated with protein molecules (Fig. 1.6).

Fig.1.6. The structure of the plasma membrane Two layers of phospholipid molecules facing each other with hydrophobic poles and covered with two layers of globular protein molecules.

CMP is associated with many enzymes and proteins involved in the transfer of nutrients, as well as enzymes and electron carriers of the final stages of biological oxidation (dehydrogenases, cytochrome system, ATPase).

Enzymes catalyzing the synthesis of peptidoglycan, cell wall proteins, and their own structures are localized on the CMP. The membrane is also the site of energy conversion during photosynthesis.

periplasmic space

The periplasmic space (periplasm) is the area between the cell wall and the CPM. The thickness of the periplasm is about 10 nm, the volume depends on the environmental conditions and, above all, on the osmotic properties of the solution.

The periplasm can include up to 20% of all water in the cell, it contains some enzymes (phosphatases, permeases, nucleases, etc.) and transport proteins that carry the corresponding substrates.

Cytoplasm

The content of the cell, surrounded by the CPM, is the cytoplasm of bacteria. That part of the cytoplasm that has a homogeneous colloidal consistency and contains soluble RNA, enzymes, substrates, and metabolic products is referred to as the cytosol. Another part of the cytoplasm is represented by various structural elements: mesosomes, ribosomes, inclusions, nucleoid, plasmids.

Ribosomes are submicroscopic ribonucleoprotein granules with a diameter of 15-20 nm. Ribosomes contain approximately 80-85% of all bacterial RNA. Ribosomes of prokaryotes have a sedimentation constant of 70 S. They are built from two particles: 30 S (small subunit) and 50 S (large subunit) (Fig. 1.7).

Rice. 1.7. Ribosome (a) and its subparticles - large (b) and small (c) Ribosomes serve as a site for protein synthesis.

Cytoplasmic inclusions

Often, various inclusions are found in the cytoplasm of bacteria, which are formed in the course of life: droplets of neutral lipids, wax, sulfur, glycogen granules, β-hydroxybutyric acid (especially in the genus Bacillus). Glycogen and β-hydroxybutyric acid serve as a reserve source of energy for bacteria.

Some bacteria have crystals of a protein nature in the cytoplasm, which have a toxic effect on insects.

Some bacteria are able to accumulate phosphoric acid in the form of polyphosphate granules (volutin grains, metachromatic grains). They play the role of phosphate depots and are detected as dense formations in the form of a ball or ellipse, located mainly at the poles of the cell. Usually there is one granule at the poles.

Nucleoid

Nucleoid is the nuclear apparatus of bacteria. Represented by a DNA molecule corresponding to one chromosome. It is closed, located in the nuclear vacuole, does not have a membrane limiting from the cytoplasm.

Small amounts of RNA and RNA polymerase are associated with DNA. DNA is coiled around a central RNA core and is a highly ordered compact structure. The chromosomes of most prokaryotes have a molecular weight in the range of 1-3 x109, a sedimentation constant of 1300-2000 S. The DNA molecule includes 1.6x10 nucleotide pairs. Differences in the genetic apparatus of prokaryotic and eukaryotic cells determine its name: the former have a nucleoid (a formation similar to the nucleus), in contrast to the nucleus of the latter.

The nucleoid of bacteria contains the main hereditary information, which is realized in the synthesis of specific protein molecules. The systems of replication, repair, transcription and translation are associated with the DNA of a bacterial cell.

A nucleoid in a prokaryotic cell can be detected in stained preparations using a light or phase contrast microscope.e

In many bacteria, extrachromosomal genetic elements, plasmids, have been found in the cytoplasm. They are double-stranded DNA closed in rings, consisting of 1500-40000 base pairs and containing up to 100 genes.

Capsule

Capsule - the mucous layer of the cell wall of bacteria, consisting of polysaccharides or polypeptides. A microcapsule (less than 0.2 µm thick) is capable of forming most bacteria.

Flagella

Flagella act as an organ of movement that allows bacteria to move at a speed of 20-60 microns / sec. Bacteria may have one or more flagella, located over the entire surface of the body or collected in bundles at one pole, at different poles. The thickness of the flagella averages 10-30 nm, and the length reaches 10-20 microns.

The basis of the flagellum is a long spiral thread (fibril), which at the surface of the cell wall turns into a thickened curved structure - a hook and is attached to the basal granule embedded in the cell wall and CPM (Fig. 1.8).

Rice. 1.8. Schematic model of the basal end of the E. coli flagellum based on electron micrographs of the isolated organelle

The basal granules are about 40 nm in diameter and consist of several rings (one pair in Gram-positive bacteria, four in Gram-negative prokaryotes). Removal of the peptidoglycan layer of the cell wall leads to the loss of the bacteria's ability to move, although the flagella remain intact.

The flagella are composed almost entirely of the protein flagellin, with some carbohydrate and RNA content.

controversy

Some bacteria at the end of the period of active growth are able to form spores. This is preceded by the impoverishment of the environment nutrients, change in its pH, accumulation poisonous products metabolism. As a rule, one bacterial cell forms one spore - the localization of spores is different (central, terminal, subterminal - Fig. 1.9).

Rice. 1.9. Typical forms of spore-forming cells.

If the size of the spores does not exceed the transverse size of a rod-shaped bacterium, then the latter is called a bacillus. When the spore diameter is larger, the bacteria are spindle-shaped and are called Clostridium.

According to the chemical composition, the difference between spores and vegetative cells is only in the quantitative content chemical compounds. Spores contain less water and more lipids.

In the state of spores, microorganisms are metabolically inactive, withstand high temperature(140-150°C) and exposure to chemical disinfectants, persist in the environment for a long time.

Getting into nutrient medium spores germinate into vegetative cells. The process of spore germination includes three stages: activation, initial stage and stages of growth. The activating agents that disturb the state of dormancy include elevated temperature, acid reaction of the environment, mechanical damage, etc. The spore begins to absorb water and, with the help of hydrolytic enzymes, destroys many of its own structural components. After the destruction of the outer layers, a period of formation of a vegetative cell begins with the activation of biosynthesis, ending with cell division.

L.V. Timoshchenko, M.V. Chubik