Science and life // Illustrations

Staphylococcus aureus.

Spirilla.

Trypanosoma.

Rotaviruses.

Rickettsia.

Yersinia.

Leishmania.

Salmonella.

Legionella.

Even 3,000 years ago, the great Greek Hippocrates guessed that contagious diseases are caused and carried by living beings. He called them miasma. But the human eye could not distinguish them. At the end of the 17th century, the Dutchman A. Leeuwenhoek created a sufficiently powerful microscope, and only then was it possible to describe and draw a variety of forms of bacteria - single-celled organisms, many of which are the causative agents of various human infectious diseases. Bacteria is one of the types of microbes (“microbe” - from the Greek “micros” - small and “bios” - life), however, the most numerous.

After the discovery of microbes and the study of their role in human life, it turned out that the world of these smallest organisms is very diverse and requires a certain systematization and classification. And today, experts use a system according to which the first word in the name of a microorganism means the genus, and the second - the species name of the microbe. These names (usually Latin or Greek) are "speaking". Thus, the name of some microorganisms reflects some of the most striking features of their structure, in particular, the form. This group primarily includes bacteria. In form, all bacteria are divided into spherical - cocci, rod-shaped - actually bacteria and convoluted - spirilla and vibrios.

globular bacteria- pathogenic cocci (from the Greek "coccus" - grain, berry), microorganisms that differ from each other in the location of cells after their division.

The most common of them are:

- staphylococci(from the Greek "stafile" - a bunch of grapes and "kokkus" - a grain, a berry), which received such a name because of the characteristic shape - a cluster resembling a bunch of grapes. The type of these bacteria has the most pathogenic effect. staphylococcus aureus(“Staphylococcus aureus”, as it forms clusters of golden color), causing various purulent diseases and food intoxications;

- streptococci(from the Greek "streptos" - a chain), whose cells after division do not diverge, but form a chain. These bacteria are the causative agents of various inflammatory diseases (tonsillitis, bronchopneumonia, otitis media, endocarditis, and others).

rod-shaped bacteria, or rods,- these are microorganisms of a cylindrical shape (from the Greek "bacterion" - a stick). From their name came the name of all such microorganisms. But those bacteria that form spores (a protective layer that protects against adverse environmental influences) are called bacilli(from the Latin "bacillum" - a stick). The spore-forming rods include the anthrax bacillus, a terrible disease known since ancient times.

The twisted shapes of bacteria are spirals. For example, spirilla(from Latin "spira" - bend) are bacteria that have the form of spirally curved rods with two or three curls. These are harmless microbes, with the exception of the causative agent of "rat bite disease" (Sudoku) in humans.

A peculiar form is also reflected in the name of microorganisms belonging to the family spirochete(from Latin "spira" - bend and "hate" - mane). For example, members of the family leptospira are distinguished by an unusual shape in the form of a thin thread with small, closely spaced curls, which makes them look like a thin twisted spiral. And the very name "leptospira" is translated as such - "narrow spiral" or "narrow curl" (from the Greek "leptos" - narrow and "spera" - gyrus, curl).

corynebacteria(causative agents of diphtheria and listeriosis) have characteristic club-shaped thickenings at the ends, as indicated by the name of these microorganisms: from lat. "korine" - a mace.

Today all known viruses also grouped into genera and families, including on the basis of their structure. Viruses are so small that in order to see them through a microscope, it must be much stronger than a conventional optical one. An electron microscope magnifies hundreds of thousands of times. Rotaviruses got its name from the Latin word "rota" - a wheel, since virus particles under an electron microscope look like small wheels with a thick sleeve, short spokes and a thin rim.

And the name of the family coronaviruses due to the presence of villi, which are attached to the virion through a narrow stem and expand towards the distant end, resembling the solar corona during an eclipse.

The name of some microorganisms is associated with the name of the organ they infect or the disease they cause. For example, title "meningococci" It is formed from two Greek words: “meningos” - the meninges, since these microbes mainly affect it, and “coccus” - a grain, indicating that they belong to spherical bacteria - cocci. The name is derived from the Greek word "pneumon" (lung). "pneumococci" These bacteria cause lung disease. Rhinoviruses- causative agents of a contagious rhinitis, hence the name (from the Greek "rhinos" - nose).

The origin of the name of a number of microorganisms is also due to their other most characteristic features. So, a distinctive feature of vibrios - bacteria in the form of a short curved rod - the ability to rapid oscillatory movements. Their name is derived from the French word vibrator- vibrate, vibrate, vibrate. Among the vibrios, the causative agent of cholera, which is called "cholera vibrio", is the most famous.

Bacteria of the genus proteus(Proteus) refer to the so-called microbes that are dangerous for some, but not for others. In this regard, they were named after the sea deity from ancient Greek mythology - Proteus, who was credited with the ability to arbitrarily change his appearance.

Monuments are erected to great scientists. But sometimes the names of microorganisms discovered by them also become monuments. For example, microorganisms that occupy an intermediate position between viruses and bacteria have been named "rickettsia" in honor of the American explorer Howard Taylor Ricketts (1871-1910), who died of typhus while studying the causative agent of this disease.

The causative agents of dysentery were thoroughly studied by the Japanese scientist K. Shiga in 1898, in his honor they subsequently received their generic name - "shigella".

Brucella(causative agents of brucellosis) are named after the English military doctor D. Bruce, who in 1886 for the first time managed to isolate these bacteria.

Bacteria grouped in a genus "yersinia", named after the famous Swiss scientist A. Yersin, who discovered, in particular, the causative agent of the plague - Yersinia pestis.

By the name of the English doctor V. Leishman, the simplest unicellular organisms (causative agents of leishmaniasis) are named leishmania, described in detail in 1903.

The generic name is associated with the name of the American pathologist D. Salmon "salmonella", a rod-shaped intestinal bacterium that causes diseases such as salmonellosis and typhoid fever.

And the German scientist T. Escherich owe their name Escherichia- Escherichia coli, first isolated and described by him in 1886.

In the origin of the name of some microorganisms, a certain role was played by the circumstances under which they were discovered. For example, generic name "legionella" appeared after an outbreak in 1976 in Philadelphia among the delegates of the convention of the American Legion (an organization that unites US citizens - participants in international wars) of a severe respiratory disease caused by these bacteria - they were transmitted through the air conditioner. BUT coxsackie viruses were first isolated from children with polio in 1948 in the village of Coxsackie (USA), hence the name.

Structure

Bacteria are very small living organisms. They can only be seen under a very high magnification microscope. All bacteria are unicellular. The internal structure of a bacterial cell is not like the cells of plants and animals. They do not have a nucleus or plastids. The nuclear substance and pigments are present, but in a "dispersed" state. The form is varied.

The bacterial cell is dressed in a special dense shell - the cell wall, which performs protective and supporting functions, and also gives the bacterium a permanent, characteristic shape. The cell wall of a bacterium resembles the shell of a plant cell. It is permeable: through it, nutrients freely pass into the cell, and metabolic products go out into the environment. Often, an additional protective layer of mucus is produced on top of the cell wall in bacteria - a capsule. The thickness of the capsule can be many times greater than the diameter of the cell itself, but it can be very small. The capsule is not an obligatory part of the cell, it is formed depending on the conditions in which the bacteria enter. It keeps bacteria from drying out.

On the surface of some bacteria there are long flagella (one, two or many) or short thin villi. The length of the flagella can be many times greater than the size of the body of the bacterium. Bacteria move with the help of flagella and villi.

Inside the bacterial cell is a dense immobile cytoplasm. It has a layered structure, there are no vacuoles, so various proteins (enzymes) and reserve nutrients are located in the very substance of the cytoplasm. Bacterial cells do not have a nucleus. In the central part of their cells, a substance carrying hereditary information is concentrated. Bacteria - nucleic acid - DNA. But this substance is not framed in the nucleus.

The internal organization of a bacterial cell is complex and has its own specific features. The cytoplasm is separated from the cell wall by the cytoplasmic membrane. In the cytoplasm, the main substance, or matrix, ribosomes and a small number of membrane structures that perform a variety of functions (analogues of mitochondria, endoplasmic reticulum, Golgi apparatus) are distinguished. The cytoplasm of bacterial cells often contains granules of various shapes and sizes. The granules may be composed of compounds that serve as a source of energy and carbon. Droplets of fat are also found in the bacterial cell.

Spore formation

Spores form inside the bacterial cell. In the process of spore formation, a bacterial cell undergoes a series of biochemical processes. The amount of free water in it decreases, enzymatic activity decreases. This ensures the resistance of spores to adverse environmental conditions (high temperature, high salt concentration, drying, etc.). Spore formation is characteristic of only a small group of bacteria. Spores are not an essential stage in the life cycle of bacteria. Sporulation begins only with a lack of nutrients or the accumulation of metabolic products. Bacteria in the form of spores can remain dormant for a long time. Bacterial spores withstand prolonged boiling and very long freezing. When favorable conditions occur, the dispute germinates and becomes viable. Bacterial spores are adaptations for survival in adverse conditions. Spores in bacteria serve to endure adverse conditions. They are formed from the inside of the contents of the cell. In this case, a new, denser shell is formed around the spore. Spores can tolerate very low temperatures (down to -273 ° C) and very high ones. Spores are not killed by boiling water.

Nutrition

Many bacteria have chlorophyll and other pigments. They carry out photosynthesis, like plants (cyanobacteria, purple bacteria). Other bacteria obtain energy from inorganic substances - sulfur, iron compounds and others, but the source of carbon, as in photosynthesis, is carbon dioxide.

reproduction

Bacteria reproduce by dividing one cell into two. Having reached a certain size, the bacterium divides into two identical bacteria. Then each of them begins to feed, grows, divides, and so on. After elongation of the cell, a transverse septum is gradually formed, and then the daughter cells diverge; in many bacteria, under certain conditions, cells after division remain connected in characteristic groups. In this case, depending on the direction of the division plane and the number of divisions, different forms arise. Reproduction by budding occurs in bacteria as an exception.

Under favorable conditions, cell division in many bacteria occurs every 20-30 minutes. With such rapid reproduction, the offspring of one bacterium in 5 days is able to form a mass that can fill all the seas and oceans. A simple calculation shows that 72 generations (720,000,000,000,000,000,000 cells) can be formed per day. If translated into weight - 4720 tons. However, this does not happen in nature, since most bacteria quickly die under the influence of sunlight, drying, lack of food, heating up to 65-100ºС, as a result of the struggle between species, etc.

The role of bacteria in nature. Distribution and ecology

Bacteria are ubiquitous: in water bodies, air, soil. There are the least of them in the air (but not in crowded places). In the waters of rivers there can be up to 400,000 of them in 1 cm 3, and in the soil - up to 1,000,000,000 in 1 g. Bacteria have different attitudes towards oxygen: for some it is necessary, for others it is destructive. For most bacteria, temperatures between +4 and +40 °C are most favorable. Direct sunlight kills many bacteria.

Occurring in huge numbers (the number of their species reaches 2500), bacteria play an exceptionally important role in many natural processes. Together with fungi and soil invertebrates, they participate in the processes of decomposition of plant residues (falling leaves, branches, etc.) to humus. The activity of saprophytic bacteria leads to the formation of mineral salts, which are absorbed by the roots of plants. Nodule bacteria living in the tissues of moth roots, as well as some free-living bacteria, have a remarkable ability to assimilate atmospheric nitrogen, which is inaccessible to plants. Thus, bacteria participate in the cycle of substances in nature.

Soil microflora. The number of bacteria in the soil is extremely high - hundreds of millions and billions of individuals in 1 gram. They are much more abundant in soil than in water and air. The total number of bacteria in soils varies. The number of bacteria depends on the type of soil, their condition, the depth of the layers. On the surface of soil particles, microorganisms are located in small microcolonies (20-100 cells each). Often they develop in the thicknesses of clots of organic matter, on living and dying plant roots, in thin capillaries and inside lumps. Soil microflora is very diverse. Different physiological groups of bacteria are found here: putrefactive, nitrifying, nitrogen-fixing, sulfur bacteria, etc. among them there are aerobes and anaerobes, spore and non-spore forms. Microflora is one of the factors of soil formation. The area of ​​development of microorganisms in the soil is the zone adjacent to the roots of living plants. It is called the rhizosphere, and the totality of microorganisms contained in it is called the rhizosphere microflora.

Microflora of water bodies. Water is a natural environment where microorganisms grow in large numbers. Most of them enter the water from the soil. A factor that determines the number of bacteria in water, the presence of nutrients in it. The cleanest are the waters of artesian wells and springs. Open reservoirs and rivers are very rich in bacteria. The greatest number of bacteria is found in the surface layers of water, closer to the shore. With increasing distance from the coast and increasing depth, the number of bacteria decreases. Pure water contains 100-200 bacteria per 1 ml, while contaminated water contains 100-300 thousand or more. There are many bacteria in the bottom silt, especially in the surface layer, where the bacteria form a film. There are a lot of sulfur and iron bacteria in this film, which oxidize hydrogen sulfide to sulfuric acid and thereby prevent fish from dying. There are more spore-bearing forms in the silt, while non-spore-bearing forms predominate in the water. In terms of species composition, the water microflora is similar to the soil microflora, but specific forms are also found. Destroying various wastes that have fallen into the water, microorganisms gradually carry out the so-called biological purification of water.

Air microflora. Air microflora is less numerous than soil and water microflora. Bacteria rise into the air with dust, can stay there for a while, and then settle to the surface of the earth and die from lack of nutrition or under the influence of ultraviolet rays. The number of microorganisms in the air depends on the geographic area, terrain, season, dust pollution, etc. Each speck of dust is a carrier of microorganisms. Most bacteria in the air over industrial enterprises. The air in the countryside is cleaner. The cleanest air is over forests, mountains, snowy spaces. The upper layers of the air contain fewer germs. In the air microflora there are many pigmented and spore-bearing bacteria that are more resistant than others to ultraviolet rays.

Microflora of the human body. The body of a person, even a completely healthy one, is always a carrier of microflora. When the human body comes into contact with air and soil, a variety of microorganisms, including pathogens (tetanus bacilli, gas gangrene, etc.), settle on clothing and skin. The exposed parts of the human body are most frequently contaminated. E. coli, staphylococci are found on the hands. There are over 100 types of microbes in the oral cavity. The mouth, with its temperature, humidity, nutrient residues, is an excellent environment for the development of microorganisms. The stomach has an acidic reaction, so the bulk of microorganisms in it die. Starting from the small intestine, the reaction becomes alkaline, i.e. favorable for microbes. The microflora in the large intestine is very diverse. Each adult excretes about 18 billion bacteria daily with excrement, i.e. more individuals than people on the globe. Internal organs that are not connected to the external environment (brain, heart, liver, bladder, etc.) are usually free from microbes. Microbes enter these organs only during illness.

The importance of bacteria in human life

Fermentation processes are of great importance; this is what is generally called the decomposition of carbohydrates. So, as a result of fermentation, milk turns into kefir and other products; ensiling fodder is also fermentation. Fermentation also occurs in the human intestine. Without the appropriate bacteria (such as E. coli), the intestines cannot function normally. Rotting, useful in nature, is highly undesirable in everyday life (for example, spoilage of meat products). Fermentation (for example, souring milk) is not always useful either. So that the products do not deteriorate, they are salted, dried, canned, kept in refrigerators. Thus, the activity of bacteria is reduced.

Pathogenic bacteria

Where do bacteria live in the human body?

1. Most of them inhabit the intestines, providing a harmonious microflora.
2. They live on mucous membranes, including in the oral cavity.
3. Many microorganisms inhabit the skin.

What are microorganisms responsible for?

1. They support immune function. With a lack of beneficial microbes, the body is immediately attacked by harmful ones.
2. By feeding on the components of plant foods, bacteria help digestion. Most of the food that reaches the large intestine is digested thanks to bacteria.
3. Benefits of intestinal microorganisms - in the synthesis of B vitamins, antibodies, absorption of fatty acids.
4. The microbiota maintains the water-salt balance.
5. Bacteria on the skin protect the integument from the penetration of harmful microorganisms into them. The same applies to the population of mucous membranes.

What happens if you remove bacteria from the human body? Vitamins will not be absorbed, hemoglobin will fall in the blood, diseases of the skin, gastrointestinal tract, respiratory organs, etc. will begin to progress. Conclusion: the main function of bacteria in the human body is protective. Let's take a closer look at what types of microorganisms exist and how to support their work.

Major groups of beneficial bacteria

Good bacteria for humans can be divided into 4 main groups:

• bifidobacteria;
• lactobacilli;
• enterococci;
• coli.

The most abundant beneficial microbiota. The task is to create an acidic environment in the intestines. In such conditions, pathogenic microflora cannot survive. Bacteria produce lactic acid and acetate. Thus, the intestinal tract is not afraid of the processes of fermentation and decay.

Another property of bifidobacteria is antitumor. Microorganisms are involved in the synthesis of vitamin C - the main antioxidant in the body. Vitamins D and B-group are absorbed thanks to this type of microbe. The digestion of carbohydrates is also accelerated. Bifidobacteria increase the ability of the intestinal walls to absorb valuable substances, including calcium, magnesium and iron ions.

Lactobacilli live in the digestive tract from the mouth to the large intestine. The joint action of these bacteria and other microorganisms controls the reproduction of pathogenic microflora. Intestinal pathogens are much less likely to infect the system if lactobacilli inhabit it in sufficient numbers.

The task of little hard workers is to normalize the work of the intestinal tract and support immune function. The microbiota is used in the food and medical industries: from healthy kefir to preparations for the normalization of the intestinal microflora.

Lactobacilli are especially valuable for women's health: the acidic environment of the mucous membranes of the reproductive system does not allow the development of bacterial vaginosis.

Advice! Biologists say that the immune system starts in the gut. The body's ability to resist harmful bacteria depends on the condition of the tract. Keep the digestive tract normal, and then not only the absorption of food will improve, but the body's defenses will also increase.

Enterococci

The habitat of enterococci is the small intestine. They block the reproduction of pathogenic microorganisms, help to digest sucrose.

The Polzateevo magazine found out that there is an intermediate group of bacteria - conditionally pathogenic. In one state, they are beneficial, and when any conditions change, they become harmful. These include enterococci. Staphylococci living on the skin also have a dual effect: they protect the integument from harmful microbes, but they themselves are able to get into the wound and cause a pathological process.

E. coli often causes negative associations, but only some species from this group bring harm. Most Escherichia coli have a beneficial effect on the tract.

These microorganisms synthesize a number of B vitamins: folic and nicotinic acid, thiamine, riboflavin. An indirect effect of such synthesis is an improvement in the composition of the blood.

What bacteria are harmful

Harmful bacteria are more widely known than beneficial ones, as they pose a direct threat. Many people know the dangers of salmonella, plague bacillus and vibrio cholerae.

The most dangerous bacteria for humans:

1. Tetanus bacillus: Lives on the skin and can cause tetanus, muscle spasms, and respiratory problems.
2. Botulism stick. If you eat a spoiled product with this pathogen, you can earn a deadly poisoning. Botulism often develops in expired sausages and fish.
3. Staphylococcus aureus can cause several ailments in the body at once, is resistant to many antibiotics and adapts incredibly quickly to drugs, becoming insensitive to them.
4. Salmonella is the cause of acute intestinal infections, including a very dangerous disease - typhoid fever.

Prevention of dysbacteriosis

Living in an urban environment with poor ecology and nutrition significantly increases the risk of dysbacteriosis - an imbalance of bacteria in the human body. Most often, the intestines suffer from dysbacteriosis, less often the mucous membranes. Signs of a lack of beneficial bacteria: gas formation, bloating, abdominal pain, upset stool. If you start the disease, vitamin deficiency, anemia, an unpleasant smell of the mucous membranes of the reproductive system, weight loss, and skin defects may develop.

Dysbacteriosis easily develops in conditions of taking antibiotic drugs. To restore the microbiota, probiotics are prescribed - formulations with living organisms and prebiotics - preparations with substances that stimulate their development. Fermented milk drinks containing live bifidus and lactobacilli are also considered useful.

In addition to therapy, the beneficial microbiota responds well to fasting days, eating fresh fruits and vegetables, and whole grains.

The role of bacteria in nature

The kingdom of bacteria is one of the most numerous on the planet. These microscopic creatures bring benefits and harm not only to humans, but also to all other species, provide many processes in nature. Bacteria are found in the air and in the soil. Azotobacter are very useful inhabitants of the soil, which synthesize nitrogen from the air, turning it into ammonium ions. In this form, the element is easily absorbed by plants. The same microorganisms cleanse soils from heavy metals and fill them with biologically active substances.

Do not be afraid of bacteria: our body is so arranged that it cannot function normally without these tiny hard workers. If their number is normal, then the immune, digestive and a number of other functions of the body will be in order.

BACTERIA
an extensive group of unicellular microorganisms characterized by the absence of a cell nucleus surrounded by a membrane. At the same time, the genetic material of a bacterium (deoxyribonucleic acid, or DNA) occupies a quite definite place in the cell - a zone called the nucleoid. Organisms with such a cell structure are called prokaryotes ("pre-nuclear"), in contrast to all the others - eukaryotes ("true nuclear"), whose DNA is located in the nucleus surrounded by a shell. Bacteria, once considered microscopic plants, are now classified as a separate kingdom, Monera, one of five in the current classification system, along with plants, animals, fungi, and protists.

fossil evidence. Bacteria are probably the oldest known group of organisms. Layered stone structures - stromatolites - dated in some cases to the beginning of the Archaeozoic (Archaean), i.e. that arose 3.5 billion years ago - the result of the vital activity of bacteria, usually photosynthetic, the so-called. blue-green algae. Similar structures (bacterial films impregnated with carbonates) are formed now, mainly off the coast of Australia, the Bahamas, in the California and Persian Gulfs, but they are relatively rare and do not reach large sizes, because herbivorous organisms, such as gastropods, feed on them. Today, stromatolites grow mainly where these animals are absent due to the high salinity of the water or for other reasons, but before the appearance of herbivorous forms in the course of evolution, they could reach enormous sizes, constituting an essential element of oceanic shallow water, comparable to modern coral reefs. Tiny charred spheres have been found in some ancient rocks, which are also thought to be the remains of bacteria. The first nuclear, i.e. eukaryotic, cells evolved from bacteria about 1.4 billion years ago.
Ecology. There are many bacteria in the soil, at the bottom of lakes and oceans - everywhere where organic matter accumulates. They live in the cold, when the thermometer is slightly above zero, and in hot acidic springs with temperatures above 90 ° C. Some bacteria tolerate very high salinity of the environment; in particular, they are the only organisms found in the Dead Sea. In the atmosphere, they are present in water droplets, and their abundance there usually correlates with the dustiness of the air. So, in cities, rainwater contains much more bacteria than in rural areas. There are few of them in the cold air of the highlands and polar regions; nevertheless, they are found even in the lower layer of the stratosphere at an altitude of 8 km. The digestive tract of animals is densely populated with bacteria (usually harmless). Experiments have shown that they are not necessary for the life of most species, although they can synthesize some vitamins. However, in ruminants (cows, antelopes, sheep) and many termites, they are involved in the digestion of plant foods. In addition, the immune system of an animal raised in sterile conditions does not develop normally due to the lack of stimulation by bacteria. The normal bacterial "flora" of the intestine is also important for the suppression of harmful microorganisms that enter there.

STRUCTURE AND LIFE OF BACTERIA

Bacteria are much smaller than the cells of multicellular plants and animals. Their thickness is usually 0.5-2.0 microns, and their length is 1.0-8.0 microns. Some forms can barely be seen with the resolution of standard light microscopes (about 0.3 µm), but there are also known species with a length of more than 10 µm and a width that also goes beyond these limits, and a number of very thin bacteria can exceed 50 µm in length. On the surface corresponding to the point put with a pencil, a quarter of a million representatives of this kingdom will fit in average in size.
Structure. According to the peculiarities of morphology, the following groups of bacteria are distinguished: cocci (more or less spherical), bacilli (rods or cylinders with rounded ends), spirilla (rigid spirals) and spirochetes (thin and flexible hair-like forms). Some authors tend to combine the last two groups into one - spirilla. Prokaryotes differ from eukaryotes mainly in the absence of a well-formed nucleus and the presence, in a typical case, of only one chromosome - a very long circular DNA molecule attached at one point to the cell membrane. Prokaryotes also lack membrane-bound intracellular organelles called mitochondria and chloroplasts. In eukaryotes, mitochondria produce energy during respiration, and photosynthesis takes place in chloroplasts (see also CELL). In prokaryotes, the entire cell (and first of all, the cell membrane) takes on the function of the mitochondria, and in photosynthetic forms, at the same time, the chloroplast. Like eukaryotes, inside the bacterium are small nucleoprotein structures - ribosomes necessary for protein synthesis, but they are not associated with any membranes. With very few exceptions, bacteria are unable to synthesize sterols, essential components of eukaryotic cell membranes. Outside of the cell membrane, most bacteria are lined with a cell wall, somewhat reminiscent of the cellulose wall of plant cells, but consisting of other polymers (they include not only carbohydrates, but also amino acids and substances specific to bacteria). This shell prevents the bacterial cell from bursting when water enters it due to osmosis. On top of the cell wall is often a protective mucosal capsule. Many bacteria are equipped with flagella, with which they actively swim. Bacterial flagella are simpler and somewhat different than similar eukaryotic structures.

"TYPICAL" BACTERIAL CELL and its main structures.

Sensory functions and behavior. Many bacteria have chemical receptors that detect changes in the acidity of the environment and the concentration of various substances, such as sugars, amino acids, oxygen and carbon dioxide. Each substance has its own type of such "taste" receptors, and the loss of one of them as a result of mutation leads to partial "taste blindness". Many motile bacteria also respond to temperature fluctuations, and photosynthetic species to changes in light. Some bacteria perceive the direction of magnetic field lines, including the Earth's magnetic field, with the help of magnetite particles (magnetic iron ore - Fe3O4) present in their cells. In water, bacteria use this ability to swim along lines of force in search of a favorable environment. Conditioned reflexes in bacteria are unknown, but they have a certain kind of primitive memory. While swimming, they compare the perceived intensity of the stimulus with its previous value, i.e. determine whether it has become larger or smaller, and, based on this, maintain the direction of movement or change it.
Reproduction and genetics. Bacteria reproduce asexually: the DNA in their cell is replicated (doubled), the cell divides in two, and each daughter cell receives one copy of the parent's DNA. Bacterial DNA can also be transferred between non-dividing cells. At the same time, their fusion (as in eukaryotes) does not occur, the number of individuals does not increase, and usually only a small part of the genome (the complete set of genes) is transferred to another cell, in contrast to the "real" sexual process, in which the descendant receives a complete set of genes from each parent. Such DNA transfer can be carried out in three ways. During transformation, the bacterium absorbs "naked" DNA from the environment, which got there during the destruction of other bacteria or deliberately "slipped" by the experimenter. The process is called transformation, because in the early stages of its study, the main attention was paid to the transformation (transformation) in this way of harmless organisms into virulent ones. Fragments of DNA can also be transferred from bacteria to bacteria by special viruses - bacteriophages. This is called transduction. There is also a process that resembles fertilization and is called conjugation: bacteria are connected to each other by temporary tubular outgrowths (copulatory fimbria), through which DNA passes from the "male" cell to the "female". Sometimes bacteria contain very small extra chromosomes - plasmids, which can also be transferred from individual to individual. If at the same time plasmids contain genes that cause resistance to antibiotics, they speak of infectious resistance. It is important from a medical point of view, because it can spread between different species and even genera of bacteria, as a result of which the entire bacterial flora, say the intestines, becomes resistant to the action of certain drugs.

METABOLISM

Partly due to the small size of bacteria, the intensity of their metabolism is much higher than that of eukaryotes. Under the most favorable conditions, some bacteria can double their total mass and abundance approximately every 20 minutes. This is due to the fact that a number of their most important enzyme systems function at a very high speed. So, a rabbit needs a few minutes to synthesize a protein molecule, and bacteria - seconds. However, in the natural environment, for example, in the soil, most bacteria are "on a starvation diet", so if their cells divide, then not every 20 minutes, but every few days.
Nutrition. Bacteria are autotrophs and heterotrophs. Autotrophs ("self-feeding") do not need substances produced by other organisms. They use carbon dioxide (CO2) as the main or only source of carbon. Including CO2 and other inorganic substances, in particular ammonia (NH3), nitrates (NO-3) and various sulfur compounds, in complex chemical reactions, they synthesize all the biochemical products they need. Heterotrophs ("feeding on others") use as the main source of carbon (some species also need CO2) organic (carbon-containing) substances synthesized by other organisms, in particular sugars. Oxidized, these compounds supply energy and molecules necessary for the growth and vital activity of cells. In this sense, heterotrophic bacteria, which include the vast majority of prokaryotes, are similar to humans.
main sources of energy. If for the formation (synthesis) of cellular components mainly light energy (photons) is used, then the process is called photosynthesis, and the species capable of it are called phototrophs. Phototrophic bacteria are divided into photoheterotrophs and photoautotrophs, depending on which compounds - organic or inorganic - serve as their main source of carbon. Photoautotrophic cyanobacteria (blue-green algae), like green plants, break down water molecules (H2O) using light energy. This releases free oxygen (1/2O2) and produces hydrogen (2H+), which can be said to convert carbon dioxide (CO2) into carbohydrates. In green and purple sulfur bacteria, light energy is not used to break down water, but other inorganic molecules, such as hydrogen sulfide (H2S). As a result, hydrogen is also produced, reducing carbon dioxide, but oxygen is not released. Such photosynthesis is called anoxygenic. Photoheterotrophic bacteria, such as purple nonsulfur bacteria, use light energy to produce hydrogen from organic substances, in particular isopropanol, but gaseous H2 can also serve as its source. If the main source of energy in the cell is the oxidation of chemicals, bacteria are called chemoheterotrophs or chemoautotrophs, depending on which molecules serve as the main source of carbon - organic or inorganic. In the former, organics provide both energy and carbon. Chemoautotrophs obtain energy from the oxidation of inorganic substances, such as hydrogen (to water: 2H4 + O2 to 2H2O), iron (Fe2+ to Fe3+) or sulfur (2S + 3O2 + 2H2O to 2SO42- + 4H+), and carbon from CO2. These organisms are also called chemolithotrophs, thus emphasizing that they "feed" on rocks.
Breath. Cellular respiration is the process of releasing chemical energy stored in "food" molecules for its further use in vital reactions. Respiration can be aerobic and anaerobic. In the first case, it needs oxygen. It is needed for the work of the so-called. electron transport system: electrons move from one molecule to another (energy is released) and eventually attach to oxygen along with hydrogen ions - water is formed. Anaerobic organisms do not need oxygen, and for some species of this group it is even poisonous. The electrons released during respiration are attached to other inorganic acceptors, such as nitrate, sulfate or carbonate, or (in one of the forms of such respiration - fermentation) to a certain organic molecule, in particular to glucose. See also METABOLISM.

CLASSIFICATION

In most organisms, a species is considered to be a reproductively isolated group of individuals. In a broad sense, this means that representatives of a given species can produce fertile offspring, mating only with their own kind, but not with individuals of other species. Thus, the genes of a particular species, as a rule, do not go beyond its limits. However, in bacteria, genes can be exchanged between individuals not only of different species, but also of different genera, so it is not entirely clear whether it is legitimate to apply here the usual concepts of evolutionary origin and kinship. In connection with this and other difficulties, a generally accepted classification of bacteria does not yet exist. Below is one of its widely used variants.
THE KINGDOM OF MONERA

Phylum Gracilicutes (thin-walled Gram-negative bacteria)

Class Scotobacteria (non-photosynthetic forms, e.g. myxobacteria) Class Anoxyphotobacteria (oxygen-releasing photosynthetic forms, e.g. purple sulfur bacteria) Class Oxyphotobacteria (oxygen-releasing photosynthetic forms, e.g. cyanobacteria)

Phylum Firmicutes (thick-walled Gram-positive bacteria)

Class Firmibacteria (hard-celled forms such as clostridia)
Class Thallobacteria (branched forms, e.g. actinomycetes)

Tenericutes phylum (gram-negative bacteria without cell wall)

Class Mollicutes (soft cell forms, e.g. mycoplasmas)

Type Mendosicutes (bacteria with defective cell wall)

Class Archaebacteria (ancient forms, e.g. methane formers)

Domains. Recent biochemical studies have shown that all prokaryotes are clearly divided into two categories: a small group of archaebacteria (Archaebacteria - "ancient bacteria") and all the rest, called eubacteria (Eubacteria - "true bacteria"). It is believed that archaebacteria are more primitive than eubacteria and closer to the common ancestor of prokaryotes and eukaryotes. They differ from other bacteria in several significant ways, including the composition of the ribosomal RNA (pRNA) molecules involved in protein synthesis, the chemical structure of lipids (fat-like substances), and the presence of some other substances in the cell wall instead of the protein-carbohydrate polymer murein. In the above classification system, archaebacteria are considered to be just one of the types of the same kingdom that includes all eubacteria. However, according to some biologists, the differences between archaebacteria and eubacteria are so profound that it is more correct to consider the archaebacteria in Monera as a separate sub-kingdom. Recently, an even more radical proposal has emerged. Molecular analysis has revealed such significant differences in the structure of genes between these two groups of prokaryotes that some consider their presence within the same kingdom of organisms illogical. In this regard, it was proposed to create a taxonomic category (taxon) of an even higher rank, calling it a domain, and to divide all living things into three domains - Eucarya (eukaryotes), Archaea (archaebacteria) and Bacteria (current eubacteria).

ECOLOGY

The two most important ecological functions of bacteria are nitrogen fixation and mineralization of organic residues.
Nitrogen fixation. The binding of molecular nitrogen (N2) to form ammonia (NH3) is called nitrogen fixation, and the oxidation of the latter to nitrite (NO-2) and nitrate (NO-3) is called nitrification. These are vital processes for the biosphere, since plants need nitrogen, but they can only assimilate its bound forms. Currently, approximately 90% (about 90 million tons) of the annual amount of such "fixed" nitrogen is provided by bacteria. The rest is produced by chemical plants or occurs during lightning discharges. Nitrogen in the air, which is approx. 80% of the atmosphere, associated mainly with the gram-negative genus Rhizobium (Rhizobium) and cyanobacteria. Rhizobium species symbiose with approximately 14,000 species of leguminous plants (family Leguminosae), which include, for example, clover, alfalfa, soybeans and peas. These bacteria live in the so-called. nodules - swellings that form on the roots in their presence. Bacteria receive organic matter (nutrition) from the plant, and in return supply the host with bound nitrogen. For a year, up to 225 kg of nitrogen per hectare is fixed in this way. Non-legume plants, such as alder, also enter into symbiosis with other nitrogen-fixing bacteria. Cyanobacteria photosynthesize like green plants, releasing oxygen. Many of them are also capable of fixing atmospheric nitrogen, which is then taken up by plants and eventually by animals. These prokaryotes serve as an important source of fixed nitrogen in the soil in general and rice fields in the East in particular, as well as its main supplier for ocean ecosystems.
Mineralization. This is the name given to the decomposition of organic residues into carbon dioxide (CO2), water (H2O) and mineral salts. From a chemical point of view, this process is equivalent to combustion, so it requires a large amount of oxygen. The upper soil layer contains from 100,000 to 1 billion bacteria per 1 g, i.e. about 2 tons per hectare. Usually, all organic residues, once in the ground, are quickly oxidized by bacteria and fungi. More resistant to decomposition is a brownish organic substance called humic acid, which is formed mainly from lignin contained in wood. It accumulates in the soil and improves its properties.

BACTERIA AND INDUSTRY

Considering the variety of chemical reactions catalyzed by bacteria, it is not surprising that they are widely used in production, in some cases since ancient times. Prokaryotes share the glory of such microscopic human helpers with fungi, primarily yeast, which provide most of the processes of alcoholic fermentation, for example, in the manufacture of wine and beer. Now that it has become possible to introduce useful genes into bacteria, causing them to synthesize valuable substances, such as insulin, the industrial use of these living laboratories has received a powerful new impetus. See also GENETIC ENGINEERING.
Food industry. Currently, bacteria are used by this industry mainly for the production of cheeses, other fermented milk products and vinegar. The main chemical reactions here are the formation of acids. Thus, when producing vinegar, bacteria of the genus Acetobacter oxidize the ethyl alcohol contained in cider or other liquids to acetic acid. Similar processes occur during sauerkraut: anaerobic bacteria ferment the sugar contained in the leaves of this plant to lactic acid, as well as acetic acid and various alcohols.
Leaching of ores. Bacteria are used to leach poor ores, i.e. transferring from them into a solution of salts of valuable metals, primarily copper (Cu) and uranium (U). An example is the processing of chalcopyrite, or copper pyrite (CuFeS2). Heaps of this ore are periodically watered with water containing chemolithotrophic bacteria of the genus Thiobacillus. In the course of their life activity, they oxidize sulfur (S), forming soluble copper and iron sulfates: CuFeS2 + 4O2 to CuSO4 + FeSO4. Such technologies greatly simplify the production of valuable metals from ores; in principle, they are equivalent to the processes occurring in nature during the weathering of rocks.
Waste recycling. Bacteria also serve to convert waste, such as sewage, into less dangerous or even useful products. Waste water is one of the acute problems of modern mankind. Their complete mineralization requires huge amounts of oxygen, and in ordinary reservoirs, where it is customary to dump these wastes, it is no longer enough to "neutralize" them. The solution lies in additional aeration of wastewater in special pools (aerotanks): as a result, mineralizing bacteria have enough oxygen to completely decompose organic matter, and drinking water becomes one of the end products of the process in the most favorable cases. The insoluble precipitate remaining along the way can be subjected to anaerobic fermentation. In order for such water treatment plants to take up as little space and money as possible, a good knowledge of bacteriology is necessary.
Other uses. Other important areas of industrial application of bacteria include, for example, flax lobe, i.e. separation of its spinning fibers from other parts of the plant, as well as the production of antibiotics, in particular streptomycin (bacteria of the genus Streptomyces).

BACTERIA CONTROL IN INDUSTRY

Bacteria are not only beneficial; the fight against their mass reproduction, for example, in food products or in the water systems of pulp and paper mills, has become a whole area of ​​activity. Food is spoiled by bacteria, fungi and their own autolysis ("self-digestion") enzymes, unless they are inactivated by heat or other means. Since bacteria are the main cause of spoilage, designing efficient food storage systems requires knowledge of the tolerance limits of these microorganisms. One of the most common technologies is milk pasteurization, which kills bacteria that cause, for example, tuberculosis and brucellosis. Milk is kept at 61-63°C for 30 minutes or at 72-73°C for only 15 seconds. This does not impair the taste of the product, but inactivates pathogenic bacteria. Wine, beer and fruit juices can also be pasteurized. The benefits of storing food in the cold have long been known. Low temperatures do not kill bacteria, but they do not allow them to grow and multiply. True, when freezing, for example, to -25 ° C, the number of bacteria decreases after a few months, but a large number of these microorganisms still survive. At temperatures just below zero, bacteria continue to multiply, but very slowly. Their viable cultures can be stored almost indefinitely after lyophilization (freezing - drying) in a medium containing protein, such as blood serum. Other well-known food preservation methods include drying (drying and smoking), adding large amounts of salt or sugar, which is physiologically equivalent to dehydration, and pickling, i.e. placed in a concentrated acid solution. With an acidity of the medium corresponding to pH 4 and below, the vital activity of bacteria is usually greatly inhibited or stopped.

BACTERIA AND DISEASE

STUDY OF BACTERIA

Many bacteria are easy to grow in the so-called. culture medium, which may include meat broth, partially digested protein, salts, dextrose, whole blood, its serum and other components. The concentration of bacteria in such conditions usually reaches about a billion per cubic centimeter, resulting in a cloudy environment. To study bacteria, it is necessary to be able to obtain their pure cultures, or clones, which are the offspring of a single cell. This is necessary, for example, to determine which type of bacteria infected the patient and to which antibiotic this type is sensitive. Microbiological samples, such as swabs taken from the throat or wounds, samples of blood, water or other materials, are highly diluted and applied to the surface of a semi-solid medium: rounded colonies develop from individual cells on it. The culture medium hardening agent is usually agar, a polysaccharide obtained from certain seaweeds and almost indigestible by any type of bacteria. Agar media are used in the form of "skewers", ie. inclined surfaces formed in test tubes standing at a large angle when the molten culture medium solidifies, or in the form of thin layers in glass Petri dishes - flat round vessels closed with a lid of the same shape, but slightly larger in diameter. Usually, after a day, the bacterial cell has time to multiply so much that it forms a colony that is easily visible to the naked eye. It can be transferred to another environment for further study. All culture media must be sterile before the bacteria are grown, and measures must be taken afterwards to prevent the settlement of undesirable microorganisms on them. To examine the bacteria grown in this way, a thin wire loop is calcined on a flame, first touching it with a colony or smear, and then with a drop of water deposited on a glass slide. Evenly distributing the taken material in this water, the glass is dried and quickly passed over the burner flame two or three times (the side with the bacteria should be turned up): as a result, the microorganisms, without being damaged, are firmly attached to the substrate. A dye is dripped onto the surface of the preparation, then the glass is washed in water and dried again. The sample can now be viewed under the microscope. Pure cultures of bacteria are identified mainly by their biochemical characteristics, i.e. determine whether they form gas or acids from certain sugars, whether they are able to digest protein (liquefy gelatin), whether they need oxygen for growth, etc. They also check whether they are stained with specific dyes. Sensitivity to certain drugs, such as antibiotics, can be determined by placing small discs of filter paper soaked with these substances on a surface inoculated with bacteria. If any chemical compound kills bacteria, a zone free from them is formed around the corresponding disk.

Collier Encyclopedia. - Open society. 2000 .

Bacteria are the smallest, most ancient microorganisms invisible to the naked eye. Only under a microscope can one see their structure, appearance and interaction with each other. The first microorganisms had a primitive structure, they developed, mutated, created colonies, adapted to a changing environment. exchange amino acids with each other, which are necessary for growth and development.

Types of bacteria

In school biology textbooks there are images of different types of bacteria that differ in shape:

1. Cocci are spherical organisms that differ in mutual arrangement. Under a microscope, it is noticeable that streptococci represent a chain of balls, diplococci live in pairs, staphylococci are clusters of arbitrary shape. A number of cocci cause various inflammatory processes when they enter the human body (gonococcus, staphylococcus, streptococcus). Not all cocci living in the human body are pathogenic. Conditionally pathogenic species take part in the formation of the body's defense against external influences and are safe if the balance of the flora is observed.
2. Rod-shaped differ in shape, size and ability to spore formation. The spore-forming species are called bacilli. Bacilli include: tetanus bacillus, anthrax bacillus. Spores are formations within a microorganism. Spores are insensitive to chemical treatment, their resistance to external influences is the key to the preservation of the species. It is known that spores are destroyed at high temperature (above 120ºС).

Forms of rod-shaped microbes:

• with pointed poles, as in Fusobacterium, which is part of the normal microflora of the upper respiratory tract;
• with thickened poles, resembling a mace, as in Corynebacterium - the causative agent of diphtheria;
• with rounded ends, such as in Escherichia coli, which is necessary for the digestion process;
• with straight ends, like anthrax.

Gram(+) and Gram(-)

Danish microbiologist Hans Gram conducted an experiment more than 100 years ago, after which all bacteria began to be classified as gram-positive and gram-negative. Gram-positive organisms create a long-term stable bond with the staining substance, which is enhanced by exposure to iodine. Gram-negative, on the contrary, are not susceptible to the dye, their shell is firmly protected.

Gram-negative microbes include chlamydia, rickettsia, gram-positive - staphylococci, streptococci, corynebacteria.

Today in medicine, the test for gram (+) and gram (-) bacteria is widely used. is one of the methods for studying mucous membranes to determine the composition of microflora.

Aerobic and anaerobic

How bacteria live

Biologists define bacteria in a separate kingdom, they are different from other living things. It is a single-celled organism without a nucleus inside. Their shape can be in the form of a ball, cone, stick, spiral. Prokaryotes use flagella to move.

Biofilm is a city for microorganisms, it goes through several stages of formation:

• Adhesion or sorption is the attachment of a microorganism to a surface. As a rule, films are formed at the interface between two media: liquid and air, liquid and liquid. The initial step is reversible and film formation can be prevented.
• Fixation - Bacteria secrete polymers, ensuring their strong fixation, form a matrix for strength and protection.
• Maturation - microbes merge, exchange nutrients, develop microcolonies.
• Growth stage - there is an accumulation of bacteria, their fusion, displacement. The number of microorganisms is from 5 to 35%, the rest of the space is occupied by the extracellular matrix.
• Dispersion - Microorganisms periodically detach from the film, which attach to other surfaces and form a biofilm.

The processes that take place in a biofilm are different from what happens with a microbe that is not an integral part of the colony. Colonies are stable, microbes organize a single system of behavioral reactions, determining the interaction of members inside the matrix and outside the film. Human mucous membranes are inhabited by a large number of microorganisms that produce a gel for protection and ensure the stability of the functioning of organs. An example is the lining of the stomach. It is known that Helicobacter pylori, which are considered the cause of gastric ulcer, is present in more than 80% of the examined people, but not everyone develops peptic ulcer. It is assumed that Helicobacter pylori, being members of the colony, are involved in digestion. Their ability to cause harm is manifested only after certain conditions are created.

The interaction of bacteria in biofilms is still poorly understood. But already today, some microbes have become human assistants in carrying out restoration work, increasing the strength of coatings. In Europe, disinfectant manufacturers offer to treat surfaces with bacterial solutions containing safe microorganisms that prevent the development of pathogenic flora. Bacteria are used to create polymer compounds, and in the future will also generate electricity.