The number of known species of bacteria is. Aerobic and anaerobic

Morphology of bacteria, structure of a prokaryotic cell.

In prokaryotic cells there is no clear boundary between the nucleus and the cytoplasm, and there is no nuclear membrane. The DNA in these cells does not form structures similar to eukaryotic chromosomes. Therefore, the processes of mitosis and meiosis do not occur in prokaryotes. Most prokaryotes do not form intracellular organelles bounded by membranes. In addition, prokaryotic cells do not have mitochondria or chloroplasts.

Bacteria, as a rule, are single-celled organisms, their cell has a fairly simple shape, a ball or cylinder, sometimes curved. Bacteria reproduce primarily by dividing into two equal cells.

spherical bacteria are called cocci and can be spherical, ellipsoidal, bean-shaped and lanceolate.

Based on the location of the cells relative to each other after division, cocci are divided into several forms. If after division the cells diverge and are located singly, then such forms are called monococci. Sometimes cocci, when dividing, form clusters resembling a bunch of grapes. Similar forms refer to staphylococcus. Cocci that remain in connected pairs after division in the same plane are called diplococci, and the generators of different chain lengths are streptococci. Combinations of four cocci that appear after cell division in two mutually perpendicular planes represent tetracocci. Some cocci divide in three mutually perpendicular planes, which leads to the formation of peculiar cubic-shaped clusters called sardines.

Most bacteria have cylindrical, or rod-shaped, shape. Rod-shaped bacteria that form spores are called bacilli, and not forming spores - bacteria.

Rod-shaped bacteria differ in shape, size in length and in diameter, the shape of the ends of the cell, and also in their relative position. They can be cylindrical with straight ends or oval with rounded or pointed ends. Bacteria can also be slightly curved, filamentous and branching forms are found (for example, mycobacteria and actinomycetes).

Depending on the relative arrangement of individual cells after division, rod-shaped bacteria are divided into rods themselves (single arrangement of cells), diplobacteria or diplobacillus (pair arrangement of cells), streptobacteria or streptobacilli (form chains of varying lengths). Crinkled, or spiral-shaped, bacteria are often found. This group includes spirilla (from Latin spira - curl), which have the shape of long curved (from 4 to 6 turns) rods, and vibrios (Latin vibrio - I bend), which are only 1/4 of a turn of a spiral, similar to a comma .

Filamentous forms of bacteria are known that live in water bodies. In addition to those listed, there are multicellular bacteria that carry ethical outgrowths on the surface of the protoplasmic cell - prostheca, triangular and star-shaped bacteria, as well as those having the shape of a closed and open ring and worm-shaped bacteria.

Bacterial cells are very small. They are measured in micrometers, and fine structure details in nanometers. Cocci usually have a diameter of about 0.5-1.5 microns. The width of the rod-shaped (cylindrical) forms of bacteria in most cases ranges from 0.5 to 1 microns, and the length is several micrometers (2-10). Small rods have a width of 0.2-0.4 and a length of 0.7-1.5 microns. Among the bacteria there can also be real giants, the length of which reaches tens and even hundreds of micrometers. The shapes and sizes of bacteria vary significantly depending on the age of the culture, the composition of the medium and its osmotic properties, temperature and other factors.

Of the three main forms of bacteria, cocci are the most stable in size; rod-shaped bacteria are more variable, with cell length changing especially significantly.

A bacterial cell placed on the surface of a solid nutrient medium grows and divides, forming a colony of descendant bacteria. After a few hours of growth, the colony already consists of such a large number of cells that it can be seen with the naked eye. Colonies may have a slimy or pasty consistency, and in some cases they are pigmented. Sometimes appearance colonies are so characteristic that it allows identification of microorganisms without any particular difficulty.

Fundamentals of bacterial physiology.

In terms of their chemical composition, microorganisms differ little from other living cells.

Water makes up 75-85%, chemicals are dissolved in it.

Dry matter 15-25%, contains organic and mineral compounds

Nutrition of bacteria. Entry into the bacterial cell nutrients carried out in several ways and depends on the concentration of substances, the size of molecules, pH of the environment, membrane permeability, etc. By food type microorganisms are divided into:

autotrophs - synthesize all carbon-containing substances from CO2;

heterotrophs - use as a carbon source organic matter;

saprophytes - feed on organic matter from dead organisms;

Respiration of bacteria.

Respiration, or biological oxidation, is based on redox reactions that occur with the formation of an ATP molecule. With respect to molecular oxygen, bacteria can be divided into three main groups:

obligate aerobes - can grow only in the presence of oxygen;

obligate anaerobes - grow in a medium without oxygen, which is toxic to them;

facultative anaerobes - can grow with or without oxygen. Growth and reproduction of bacteria.

Most prokaryotes reproduce by binary fission, less commonly by budding and fragmentation. Bacteria are generally characterized by a high reproduction rate. The time of cell division in various bacteria varies quite widely: from 20 minutes for E. coli to 14 hours for Mycobacterium tuberculosis. On solid nutrient media, bacteria form clusters of cells called colonies. Bacterial enzymes.

Enzymes play an important role in the metabolism of microorganisms. There are:

endoenzymes - localized in the cytoplasm of cells;

exoenzymes - released into the environment.

Aggression enzymes destroy tissue and cells, causing widespread distribution of microbes and their toxins in the infected tissue. The biochemical properties of bacteria are determined by the composition of enzymes:

saccharolytic – breakdown of carbohydrates;

proteolytic – breakdown of proteins,

lipolytic – breakdown of fats,

and are an important diagnostic feature in the identification of microorganisms. For many pathogenic microorganisms

the optimal temperature is 37°C and pH 7.2-7.4. Water. The importance of water for bacteria. Water makes up about 80% of the mass of bacteria. The growth and development of bacteria obligately depend on the presence of water, since all chemical reactions occurring in living organisms are realized in aquatic environment

For bacteria, the water content in the substrate must be more than 20%. Water must be in an accessible form: in the liquid phase in the temperature range from 2 to 60 ° C; this interval is known as the biokinetic zone. Although water is chemically very stable, the products of its ionization - H+ and OH" ions have a very great influence on the properties of almost all components of the cell (proteins, nucleic acids, lipids, etc.). Thus, the catalytic activity of enzymes is largely depends on the concentration of H+ and OH ions."

Fermentation is the main way bacteria obtain energy.

Fermentation is a metabolic process that results in the formation of ATP, and electron donors and acceptors are products formed during the fermentation itself.

Fermentation is the process of enzymatic breakdown of organic substances, mainly carbohydrates, occurring without the use of oxygen. It serves as a source of energy for the life of the body and plays a large role in the cycle of substances and in nature. Some types of fermentation caused by microorganisms (alcoholic, lactic acid, butyric acid, acetic acid) are used in the production of ethyl alcohol, glycerin and other technical and food products.

Alcoholic fermentation(carried out by yeast and some types of bacteria), during which pyruvate is broken down into ethanol and carbon dioxide. One molecule of glucose results in two molecules of alcohol (ethanol) and two molecules of carbon dioxide. This type of fermentation is very important in bread production, brewing, winemaking and distilling.

Lactic acid fermentation, during which pyruvate is reduced to lactic acid, is carried out by lactic acid bacteria and other organisms. When milk is fermented, lactic acid bacteria convert lactose into lactic acid, turning milk into fermented milk products (yogurt, curdled milk, etc.); Lactic acid gives these products a sour taste.

Lactic acid fermentation also occurs in the muscles of animals when the need for energy is higher than that provided by respiration, and the blood does not have time to deliver oxygen.

The burning sensation in the muscles during strenuous exercise correlates with the production of lactic acid and a shift to anaerobic glycolysis, since oxygen is converted to carbon dioxide by aerobic glycolysis faster than the body replenishes oxygen; and muscle soreness after exercise is caused by microtrauma of muscle fibers. The body switches to this less efficient but faster method of producing ATP when there is a lack of oxygen. The liver then gets rid of excess lactate, converting it back into the important glycolytic intermediate pyruvate.

Acetic acid fermentation carried out by many bacteria. Vinegar ( acetic acid) is a direct result of bacterial fermentation. When pickling foods, acetic acid protects food from pathogenic and rotting bacteria.

Butyric acid fermentation leads to the formation of butyric acid; its causative agents are some anaerobic bacteria of the genus Clostridium.

Reproduction of bacteria.

Some bacteria do not have a sexual process and reproduce only by equal binary transverse fission or budding. For one group of unicellular cyanobacteria, multiple fission (a series of rapid successive binary divisions leading to the formation of 4 to 1024 new cells) has been described. To ensure the plasticity of the genotype necessary for evolution and adaptation to a changing environment, they have other mechanisms.

When dividing, most gram-positive bacteria and filamentous cyanobacteria synthesize a transverse septum from the periphery to the center with the participation of mesosomes. Gram-negative bacteria divide by constriction: at the site of division, a gradually increasing inward curvature of the CPM and cell wall is detected. When budding, a bud forms and grows at one of the poles of the mother cell; the mother cell shows signs of aging and usually cannot produce more than 4 daughter cells. Budding occurs in different groups bacteria and presumably arose several times during evolution.

In other bacteria, in addition to reproduction, the sexual process is observed, but in the most primitive form. The sexual process of bacteria differs from the sexual process of eukaryotes in that bacteria do not form gametes and cell fusion does not occur. The mechanism of recombination in prokaryotes. However, the most important event of the sexual process, namely the exchange of genetic material, also occurs in this case. This is called genetic recombination. Some of the DNA (very rarely all of the DNA) from the donor cell is transferred to a recipient cell whose DNA is genetically different from the donor's DNA. In this case, the transferred DNA replaces part of the recipient's DNA. The process of DNA replacement involves enzymes that split and rejoin DNA strands. This produces DNA that contains the genes of both parent cells. This DNA is called recombinant. The offspring, or recombinants, exhibit marked variation in traits due to gene shifts. This variety of characters is very important for evolution and is the main advantage of the sexual process.

There are 3 known methods for obtaining recombinants. These are - in the order of their discovery - transformation, conjugation and transduction.

Origin of bacteria.

Bacteria, along with archaea, were among the first living organisms on Earth, appearing about 3.9-3.5 billion years ago. The evolutionary relationships between these groups have not yet been fully studied; there are at least three main hypotheses: N. Pace suggests that they have a common ancestor of protobacteria; Zavarzin considers archaea to be a dead-end branch of the evolution of eubacteria that has mastered extreme habitats; finally, according to the third hypothesis, archaea are the first living organisms from which bacteria originated.

Eukaryotes arose as a result of symbiogenesis from bacterial cells much later: about 1.9-1.3 billion years ago. The evolution of bacteria is characterized by a pronounced physiological and biochemical bias: with the relative poverty of life forms and primitive structure, they have mastered almost all currently known biochemical processes. The prokaryotic biosphere already had all the currently existing ways of transforming matter. Eukaryotes, having penetrated into it, changed only the quantitative aspects of their functioning, but not the qualitative ones; at many stages of the cycles of elements, bacteria still retain a monopoly position.

Some of the oldest bacteria are cyanobacteria. In rocks formed 3.5 billion years ago, products of their vital activity were found - stromatolites; indisputable evidence of the existence of cyanobacteria dates back to 2.2-2.0 billion years ago. Thanks to them, oxygen began to accumulate in the atmosphere, which 2 billion years ago reached concentrations sufficient for the start of aerobic respiration. Formations characteristic of the obligate aerobic Metallogenium date back to this time.

The appearance of oxygen in the atmosphere (oxygen catastrophe) dealt a serious blow to anaerobic bacteria. They either die out or move into locally preserved oxygen-free zones. The overall species diversity of bacteria decreases at this time.

It is assumed that due to the absence of the sexual process, the evolution of bacteria follows a completely different mechanism than that of eukaryotes. Constant horizontal gene transfer leads to ambiguities in the picture of evolutionary connections; evolution proceeds extremely slowly (and, perhaps, stopped altogether with the advent of eukaryotes), but under changing conditions there is a rapid redistribution of genes between cells with a constant common genetic pool.

Systematics of bacteria.

The role of bacteria in nature and in human life.

Bacteria play an important role on Earth. They take an active part in the cycle of substances in nature. All organic compounds and a significant part of inorganic ones undergo significant changes with the help of bacteria. This role in nature is of global importance. Having appeared on Earth earlier than all organisms (more than 3.5 billion years ago), they created the living shell of the Earth and continue to actively process living and dead organic matter, involving the products of their metabolism in the cycle of substances. The cycle of substances in nature is the basis for the existence of life on Earth.

The decomposition of all plant and animal residues and the formation of humus and humus is also carried out mainly by bacteria. Bacteria are a powerful biotic factor in nature.

The soil-forming work of bacteria is of great importance. The first soil on our planet was created by bacteria. However, even in our time, the condition and quality of the soil depend on the functioning of soil bacteria. The so-called nitrogen-fixing nodule bacteria, symbionts of leguminous plants, are especially important for soil fertility. They saturate the soil with valuable nitrogen compounds.

Bacteria purify dirty wastewater by breaking down organic matter and converting it into harmless inorganic matter. This property of bacteria is widely used in wastewater treatment plants.

In many cases, bacteria can be harmful to humans. Thus, saprotrophic bacteria spoil food products. To protect products from spoilage, they are subjected to special processing (boiling, sterilization, freezing, drying, chemical cleaning, etc.). If this is not done, food poisoning may occur.

Among bacteria there are many disease-causing (pathogenic) species that cause diseases in humans, animals or plants. Typhoid fever is caused by the bacterium Salmonella, while dysentery is caused by the bacterium Shigella. Pathogenic bacteria are spread through the air with droplets of saliva from a sick person when sneezing, coughing, and even during normal conversation (diphtheria, whooping cough). Some pathogenic bacteria are very resistant to drying and persist in dust for a long time (tuberculosis bacillus). Bacteria of the genus Clostridium live in dust and soil - the causative agents of gas gangrene and tetanus. Some bacterial diseases are transmitted through physical contact with a sick person (sexually transmitted diseases, leprosy). Often pathogenic bacteria are transmitted to humans using so-called vectors. For example, flies, crawling through sewage, collect thousands of pathogenic bacteria on their legs, and then leave them on food consumed by humans.

True, bacteria), microorganisms with a prokaryotic type of cell structure: their genetic apparatus is not enclosed in a cell nucleus isolated by a membrane.

Sizes and shapes of cells. Most bacteria are single-celled organisms with a size of 0.2-10.0 microns. Among the bacteria, there are also “dwarfs”, the so-called nanobacteria (about 0.05 microns), and “giants”, for example, bacteria of the genera Achromatium and Macromonas (length up to 100 microns), an inhabitant of the intestines of the surgeon fish Epulopiscium fishelsoni (length up to 600 microns) and isolated from coastal sea ​​waters Namibia and Chile Thiomargarita namibiensis (up to 800 µm). Most often, the bacterial cell has a rod-shaped, spherical (cocci) or convoluted (vibrios, spirilla and spirochetes) shape. Species with triangular, square, stellate and flat (plate-shaped) cells have been found. Some bacteria contain cytoplasmic projections called prosteks. Bacteria can be single, form pairs, short and long chains, clusters, form packages of 4, 8 or more cells (sarcinae), rosettes, networks and mycelium (actinomycetes). Multicellular forms are also known, forming straight and branching trichomes (microcolonies). Both motile and nonmotile bacteria are found. The former most often move with the help of flagella, sometimes by sliding cells (myxobacteria, cyanobacteria, spirochetes, etc.). A “jumping” movement is also known, the nature of which is not clear. For mobile forms, the phenomena of active movement in response to the action of physical or chemical factors are described.

Chemical composition and structure of cells. A bacterial cell is usually 70-80% water. In the dry residue, protein accounts for 50%, cell wall components 10-20%, RNA 10-20%, DNA 3-4% and lipids 10%. On average, the amount of carbon is 50%, oxygen 20%, nitrogen 14%, hydrogen 8%, phosphorus 3%, sulfur and potassium 1% each, calcium and magnesium 0.5% each and iron 0.2%.

With few exceptions (mycoplasmas), bacterial cells are surrounded by a cell wall, which determines the shape of the bacterium and performs mechanical and important physiological functions. Its main component is the complex biopolymer murein (peptidoglycan). Depending on the characteristics of the composition and structure of the cell wall, bacteria behave differently when stained according to the method of H. K. Gram (the Danish scientist who proposed the staining method), which served as the basis for dividing bacteria into gram-positive, gram-negative and those lacking a cell wall (for example , mycoplasma). The former are distinguished by a high (up to 40 times) murein content and a thick wall; in gram-negatives it is significantly thinner and covered on the outside outer membrane, consisting of proteins, phospholipids and lipopolysaccharides and, apparently, involved in the transport of substances. Many bacteria have villi (fimbriae, pili) and flagella on their surface that enable their movement. Often the cell walls of bacteria are surrounded by mucous capsules of varying thickness, formed mainly by polysaccharides (sometimes glycoproteins or polypeptides). In a number of bacteria, so-called S-layers (from English surface) were also found, lining outer surface cell membrane with evenly packed protein structures of regular shape.

The cytoplasmic membrane, which separates the cytoplasm from the cell wall, serves as the osmotic barrier of the cell and regulates the transport of substances; the processes of respiration, nitrogen fixation, chemosynthesis, etc. are carried out in it. It often forms invaginations - mesosomes. The biosynthesis of the cell wall, sporulation, etc. are also associated with the cytoplasmic membrane and its derivatives. Flagella and genomic DNA are attached to it.

The bacterial cell is organized quite simply. In the cytoplasm of many bacteria there are inclusions represented by various types of bubbles (vesicles) formed as a result of invagination cytoplasmic membrane. Phototrophic, nitrifying and methane-oxidizing bacteria are characterized by a developed network of cytoplasmic membranes in the form of undivided vesicles, reminiscent of the grana of eukaryotic chloroplasts. The cells of some water-dwelling bacteria contain gas vacuoles (aerosomes) that act as density regulators; In many bacteria, inclusions of reserve substances are found - polysaccharides, poly-β-hydroxybutyrate, polyphosphates, sulfur, etc. Ribosomes are also present in the cytoplasm (from 5 to 50 thousand). Some bacteria (for example, many cyanobacteria) have carboxysomes - bodies that contain an enzyme involved in CO 2 fixation. The so-called parasporal bodies of some spore-forming bacteria contain a toxin that kills insect larvae.

The bacterial genome (nucleoid) is represented by a circular DNA molecule, which is often called the bacterial chromosome. The bacterial genome is characterized by the combination of many functionally related genes into so-called operons. In addition, the cell may contain extrachromosomal genetic elements - plasmid DNA, which carry several genes useful for bacteria (including antibiotic resistance genes). It can exist autonomously or be temporarily included in the chromosome. But sometimes, as a result of mutations, this DNA loses its ability to leave the chromosome and becomes a permanent component of the genome. The appearance of new genes can also be caused by genetic transfer as a result of unidirectional transfer of DNA from a donor cell to a recipient cell (an analogue of the sexual process). Such transfer can occur through direct contact of two cells (conjugation), with the participation of bacteriophages (transduction), or by the entry of genes into the cell from the external environment without intercellular contact. All this is of great importance for the microevolution of bacteria and their acquisition of new properties.

Reproduction. Most bacteria reproduce by fission in two, less often by budding, and some (for example, actinomycetes) - with the help of exospores or fragments of mycelium. There is a known method of multiple division (with the formation of small reproductive cells-baeocytes in a number of cyanobacteria). Multicellular prokaryotes can reproduce by detaching one or more cells from the trichomes. Some bacteria are characterized by a complex development cycle, during which the morphology of cells can change and resting forms can be formed: cysts, endospores, akinetes. Myxobacteria are capable of forming fruiting bodies, often of bizarre configurations and colors.

A distinctive feature of bacteria is their ability to reproduce quickly. For example, the doubling time of Escherichia coli cells is 20 minutes. It is estimated that the progeny of one cell, in the case of unlimited growth, in just 48 hours would exceed the mass of the Earth by 150 times.

Living conditions. Bacteria have adapted to different conditions existence. They can develop in a temperature range from -5 (and below) to 113 °C. Among them are: psychrophiles, growing at temperatures below 20 ° C (for Bacillus psichrophilus, for example, the maximum growth temperature is -10 ° C), mesophiles (optimum growth at 20-40 ° C), thermophiles (50-60 ° C), extreme thermophiles (70 °C) and hyperthermophiles (80 °C and above). Spores of certain types of bacteria can withstand short-term heating to 160-180 °C and long-term cooling to -196 °C and below. Some bacteria are extremely resistant to ionizing radiation and even live in the cooling water of nuclear reactors (Deinococcus radiodurans). A number of bacteria (barophiles, or piezophiles) tolerate hydrostatic pressure up to 101 thousand kPa, and certain species do not grow at pressures below 50 thousand kPa. At the same time, there are bacteria that cannot withstand even a slight increase in atmospheric pressure. Most types of bacteria do not develop if the concentration of salts (NaCl) in the medium exceeds 0.5 mol/l. Optimal conditions for the development of moderate and extreme halophiles are observed in environments with NaCl concentrations of 10 and 30%, respectively; they can grow even in saturated salt solutions.

As a rule, bacteria prefer neutral environmental conditions (pH about 7.0), although there are both extreme acidophiles, capable of growth at pH 0.1-0.5, and alkaliphiles, developing at pH up to 13.0.

The vast majority of bacteria studied are aerobes. Some of them can grow only at low concentrations of O 2 - up to 1.0-5.0% (microaerophiles). Facultative anaerobes grow both in the presence of O 2 and in its absence; they are able to switch metabolism from aerobic respiration to fermentation or anaerobic respiration (enterobacteria). The growth of aerotolerant anaerobes is not inhibited in the presence of a small amount of O 2, because they do not use it in the process of life (for example, lactic acid bacteria). For strict anaerobes, even traces of O 2 in the habitat are destructive.

Many bacteria survive unfavorable environmental conditions, forming dormant forms.

Most bacteria that utilize nitrogen compounds, as a rule, use its reduced forms (most often ammonium salts), some require ready-made amino acids, while others also assimilate its oxidized forms (mainly nitrates). A significant number of free-living and symbiotic bacteria are capable of fixing molecular nitrogen (see the article Nitrogen fixation). Phosphorus, which is part of nucleic acids and other cell compounds, is obtained by bacteria mainly from phosphates. The source of sulfur necessary for the biosynthesis of amino acids and some enzyme cofactors is most often sulfates; Some types of bacteria require reduced sulfur compounds.

Taxonomy. There is no officially accepted classification of bacteria. Initially, an artificial classification was used for these purposes, based on the similarity of their morphological and physiological characteristics. A more advanced phylogenetic (natural) classification unites related forms based on their common origin. This approach became possible after the choice of the 16S rRNA gene as a universal marker and the advent of methods for determining and comparing nucleotide sequences. The gene encoding 16S rRNA (part of the small subunit of the prokaryotic ribosome) is present in all prokaryotes and is characterized by a high degree of conservation of the nucleotide sequence and functional stability.

The most commonly used is the classification published in the periodical of the determinant Bergi (Bergi); see also the website on the Internet - http://141. 150.157.117:8080/prokPUB/index.htm. According to one of existing systems organisms, bacteria together with archaea constitute the kingdom of prokaryotes. Many researchers consider them as a domain (or superkingdom), along with the domains (or superkingdoms) of archaea and eukaryotes. Within the domain, the largest taxa of bacteria are the phyla: Proteobacteria, including 5 classes and 28 orders; Actinobacteria (5 classes and 14 orders) and Firmicutes (3 classes and 9 orders). In addition, taxonomic categories of lower rank are distinguished: families, genera, species and subspecies.

According to modern concepts, bacterial strains in which the nucleotide sequences in the genes encoding 16S rRNA coincide by more than 97%, and the level of homology of nucleotide sequences in the genome exceeds 70%, are classified as one species. No more than 5,000 species of bacteria have been described, which represent only a small part of those inhabiting our planet.

Bacteria actively participate in biogeochemical cycles on our planet (including the cycle of most chemical elements). The modern geochemical activity of bacteria is also global in nature. For example, out of 4.3 10 10 tons (gigatons) of organic carbon fixed during photosynthesis in the World Ocean, about 4.0 10 10 tons are mineralized in the water column, and 70-75% of them are bacteria and some other microorganisms , and the total production of reduced sulfur in ocean sediments reaches 4.92·10 8 tons per year, which is almost three times the total annual production of all types of sulfur-containing raw materials used by humanity. The bulk of the greenhouse gas methane entering the atmosphere is produced by bacteria (methanogens). Bacteria are a key factor in soil formation, oxidation zones of sulfide and sulfur deposits, the formation of iron and manganese sedimentary rocks, etc.

Some bacteria cause serious diseases in humans, animals and plants. They often become the cause of damage to agricultural products, destruction of underground parts of buildings, pipelines, metal structures of mines, underwater structures, etc. Studying the characteristics of the life activity of these bacteria makes it possible to develop effective ways protection from the damage they cause. At the same time, the positive role of bacteria for humans cannot be overestimated. With the help of bacteria, wine, dairy products, starter cultures and other products, acetone and butanol, acetic and citric acids, some vitamins, a number of enzymes, antibiotics and carotenoids are produced; bacteria are involved in the transformation of steroid hormones and other compounds. They are used to produce protein (including enzymes) and a number of amino acids. The use of bacteria for processing agricultural waste into biogas or ethanol makes it possible to create fundamentally new renewable energy resources. Bacteria are used to extract metals (including gold), increase oil recovery (see articles Bacterial leaching, Biogeotechnology). Thanks to bacteria and plasmids, the development of genetic engineering became possible. The study of bacteria played huge role in the development of many areas of biology, medicine, agronomy, etc. Their importance in the development of genetics is great, because they have become a classic object for studying the nature of genes and the mechanisms of their action. The establishment of metabolic pathways for various compounds, etc., is associated with bacteria.

The potential of bacteria is practically inexhaustible. Deepening knowledge about their life activities opens up new directions effective use bacteria in biotechnology and other industries.

Lit.: Schlegel G. General microbiology. M., 1987; The Prokaryotes: Electronic release 3.0-3.17-. N. Y., 1999-2004-; Zavarzin G. A., Kolotilova N. N. Introduction to natural history microbiology. M., 2001; Madigan M. T., Martinko J., Parker J. Brock biology of microorganisms. 10th ed. Upper Saddle River, 2003; Ecology of microorganisms. M., 2004.

Science and life // Illustrations

Staphylococcus aureus.

Spirilla.

Trypanosoma.

Rotaviruses.

Rickettsia.

Yersinia.

Leishmania.

Salmonella.

Legionella.

Even 3,000 years ago, the great Greek Hippocrates realized that infectious diseases are caused and transmitted 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 fairly powerful microscope, and only then was it possible to describe and sketch the most diverse forms of bacteria - single-celled organisms, many of which are causative agents of various human infectious diseases. Bacteria are one of the types of microbes (“microbe” - from the Greek “micros” - small and “bios” - life), although they are 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 small 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 word means the specific 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 their shape. This group primarily includes bacteria. According to their shape, all bacteria are divided into spherical - cocci, rod-shaped - the bacteria themselves, and convoluted - spirilla and vibrio.

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 “staphyle” - a bunch of grapes and “kokkus” - grain, berry), which received this name because characteristic shape- clusters resembling bunches of grapes. The type of these bacteria that has the most pathogenic effect is staphylococcus aureus(“Staphylococcus aureus”, as it forms clusters of golden color), causing various purulent diseases and food intoxication;

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

Rod-shaped bacteria, or rods,- these are cylindrical microorganisms (from the Greek “bacterion” - stick). From their name comes the name of all such microorganisms. But those bacteria that form spores ( protective layer, protecting against adverse effects environment), are called bacilli(from the Latin “bacillum” - stick). The spore-forming bacilli include the anthrax bacillus, a terrible disease known since ancient times.

The twisted shapes of bacteria are spirals. For example, spirilla(from the Latin “spira” - bend) are bacteria that have the shape 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.

The peculiar form is reflected in the name of microorganisms belonging to the family spirochete(from the Latin “spira” - bend and “hate” - mane). For example, representatives of the family Leptospira They 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 name “leptospira” itself is translated as “narrow spiral” or “narrow curl” (from the Greek “leptos” - narrow and “spera” - gyrus, curl).

Corynebacteria(the 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" - mace.

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

And the name of the family coronaviruses explained by the presence of villi, which are attached to the virion by means of a narrow stalk and expand towards the distal end, reminiscent of the solar corona during an eclipse.

Some microorganisms are named after the organ they infect or the disease they cause. For example, title "meningococcus" formed from two Greek words: “meningos” - the meninges, since it is this that is predominantly affected by these microbes, and “coccus” - a grain, indicating that they belong to spherical bacteria - cocci. From Greek word“pneumon” (lung) is the name formed "pneumococci"- These bacteria cause lung diseases. Rhinoviruses- causative agents of contagious runny nose, hence the name (from the Greek “rhinos” - nose).

The origin of the name for a number of microorganisms is also due to their other most characteristic features. So, distinguishing feature vibrios - bacteria in the shape of a short curved rod - the ability to rapid oscillatory movements. Their name is derived from the French word "vibrer"- vibrate, oscillate, wiggle. Among the vibrios, the most famous is the causative agent of cholera, which is called Vibrio cholerae.

Bacteria genus proteus(Proteus) belong to the so-called microbes, which 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 the microorganisms they discovered also become monuments. For example, microorganisms that occupy an intermediate position between viruses and bacteria have been called "rickettsia" in honor of the American researcher 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, and in his honor they subsequently received their generic name - "Shigella".

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

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

The simplest single-celled organisms (the causative agents of leishmaniasis) are named after the English doctor V. Leishman. leishmania, described in detail by him in 1903.

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

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

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

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

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

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

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

Structure of a bacterial cell

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

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

Under the cell wall is cytoplasmic membranenA.

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

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

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

Nutrition of bacteria

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

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

Autotrophic bacteria

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

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

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

Heterotrophic bacteria

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

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

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

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

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

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

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

Bacteria reproduction

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

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

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

Bacterial spores

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

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

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

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

The importance of bacteria

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

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

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

The great positive role of bacteria in Food Industry. Many types of bacteria are used to produce lactic acid products, butter and cheese, pickling vegetables, as well as in winemaking.

IN chemical industry bacteria are used in the production of alcohols, acetone, and acetic acid.

In medicine, a number of antibiotics, enzymes, hormones and vitamins are obtained with the help of bacteria.

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