Bacteria is a very simple form of plant life that consists of a single living cell. Reproduction is accomplished by cell division. Upon reaching the maturity stage, the bacterium divides into two equal cells. In turn, each of these cells reaches maturity and also divides into two equal cells. In ideal conditions bacterium reaches maturity and reproduces in less than 20-30 minutes. At this rate of reproduction, one bacterium could theoretically produce 34 trillion offspring in 24 hours! Fortunately, the life cycle of bacteria is relatively short, lasting from a few minutes to a few hours. Therefore, even under ideal conditions they cannot reproduce at such a rate.

Growth rate and bacterial growth and other microorganisms depends on environmental conditions. Temperature, light, oxygen, humidity and pH (level of acidity or alkalinity), along with nutrition, influence the rate of bacterial growth. Of these, temperature is of particular interest to technicians and engineers. For each type of bacteria there is a minimum temperature at which they can grow. Below this threshold, bacteria hibernate and are unable to reproduce. Exactly the same for each types of bacteria there is a maximum temperature threshold. At temperatures above this limit, bacteria are destroyed. Between these limits is the optimal temperature at which bacteria multiply at maximum speed. The optimal temperature for most bacteria that feed on animal droppings and dead animal and plant tissue (saprophytes) is 24 to 30°C. The optimal temperature for most bacteria that cause infections and diseases in the host (pathogenic bacteria) is about 38°C. In most cases, you can significantly reduce bacterial growth rate, if the environment. Finally, there are several varieties of bacteria that thrive best at water temperatures, while others thrive at freezing temperatures.

Addition to the above

Origin, evolution, place in the development of life on Earth

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 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 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.

Structure

The vast majority of bacteria (with the exception of actinomycetes and filamentous cyanobacteria) are unicellular. According to the shape of the cells, they can be round (cocci), rod-shaped (bacilli, clostridia, pseudomonads), convoluted (vibrios, spirillum, spirochetes), less often - stellate, tetrahedral, cubic, C- or O-shaped. The shape determines the abilities of bacteria such as attachment to the surface, mobility, and absorption of nutrients. It has been noted, for example, that oligotrophs, that is, bacteria living with a low nutrient content in the environment, strive to increase the surface-to-volume ratio, for example, through the formation of outgrowths (the so-called prostek).

Of the obligatory cellular structures, three are distinguished:

• nucleoid
• ribosomes
• cytoplasmic membrane (CPM)

On the outer side of the CPM there are several layers (cell wall, capsule, mucous membrane), called the cell membrane, as well as surface structures (flagella, villi). The CPM and cytoplasm are combined together into the concept of protoplast.

Protoplast structure

The CPM limits the contents of the cell (cytoplasm) from the external environment. The homogeneous fraction of the cytoplasm, containing a set of soluble RNA, proteins, products and substrates of metabolic reactions, is called cytosol. The other part of the cytoplasm is represented by various structural elements.

One of the main differences between a bacterial cell and a eukaryotic cell is the absence of a nuclear membrane and, strictly speaking, the general absence of intracytoplasmic membranes that are not derivatives of the CPM. However, different groups of prokaryotes (especially often gram-positive bacteria) have local invaginations of the CPM - mesosomes, which perform various functions in the cell and divide it into functionally different parts. Many photosynthetic bacteria have a developed network of photosynthetic membranes derived from the CPM. In purple bacteria they have retained a connection with the CPM, which is easily detectable in sections under an electron microscope; in cyanobacteria this connection is either difficult to detect or has been lost in the process of evolution. Depending on the conditions and age of the culture, photosynthetic membranes form various structures - vesicles, chromatophores, thylakoids.

All the genetic information necessary for the life of bacteria is contained in one DNA (bacterial chromosome), most often in the form of a covalently closed ring (linear chromosomes are found in Streptomyces and Borrelia). It is attached to the CPM at one point and is placed in a structure that is separate, but not separated by a membrane from the cytoplasm, and is called a nucleoid. Unfolded DNA is more than 1 mm long. The bacterial chromosome is usually presented in a single copy, that is, almost all prokaryotes are haploid, although under certain conditions one cell can contain several copies of its chromosome, and Burkholderia cepacia has three different ring chromosomes (length 3.6, 3.2 and 1.1 million nucleotide pairs). The ribosomes of prokaryotes are also different from those of eukaryotes and have a sedimentation constant of 70 S (80 S in eukaryotes).

In addition to these structures, inclusions of reserve substances may also be present in the cytoplasm.

Cell membrane and surface structures

The cell wall is an important structural element of the bacterial cell, but it is not essential. Forms with a partially or completely absent cell wall (L-forms) were artificially obtained, which could exist in favorable conditions, but sometimes lost the ability to divide. There is also a known group of natural bacteria that do not contain a cell wall - mycoplasmas.

In bacteria, there are two main types of cell wall structure, characteristic of gram-positive and gram-negative species.

The cell wall of Gram-positive bacteria is a homogeneous layer 20-80 nm thick, built mainly of peptidoglycan with a smaller amount of teichoic acids and a small amount of polysaccharides, proteins and lipids (the so-called lipopolysaccharide). The cell wall has pores with a diameter of 1-6 nm, which make it permeable to a number of molecules.

In gram-negative bacteria, the peptidoglycan layer is loosely adjacent to the CPM and has a thickness of only 2-3 nm. It is surrounded by an outer membrane, which, as a rule, has an uneven, curved shape. Between the CPM, the peptidoglycan layer and the outer membrane there is a space called the periplasmic space, which is filled with a solution that includes transport proteins and enzymes.

On the outside of the cell wall there may be a capsule - an amorphous layer that maintains connection with the wall. The mucous layers have no connection with the cell and are easily separated, while the covers are not amorphous, but have a fine structure. However, between these three idealized cases there are many transitional forms.

There can be from 0 to 1000 bacterial flagella. Possible options include the arrangement of one flagellum at one pole (monopolar monotrichous), a bundle of flagella at one (monopolar peritrichous or lophotrichial flagellation) or two poles (bipolar peritrichous or amphitrichyal flagella), as well as numerous flagella at the entire surface of the cell (peritrich). The thickness of the flagellum is 10-20 nm, length - 3-15 µm. Its rotation is carried out counterclockwise with a frequency of 40-60 rps.

In addition to flagella, among the surface structures of bacteria it is necessary to mention villi. They are thinner than flagella (diameter 5-10 nm, length up to 2 µm) and are necessary for attaching bacteria to the substrate, take part in metabolites, and special villi - F-pili - thread-like formations, thinner and shorter (3-10 nm x 0 , 3-10 µm) than flagella - they are necessary for the donor cell to transfer DNA to the recipient during conjugation.

Dimensions

The average size of bacteria is 0.5-5 microns. Escherichia coli, for example, has dimensions of 0.3-1 by 1-6 microns, Staphylococcus aureus has a diameter of 0.5-1 microns, Bacillus subtilis 0.75 by 2-3 microns. The largest known bacterium is Thiomargarita namibiensis, reaching a size of 750 microns (0.75 mm). The second is Epulopiscium fishelsoni, which has a diameter of 80 microns and a length of up to 700 microns and lives in the digestive tract of the surgical fish Acanthurus nigrofuscus. Achromatium oxaliferum reaches sizes of 33 by 100 microns, Beggiatoa alba - 10 by 50 microns. Spirochetes can grow up to 250 µm in length with a thickness of 0.7 µm. At the same time, bacteria include the smallest organisms with a cellular structure. Mycoplasma mycoides is 0.1-0.25 microns in size, which is similar to the size of large viruses such as tobacco mosaic, cowpox or influenza. According to theoretical calculations, a spherical cell with a diameter of less than 0.15-0.20 microns becomes incapable of independent reproduction, since it physically does not contain all the necessary biopolymers and structures in sufficient quantities.

However, nanobacteria have been described that are smaller than the “acceptable” size and are very different from ordinary bacteria. They, unlike viruses, are capable of independent growth and reproduction (extremely slow). They have so far been little studied, their living nature is being questioned.

With a linear increase in the radius of a cell, its surface increases in proportion to the square of the radius, and its volume in proportion to the cube, therefore, in small organisms the ratio of surface to volume is higher than in larger ones, which means for the former a more active exchange of substances with the environment. Metabolic activity, measured by various indicators, per unit of biomass is higher in small forms than in large ones. Therefore, small sizes even for microorganisms give bacteria and archaea advantages in the rate of growth and reproduction compared to more complex eukaryotes and determine their important ecological role.

Multicellularity in bacteria

Single-celled forms are capable of performing all the functions inherent in the body, regardless of neighboring cells. Many single-celled prokaryotes tend to form cellular prokaryotes, often held together by the mucus they secrete. Most often, this is only a random association of individual organisms, but in some cases, a temporary association is associated with the implementation of a certain function, for example, the formation of fruiting bodies by myxobacteria makes it possible to develop cysts, although individual cells are not able to form them. Such phenomena, along with the formation of morphologically and functionally differentiated cells by unicellular eubacteria, are necessary prerequisites for the emergence of true multicellularity in them.

A multicellular organism must meet the following conditions:

• its cells must be aggregated,
• there must be a division of functions between cells,
• stable specific contacts must be established between aggregated cells.

Multicellularity in prokaryotes is known; the most highly organized multicellular organisms belong to the groups of cyanobacteria and actinomycetes. In filamentous cyanobacteria, structures in the cell wall are described that ensure contact between two neighboring cells - microplasmodesmata. The possibility of exchange between cells of substance (dye) and energy (electrical component of the transmembrane potential) has been shown. Some of the filamentous cyanobacteria contain, in addition to the usual vegetative cells, functionally differentiated cells: akinetes and heterocysts. The latter perform nitrogen fixation and intensively exchange metabolites with vegetative cells.

Bacteria reproduction

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 fissions 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 of bacteria and presumably arose several times during the course of evolution.

Bacteria also exhibit sexual reproduction, but in the most primitive form. Sexual reproduction of bacteria differs from sexual reproduction of eukaryotes in that bacteria do not form gametes and do not undergo cell fusion. However, the most important event of sexual reproduction, namely the exchange of genetic material, also occurs in this case. This process 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. In the progeny, or recombinants, there is marked variation in traits caused by gene displacement. This variety of traits is very important for evolution and is the main advantage of sexual reproduction. There are 3 known methods for obtaining recombinants. These are - in the order of their discovery - transformation, conjugation and transduction.

To understand the importance of bacteria, it is enough to know that they arose approximately 3.5 billion years ago and that it is bacteria that prepare solutions of nutrients that feed both animals and plants!

BACTERIA, a large group of single-celled microorganisms characterized by the absence of a cell nucleus surrounded by a membrane. At the same time, the genetic material of the bacterium (deoxyribonucleic acid, or DNA) occupies a very specific place in the cell - a zone called the nucleoid. Organisms with such a cell structure are called prokaryotes (“pre-nuclear”), in contrast to all others - eukaryotes (“truly nuclear”), whose DNA is located in a nucleus surrounded by a shell.

Bacteria, previously considered microscopic plants, are now classified into the independent 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 Archeozoic (Archean), i.e. arose 3.5 billion years ago, is the result of the vital activity of bacteria, usually photosynthesizing, the so-called. blue-green algae.

Similar structures (bacterial films impregnated with carbonates) are still formed today, 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.

Nowadays, stromatolites grow mainly where these animals are absent due to high salinity of water or for other reasons, but before the emergence of herbivorous forms during the evolution, they could reach enormous sizes, constituting an essential element of oceanic shallow water, comparable to modern coral reefs.

In some ancient rocks, tiny charred spheres have been found, which are also believed to be the remains of bacteria. The first nuclear ones, i.e. eukaryotic, cells evolved from bacteria approximately 1.4 billion years ago.

Ecology.

Bacteria are abundant in soil, at the bottom of lakes and oceans—anywhere organic matter accumulates. They live in the cold, when the thermometer is just above zero, and in hot acidic springs with temperatures above 90° C.

Some bacteria tolerate very high salinity environments; 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.

Thus, in cities, rainwater contains much more bacteria than in rural areas. There are few of them in the cold air of high mountains and polar regions, however, 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 food. Additionally, the immune system of an animal raised under sterile conditions does not develop normally due to lack of bacterial stimulation. The normal bacterial “flora” of the intestines is also important for suppressing harmful microorganisms that enter there.

STRUCTURE AND LIFE ACTIVITY OF BACTERIA

Bacteria are much smaller than the cells of multicellular plants and animals. Their thickness is usually 0.5–2.0 µm, and their length is 1.0–8.0 µm.

Some forms are barely visible at the resolution of standard light microscopes (approximately 0.3 microns), but species are also known with a length of more than 10 microns and a width that also goes beyond the specified limits, and a number of very thin bacteria can exceed 50 microns in length.

On the surface corresponding to the point marked with a pencil, a quarter of a million medium-sized representatives of this kingdom will fit.

Structure.

Based on their morphological features, 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 formed nucleus and the typical presence of only one chromosome - a very long circular DNA molecule attached at one point to the cell membrane.

Prokaryotes also do not have membrane-enclosed intracellular organelles called mitochondria and chloroplasts. In eukaryotes, mitochondria produce energy during respiration, and photosynthesis occurs in chloroplasts (see also CELL). In prokaryotes, the entire cell (and primarily the cell membrane) takes on the function of a mitochondrion, and in photosynthetic forms, it also takes on the function of a chloroplast.

Like eukaryotes, inside bacteria there 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, important components of eukaryotic cell membranes.

Outside the cell membrane, most bacteria are covered 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 bacteria-specific substances).

This membrane prevents the bacterial cell from bursting when water enters it through osmosis. On top of the cell wall is often a protective mucous capsule.

Many bacteria are equipped with flagella, with which they actively swim. Bacterial flagella are structured simpler and somewhat differently than similar structures of eukaryotes.

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 respond to changes in light intensity.

Some bacteria perceive the direction of magnetic field lines, including the Earth's magnetic field, with the help of particles of magnetite (magnetic iron ore - Fe 3 O 4) 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 do 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.

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History of the study

The foundations of general microbiology and the study of the role of bacteria in nature were laid by Beijerinck, Martinus Willem and Vinogradsky, Sergei Nikolaevich.

The study of the structure of bacterial cells began with the invention of the electron microscope in the 1930s. In 1937, E. Chatton proposed dividing all organisms according to the type of cellular structure into prokaryotes and eukaryotes, and in 1961 Steinier and Van Niel finally formalized this division. The development of molecular biology led to the discovery in 1977 of K. Woese of fundamental differences among prokaryotes themselves: between bacteria and archaea.

Structure

The vast majority of bacteria (with the exception of actinomycetes and filamentous cyanobacteria) are unicellular. According to the shape of the cells, they can be round (cocci), rod-shaped (bacilli, clostridia, pseudomonads), convoluted (vibrios, spirilla, spirochetes), less often - stellate, tetrahedral, cubic, C- or O-shaped. The shape determines the abilities of bacteria such as attachment to the surface, mobility, and absorption of nutrients. It has been noted, for example, that oligotrophs, that is, bacteria living with a low nutrient content in the environment, strive to increase the surface-to-volume ratio, for example, through the formation of outgrowths (the so-called prostek).

Of the obligatory cellular structures, three are distinguished:

On the outside of the CPM there are several layers (cell wall, capsule, mucous membrane), called cell membrane, and surface structures(flagella, villi). CPM and cytoplasm are combined together into the concept protoplast.

Protoplast structure

The CPM limits the contents of the cell (cytoplasm) from the external environment. The homogeneous fraction of the cytoplasm containing a set of soluble RNA, proteins, products and substrates of metabolic reactions is called cytosol. The other part of the cytoplasm is represented by various structural elements.

All the genetic information necessary for the life of bacteria is contained in one DNA (bacterial chromosome), most often in the form of a covalently closed ring (linear chromosomes are found in Streptomyces And Borrelia). It is attached to the CPM at one point and is placed in a structure isolated, but not separated by a membrane from the cytoplasm, and called nucleoid. Unfolded DNA is more than 1 mm long. The bacterial chromosome is usually presented in a single copy, that is, almost all prokaryotes are haploid, although under certain conditions one cell can contain several copies of its chromosome, and Burkholderia cepacia has three different circular chromosomes (length 3.6, 3.2 and 1.1 million base pairs). The ribosomes of prokaryotes are also different from those of eukaryotes and have a sedimentation constant of 70 S (80 S in eukaryotes).

In addition to these structures, inclusions of reserve substances may also be present in the cytoplasm.

Cell membrane and surface structures

In bacteria, there are two main types of cell wall structure, characteristic of gram-positive and gram-negative species.

The cell wall of Gram-positive bacteria is a homogeneous layer 20-80 nm thick, built mainly of peptidoglycan with a smaller amount of teichoic acids and a small amount of polysaccharides, proteins and lipids (the so-called lipopolysaccharide). The cell wall has pores with a diameter of 1-6 nm, which make it permeable to a number of molecules.

In gram-negative bacteria, the peptidoglycan layer is loosely adjacent to the CPM and has a thickness of only 2-3 nm. It is surrounded by an outer membrane, which, as a rule, has an uneven, curved shape. Between the CPM, the peptidoglycan layer and the outer membrane there is a space called periplasmic and filled with a solution including transport proteins and enzymes.

On the outside of the cell wall there may be a capsule - an amorphous layer that maintains connection with the wall. The mucous layers have no connection with the cell and are easily separated, while the covers are not amorphous, but have a fine structure. However, between these three idealized cases there are many transitional forms.

Dimensions

The average size of bacteria is 0.5-5 microns. Weight - 4⋅10−13 g. Escherichia coli, for example, has dimensions of 0.3-1 by 1-6 microns, Staphylococcus aureus- diameter 0.5-1 microns, Bacillus subtilis- 0.75 by 2-3 microns. The largest known bacteria is Thiomargarita namibiensis, reaching a size of 750 microns (0.75 mm). The second one is Epulopiscium fishelsoni, having a diameter of 80 microns and a length of up to 700 microns and living in the digestive tract of surgical fish Acanthurus nigrofuscus. Achromatium oxaliferum reaches dimensions of 33 by 100 microns, Beggiatoa alba- 10 by 50 microns. Spirochetes can grow up to 250 µm in length with a thickness of 0.7 µm. At the same time, bacteria include the smallest organisms with a cellular structure. Mycoplasma mycoides has a size of 0.1-0.25 microns, which corresponds to the size of large viruses, for example, tobacco mosaic, cowpox or influenza. According to theoretical calculations, a spherical cell with a diameter of less than 0.15-0.20 microns becomes incapable of independent reproduction, since it physically cannot accommodate all the necessary biopolymers and structures in sufficient quantities.

With a linear increase in the radius of a cell, its surface increases in proportion to the square of the radius, and its volume in proportion to the cube, therefore, in small organisms the ratio of surface to volume is higher than in larger ones, which means for the former a more active exchange of substances with the environment. Metabolic activity, measured by various indicators, per unit of biomass is higher in small forms than in large ones. Therefore, small sizes even for microorganisms give bacteria and archaea advantages in the rate of growth and reproduction compared to more complex eukaryotes and determine their important ecological role.

Multicellularity in bacteria

A multicellular organism must meet the following conditions:

• its cells must be aggregated,
• there must be a division of functions between cells,
• stable specific contacts must be established between aggregated cells.

Multicellularity in prokaryotes is known; the most highly organized multicellular organisms belong to the groups of cyanobacteria and actinomycetes. In filamentous cyanobacteria, structures in the cell wall are described that ensure contact between two neighboring cells - microplasmodesmata. The possibility of exchange between cells of substance (dye) and energy (electrical component of the transmembrane potential) has been shown. Some of the filamentous cyanobacteria contain, in addition to the usual vegetative cells, functionally differentiated ones: akinetes and heterocysts. The latter perform nitrogen fixation and intensively exchange metabolites with vegetative cells.

Movement patterns and irritability

Many bacteria are motile. There are several fundamentally different types of bacterial movement. The most common movement is with the help of flagella: single bacteria and bacterial associations (swarming). A special case of this is also the movement of spirochetes, which wriggle thanks to axial filaments, similar in structure to flagella, but located in the periplasm. Another type of movement is the sliding of bacteria without flagella on the surface of solid media and the movement in water of flagellated bacteria of the genus Synechococcus. Its mechanism is not yet well understood; it is assumed that it involves the secretion of mucus (pushing the cell) and fibrillar filaments located in the cell wall, causing a “running wave” along the surface of the cell. Finally, bacteria can float and submerge in liquids, changing their density, filling with gases or emptying aerosomes.

Bacteria actively move in the direction determined by certain stimuli. This phenomenon is called taxis. There are chemotaxis, aerotaxis, phototaxis, etc.

Metabolism

Constructive Metabolism

With the exception of some specific points, the biochemical pathways through which the synthesis of proteins, fats, carbohydrates and nucleotides is carried out in bacteria are similar to those in other organisms. However, they differ in the number of possible options for these pathways and, accordingly, in the degree of dependence on the supply of organic substances from the outside.

Some of them can synthesize all the organic molecules they need from inorganic compounds (autotrophs), while others require ready-made organic compounds, which they can only transform (heterotrophs).

Bacteria can satisfy their nitrogen needs both through its organic compounds (like heterotrophic eukaryotes) and through molecular nitrogen (like some archaea). Most bacteria use inorganic nitrogen compounds to synthesize amino acids and other nitrogen-containing organic substances: ammonia (entering cells in the form of ammonium ions), nitrites and nitrates (which are previously reduced to ammonium ions). They are able to absorb phosphorus in the form of phosphate, sulfur in the form of sulfate or, less commonly, sulfide.

Energy metabolism

The ways in which bacteria obtain energy are unique. There are three types of energy production (and all three are known in bacteria): fermentation, respiration and photosynthesis.

Bacteria that carry out only oxygen-free photosynthesis do not have photosystem II. Firstly, these are purple and green filamentous bacteria in which only the cyclic electron transfer pathway functions, aimed at creating a transmembrane proton gradient, due to which ATP is synthesized (photophosphorylation), and NAD(P) + is reduced, which is used for the assimilation of CO 2 . Secondly, these are green sulfur and heliobacteria, which have both cyclic and non-cyclic electron transport, which makes direct reduction of NAD(P) + possible. Reduced sulfur compounds (molecular, hydrogen sulfide, sulfite) or molecular hydrogen are used as an electron donor that fills a “vacancy” in a pigment molecule in oxygen-free photosynthesis.

There are also bacteria with very specific energy metabolism. Thus, in October 2008, a report appeared in the journal Science about the discovery of an ecosystem consisting of representatives of one single previously unknown species of bacterium - Desulforudis audaxviator, which obtain energy for their life activity from chemical reactions involving hydrogen formed as a result of the disintegration of water molecules under the influence of radiation from uranium ore bacteria located near the colony. Some colonies of bacteria that live on the ocean floor use electric current to transfer energy to their fellows.

Types of life

You can combine the types of constructive and energy metabolism in the following table:

Ways of existence of living organisms (Lvov matrix)
Energy source	Electron donor	Carbon source	Name of way of existence	Representatives
OVR	Inorganic compounds	Carbon dioxide	Chemolithoautotrophy	Nitrifying, thionic, acidophilic iron bacteria
		Organic compounds	Chemolithoheterotrophy	Methane-producing archaebacteria, hydrogen bacteria
	Organic matter	Carbon dioxide	Chemoorganoautotrophy	Facultative methylotrophs, formic acid-oxidizing bacteria
		Organic compounds	Chemoorganoheterotrophy	Most prokaryotes, eukaryotes: animals, fungi, humans
Light	Inorganic compounds	Carbon dioxide	Photolithoautotrophy	Cyanobacteria, purple, green bacteria, from eukaryotes: plants
		Organic compounds	Photolithoheterotrophy	Some cyanobacteria, purple, green bacteria
	Organic matter	Carbon dioxide	Photoorganoautotrophy	Some purple bacteria
		Organic matter	Photoorganoheterotrophy	Halobacteria, some cyanobacteria, purple, green bacteria

The table shows that the variety of nutritional types of prokaryotes is much greater than that of eukaryotes (the latter are only capable of chemoorganoheterotrophy and photolithoautotrophy).

Reproduction and structure of the genetic apparatus

Bacteria reproduction

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 fissions 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.

Genetic apparatus

Genes necessary for life and determining species specificity are most often located in bacteria in a single covalently closed DNA molecule - the chromosome (sometimes the term genophore is used to designate bacterial chromosomes to emphasize their differences from eukaryotic ones). The region where the chromosome is located is called the nucleoid and is not surrounded by a membrane. In this regard, newly synthesized mRNA is immediately available for binding to ribosomes, and transcription and translation are coupled.

A single cell can contain only 80% of the sum of genes present in all strains of its species (the so-called “collective genome”).

In addition to the chromosome, bacterial cells often contain plasmids - also closed in a DNA ring, capable of independent replication. They can be so large that they become indistinguishable from a chromosome, but contain additional genes needed only under specific conditions. Special distribution mechanisms ensure that the plasmid is retained in daughter cells so that they are lost at a frequency of less than 10 −7 per cell cycle. The specificity of plasmids can be very diverse: from being present in only one host species to the RP4 plasmid, which is found in almost all Gram-negative bacteria. Plasmids encode mechanisms of antibiotic resistance, destruction of specific substances, etc.; nif genes necessary for nitrogen fixation are also found in plasmids. The plasmid gene can be included in the chromosome with a frequency of about 10−4 - 10−7.

The DNA of bacteria, as well as the DNA of other organisms, contains transposons - mobile segments that can move from one part of the chromosome to another, or to extrachromosomal DNA. Unlike plasmids, they are incapable of autonomous replication and contain IS segments - regions that encode their transport within the cell. The IS segment can act as a separate transposon.

Horizontal gene transfer

In prokaryotes, partial unification of genomes can occur. During conjugation, the donor cell transfers part of its genome (in some cases the entire genome) to the recipient cell during direct contact. Sections of the donor's DNA can be exchanged for homologous sections of the recipient's DNA. The probability of such an exchange is significant only for bacteria of one species.

Similarly, a bacterial cell can absorb DNA freely present in the environment, incorporating it into its genome in the case of a high degree of homology with its own DNA. This process is called transformation. Under natural conditions, genetic information is exchanged with the help of temperate phages (transduction). In addition, the transfer of non-chromosomal genes is possible using plasmids of a certain type that encode this process, the process of exchange of other plasmids and transposon transfer.

With horizontal transfer, new genes are not formed (as is the case with mutations), but different gene combinations are created. This is important for the reason that natural selection acts on the entire set of characteristics of an organism.

Cell differentiation

Cellular differentiation is a change in the set of proteins (usually also manifested in a change in morphology) with an unchanged genotype.

Formation of resting forms

The formation of especially resistant forms with a slow metabolism, serving for preservation in unfavorable conditions and distribution (less often for reproduction) is the most common type of differentiation in bacteria. The most stable of them are endospores, formed by representatives Bacillus, Clostridium, Sporohalobacter, Anaerobacter(forms 7 endospores from one cell and can reproduce with their help) and Heliobacterium. The formation of these structures begins as normal division and in the early stages can be converted into it by certain antibiotics. The endospores of many bacteria can withstand boiling for 10 minutes at 100 °C, drying for 1000 years and, according to some data, remain viable in soils and rocks for millions of years.

Less stable are exospores, cysts ( Azotobacter, gliding bacteria, etc.), akinetes (cyanobacteria) and myxospores (myxobacteria).

Other types of morphologically differentiated cells

Actinomycetes and cyanobacteria form differentiated cells that serve for reproduction (spores, as well as hormogonium and baeocytes, respectively). It is also necessary to note structures similar to bacteroids of nodule bacteria and heterocysts of cyanobacteria, which serve to protect nitrogenase from the effects of molecular oxygen.

Classification

The most famous is the phenotypic classification of bacteria based on the structure of their cell wall, included, in particular, in the IX edition of Bergey’s Key to Bacteria (1984-1987). The largest taxonomic groups in it were 4 divisions: Gracilicutes(gram negative), Firmicutes(gram-positive), Tenericutes(mycoplasma) and Mendosicutes(archaea).

Recently, the phylogenetic classification of bacteria (and this is what is used in Wikipedia), based on molecular biology data, has been increasingly developed. One of the first methods for assessing relatedness based on genome similarity was the method of comparing the content of guanine and cytosine in DNA, proposed back in the 1960s. Although the same values ​​for their content cannot provide any information about the evolutionary proximity of organisms, their differences by 10% mean that the bacteria do not belong to the same genus. Another method that revolutionized microbiology in the 1970s was the analysis of gene sequences in 16s rRNA, which made it possible to identify several phylogenetic branches of eubacteria and evaluate the relationships between them. For classification at the species level, the DNA-DNA hybridization method is used. Analysis of a sample of well-studied species suggests that 70% of the level of hybridization characterizes one species, 10-60% - one genus, less than 10% - different genera.

The phylogenetic classification partly repeats the phenotypic one, for example, the group Gracilicutes is present in both. At the same time, the taxonomy of gram-negative bacteria was completely revised, archaebacteria were completely separated into an independent taxon of the highest rank, some taxonomic groups were divided into parts and regrouped, organisms with completely different ecological functions were combined into one group, which caused a number of inconveniences and dissatisfaction of part of the scientific community . The object of criticism is also the fact that the classification of molecules, and not organisms, is actually carried out.

Origin, evolution, place in the development of life on Earth

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.

Pathogenic bacteria

Bacteria that parasitize other organisms are called pathogenic. Bacteria cause a large number of human diseases such as plague ( Yersinia pestis), anthrax ( Bacillus anthracis), leprosy (leprosy, pathogen: Mycobacterium leprae), diphtheria ( Corynebacterium diphtheriae), syphilis ( Treponema pallidum), cholera ( Vibrio cholerae), tuberculosis ( Mycobacterium tuberculosis), listeriosis ( Listeria monocytogenes) etc. The discovery of pathogenic properties in bacteria continues: in 1976 Legionnaires' disease, caused by Legionella pneumophila, in the 1980s-1990s it was shown that Helicobacter pylori causes peptic ulcers and even stomach cancer, as well as chronic

The kingdom “Bacteria” consists of bacteria and blue-green algae, the general characteristic of which is their small size and the absence of a nucleus separated by a membrane from the cytoplasm.

Who are bacteria

Translated from Greek “bakterion” means stick. For the most part, microbes are single-celled organisms invisible to the naked eye that reproduce by division.

Who discovered them

For the first time, a Dutch researcher who lived in the 17th century, Anthony Van Leeuwenhoek, was able to see the smallest single-celled organisms in a homemade microscope. He began studying the world around him through a magnifying glass while working in a haberdashery store.

Anthony Van Leeuwenhoek (1632 - 1723)

Leeuwenhoek subsequently focused on making lenses capable of magnification up to 300 times. In them he examined the smallest microorganisms, describing the information received and transferring what he saw to paper.

In 1676, Leeuwenhoek discovered and presented information about microscopic creatures, to which he gave the name “animalcules.”

What do they eat?

The smallest microorganisms existed on Earth long before the appearance of humans. They have a ubiquitous distribution, feeding on organic food and inorganic substances.

Based on the methods of assimilation of nutrients, bacteria are usually divided into autotrophic and heterotrophic. For existence and development, heterotrophs use waste products from the organic decomposition of living organisms.

Representatives of bacteria

Biologists have identified about 2,500 groups of different bacteria.

According to their form they are divided into:

• cocci having spherical outlines;
• bacilli - rod-shaped;
• vibrios that have curves;
• spirilla - spiral shape;
• streptococci, consisting of chains;
• staphylococci that form grape-like clusters.

According to the degree of influence on the human body, prokaryotes can be divided into:

• useful;
• harmful.

Microbes dangerous to humans include staphylococci and streptococci, which cause purulent diseases.

The bacteria bifido and acidophilus are considered beneficial, stimulating the immune system and protecting the gastrointestinal tract.

How do real bacteria reproduce?

Reproduction of all types of prokaryotes occurs mainly by division, followed by growth to the original size. Having reached a certain size, an adult microorganism splits into two parts.

Less commonly, reproduction of similar unicellular organisms is performed by budding and conjugation. When budding on the mother microorganism, up to four new cells grow, followed by the death of the adult part.

Conjugation is considered the simplest sexual process in unicellular organisms. Most often, bacteria that live in animal organisms reproduce in this way.

Bacteria symbionts

Microorganisms involved in digestion in the human intestine are a prime example of symbiont bacteria. Symbiosis was first discovered by the Dutch microbiologist Martin Willem Beijerinck. In 1888, he proved the mutually beneficial close coexistence of unicellular and legume plants.

Living in the root system, symbionts, feeding on carbohydrates, supply the plant with atmospheric nitrogen. Thus, legumes increase fertility without depleting the soil.

There are many successful symbiotic examples involving bacteria and:

• person;
• algae;
• arthropods;
• sea ​​animals.

Microscopic single-celled organisms assist the systems of the human body, help purify wastewater, participate in the cycle of elements and work to achieve common goals.

Why are bacteria classified into a special kingdom?

These organisms are characterized by their small size, lack of a formed nucleus, and exceptional structure. Therefore, despite their external similarity, they cannot be classified as eukaryotes, which have a formed cell nucleus limited from the cytoplasm by a membrane.

Thanks to all their features, in the 20th century scientists identified them as a separate kingdom.

The most ancient bacteria

The smallest single-celled organisms are considered the first life to emerge on Earth. Researchers in 2016 discovered buried cyanobacteria in Greenland that were about 3.7 billion years old.

In Canada, traces of microorganisms that lived approximately 4 billion years ago in the ocean have been found.

Functions of bacteria

In biology, between living organisms and their environment, bacteria perform the following functions:

• processing of organic substances into minerals;
• nitrogen fixation.

In human life, single-celled microorganisms play an important role from the first minutes of birth. They provide a balanced intestinal microflora, influence the immune system, and maintain water-salt balance.

Bacterial reserve substance

In prokaryotes, reserve nutrients accumulate in the cytoplasm. They accumulate under favorable conditions and are consumed during periods of fasting.

Bacterial reserve substances include:

• polysaccharides;
• lipids;
• polypeptides;
• polyphosphates;
• sulfur deposits.

The main sign of bacteria

The function of the nucleus in prokaryotes is performed by the nucleoid.

Therefore, the main characteristic of bacteria is the concentration of hereditary material in one chromosome.

Why are representatives of the kingdom of bacteria classified as prokaryotes?

The absence of a formed nucleus was the reason for classifying bacteria as prokaryotic organisms.

How bacteria survive unfavorable conditions

Microscopic prokaryotes are able to endure unfavorable conditions for a long time, turning into spores. There is a loss of water from the cell, a significant decrease in volume and a change in shape.

Spores become insensitive to mechanical, temperature and chemical influences. In this way, the property of viability is preserved and effective resettlement is carried out.

Conclusion

Bacteria are the oldest form of life on Earth, known long before the appearance of humans. They are present everywhere: in the surrounding air, water, and in the surface layer of the earth’s crust. Habitats include plants, animals and humans.

Active study of single-celled organisms began in the 19th century and continues to this day. These organisms are a major part of people's daily lives and have a direct impact on human existence.

Creation date: 2014/01/08

General characteristics of bacteria

Bacteria are the smallest living creatures, the size of which in most cases does not exceed 01-0.2 mm, which makes them invisible to the human eye without magnification. The world of bacteria inhabiting the planet is large and diverse. They differ from each other morphologically, as well as physiological and biochemical properties. A common characteristic for bacteria is that they do not have a nucleus; they are all prokaryotes. The main structures of a bacterial cell are: the cell wall, the cytoplasmic membrane, the cytoplasm with inclusions and the nucleus, called the nucleoid. Bacteria may have additional structures: capsule, microcapsule, mucus, flagella, fimbriae, pili. (Vorobiev A.A. Medical and sanitary microbiology. M. Academy, 2003)

Shapes and size of bacterial cells

Most prokaryotes are unicellular forms. The size of the cells of many prokaryotes is in the range of 0.2-10.0 microns. However, among them there are “dwarfs” (01 µm - treponema, mycoplasma) and “giants” (up to 100 µm long Akhromatium Makromonas). The shapes of bacterial cells are not very diverse. These are most often rods of different lengths, spherical cells (cocci), as well as convoluted forms - vibrios (slightly curved rod), spirilla (convoluted form with several spiral curls), spirochetes (spiral curls twisted into a ball). Many bacteria are motile. There are floating and sliding modes of movement. The most common swimming movement of bacteria is with the help of flagella. Species with triangles, square and flat (plate-shaped) cells have been found, some have processes - prostecas.

The type of cell grouping sometimes helps determine the systematic affiliation of bacteria. They can be single, united in pairs, short and long chains of regular and irregular shapes, form packages of 4.8 or more cells, form rosettes, networks. A significant number of bacteria from the actinomycete group form mycelium.

Colonial forms of bacteria

Spherical bacteria (cocci), depending on the plane of division and the location of individual individuals relative to each other, are divided into:

• micrococci (monococci) - separately lying cells;
• diplococci - paired, connected in twos;
• streptococci - bacteria that form chains of varying lengths as a result of cell division in one direction;
• staphylococci (bunch of grapes) - are cocci located in the form of a bunch of grapes as a result of division in different planes;
• formation of four cocci;
• sarcinae (ligament, bale) - are arranged in the form of packets of 8 or more cocci, as they are formed during cell division in three mutually perpendicular planes (Gromov B.V. Structure of bacteria.)

Among prokaryotes there are mobile and immobile species. Cell movement is most often accomplished by the rotation of flagella. Another method of movement is cell sliding, the mechanism of which has not been sufficiently studied. There is a “jumping” movement, the mechanism of which has not yet been clarified. Motile bacteria are capable of carrying out taxis reactions: aero- and phyto-taxis, chemo- and magnetotaxis.

Prokaryotes differ from eukaryotes mainly in the absence of a formed nucleus and the typical presence of only one chromosome - a very long circular DNA molecule attached at one point to the cell membrane. Prokaryotes also do not have membrane-enclosed intracellular organelles called mitochondria and chloroplasts. In eukaryotes, mitochondria produce energy during respiration, and photosynthesis occurs in chloroplasts. In prokaryotes, the entire cell (and primarily the cell membrane) takes on the function of a mitochondrion, and in photosynthetic forms, it also takes on the function of a chloroplast. Like eukaryotes, inside bacteria there 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, important components of eukaryotic cell membranes.

Outside the cell membrane, most bacteria are covered 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 bacteria-specific substances). This membrane prevents the bacterial cell from bursting when water enters it through osmosis. On top of the cell wall is often a protective mucous capsule. Many bacteria are equipped with flagella, with which they actively swim. Bacterial flagella are structured simpler and somewhat differently than similar structures of eukaryotes.

Reproduction and development of prokaryotes

Most bacteria reproduce as a result of binary fission, less often by budding, and some with the help of exospores or fragments of mycelium. Multicellular prokaryotes can reproduce by detaching several or one cell from the trichome. Conjugation has been discovered in a number of bacteria, but it does not ensure complete transfer of genetic material from one cell to another.

When 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 DNA. can also be transmitted 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.

This DNA transfer can occur in three ways. During transformation, the bacterium absorbs “naked” DNA from the environment, which got there during the destruction of other bacteria or was 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) of harmless organisms into virulent ones in this way. DNA fragments can also be transferred from bacteria to bacteria by special viruses - bacteriophages. This is called transduction. A process reminiscent of fertilization and called conjugation is also known: bacteria are connected to each other by temporary tubular projections (copulatory fimbriae), through which DNA passes from a “male” cell to a “female” one.

Sometimes bacteria contain very small additional chromosomes - plasmids, which can also be transferred from individual to individual. If the 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 of, say, the intestines becomes resistant to the action of certain drugs.

Some cells form resting forms: cysts, endospores, akinetes. Bacteria are known to form fruiting bodies, often of bizarre configurations and colors. A distinctive feature of bacteria is their ability to multiply quickly. The “champions” in this regard are phytobacteria, the generation time of which is approximately 8 minutes.

Very often a person visits a store or market where he buys food for himself. The question is how they are sold and what he buys. A person uninitiated in the intricacies of the “sanitary organization of trade” will not notice that he was served poorly, and then will not understand why he developed health problems after eating the purchased food. The innocent proximity of incompatible goods, even simply incorrectly served bread, can cause serious food poisoning and infectious diseases. In the environment - in the air, on furniture, kitchen utensils and on the products themselves - there are many microorganisms that, under favorable conditions, multiply quickly. Some of them are capable of producing strong poisons (toxins). Often in markets they sell semi-finished meat products, chickens along with sausages, cheese, and dairy products. Microorganisms from raw foods transfer to ready-to-eat foods, causing food poisoning. This can also happen when using kitchen equipment: knives, spatulas, cutting boards, scales - first for meat, and then for prepared foods. Improper storage of food in the refrigerator (in an unclosed container next to raw fish and other products) can also lead to salmonella infection.

The likelihood of food contamination and, consequently, poisoning of people is especially high in late summer and autumn. At this time, the amount of fruit imported from the southern regions of the country increases several times, and their sale in city markets increases, while the rules for trading these types of food products are not always observed. (Vorobiev A.A. Medical and sanitary microbiology. M. Academy, 2003)

Fruits and vegetables are a special group of food products that require individual equipment and a workplace. According to sanitary standards, fruits and vegetables must be sold from market tables; it is prohibited to sell fruits and vegetables from the ground, but they are sold from the ground in all markets and spontaneously emerging retail outlets. Often fruits that have lost their marketable appearance - broken or cracked watermelons and melons, peaches, apricots, rotten fruits - are sold next to fresh fruit, reducing the price. The rotten stuff is in one drawer, the good vegetables are nearby in another. Storing them on the same shelf is not just a violation of the commodity neighborhood. Rotten fruit and vegetable products cannot be sold at all. It contains toxins that contribute to the development of cancer. Fruits are a good environment for the development of pathogens of dangerous infectious diseases, and violations of the rules for trading this type of product can cause health problems for many people.

The environment contains many microorganisms that, under favorable conditions, multiply rapidly. That is why fruits and vegetables are included in the black list of food products, which may harbor pathogenic microorganisms if trade is not organized correctly.

To conduct the study, fruits and vegetables were purchased from city markets and retail outlets. Fruits were purchased: bananas, apples, lemons, tangerine pears, persimmons, grapes and a vegetable - tomato. Each fruit or vegetable was placed in a separate plastic bag to avoid contact with other fruits. Solid nutrient media were prepared, which were previously poured into Petri dishes.

The nutrient medium must contain all the substances necessary for the growth and development of bacteria. Raw materials for nutrient media were taken from the sanitary and epidemiological station of Surgut. Mainly agar medium with various fillers and universal nutrient media were used.

Excipients for various microorganisms are added to the agar. Endo-agar - any microorganisms can multiply here, because it is a universal nutrient medium for many bacteria. Yellow agar is a yolk-salt medium on which only staphylococci survive. All other microorganisms - both harmless and pathogenic - cannot tolerate salt. Staphylococcus can grow on such a medium. The main thing is, what is he like? After all, there are many staphylococci, and among them only one is pathogenic - aureus, which causes inflammation, including sepsis. Others are harmless to humans: for example, Staphylococcus epidermidis is present on the skin of all people without exception.

Sabouraud's environment is a medium for the development of mold and yeast-like fungi, the spores of which are strewn with unwashed human hands, the surfaces of objects, handrails of public transport and quite possibly fruits. The most unpleasant of the pathogenic yeast-like fungi are fungi of the genus Candida, which affect the skin, hair, nails and even the lungs.

Bismuth sulfite agar - the properties of the medium are based on the ability of microorganisms to produce hydrogen sulfide, which reacts with bismuth citrate and forms a black compound - bismuth sulfide. (Egorova N.S. Workshop on microbiology.) Before the experiment, Petri dishes are sterilized, all tests are carried out in sterile medical gloves, the table is treated with alcohol. Petri dishes are covered with lids on top and numbered; each number corresponds to a specific crop from fruits or vegetables. Sowing is carried out with a special sterile stick or bacteriological loop, which is pre-heated in the flame of an alcohol lamp. The enrichment culture is dispersed using a loop or a cotton swab using the exhaustion stroke method. After sowing, all cups are placed in a warm (t 37 C) dry place.

After growing bacteria

Putrid proteus and E. coli were found on tomatoes and grapes and on humans. Proteus, if it enters the intestines, causes poisoning. Escherichia coli can cause acute intestinal disorders. In addition, non-pathogenic staphylococci and mold fungi appeared.

After washing a person’s hands under running water with soap and a brush, only non-pathogenic staphylococci (bacteria that are found in the indoor air) appeared on the nutrient media. Staphylococcus aureus has appeared, causing inflammation up to sepsis and mold fungi on tangerines, persimmons, pears and bananas - pathogenic fungi have been discovered - the so-called leathery ones - fungi from the genus Candida, from which you can get a variety of skin diseases and even internal pneumonia.

Staphylococci and streptococci contribute to the occurrence of various purulent inflammatory processes, abscesses, cystitis, pharyngitis, and colitis. Yeast-like fungi were found on nutrient media from apples, pears, grapes and bananas. Numerous molds, E. coli, aureus and non-pathogenic staphylococci from grapes grew on the nutrient media. After washing the grapes under warm running water with the addition of citric acid, E. coli, as well as aureus and non-pathogenic staphylococci, disappeared. Dysentery pathogens were found only on tangerines and persimmons. After washing with warm running water, the dysentery bacillus in the second culture disappeared. No pathogens of salmonellosis were found. Although no one can guarantee that they won’t appear on other fruits. In principle, fruits can retain:

• tuberculosis bacteria (although they are sensitive to bright sunlight);
• hepatitis A viruses live for several months in a dry state;
• Dysentery pathogens remain active on greens for two days, on pears and apples for three days, on persimmons for about four days, on grapes for a week, and on tomatoes for up to eight days.

The human body has means of protection against pathogens:

• on the skin, in the form of skin discharge from the pores;
• human saliva has an alkaline environment in which many microorganisms and substances that kill bacteria do not survive;
• the blood contains antibodies and leukocytes that fight bacteria through the process of phagocytosis;
• Human gastric juice contains hydrochloric acid and, therefore, has an acidic environment, in which many bacteria also cannot multiply.

But, however, there are people who have weakened immune systems. These are usually children, the elderly, as well as people who have had an illness and may form a special risk group when, if the rules of personal hygiene are not observed, it is fruits that can cause various infectious diseases. (Steiner R., Edelberg E., Ingrm J., World of Microbes)

Fruits and vegetables purchased at the market are indeed very dirty. The study showed the presence of various microorganisms on fruits, including pathogenic ones. Various molds were found on the fruit, including Candida, Staphylococcus aureus, Streptococcus, Proteus putrefactive, and E. coli. Human hands and other objects may contain various types of bacteria; it is necessary to wash your hands with soap and water before eating. The human body has means of protection against pathogenic microorganisms on the skin, in saliva, in the blood, in gastric juice, however, those who have a weakened immune system - children, the elderly, as well as those who have had the disease - can form a special risk group when, if personal hygiene rules are not followed, Fruits can cause various diseases.

Maintaining hygiene and eating good quality food is the key to human health and longevity.

• Do not eat dirty fruits and vegetables.
• Wash fruits and vegetables thoroughly with a brush, then rinse them with running water.
• Before putting fresh fruits and vegetables in the refrigerator, they must be washed, since even at low temperatures, germs can “crawl” from dirty fruits and vegetables to other foods stored in the refrigerator.
• Before eating food, you should wash your hands thoroughly with soap and warm water.

A living simple microorganism with a cellular structure is a bacterium. But, despite its simplicity, it is one of the most interesting to study. All bacteria are capable of reproducing by fission.

Scientists have always been interested in observing how bacteria reproduce. The study and observation of bacteria is carried out by the micro branch of biology - bacteriology.

Currently, approximately ten thousand species of bacteria have already been studied and described. But it is believed that in reality their number is in the millions.

They surround us all our lives, they can be found in water, land, on our body and even in the atmosphere. The lifestyle of bacteria is unique in its own way. Their peculiarity is that, unlike fungi, bacteria do not have a clearly defined nucleus.

On microscopic examination it can be noted that. Cocci, for example, are round in shape, chlamydia are spherical in shape, and mycoplasma is flask or thread shaped.

They, like all humanity, have a macromolecule called DNA (Deoxyribonucleic acid). DNA in bacteria is responsible for storing and transmitting genetic information from one generation of microorganisms to the next. The metabolism of bacteria (metabolism) is almost the same as that of many living organisms.

The role of bacteria in the biosphere and our lives cannot be underestimated. For example, soil fertility is achieved by the active work and waste products of soil bacteria. In agriculture, fertilizers are created for these purposes.

They also play their role in a person’s life. There are bacteria that can harm humans, such as E. coli. As well as useful lacto and bifido, components of the human microflora.

Everyone knows such words as probiotics and prebiotics.

So why are they still needed?

Probiotics help our gastrointestinal tract carry out its daily function - digest food, create local immunity, and produce hormones such as serotonin.

There are microorganisms that are pests for humans. Many bacteria are pathogenic and can cause disease and bacterial infections. For example, tuberculosis, diphtheria, whooping cough, diphtheria, tetanus and cholera. There are a great many of them and modern medicine has already learned to defeat most of them.

Factors influencing the growth and development of bacteria:

• Humidity level
• Lighting
• pH level
• Environmental composition
• Temperature

Let us consider the most important of them, their influence on division and reproduction.

Bacterial cells require a certain percentage of humidity levels to grow and develop. The bacteria need this in order to maintain their vital functions. Almost all bacteria and living organisms love moisture.

In such conditions they feel great. If the humidity level suddenly drops below 20%, this leads to destructive and development-stopping consequences.

Acidity and pH – balance

Acidity plays an almost dominant role in influencing the development of bacteria. It is usually denoted by the pH sign and takes into account the range from zero to fourteen. For growth, limit values ​​from 4 to 9 are required. At 9, almost all microorganisms familiar to us stop growing.

For the most part, they stop growing at a pH of 4. Neutral acidity is considered the ideal habitat.

• Acidic environment - from 0 to 6 pH
• Alkaline environment - from 8 to 14 pH
• Neutral environment - 7.07 pH.

It is worth highlighting lactic acid bacteria (acidophilus) separately. They love an acidic environment and when they get into it, for example, in milk, they begin to work in a special way, converting carbohydrates into lactic acid. They are the most important producers of products containing probiotics beneficial for human microflora.

The beneficial properties of acidophiles are also used in pharmaceuticals. Scientists have found positive properties and use them in the production of medicines not only for the intestines, but also for many other organs. In the household, women often use the beneficial properties of bacteria.

Many people make preparations and twists for the upcoming season without vegetables and fruits every year. By lowering the acidity level by adding vinegar, it creates an acidic environment. By doing this we achieve the death of pathogenic microorganisms.

Changes in these factors lead to death, increased reproduction or mutation of bacteria.

Under favorable conditions, bacteria divide, thereby increasing their population, every twenty minutes. With increased sunlight from exposure to rays, reproduction stops. Some bacteria even react to the planet's magnetic field.

Bacteria make up the normal human microflora and are found on the skin, mucous membranes and even inside a person, for example in the intestines. Bacteria even exist in the air. You could say our whole world is bacterial in its own way.

Bacteria have different methods of reproduction, some do not have a sexual process and reproduce by budding or by transverse fission. Others have the sexual process, but in the most primitive form.

To have an idea of ​​the life cycle of this microorganism, you need to study the main eight phases of development:

First phase

"Latent"– a resting phase, lasting from the moment of settlement in the plant environment until the population begins to increase (approximately from 60 to 120 minutes). The pace is directly proportional to environmental conditions.

Second phase

"Reproduction Delay"– the process of multiplication occurs, cells quickly multiply and divide, and increase in size at high speed. Duration up to 120 minutes.

Third phase

"Logarithms"– This is the phase of active reproduction. During this phase, the maximum possible development and division of bacteria is achieved. Division occurs in progression. From two to four cells. From four to eight cells. From eight to sixteen, etc.

Fourth phase

"Negative acceleration"– the rate of reproduction sharply decreases, and the rate of death increases. Duration ranges from 100 to 120 minutes.

Fifth phase

"Stationary maximum"- a phase created so that cells can reproduce. Reproduction picks up speed again and covers the number of previously dead cells.

Sixth phase

"Acceleration of Death"– from the name of this phase we can conclude that the number of dead bacteria is several times greater than the number of surviving cells; we can say the phase of meager existence.

Seventh phase

"Logarithmic Doom"– cells die at the same speed, at the same time, the division process first slows down and then stops altogether.

Eighth phase

The well-known “salmonella” causes a serious infectious disease, salmonellosis. It also develops under certain conditions. To develop, it requires a temperature of 37 degrees Celsius. And even in a cooled state, they can be in a resting phase with the ability to divide for up to 140 days and not die.

If a product contaminated with salmonella does not undergo the necessary heat treatment, human infection cannot be avoided. Infection with salmonellosis is accompanied by all the “unpleasant” symptoms of poisoning.

A product that is in the public domain has every chance of becoming contaminated. You also need to be careful when preparing food. If you are not sure that the knife is on a clean table, it is better not to neglect washing it again. A knife used to cut raw meat should be immediately washed to prevent its accidental use for other products.

At home, it is impossible to know in advance whether meat is contaminated. The bacterium does not change the product. The taste, color, appearance of the product remains the same. Most often, salmonella can be found on eggs, milk, and meat.

Over time, many strains have mutated and become resistant to basic disinfection solutions and outdated antibiotics. Salmonella is so tenacious that it can live and live for about five months in open water bodies, and on chicken eggs for almost the entire year.

The disease in farm animals passes without symptoms and breeders most often do not know about the disease.

You can become infected with salmonellosis through at least two ways:

1. Contact - household method– infection occurs from one sick person to another.
2. Food method– infection through dairy products, unwashed eggs or raw meat.

Understanding the structure of life, development, growth and reproduction of microorganisms, the question “what are bacteria for” disappears by itself. At the heart of all living things are bacteria. Any microorganism that lives on our body and in our home performs its function.

There are a number of factors that have a significant impact on. Among the main reasons are:

• temperature;
• chemical composition of the environment;
• acidity (level, pH);
• humidity;
• light.

Changing any one or a number of conditions can suppress or accelerate the development of a bacterium, force it to adapt to a new environment or lead to death.

For prokaryotes, the concepts of growth and development are almost identical. They mean that in the process of life, an individual microorganism or group of bacteria synthesizes cellular material (protein, DNA, RNA), due to which an increase in cytoplasmic mass occurs. Growth continues for some time until the cell becomes capable of reproduction, and then the development of bacteria stops.

Reproduction is characterized by the ability to reproduce itself. The result of this process is an increase in the number of microorganisms per unit volume, that is, population growth occurs.

All substances and structures of the cell can grow and develop proportionally. In this case, microbiologists talk about balanced growth. It is not such if the characteristics of the environment change. Then certain metabolic products begin to predominate, and the production of other substances stops. Knowing this pattern, scientists make the growth process deliberately unbalanced in order to synthesize useful compounds.

Life cycle of a bacterial cell

The division of a microorganism's cell, through which reproduction occurs, is characterized by a fairly short time cycle. The rate of formation of a microbial colony is influenced by all of the factors listed above. In a sufficiently nutritious environment with the desired pH level and at the optimal temperature, the generation time can range from 20 minutes to half an hour. In running water, the development cycle can be shortened to 15–18 minutes.

Ideal conditions that guarantee such rapid growth are quite rare: there is no nutrition in the required amount, and accumulating decay products interfere. If the scenario with the best conditions for the bacterial reproduction cycle were to come true, then within a day only one E. coli cell would form a vast colony weighing several tens of thousands of tons!

The growth of microorganisms was studied in closed tanks, where, while in water, bacteria did not immediately begin to develop and multiply. Only once they got into the nutrient medium did they adapt to the new conditions for some time. Reproduction took place gradually until it began to subside and stopped altogether. These observations made it possible to identify certain developmental phases that form the overall life cycle of bacteria.

1. The initial phase is characterized by the absence of cell growth and division. The adaptation process is underway (from 1 to 2 hours).
2. The period of intensive growth is called the lag phase. Cell division begins, but so far very slowly. The duration of this stage of development is individual for different types of bacteria. In addition, the time of its occurrence is influenced by environmental conditions.
3. The third phase is characterized by the beginning of intensive reproduction, the speed of which increases exponentially.
4. The generation period begins to increase towards the beginning of the fourth phase. But the nutrient medium is depleted, and the concentration of metabolic products in it increases. The rate of reproduction decreases and some cells die.
5. This phase of the cycle is characterized by the preservation of the equal sign between newly appearing cells and the number of dead microorganisms. The population continues to increase slightly.
6. The sixth and seventh phases complete the development cycle. This is the time of cell death, the number of dying cells begins to dominate.
7. At the final eighth stage, the life cycle of bacteria ends. The rate of death decreases, but under the influence of unfavorable environmental factors, death continues.

The described stages correspond to a non-flowing culture of bacteria. To prevent growth from slowing down, new portions of nutrients can be constantly introduced into the environment, removing metabolic products from it. This makes it possible to ensure that the necessary microorganisms are constantly in the development period. This flow principle is used, for example, in an aquarium.

Humidity as a necessary condition for the life of microorganisms

To grow and develop, bacteria need the humidity level in their environment to be maintained at a certain level. Water plays an important role in metabolism; it helps maintain normal osmotic pressure in the bacterial cell and makes it viable. Therefore, almost all prokaryotes are moisture-loving, and a drop in this indicator to a value below 20% is considered a growth-destructive factor.

The less water is contained in the environment, the more passive the reproduction process is. This statement is most easily verified on food products: they last much longer when dry. But this method of processing and storage is not universal. Drying retards the growth of some bacteria and microbes, but there are those that will retain their functionality.

The influence of medium acidity on the viability of bacteria

The acidity of the environment is one of the most important indicators for the growth and development of microorganisms. It is denoted by the symbol pH and is considered in the range from 0 to 14. Acidic environments correspond to values ​​from 0 to 6, for alkaline environments the indicator ranges from 8 to 14, and the neutral point is considered to be a pH level of 7.07. The optimum for the development of microorganisms are the numbers characterizing a neutral environment.

The pH range from 1 to 11 is the limit at which some bacteria managed to survive. But for the most part, their growth stops at an acidity level of 4. If the pH value is determined to be 9, then almost all known microorganisms stop reproducing. That is, for the development and growth of bacteria, it is important that the acidity is in the range from 4 to 9.

There is a type of prokaryotes for which it is vital that the pH be as acidic as possible. They are called acidophilic and belong to the type of lactic acid bacteria. When they find themselves in milk, they begin to convert the carbohydrates it contains into lactic acid. They are important participants in the process of obtaining probiotic products.

The beneficial properties of lactic acidophilic microorganisms are also used to create medicines. They have a beneficial effect not only on intestinal function, but also help cope with a number of other diseases. Lowering the pH level in order to preserve food for the winter is used by every housewife. Adding vinegar creates an acidic environment in which pathogenic microorganisms cannot survive.

Some lactic acid bacteria, during the process of growth and development, are characterized by the synthesis of acid in such large quantities that the pH drops to a critical level, and they stop developing or die. There are also real record holders for survival and successful functioning in acidic environments. Thus, at an optimal pH value of 2.5, the lactic acidophilic bacterium Thiobacillus thooxidans can develop at an acidity level of 0.9.

What happens to microorganisms during the bactericidal phase?

If bacteria under ideal conditions are capable of developing very quickly, then why, for example, in freshly received milk do they not grow for some time? The environment is quite favorable, and even aseptic milking conditions do not exclude the presence of a large number of microorganisms. But fresh milk contains lactenins - bactericidal substances that can inhibit the development of bacteria for a certain period of time.

The effect of lactenins is so strong that many microorganisms not only slow down their growth, but also die. The period of their action, called the bactericidal phase, gradually ends. This depends on the initial number of bacteria in the milk and the increase in temperature of the product. The effect of lactenins can last from 2 to 40 hours. They try to prolong the bactericidal phase and cool the milk. After its expiration, the growth of microbes and bacteria resumes.

Even if initially there was a small amount of lactic acid microorganisms in the milk, they gradually begin to predominate. And in order to prevent souring and get rid of harmful bacteria, heat treatment methods are used. Heating, boiling and other types of heat treatment are another way to eliminate unwanted microflora in products. And we can name another important component of the environment that influences the growth and development of bacteria - temperature.

What are mesophiles afraid of?

The structural features of bacteria exclude the presence of mechanisms that could regulate temperature. Therefore, they are very dependent on how much their environment cools or warms. According to temperature preferences, prokaryotes are usually divided into:

• Psychrophiles – lovers of low temperatures (range from 0 to 35°C, optimum 5–15°C).
• Thermophiles - they prefer high temperatures (40–80°C are acceptable conditions for existence, but the optimal value is from 55 to 75°C).
• Mesophiles. These include most bacteria, including pathogenic ones. Their growth and development require temperatures of 30–45°C. The range for their survival is much wider (from 40 to 80°C), but only at optimum life activity is most active.

The direct effect of increasing or decreasing temperature on the development of microflora helps combat its presence on products. This treatment measure is of particular importance in the context of preventing botulism.

Clostridium botulinum, or Another reason for careful heat treatment of products

In the process of growth and development, some microorganisms are capable of producing substances that are particularly dangerous to human health - toxins. The bacterium Clostridium botulinum causes botulism, which is most likely fatal. There are two types of bacteria:

• vegetative;
• spore

The vegetative variant of botulism is not so dangerous. A microorganism with this form of existence dies after the product has been boiled for 5 minutes. But botulism spores will die only after five hours of treatment, and the temperature must reach a certain point. Spores are a kind of protective shell that preserves the dormant bacterium for a long time. After a few months, they germinate and botulism “wakes up.”

Spores reliably store their valuable cargo both in cold conditions and under the influence of ultraviolet radiation. A critical temperature will be 80°C for the vegetative form of botulism and a longer treatment at 120°C for the spore form. These conditions are not always observed by housewives when canning products, so you can also become infected from improperly prepared home-canned food.

The following first signs are characteristic of botulism:

• pain in the central part of the abdomen;
• attacks of diarrhea (from 3 to 10 times a day);
• headache;
• feeling of weakness, malaise and fatigue;
• periodic vomiting;
• high body temperature (up to 40°C).

The onset of botulism is somewhat less common, but can still be accompanied by visual disturbances, blurry vision of objects, the presence of fog or spots in front of the eyes, and previously not manifested farsightedness. Breathing problems and difficulty swallowing are other possible symptoms.

Complications of botulism manifest themselves in the form of secondary bacterial infections, for example, pneumonia, pyelonephritis, sepsis, purulent tracheobronchitis. Arrhythmia may develop, and myositis affects the calf and thigh muscles. The disease lasts for about three weeks, and as a result of competent and timely treatment of botulism, lost vision and breathing functions are restored and the ability to swallow returns.

How do bacteria grow in food?

Any food consumed by humans has its own microflora. It can be divided into two types:

• specific - these are microorganisms that were added intentionally in order to impart certain taste or aromatic qualities;
• non-specific - it consists of bacteria that got on the product by accident (the sanitary regime was not observed at the factory or in the store, the shelf life and processing rules were violated).

At the same time, different representatives of pathogenic prokaryotes prefer their own specific type of products. Salmonella, for example, are avid eaters of eggs, meat and milk. The danger of infection lies in the fact that the purity of the product cannot be verified by its appearance. Salmonella in contaminated meat, offal or minced meat does not change their color, taste or smell in any way. If dishes prepared from such raw materials do not undergo proper heat treatment, then disease is inevitable.

Salmonella rods require a temperature of 37°C to develop; they do not form spores or capsules, but are very resistant to environmental conditions. Even in meat chilled to 0°C, they can survive up to 140 days. In this case, the ability to divide is not lost. In open reservoirs, salmonella will remain viable for about 4 months, and in bird eggs for about a year. Most strains are able to survive exposure to antibiotics and disinfectants.

Salmonella, which is the causative agent of infection, most often lives in the body of farm animals. The disease occurs without symptoms in cows, horses, sheep, pigs or birds. Pathogens are excreted in urine, saliva, feces and nasal mucus, but people most often become infected through milk, meat or eggs (food route). Salmonella can also be transmitted from an already sick person (contact and household transmission).

Poultry or animal meat may become contaminated during transportation or processing. To prevent salmonella from causing illness, at home you can only follow simple rules for the prevention of any intestinal infections.

• high-quality processing of meat, fish, eggs and milk;
• purchase of semi-finished meat products, unprocessed products from private farms only if there is a conclusion from the SES on safety;
• compliance with personal hygiene rules;
• Separate equipment for cutting raw and cooked foods will help you avoid becoming carriers of salmonella.

Farms and the relevant supervisory authorities must constantly monitor the living conditions of animals, their health and the quality of products (especially meat) at the exit.

Preparations that improve the condition of water in an aquarium break down organic matter and stop the reproduction and growth of algae. There are also solutions that can restore acidity and maintain it at the required level. But they will be effective only if the aquarium is not in a state of disrepair and the filter materials are replaced with new ones.

Special preparations can also speed up the transition of nitrogen into simple form and reduce water hardness. The biological balance they create in the aquarium ensures that the rate of formation of waste products will be equal to the rate of their elimination. And in water uncontaminated by waste, beneficial bacteria readily develop and function.

The so-called starting microorganisms are contained in the preparations in a dormant state. As soon as they are in the aquarium, they are activated. They spread in water and transform the soil into a high-performance biofilter. Other species begin to convert nitrites and ammonia into nitrates. This ensures high quality of the aquatic environment.

Concentrated suspensions work very effectively in an aquarium; the following brands are popular:

• Tetra.
• Dennerle.
• Sera.
• Aqua Med.

The development and growth of bacteria can be made a controlled process, which is why knowledge of the factors influencing these processes is so important. And you don’t need to be a highly specialized specialist to be interested in the life activity of microorganisms - their guaranteed presence everywhere allows you to competently apply the available information in everyday life.