In order to study microorganisms, determine the etiological factors of infectious diseases, deal with the prevention and treatment of infectious diseases, and solve many other issues related to microorganisms, it is necessary to have enough of them, which means creating all conditions for the normal growth and reproduction of microorganisms.

The term "reproduction" of microbes means their ability to self-reproduce, to increase the number of individuals.

Reproduction of microorganisms occurs by transverse division, budding, spore formation, reproduction.

The growth of microorganisms means an increase in the mass of microbes as a result of the synthesis of cellular material and the reproduction of all cellular components and structures.

Bacteria, spirochetes, actinomycetes, fungi, rickettsiae, mycoplasmas, protozoa, chlamydia are said to reproduce, while viruses and phages (microbial viruses) reproduce.

The reproduction of microorganisms corresponds to certain patterns. The rate of division of microorganisms is different, it depends on the type of microbe, the age of the culture, the characteristics of the natural and artificial nutrient medium, temperature, carbon dioxide concentration and many other factors.

In the process of reproduction, microorganisms undergo morphological and physiological changes at various stages (in shape, size, staining, biochemical activity, sensitivity to physical and chemical factors, etc.).

Microorganisms have age-related variability, i.e. individuals change at different stages of growth, maturation and aging. These changes are observed in the normal cycle of the individual development of a microorganism, which depends on the nature of the organism, on the complexity of its structure and sequence in development.

Bacteria have the simplest cycle of development among microorganisms. They reproduce by simple transverse division in different planes. Depending on this, cells can be arranged randomly, in clusters, chains, packages, in pairs, in fours, etc.

A characteristic feature of bacteria, which distinguishes them from numerous animals and plants, is their extraordinary rate of reproduction.

Each bacterial cell, on average, undergoes division within half an hour, which is due to increased metabolism, the speed with which the nutrient material enters the cell.

The factor inhibiting the reproduction of bacteria is the depletion of the nutrient substrate and the poisoning of the environment by decay products.

There are eight main phases of reproduction in bacteria.

1. The initial stationary phase, which is a period of time of one to two hours from the moment of sowing bacteria on a nutrient medium. No reproduction occurs during this phase.

2. The phase of reproduction delay (lag - phase), during which the reproduction of bacteria occurs very slowly, and their growth rate increases. The duration of the second phase is about two hours.

3. The phase lasts five to six hours. The third phase is characterized by the maximum rate of division, a decrease in cell size.

4. Phase of negative acceleration (lasts about two hours). The rate of reproduction of bacteria decreases, the number of dividing cells decreases.

5. Stationary phase, lasting about two hours. The number of new bacteria is almost equal to the number of dead individuals.

6. Phase of cell death acceleration (lasts about three hours).

7. Phase of logarithmic cell death (lasts about five hours), in which cell death occurs at a constant rate

8. Phase of decrease in the rate of death. The surviving individuals go into a state of rest.

The duration of the breeding phases is not a constant value. It can be different depending on the type of microorganisms and cultivation conditions.

The development cycle of coccoid bacteria is reduced to the growth of the cell and its subsequent division. Rod-shaped asporogenic bacteria grow at a young age, reach a maximum size, then divide into two daughter cells, which repeat the same cycle. In bacilli and clostridia, the process of spore formation is included in the development cycle under certain conditions.

Spirochetes and rickettsia, like bacteria, reproduce by binary fission.

Among mycoplasmas, all elementary bodies of a spherical or ovoid shape have the ability to reproduce. In the process of development, several filamentous outgrowths appear on the elementary body, in which spherical bodies are formed. Gradually, the threads become thinner and chains are formed with clearly defined spherical bodies. Then the threads are divided into fragments and the spherical bodies are released.

Reproduction of some mycoplasmas occurs by budding of daughter cells from larger spherical bodies. Mycoplasmas reproduce by transverse fission if the processes of mycoplasma division proceed synchronously with the replication of the nucleoid DNA. If synchrony is disturbed, filamentous multinucleoid forms are formed, subsequently dividing into coccoid cells.

Actinomycetes and fungi have two different stages of development: the stage of vegetative growth, in which the formation of mycelium is characteristic, and the stage of formation of spores that form on sporophores.

An important feature of actinomycetes and fungi is a significant variety of ways of their reproduction. They are characterized by vegetative, asexual and sexual reproduction.

Vegetative propagation is carried out by dividing into fragments of hyphae, followed by the formation of individual rod-shaped and cocci-shaped cells.

Asexual reproduction occurs vegetatively (growth of fragments of hyphae or their individual cells) and with the help of more or less specialized reproductive organs (spores and conidia). The most frequent, asexual, way of reproduction is manifested in the formation of exogenous and endogenous spores. Exospores or conidia are formed at the ends of fruiting hyphae, but are enclosed within a common sac - sporangia. Hyphae that carry sporangia are called sporangiophores. Sporangiophores can be straight, wavy, spiral.

Sexual reproduction occurs with the help of special organs - ascospores, basidiospores, the formation of which is preceded by the sexual process. According to the biological purpose, spores of actinomycetes and fungi are dormant, serving to preserve the species for a certain period and serving for rapid reproduction.

Spores of actinomycetes and fungi are formed by each individual in large numbers, since, unlike spores of bacteria, they serve mainly for the purposes of reproduction. They are less resistant to environmental factors than bacterial spores.

In protozoa, as well as in actinomycetes and fungi, along with reproduction by division, there is also a sexual process.

Chlamydia, viruses and phages have peculiar cycles of development.

Reproduction of chlamydia begins with the penetration of elementary bodies into a sensitive tissue cell by endocytosis. These bodies in the vacuole of the cell turn into vegetative forms, called initial or reticular bodies, which have the ability to divide. Reticular bodies have a lamellar cell wall, and in the cytoplasm there are loosely located nuclear fibrils and numerous ribosomes. After repeated division, the reticular bodies turn into intermediate forms, from which a new generation of elementary bodies develops. The whole cycle of development of chlamydia lasts 40-48 hours and ends with the formation of a microcolony of chlamydia in the cytoplasm of the host cell.

After the rupture of the vacuole wall and the complete destruction of the host cell, the microcolonies of chlamydia, being outside the whole cell, break up into independent elementary bodies, and the cycle of penetration of chlamydia into the cell with their subsequent reproduction is repeated.

The reproduction of viruses is characterized by a sequence of individual stages.

1. Stage of adsorption. Virions are adsorbed on the surface structures of the cell. In this case, the interaction of complementary structures of the virion and the cell, which are called receptors, occurs.

2. The stage of penetration of the virion into the host cell. The ways of introduction of viruses into cells sensitive to them are not the same. Many virions enter the cell by pinocytosis, when the resulting pinocytic vacuole "pulls" the virion into the cell. Some viruses enter the cell directly through its membrane.

3. The stage of destruction of the outer shell and capsid of the virion with the help of proteolytic enzymes of the host cell. In some virions, the process of destruction of their shell begins at the stage of adsorption, in others - in the pinocytic vacuole, in others - directly in the cytoplasm of the cell with the participation of the same proteolytic enzymes.

4. Stage of viral protein synthesis and nucleic acid replication. After the complete or partial release of the viral nucleic acid, the process of viral protein synthesis and nucleic acid replication begins.

5. Assembly stage or virion morphogenesis. The formation of virions is possible only under the condition of a strictly ordered connection of viral structural polypeptides and their nucleic acid, which is ensured by the self-assembly of protein molecules around the nucleic acid. In some viruses, this process occurs in the cytoplasm, in others, in the nucleus of the host cell. In complexly organized viruses with an outer shell, further assembly occurs in the cytoplasm during their release from the cell.

6. The stage of release of virions from the host cell. A number of complex viruses leave the host cell, while the cells remain viable for some time, and then die. Simple virions leave the cell through the holes formed in its shell, the host cell dies, not maintaining viability for some time.

In some cases, the reproduction of virions in cells can occur over many months and even years. Viruses are shed through the cell wall. When such cells divide, the virions are transferred to daughter cells, which in turn begin to produce viral particles.

There are three types of interaction between a virus and a cell: productive, abortive, and virogenic.

Productive the type of interaction is the formation of new virions.

Abortive the type of interaction can be abruptly interrupted at the stage of viral nucleic acid replication or viral protein synthesis, or virion morphogenesis.

Virogenic the type is characterized by the incorporation (integration) of the viral nucleic acid into the DNA of the cell, which ensures synchronous replication of the viral and cellular DNA.

During phage reproduction, it is also adsorbed on the cell surface (stage 1) as a result of the interaction of amino groups of proteins localized in the peripheral part of the phage tail process and negatively charged carboxyl groups on the surface of the bacterial cell.

There are reversible and irreversible phases of adsorption. The reversible phase is characterized by the fact that fixed phages can be separated from the cell by vigorous agitation or the concentration of ions can be sharply reduced. The released phages retain their viability.

During the second irreversible phase of adsorption, the phage does not separate from the microbial cell body. The adsorption process takes several minutes. Under the influence of an enzyme located in the tail process of the phage, a hole is formed in the body of the microbial cell at the site of attachment of the phage, through which the phage DNA penetrates into the cell. The phage shell remains outside (stage 2).

Some phages introduce their nucleic acid into the cell without prior mechanical damage to the cell wall. During the latent period following the penetration of the phage nucleic acid into the cell, the biosynthesis of the phage nucleic acid and phage capsid proteins takes place.

There is a synthesis of enzymes necessary for the replication of phage nucleic acid and structural proteins of the phage (stage 3).

In the fourth stage, the hollow phage particles are filled with the phage nucleoacid and mature phages are formed. Phage morphogenesis is carried out.

At the end of the latent period, the infected microbial cells are lysed and mature phage particles are released (stage 5).

It is believed that the adsorption of the phage lasts 40 minutes, the latent period is 75 minutes. The entire cycle of interaction between a phage and a microbial cell lasts a little more than three hours.

The introduction of a phage into a microbial cell is not always accompanied by its lysis. Often, the interaction of a phage with a microbial cell leads to the formation of lysogenic cultures.

By the nature of the interaction with the microbial cell, temperate and virulent phages are distinguished. The state of lysogeny is caused by temperate phages. Lysogenic microbial cells are resistant to virulent phages. Virulent phages cause the formation of new phages and the lysis of the microbial cell.

Growth- this is a coordinated increase in all components of the cell, the result of growth is reproduction.

Reproduction of bacteria– increase in the number of cells in the population.

In the process of growth, the bacterial cell increases by 2-3 times, it is intensely stained and RNA accumulates. Under favorable conditions, growth ends with reproduction. In bacteria, reproduction occurs by dividing in half - binary fission is the main method of reproduction.

growth curve characterizes the growth and reproduction of bacteria in certain environmental conditions. The growth curve is obtained from a batch culture study.

periodical culture- this is a population of m / o that develops in a limited volume of the environment without the supply of nutrients.

Phase 1 - initial - bacteria grow, but do not multiply

Phase 2 - phase of logarithmic growth - bacteria multiply intensively, their number increases in a logarithmic progression.

3 phase - stationary - reproduction - equal to mortality

Phase 4 - death - metabolic products accumulate, nutrients are depleted and bacteria die.

External factors can have:

bacteriostatic action - inhibit the reproduction and growth of bacteria

bactericidal action - cause the death of bacteria

Reproduction of bacteria.

It begins with the replication (doubling) of the genome, and then division occurs.

Bacteria have vegetative replication - information is transferred from the parent cell to the daughter cell.

In bacteria, replication is self-regulating - the genome contains genes responsible for replication.

Replication is semi-conservative in nature - daughter cells receive an evenly distributed genetic material (one strand of DNA is maternal, the second is newly synthesized).

Replication starts from a certain point, from which the DNA unwinds, a replication fork is formed, and the SSB protein is synthesized, which prevents the re-twisting of the strands. The process is carried out by DNA polymerase, which is able to attach complementary nucleotides to the free 3" end.

The synthesis of complementary regions is triggered by primer loading. This is a section of RNA that is complementary to template DNA and the primer has a free 3 "end. Filling with a primer starts DNA synthesis, Okazaki fragments are built on the matrix, which are sewn into a single thread by DNA ligases. In a bacterial cell, 2 identical DNA strands are formed, which are pulled apart along the poles cells and after replication, bacterial division starts.

Division begins with the elongation of the cytoplasmic membrane, an intercellular septum is formed along the equator, along which the bacterium divides binaryally and 2 identical daughter cells are formed.

Indicators of growth and reproduction of bacteria:

Increase in cell size

The concentration of bacteria - the number of cells in 1 ml

Density of bacteria - the mass of bacteria in mg per ml

Generation time is the time it takes for the number of cells to double.

22. Cultivation and methods for isolating a pure culture of aerobes and anaerobes.

Cultivation m/o- This is the production of a large number of bacteria on a nutrient medium.

Purpose of cultivation: The study of microbiological properties, To diagnose infections and To obtain a biological product from bacteria or obtained using bacteria.

Bacteria cultivation conditions:

The presence of a complete nutrient medium.

Optimum t (≈37 0 C)

Culture atmosphere (with or without O2).

Culture time - visible growth in 18-48 hours, or for some 3-4 weeks (tbc)

Illumination of the nutrient medium for photosynthetic (grow only in the presence of light).

Cells, like any living organism, are born, live and die. The growth and reproduction of bacteria is very fast, they could capture the entire living space on the planet, if not for their fragility and limiting factors (temperature, acidity level, lack of food, etc.). Under favorable conditions, cell doubling takes an average of about half an hour. However, in critical situations, some types of microorganisms (spore-forming bacteria) are able to form spores and “hibernate” for a rather long period.

The rapid multiplication of bacteria has its pros and cons. The use of microorganisms in biotechnology (yeast, lactic acid, nitrogen-fixing organisms, molds, etc.) is aimed at improving the quality of life. However, the uncontrolled growth of disease-causing (pathogenic) microbes is dangerous for humans. A person's own microflora can also harm health. In medicine, there is the concept of bacterial overgrowth syndrome, in which the number of opportunistic microbes in the human body increases dramatically, which poses a threat to health.

Where does it all start

Cell growth and reproduction are two different processes. Growth is understood as an increase in cell mass due to the formation of all cellular structures. Reproduction is the increase in the number of cells in a colony. There are binary fission, budding and genetic recombination (a process resembling sexual reproduction).

Most prokaryotic (non-nuclear) cells, to which all bacteria belong, reproduce by splitting in two (binary fission). In this way, for example, lactic acid bacteria multiply. The process begins with the duplication of the bacterial chromosome (a DNA molecule that replaces the nucleus) and proceeds in several stages:

• the cell lengthens;
• the outer shell "grows" inward and forms a transverse partition (constriction);
• two new (daughter) cells diverge in different directions.

The result is two identical organisms.

Individual microorganisms divide by budding, but this is rather an exception to the general rule. The process consists in the formation of a short protrusion at one of the poles of the cell, into which one of the halves of the separated nucleoid (DNA molecules with genetic information) “drifts”. Then the protrusion grows and separates from the mother cell.

There is another option that resembles sexual reproduction - genetic recombination. In this case, an exchange of genetic information takes place and the result is a cell containing the genes of its parents. There are three ways to transfer genetic information:

• conjugation - direct transfer (not exchange) of a part of DNA upon contact from one bacterium to another (the process goes only in one direction);
• transduction - the transfer of a DNA fragment using a bacteriophage (bacteria virus);
• transformation is the absorption of the genetic information of dead or destroyed cells from the environment.

Thus, cells identical to each other are obtained only as a result of binary fission and budding. During genetic recombination, the cell undergoes changes, developing new properties and receiving other functions.

Speed ​​and phases of growth of microorganisms

In nutrient media, the growth and reproduction of bacteria take place in several stages, which differ in the amount of food available and the accumulation of waste products:

1. The first phase (latent) is determined by the factors of adaptation to the nutrient medium. At this time, microorganisms are just getting used to new conditions. Bacterial growth is not observed.
2. The second phase (exponential) is characterized by growth exponentially (increase along the exponential curve). During this period, bacterial cells actively grow using all available food (maximum growth rate). Having reached a certain size, the bacterium begins to divide, and the process of reproduction proceeds at a constant rate, since food supplies are still sufficient. As a result of the increased rate of growth and reproduction, waste products (toxins) accumulate in the environment. Towards the end of the phase, the growth rate begins to decrease.
3. The third phase is characterized by stationary growth, i.e. the number of "newborn" cells coincides with the number of dead ones. The curve of growth and reproduction in this segment no longer rises. The growth rate slows down. For some time, the total number of bacteria in the nutrient medium remains unchanged. However, due to the appearance of new "family members", nutrient reserves are reduced, and the toxicity of the environment increases. This process worsens the living conditions of the entire colony.
4. The fourth phase - the death of microorganisms - occurs as a result of a catastrophic decrease in food and an increase in the toxicity of the environment. The number of living organisms is steadily decreasing, eventually, there are fewer viable cells than their dead counterparts.

The rate of kinetic growth of a bacterial colony largely depends on the type of bacteria, the composition of nutrient media, the number of seeded (introduced into the medium) cells, the age of the culture, the method of respiration, and a number of other factors. For example, for the reproduction of lactic acid bacteria, it is important to maintain temperatures in a rather narrow range (25-30⁰С) and a certain level of acidity of the medium (pH). For the reproduction of aerobic and anaerobic cells, the presence or absence of oxygen for respiration becomes a decisive factor, and spore-forming cells need a sufficient amount of food.

Conditions for growing microbes in artificial environments

For study (medicine, microbiology) and use (industry), bacterial cultures are grown on artificial nutrient media, which are divided according to consistency, origin and purpose:

• liquid, semi-liquid and dense (solid) artificial media;
• animal, vegetable or synthetic media (chemically pure compounds in a strictly defined concentration);
• conventional (universal), differential (different types of bacteria), special, selective or enrichment media (suppressing the growth of unwanted microbes).

There are bacteria that require special conditions. For example, anaerobic microorganisms (both spore-forming and non-spore-forming) are cultivated under anaerobic conditions (without oxygen). For aerobic cells, oxygen becomes a decisive factor in reproduction. Facultative anaerobes are able to change the way they breathe depending on the conditions. The spore-forming aerobic organisms used to produce probiotics are very sensitive to reduced nutrition and quality. Spore-forming anaerobes require the complete absence of oxygen. The basic principle of cultivating microorganisms is the creation of favorable conditions (nutrition, respiration, temperature), which sometimes presents certain difficulties.

So, for the cultivation of anaerobes, the deep seeding method is used, i.e., the culture of bacteria is introduced into the depth of a dense nutrient medium, chemical substances that absorb oxygen are added to the growth atmosphere, or air is pumped out, replacing it with an inert gas. In the case of spore-forming bacteria, an inhibitor of protein synthesis is introduced into the nutrient medium, thereby stopping the spore formation process.

Cultivation of microorganisms

Cultivation refers to the artificial cultivation of cells under controlled conditions. The ultimate goal is to obtain a biological product from bacteria or with the help of bacteria. Such drugs can be therapeutic, diagnostic, prophylactic. There are several cultivation methods:

1. The stationary method is characterized by the constancy of the environment, there is no intervention in the process. However, with this method of cultivation in liquid nutrient media, anaerobic organisms give an insignificant yield.
2. The submerged culture method is used in industry to grow bacterial biomass. For this purpose, special containers are used. Growth factors are maintaining temperature and supplying nutrients to liquid media. In addition, if necessary, mixing or oxygen supply (for respiration of aerobic bacteria) is carried out.
3. The flow media method (industrial cultivation) is based on the constant maintenance of the culture in the exponential growth phase. This is achieved by the continuous supply of nutrients and the removal of toxic waste products from cells. This technology makes it possible to achieve the maximum yield of various biologically active substances (antibiotic preparations, vitamins, etc.).

One of the most important industrial preparations is the culture of lactic acid bacteria, which are used for the preparation of lactic ferment, sauerkraut, forage ensiling, and the production of a blood plasma substitute. To obtain a guaranteed end result, the resulting quality of lactic acid bacteria must be strictly controlled.

You need an appropriate nutrient medium and a preparation with a pure culture of lactic acid bacteria grown in the laboratory. Further, the cultivation process is left until the onset of the third phase (equilibrium), after which you can begin to collect the "harvest" of lactic acid bacteria.

bacterial overgrowth syndrome

Not always the growth of bacterial cells is beneficial, an excessive increase in the population of bacteria in the human body can be hazardous to health. Violation of the qualitative and quantitative composition of the intestinal microflora is called the clinical syndrome of bacterial overgrowth. Doctors say that it is not entirely correct to use the term "dysbacteriosis" to describe this process. The fact is that the number of anaerobic bacteria (bifidobacteria) useful for the body is really decreasing, but the number of conditionally pathogenic cells (for example, aerobic Escherichia coli) is increasing.

Various bacteria live in different parts of the gastrointestinal tract. In the small intestine, as you move, the composition of the microflora and the number of microorganisms gradually change. Aerobic (growing in an oxygen environment) species of bacteria gradually give way to anaerobic (oxygen-free environment). In the clinical syndrome of overgrowth, the bacterial spectrum shifts towards gram-negative (most pathogenic), facultative aerobic and anaerobic organisms.

As you approach the large intestine, the number of anaerobic bacteria (bifidobacteria and bacteroids) increases. The main representatives of the anaerobic microflora - bifidobacteria - are responsible for the synthesis of proteins, B vitamins, various acids and other substances necessary for life. Aerobic microorganisms (E. coli) produce a number of vitamins and acids involved in digestion and supporting immunity.

Lactic acid bacteria are another representative of the intestinal microflora. They belong to microaerophilic organisms, i.e. one of the factors for the growth and reproduction of lactic acid bacteria is oxygen, but in very small quantities. These microorganisms are responsible for regulating the acidity of the gastrointestinal tract, thereby inhibiting the growth of putrefactive bacteria.

Each type of bacteria performs its own, clearly defined function. With overgrowth syndrome, the fecal microflora that normally lives in the large intestine (E. coli or anaerobic cells) enters the small intestine. The quantitative and qualitative composition of the bacterial microflora changes, the performance of certain functions slows down or becomes impossible. There are conditions for the growth and reproduction of pathogenic bacteria.

Clinical criteria for the disease

The criterion for the development of bacterial overgrowth syndrome can be:

• indigestion, decreased immunity, changes in the acidity of the stomach;
• violation of the integrity of the intestinal tract;
• consequences of surgical intervention;
• diseases of the gastrointestinal tract;
• stress;
• uncontrolled intake of antibiotic drugs.

Clinical manifestations of bacterial overgrowth syndrome are easily confused with other diseases, often they overlap each other, completely distorting the picture. In such cases, it is possible to make a diagnosis only with the help of special tests aimed at identifying the overgrowth syndrome, which determine not only the number, but also the species of bacteria. This approach will allow you to select the necessary medications to correct the composition of the microflora.

Clinical symptoms of the disease:

• diarrhea and flatulence appear at an early stage of the disease;
• bloating and spasmodic pain;
• fatigue, weakness;
• fast weight loss.

Antibacterial drugs are used to treat overgrowth syndrome. In the future, to restore the microflora, probiotic and prebiotic preparations will be needed.

A wide variety of bacterial cells (autotrophs and heterotrophs, aerobic and anaerobic, spore-forming and non-spore-forming, etc.) dictates certain conditions for their reproduction. The basic principle of cultivation on an industrial scale is the strict control of environmental conditions and growth rates. In nature, there are rarely ideal environments for the development of microorganisms. Otherwise, bacteria would have filled all available space long ago.

The term "growth" when applied to microorganisms means an increase in the size of an individual, and "reproduction" - an increase in the number of individuals in a population. With the growth of a microbial cell, its volume increases much faster than the surface, so the distribution of nutrients in the cytoplasm of the cell becomes less efficient and the cell divides. Before dividing it, the DNA molecules are duplicated. Each daughter cell receives a copy of the mother's DNA.

The rate of reproduction of different microbes grown under the same conditions is different. For most bacteria, the generation period (time elapsed) rhoorganisms can use a wide range of oxidizable organic compounds, most often glucose. Energy is obtained from these compounds as a result of their oxidation, or, more precisely, the donation of electrons by them.

The totality of biochemical processes, as a result of which the energy necessary for the life of the cell is released, is called respiration, or biological oxidation. In relation to microorganisms, they speak of anaerobic and aerobic types of respiration.

Between two successive cell divisions) is on average 15-30 minutes; for example, for Escherichia coli - 15-17 minutes, causative agents of typhoid fever - 23 minutes, corynebacteria diphtheria - 34 minutes. Mycobacterium tuberculosis divides more slowly - once in 18 hours, spirochetes - in 10 hours.

The methods of reproduction in different groups of microorganisms are not the same: bacteria, rickettsia, spirochetes reproduce by transverse division into two equivalent individuals. Gram-positive bacteria divide by forming a septum that grows from the periphery to the center. In Mycobacterium tuberculosis, a transverse septum is formed inside the cell, then it splits into two layers and the cell is divided into two parts. Both the cytoplasmic membrane and the cell wall take part in the formation of the septum. Apparently, the mesosome, which is closely associated with the cytoplasmic membrane, takes an active part in the process of bacterial division. Gram-negative bacteria and rickettsia become thinner in the center and are divided by constriction into two individuals. Reproduction of nodule bacteria and fraicisella occurs by the formation of a kidney, which, in size, is smaller than the original cell. In bacteria, there is also a process of conjugation - a temporary connection of two individuals.

The growth of bacteria and spirochetes is not always accompanied by their division. Bile salts, soaps, penicillin, ultraviolet rays delay cell division, resulting in the formation of long filaments much larger than the original cells.
When bacteria are introduced into a nutrient medium, the phases of their growth and reproduction are distinguished, which are determined by the availability of available food sources and the accumulation of toxic metabolic products (Fig. 21).

The first phase - latent (lag phase) - corresponds to the adaptation of bacteria to new conditions of existence. During this period, the bacteria adapt to the nutrient medium, their growth is not observed.

The second phase is logarithmic growth (exponential), when the bacteria grow vigorously, increase, and upon reaching a certain size, they begin to divide into two daughter cells. Division during this period occurs at a constant rate. The average generation (or doubling) time for each type of bacteria is different. At this time, bacteria extract nutrients from the medium, as a result of which metabolic products begin to accumulate in it.

The third phase is stationary growth, during which the number of organisms in the culture remains constant all the time. During this period, the amount of nutrients in the nutrient medium decreases significantly, and the accumulation of metabolic products increases. Living conditions for microorganisms are becoming less and less favorable. The duration of the stationary phase is different for different bacteria.

The fourth phase is death, when bacterial cells become smaller and they die. At the end of this phase, the number of dying bacteria begins to prevail over the number of viable cells. The complete death of microbes in culture can occur in a few weeks or months, depending on the type of microbe, the reaction of the environment, and other factors.

The simplest can reproduce by transverse division, constriction into two equivalent individuals - amoeba and longitudinal division - trypanosomes, giardia, balantidia. Before dividing into two individuals, balantidia can exchange their nuclei - micronuclei (conjugation process), malarial plasmodium has an asexual and sexual development cycle.

Viruses reproduce (reproduce) only inside a living cell of the host organism.

The virus reproduction process consists of several stages:

1) penetration of the virus into the cell;

2) intracellular reproduction;

3) maturation of the virus and the formation of outer shells in some viruses; 4) isolation of the virus from the cell.

The process of virus penetration into a sensitive cell begins with its adsorption on the cell surface, which has specific viral receptors. The process of release of nucleic acid from the capsid and outer shells begins already in the cytoplasmic membrane of the cell and ends in the cytoplasm (influenza virus, vaccinia).

The phase of intracellular reproduction of the virus, or its reproduction, usually begins with the suppression of cellular macromolecular synthesis. All energy systems of the cell, its enzymes, RNA, ribosomes begin to work to reproduce the virus. The affected cell supplies the virus with nucleotides for building nucleic acids, amino acids for proteins. Replication (English replicate - copy, repeat) of viral RNA is carried out with the help of enzymes - polymerases, and the RNA molecule of the virus itself serves as a matrix. In DNA-containing viruses, specific RNA is synthesized on the DNA template in the cell nucleus, which then determines the synthesis of viral DNA and protein. Virus proteins are synthesized in the ribosomes of the cell.

The maturation of the viral particle, the conclusion of the viral nucleic acid in the capsid, occurs in the nucleus of the affected cell (herpesviruses, adenoviruses) or in the cytoplasm (variola group viruses, rhabdoviruses, picornaviruses). The formation of outer shells in myxoviruses, togaviruses occurs when passing through the cytoplasmic membrane of the host cell. The herpes virus receives part of its outer shell by passing through the membrane of the cell nucleus.

Isolation of the virus from the cell can occur in different ways. Myxoviruses and togaviruses, as they mature, can be secreted by the cell for hours without damaging it. The polio virus (which does not have an outer shell) is formed in the cell quickly, remains in it for a long time and is released instantly, in the form of a flash. The end result of the interaction between the virus and the host cell can be rapid destruction and death of the cell. Sometimes viruses can be present in a cell for a long time without causing its death, and remain in an infinite number of cell generations - latent viruses. In some cases, the virus can be destroyed by the cell without visible consequences for it (abortive viral infection).

Microbiology: lecture notes Tkachenko Ksenia Viktorovna

1. Growth and reproduction of bacteria

Bacterial growth is an increase in the size of a bacterial cell without increasing the number of individuals in the population.

Reproduction of bacteria is a process that ensures an increase in the number of individuals in a population. Bacteria are characterized by a high rate of reproduction.

Growth always precedes reproduction. Bacteria reproduce by transverse binary fission, in which two identical daughter cells are formed from one mother cell.

The process of bacterial cell division begins with the replication of chromosomal DNA. At the point of attachment of the chromosome to the cytoplasmic membrane (replicator point), an initiator protein acts, which causes the chromosome ring to break, and then its threads are despiralized. The filaments unwind and the second filament attaches to the cytoplasmic membrane at the pro-replicator point, which is diametrically opposed to the replicator point. Due to DNA polymerases, an exact copy of it is completed in the matrix of each strand. The doubling of genetic material is the signal for doubling the number of organelles. In septal mesosomes, a septum is being built, dividing the cell in half.

Double-stranded DNA spiralizes, twists into a ring at the point of attachment to the cytoplasmic membrane. This is a signal for the divergence of cells along the septum. Two daughter individuals are formed.

On dense nutrient media, bacteria form clusters of cells - colonies, different in size, shape, surface, color, etc. On liquid media, bacterial growth is characterized by the formation of a film on the surface of the nutrient medium, uniform turbidity or sediment.

Reproduction of bacteria is determined by the time of generation. This is the period during which cell division takes place. The duration of generation depends on the type of bacteria, age, composition of the nutrient medium, temperature, etc.

Phases of reproduction of a bacterial cell on a liquid nutrient medium:

1) initial stationary phase; the number of bacteria that got into the nutrient medium and is in it;

2) lag phase (rest phase); duration - 3-4 hours, bacteria adapt to the nutrient medium, active cell growth begins, but there is no active reproduction yet; at this time, the amount of protein, RNA increases;

3) phase of logarithmic multiplication; the processes of cell reproduction in the population are actively going on, reproduction prevails over death;

4) maximum stationary phase; bacteria reach the maximum concentration, i.e., the maximum number of viable individuals in the population; the number of dead bacteria is equal to the number of formed; there is no further increase in the number of individuals;

5) accelerated death phase; the processes of death prevail over the process of reproduction, since nutrient substrates in the environment are depleted. Accumulate toxic products, metabolic products. This phase can be avoided by using the flow culture method: metabolic products are constantly removed from the nutrient medium and nutrients are replenished.

From the book The Story of the Life of Fish author Pravdin Ivan Fyodorovich

Age and growth of fish Without knowing the growth rate and life span of trees, it is impossible to conduct forestry; without knowing the age and height of domestic animals, it is impossible to properly engage in cattle breeding. The arborist has long learned to determine the age of trees by annual

From the book Hydroponics for Amateurs author Salzer Ernst X

Why plant growth can stop If this happens, then you should immediately remember the "law of the minimum." What is meant by this? Let us allow ourselves a slight digression here and mentally imagine a family walk with small and older children. Family

From the book Microbiology: lecture notes author Tkachenko Ksenia Viktorovna

2. Nutrition of bacteria Nutrition is understood as the processes of entry and removal of nutrients into and out of the cell. Nutrition primarily ensures the reproduction and metabolism of the cell. Among the necessary nutrients, organogens are distinguished - these are eight

From the book Microbiology author Tkachenko Ksenia Viktorovna

2. Variability in bacteria There are two types of variability - phenotypic and genotypic. Phenotypic variability - modification - does not affect the genotype. Modifications affect the majority of individuals in a population. They are not inherited and over time

From the book Seeds of Destruction. The secret behind genetic manipulation author Engdahl William Frederick

6. Growth, reproduction, nutrition of bacteria Growth of bacteria is an increase in the size of a bacterial cell without an increase in the number of individuals in a population. Bacterial reproduction is a process that ensures an increase in the number of individuals in a population. Bacteria are characterized by high speed

From the book Ant, family, colony author Zakharov Anatoly Alexandrovich

Population Growth and National Security In April 1974, as the world drought and American agricultural policy were gaining momentum, Nixon's Cabinet Secretary of State and National Security Adviser Henry Kissinger sent out a

From the book Age Anatomy and Physiology author Antonova Olga Alexandrovna

GROWTH OF THE FAMILY AND THE IMPROVEMENT OF ITS ORGANIZATION To a certain extent, the structure is, as it were, the result of various aspects of life, the characteristics of the ant family. The structure finds a fairly complete expression of the composition of the community and its size, species features

From the book Ecology by Mitchell Paul

GROWTH OF FAMILY ADAPTABILITY The large size of the family is in itself an important new property. (Roughly to the same extent as the size of an individual). A large family is always more competitive, it is easier for it to defend its fodder plot from

From the book Escape from Loneliness author Panov Evgeny Nikolaevich

3.3. Growth and muscle work

From the book Journey to the land of microbes author Betina Vladimir

3.6. Spinal growth. The spine of an adult and a child The spine consists of 24 free vertebrae (7 cervical, 12 thoracic and 5 lumbar) and 9-10 non-free (5 sacral and 4-5 coccygeal). Free vertebrae, articulated with each other, are connected by ligaments, between which are

From the book Microcosm author Zimmer Carl

POPULATION GROWTH In one of the publications it was said that if the human population continued to grow at the current rate, then in 200 years a huge mass of people would rush into space at the speed of light. This, of course, will not happen; this is just a joke to show

From the book Genes and Development of the Body author Neifakh Alexander Alexandrovich

"Growth beyond the limits of the individual" So, before our eyes passed the main characters of a spectacular evolutionary performance, which brought many absolutely amazing creatures to the stage of life. With all those differences that give the indisputable originality of each vast

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Growth and reproduction of microorganisms As the famous French physiologist of the XIX century Claude Bernard said, life is creation. Living organisms differ from inanimate nature mainly in that they grow and reproduce. Their growth and reproduction is best observed in such

From the author's book

Microbes Accelerate Plant Growth Substances are formed in various plant organs that regulate and to a certain extent accelerate their growth. These substances include, for example, f3-indoleacetic acid (heteroauxin). It is interesting that heteroauxin is produced and isolated

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"Luxury growth" Escherichia coli lived in the body of our ancestors for millions of years even when these ancestors were not at all people. But it wasn't until 1885 that Homo sapiens and its inhabitants were officially introduced to each other. A German pediatrician named Theodor Escherich

From the author's book

1. Reproduction is growth, heredity and development Reproduction is one of the most specific and most complex properties of life. This is natural, since in evolution selection goes precisely to this ability: in the struggle for existence, those organisms win that