Growth and reproduction of microorganisms. Reproduction methods and speed

Reproduction of microorganisms is an increase in the concentration of microorganisms per unit volume of the environment, aimed at preserving the species.

Microorganisms are characterized by:

variety of reproduction methods;

switching from one method of reproduction to another;

possibility of simultaneous use of several methods;

high reproduction rate.

Methods of propagation of microorganisms

I.Sexual with reproduction method

observed only in eukaryotes.

II. Asexual methods of reproduction. Equal area binary transverse division (simple division, isomorphic division, mitosis)

observed in most unicellular microorganisms (bacteria, rickettsia, protozoa, yeast), as a result, two new daughter full-fledged individuals are formed, endowed with the genetic information of the mother cell, symmetrical in relation to the longitudinal and transverse axis, the mother cell itself disappears.

Moreover, in most Gram+ bacteria, division occurs through the synthesis of a transverse septum running from the periphery to the center (Fig. 63A). The cells of most Gram bacteria divide by cell constriction (the cell becomes thinner in the middle) (Fig. 63B). Budding (unequal binary fission) observed in representatives of the genera Francisella And Mycoplasma

and yeast-like fungi. During budding, the mother cell gives rise to a daughter cell: at one of the poles of the mother cell, a small outgrowth (bud) is formed, which increases in size during growth. Gradually, the bud reaches the size of the mother cell, after which it separates. The kidney CS is completely synthesized anew (Fig. 63B). During the budding process, symmetry is observed only in relation to the longitudinal axis. There are morphological and physiological differences between mother and daughter cells. The new daughter cell adapts better to changing conditions. Fragmentation of filamentous forms characteristic of the genus Francisella And.

Actinomyces Exospore formation typical for Streptomycetes

, yeast-like and mold fungi. A special development cycle Tia observed in. Only vegetative forms of chlamydia (reticular or initial bodies) are capable of dividing in the cells of the macroorganism. Their cycle, consisting of several divisions, ends with the formation of intermediate forms, from which elementary bodies are formed, giving rise to vegetative forms.

After destruction of the vacuole wall and the host cell, the elementary bodies are released and the cycle repeats. The cycle lasts 40–48 hours.

Multiple division described for one group of unicellular cyanobacteria. Multiple fission is based on the principle of equal-area binary fission. The difference is that in this case, after binary fission, the resulting daughter cells do not grow, but they undergo division again (Fig. 63D).

Multiple fission (schizogony)

also described in protozoa (malarial plasmodia): the nuclear material is divided into many nucleoli, surrounded by areas of cytoplasm, resulting in the formation of many daughter cells. Mechanism and phases of simple division

A. Growth to a certain degree of maturity. Cell growth is not unlimited and after reaching a certain size, the bacterial cell begins to divide. During division, cell growth slows down and begins again after division. B. Karyokinesis ( DNA replication and d

division of the nucleoid).

A signal comes from the mature cytoplasm that activates the initiator gene on the DNA. Microorganisms, under the influence of the initiator gene, synthesize an initiator protein, which acts on the replicator gene - a special section of DNA from which DNA doubling and division into two strands begins.

Normally, there is a certain temporal relationship between chromosome replication and bacterial cell division. Exposure to various chemicals and physical factors, leading to the suppression of DNA replication, also stops cell division. However, under certain conditions, the connection between both processes can be broken, and cells are able to divide in the absence of DNA synthesis.

B. Cytokinesis (cell division). In parallel with the replication of DNA molecules, membrane synthesis occurs next to the mesosome, in the area of ​​contact of DNA with the CPM. The formation of a septum leads to cell division. The moment that initiates cell division is the end of DNA replication. This leads to the separation of daughter DNA molecules and the formation of separate chromosomes. The newly formed daughter cells separate from each other.

Inhibition of membrane synthesis before the end of replication leads to disruption of the division process: the cell stops dividing and grows in length. In some bacteria, the formation of a septum does not lead to cell division: multilocular cells are formed.

D. Divergence of the resulting daughter cells occurs as a result of lysis of the middle layer of the CS. If, after repeated division in one plane, the cells do not diverge, chains of rod-shaped (Bacillus) or spherical(Streptococcus) cells or paired cells(Neisseria) . Cell separation is possible with the separation of one of the cells by moving along the surface of another, as a result of which the bacteria are located (randomly). Escherichia If, during separation, one of the daughter cells, without breaking away from the division point, moves along an arc, aV-shaped (form, Corynebacterium). Bifidobacterium After binary fission and divergence of cells in several planes, cell clusters of various shapes: (bunches Staphylococcus (), packages Sarcina ) (Fig. 65). If nucleoid division precedes cell division, polynucleoid microorganisms. Under the influence of unfavorable external factors (bile salts, UV rays, surfactants, antibiotics), cell division can stop while its growth continues. In this case, the formation of elongated threadlike

cells. Rice. 65.

Division of cocci- the time interval during which the number of bacteria doubles. The rate of reproduction of microorganisms and the generation period depend on the type of microorganism, the size and properties of the inoculum, the composition of the nutrient medium, its pH, aeration, incubation temperature, and other factors. Under favorable conditions, many microorganisms divide within 15–30 minutes (E. coli, S. typhi). In fastidious microorganisms, division occurs within 45–90 minutes (Streptococcus, form) and even after 18 hours (M. tuberculosis).

The term “growth” when applied to microorganisms means an increase in the size of an individual, and “reproduction” means an increase in the number of individuals in a population. As a microbial cell grows, its volume increases much faster than its surface, so the distribution of nutrients in the cell's cytoplasm becomes less efficient and the cell divides. Before dividing, DNA molecules double. 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 (the time elapsed) organisms can use a large set 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 set of biochemical processes, as a result of which the energy necessary for the life of a 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 E. coli - 15-17 minutes, typhoid pathogens - 23 minutes, Corynebacterium diphtheria - 34 minutes. Mycobacterium tuberculosis divides more slowly - once every 18 hours, spirochetes - every 10 hours.

The methods of reproduction in different groups of microorganisms are not the same: bacteria, rickettsia, spirochetes reproduce by transverse division into two equal individuals. Gram-positive bacteria divide by forming a septum growing 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, 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 into two individuals by the constriction. Reproduction of nodule bacteria and Fraicisella occurs through the formation of a bud, which is smaller in size than the original cell. Bacteria also have 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, and 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, their growth and reproduction phases 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 living conditions. During this period, the bacteria adapt to the nutrient medium and no growth is observed.

The second phase is logarithmic growth (exponential), when bacteria grow vigorously, increase in size, and upon reaching a certain size begin to divide into two daughter cells. Division during this period occurs at a constant rate. The average generation (or doubling) time for each bacterial species is different. At this time, bacteria extract nutrients from the environment, 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 varies among bacteria.

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

Protozoa can reproduce by transverse division, constriction into two equal individuals - amoebas, and by longitudinal division - trypanosomes, lamblia, balantidia. Before dividing into two individuals, balantidia can exchange their nuclei - micronuclei (the process of conjugation); the malarial plasmodium has an asexual and sexual development cycle.

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

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 surface of a cell that has specific viral receptors. The process of releasing nucleic acid from the capsid and outer shells begins 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 processes of 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, and 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 the matrix. In DNA-containing viruses, specific RNA is synthesized on a DNA matrix in the cell nucleus, which then determines the synthesis of viral DNA and protein. Viral proteins are synthesized in cell ribosomes.

The maturation of the viral particle, the enclosure of the viral nucleic acid in the capsid, occurs in the nucleus of the affected cell (herpesviruses, adenoviruses) or in the cytoplasm (smallpox viruses, rhabdoviruses, picornaviruses). The formation of outer shells in myxoviruses and 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 a virus from a 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) forms quickly in a cell, remains in it for a long time and is released instantly, in the form of an outbreak. The final 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 cellular generations - latent viruses. In some cases, the virus can be destroyed by the cell without visible consequences for it (abortive viral infection).

There are a number of factors that have a significant impact on the growth and development of all bacteria. 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.

Basic Concepts

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 reduced 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 an extensive colony weighing several tens of thousands of tons!

The growth of microorganisms was studied in closed tanks, where, being 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 principle of flow-through cultivation of microorganisms 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 species 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 to be 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 a five-hour 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 contamination 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.

The disease proceeds as follows. Salmonella rods enter the digestive tract. In the upper intestines they destroy part of the beneficial microflora, then begin to multiply in the small intestine. In this case, the work of this section of the gastrointestinal tract is disrupted, peristalsis suffers. Then the disease becomes acute, with intoxication of the body, dehydration, convulsions and acute renal failure. So it is very reckless to underestimate salmonellosis.

How to maintain the population of microorganisms in an aquarium

As already mentioned, the number of bacteria in water can increase dramatically. And this is not always a beneficial microflora. So that the fish and plants in the aquarium do not get sick, and the water remains clean and unclouded, there are special preparations that help beneficial microorganisms function or contain the necessary bacteria.

Aquarists strive to ensure that the protozoa responsible for the nitrogen cycle are always present in the aquatic environment. Preparations aimed at maintaining such microflora are responsible for ensuring that natural enzymes and colloids are replenished in the aquarium water. Damaged or diseased microorganisms, with such support, return to normal and regain their lost abilities.

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 types of aquarium bacteria 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.

The term "growth" refers to the increase in the cytoplasmic mass of an individual cell or group of bacteria as a result of the synthesis of cellular material (for example, protein, RNA, DNA). Having reached a certain size, the cell stops growing and begins to multiply.

The reproduction of microbes means their ability to reproduce themselves, to increase the number of individuals per unit volume. In other words, we can say: reproduction is an increase in the number of individuals in a microbial population.

Bacteria reproduce predominantly by simple transverse division (vegetative propagation), which occurs in different planes, with the formation of diverse combinations of cells (a bunch of grapes - staphylococci, chains - streptococci, compounds in pairs - diplococci, bales, bags - sarcina, etc.). The division process consists of a number of successive stages. The first stage begins with the formation of a transverse partition in the middle part of the cell (Fig. 6), initially consisting of a cytoplasmic membrane that divides the cytoplasm of the mother cell into two daughter cells. In parallel with this, a cell wall is synthesized, forming a full-fledged partition between the two daughter cells. In the process of bacterial division, an important condition is the replication (doubling) of DNA, which is carried out by DNA polymerase enzymes. When DNA doubles, hydrogen bonds are broken and two DNA helices are formed, each of which is located in the daughter cells. Next, the daughter single-stranded DNAs restore hydrogen bonds and again form double-stranded DNAs.

DNA replication and cell division occur at a certain speed inherent in each type of microbe, which depends on the age of the culture and the nature of the nutrient medium. For example, the growth rate of E. coli ranges from 16 to 20 minutes; in Mycobacterium tuberculosis, division occurs only after 18-20 hours; Mammalian tissue culture cells require 24 hours. Consequently, bacteria of most species multiply almost 100 times faster than tissue culture cells.

Types of bacterial cell division. 1. Cell division precedes division, which leads to the formation of “multicellular” rods and cocci. 2. Synchronous cell division, in which the division and fission of the nucleoid are accompanied by the formation of single-celled organisms. 3. Nucleoid division precedes cell division, causing the formation of multinucleoid bacteria.

The separation of bacteria, in turn, occurs in three ways: 1) breaking separation, when two individual cells, repeatedly breaking at the junction, break the cytoplasmic bridge and repel each other, and chains are formed (anthrax bacilli); 2) sliding separation, in which after division the cells separate and one of them slides over the surface of the other (individual forms of Escherichia); 3) secant division, when one of the divided cells with its free end describes an arc of a circle, the center of which is the point of its contact with another cell, forming a Roman quinque or cuneiform (Corynebacterium diphtheria, l hysteria).

Phases of bacterial population development. Theoretically, it is assumed that if bacteria are provided with conditions for a continuous influx and progressive increase in the mass of fresh nutrient medium and the outflow of excretory products, then reproduction will increase logarithmically, and death arithmetically.

The general pattern of growth and reproduction of a bacterial population is usually shown graphically in the form of a curve that reflects the dependence of the logarithm of the number of living cells on time. A typical growth curve is S-shaped and allows one to distinguish several growth phases that follow each other in a certain sequence:

1. Initial (stationary, latent, or resting phase). Represents the time from the moment bacteria are inoculated on a nutrient medium until they grow. During this phase, the number of living bacteria does not increase and may even decrease. The duration of the initial phase is 1-2 hours.

2. Reproduction delay phase. During this phase, bacterial cells grow rapidly but reproduce weakly. The period of this phase takes about 2 hours and depends on a number of conditions: the age of the crop (young crops adapt faster than old ones); biological characteristics of microbial cells (bacteria of the intestinal group are characterized by a short period of adaptation, while mycobacterium tuberculosis is characterized by a long period); the usefulness of the nutrient medium, growing temperature, CO2 concentration, pH, degree of aeration of the medium, redox potential, etc. Both phases are often combined with the term “lag phase” (English lag - lag, delay).

3. Logarithmic phase. In this phase, the rate of cell reproduction and increase in bacterial population is maximum. The generation period (Latin generatio - birth, reproduction), i.e. the time elapsed between two successive divisions of bacteria, at this stage will be constant for a given species, and the number of bacteria will double in geometric progression. This means that at the end of the first generation, two bacteria are formed from one cell, at the end of the second generation, both bacteria, dividing, form four, eight are formed from the resulting four, etc. Consequently, after n generations, the number of cells in the culture will be equal to 2n. The duration of the logarithmic phase is 5-6 hours.

4. Negative acceleration phase. The rate of bacterial reproduction ceases to be maximum, the number of dividing individuals decreases, and the number of deaths increases (duration about 2 hours). One of the possible reasons that slow down the proliferation of bacteria is the depletion of the nutrient medium, that is, the disappearance from it of substances specific to a given bacterial species.

5. Stationary maximum phase. In it, the number of new bacteria is almost equal to the number of dead ones, i.e., an equilibrium occurs between dead cells and newly formed ones. This phase lasts 2 hours.

6. Acceleration phase of death. It is characterized by a progressive superiority of the number of dead cells over the number of newly born ones. It lasts about 3 hours.

7. Logarithmic death phase. Cell death occurs at a constant rate (duration about 5 hours).

8. Phase of decreasing rate of death. The surviving cells go into a state of rest.

№ 10 Growth and reproduction of bacteria. Reproduction phases.
The vital activity of bacteria is characterized by growth - the formation of structural and functional components of the cell and the increase in the bacterial cell itself, as well as reproduction- self-reproduction, leading to an increase in the number of bacterial cells in the population.
Bacteria multiply by binary fission in half, less often by budding. Actinomycetes, like fungi, can reproduce by spores. Actinomycetes, being a branching tankteria, reproduce by fragmentation of filamentous cells. Gram-positive bacteria divide by ingrowth of synthesized division septa into the cell, and gram-negative bacteria by constriction, resulting in the formation of dumbbell-shaped figures from which two identical cells are formed.
Cell division is preceded byreplication of the bacterial chromosome according to a semi-conservative type (the double-stranded DNA strand opens and each strand is completed by a complementary strand), leading to doubling of the DNA molecules of the bacterial nucleus - the nucleoid.
DNA replication occurs in three stages: initiation, elongation, or chain growth, and termination.
Reproduction of bacteria in a liquid nutrient medium. Bacteria seeded in a certain, unchanging volume of the nutrient medium, multiplying, consume nutrients, which subsequently leads to the depletion of the nutrient medium and the cessation of bacterial growth. Cultivation of bacteria in such a system is called batch cultivation, and the culture is called batch culture. If the cultivation conditions are maintained by continuous supply of fresh nutrient medium and the outflow of the same volume of culture fluid, then such cultivation is called continuous, and the culture is called continuous.
When bacteria are grown on a liquid nutrient medium, bottom, diffuse or surface (in the form of a film) growth of the culture is observed. The growth of a batch culture of bacteria grown in a liquid nutrient medium is divided into several phases, or periods:
1. lag phase;
2. logarithmic growth phase;
3. phase of stationary growth, or maximum concentration of bacteria;
4. bacterial death phase.
These phases can be depicted graphically in the form of segments of a bacterial reproduction curve, reflecting the dependence of the logarithm of the number of living cells on the time of their cultivation.
Lag phase - the period between the sowing of bacteria and the beginning of reproduction. The duration of the lag phase is on average 4-5 hours. At the same time, the bacteria increase in size and prepare to divide; the amount of nucleic acids, proteins and other components increases.
Logarithmic (exponential) growth phaseis a period of intense bacterial division. Its duration is about 5-6 hours. Under optimal growth conditions, bacteria can divide every 20-40 minutes. During this phase, bacteria are most vulnerable, which is explained by the high sensitivity of the metabolic components of an intensively growing cell to inhibitors of protein synthesis, nucleic acids, etc.
Then comes the stationary growth phase, at which the number of viable cells remains unchanged, constituting the maximum level (M-concentration). Its duration is expressed in hours and varies depending on the type of bacteria, their characteristics and cultivation.
The death phase completes the bacterial growth process., characterized by the death of bacteria under conditions of depletion of sources of nutrient medium and accumulation of bacterial metabolic products in it. Its duration ranges from 10 hours to several weeks. The intensity of bacterial growth and reproduction depends on many factors, including the optimal composition of the nutrient medium, redox potential, pH, temperature, etc.
Reproduction of bacteria on a solid nutrient medium. Bacteria growing on dense nutrient media form isolated round-shaped colonies with smooth or uneven edges ( S- and R -shape), varying consistency and color, depending on the pigment of the bacteria.
Water-soluble pigments diffuse into the nutrient medium and color it. Another group of pigments is insoluble in water, but soluble in organic solvents. And finally, there are pigments that are insoluble neither in water nor in organic compounds.
The most common pigments among microorganisms are carotenes, xanthophylls and melanins. Melanins are insoluble black, brown or red pigments synthesized from phenolic compounds. Melanins, along with catalase, superoxide dismutase and peroxidases, protect microorganisms from the effects of toxic oxygen peroxide radicals. Many pigments have antimicrobial, antibiotic-like effects.