IV. Periods (stages) of organism development
When growing bacteria in a liquid nutrient medium, several phases of crop growth are observed:
1. Initial (latent) phase - microbes adapt to the nutrient medium, cell size increases. Towards the end of this phase, bacteria begin to multiply.
2. Phase of logarithmic incubation growth - intensive cell division occurs. This phase lasts about 5 hours. At optimal conditions a bacterial cell can divide every 15-30 minutes.
3. Stationary phase - the number of newly appeared bacteria is equal to the number of dead ones. The duration of this phase is expressed in hours and varies depending on the type of microorganism.
4. The dying phase is characterized by cell death under conditions of depletion of the nutrient medium and the accumulation of metabolic products of microorganisms in it.
The seed material, once in a fresh, complete environment, does not immediately begin to reproduce. This period is called lag phase I. Only after a certain time, sometimes several hours, do cells adapt to the environment and environmental conditions. During this period, enzymes are activated, and, if necessary, new enzyme systems are synthesized. During the lag phase, the number of nucleic acids, especially RNA, which is necessary for the biosynthesis of proteins.
Rice. 1. Growth phases of microorganism culture: I - lag phase, II - logarithmic phase, III - slow growth phase, IV - stationary phase, V - death phase, N - number of cells (millions/ml)
After the lag phase comes the logarithmic, or exponential, phase II, in which cells multiply at the maximum rate for a given culture. As a result, the supply of necessary nutrients in the environment decreases, in addition, there is an accumulation of various metabolic products, which in a certain concentration can interfere with the normal course of biochemical metabolic processes. Sometimes so many cells accumulate in the nutrient medium that there is not enough space, or more specifically, surface, for new generations of cells. It is through the surface that metabolic processes occur - the entry of nutrients into the cell and the excretion of metabolites. If a cell is in close surroundings of other cells, then the surface area decreases and at the same time the intensity of metabolic processes decreases. The growth rate of the culture also decreases if the cell surface per unit volume is reduced. This occurs with an increase in cell size and, thus, especially for spherical cells, nutritional conditions deteriorate significantly.
As is known, the surface of spherical bodies varies proportionally to the square of their radius, and the volume is proportional to the cube of the radius. Limiting surfaces are obviously located inside cells. In molecular biology, more and more facts are accumulating that indicate that the functioning of life processes must be associated with biopolymers, membrane structures and their surface.
During intensive growth and reproduction within closed system Negative influence limiting factors increases and, as a result, the growth rate decreases, and phase III of slow growth begins. After a certain time in stationary phase IV, the mass of cells in the nutrient medium reaches its maximum level. Then comes a period when the number of dead and autolyzed cells exceeds the increase. As a result, the amount of biomass decreases - the dying phase V begins.
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The life of an organization proceeds according to certain laws: the formation stage is replaced by a stage of intensive growth, which can go into a stage of stabilization, and then decline.
The stage of intensive growth and consolidation in the market is characterized by the organization’s orientation towards expanding the circle of consumers, suppliers and partners, as well as the formation of its own style (image).
Dynamic growth (intensive growth stage)
Intensive growth stage
The organization managed to get through the most difficult period - the formation stage. A new idea was formulated, a product was found, funds were received, production was established, and the product entered the market. The project was well thought out, the enterprise started working, and the number of consumers began to increase significantly. You can be happy that the organization is growing, more and more new clients are appearing. However, this is already the next stage of the formation of an organization - a stage of intensive growth.
However, the most significant problem facing human resource management is the problem of erosion of corporate culture. During a period of intense growth, an organization may include many more personnel than in previous stages. If an organization was able to reach the stage of intensive growth, found its consumer, and remained in the market, of course, there is a lot of productive things in the corporate culture; it can give the organization an incentive for further growth. But with the arrival of new employees who previously worked in other companies and enterprises, the HR manager is faced with the problem of maintaining the productivity and integrity of the corporate culture, its values, borrowing all the most interesting things, including them in the culture, but not allowing group ideas to die under the pressure of many new ideas.
The next crisis situation awaits an organization moving from the stage of intensive growth to the stage of stabilization. Let's call it a crisis of maturity. The stabilization stage requires specialists capable of creating effective technologies, recording (again in technological schemes) the most successful approaches discovered during the intensive growth of the
At the stage of intensive growth, personnel management is mainly aimed at the formation of personnel - attracting and hiring personnel, assessing candidates, placing and adapting newcomers.
Rotation. For some organizations, especially those in the stage of intensive growth, the use of managerial staffing, such as the transfer of managers, is considered very effective. The following options for relocating managers are possible:
Analysis of the presented dependencies shows that the most intensive increase in the cost of oil production for Devonian fields begins approximately after 70% of the recoverable oil reserves are withdrawn, and for fields with more complex geological structure and high-viscosity oils - somewhat earlier (after 50%), i.e. in both cases at a late stage of operation.
The patterns of dynamics of the cost of oil production for most oil fields developed under active water-pressure conditions are very similar in nature and are largely determined by the stage of field development. At the late stage of development, the level of cost of oil production is greatly influenced by the water cut of well production. An increase in the water cut of the extracted liquid is reflected in the cost of oil production, mainly in changes in variable costs. In conditions of intensive growth of water cut, variable costs largely determine the level and nature of the dynamics of the cost of oil production. These include energy costs, costs of collecting, transporting and preparing oil and increasing reservoir recovery. In this regard, a multifactor analysis of the cost of oil production in terms of only variable costs, taking into account the stage of field development, is of particular interest. The main focus of the analysis is on identifying the impact of an increase in the water cut of the extracted liquid on the level and dynamics of variable costs. Other factors are also taken into account.
The considered examples show the need to take into account the requirements of the sphere of consumption of new equipment in the process of its design. This will make it possible to create technology with exactly the parameters that society really needs. In order to take into account consumer requirements for the designed equipment, you need to know, first of all, the general patterns of changes in its parameters. These laws are based on the law of mutual transition of quantitative and qualitative changes, which shows how technology develops, and the law of the negation of negation, which reveals the direction in which this development occurs. The evolutionary stage of development of technology parameters includes three stages. The first, in which the emergence of new technology occurs, is characterized by an insignificant growth rate of its pa-
As a rule, experts, despite ongoing discussions, agree that the full life cycle of an organization necessarily includes such stages as the formation of an organization, its intensive growth or reproduction, stabilization and crisis (recession)1. Moreover, the last stage does not necessarily have to end with the death or liquidation of the organization. The option of its revival or transformation is also considered quite possible (Fig. 6.1).
An organization can survive and move on to the next development cycle only if it can find a new product that is attractive to consumers and occupy a new place in the market. If this is successful, then in a transformed form it can again experience the stages of formation, intensive growth and stabilization, which will inevitably be replaced by a new crisis. In the development of an organization, crises are inevitable. According to management consultants, even the most conservative companies, characterized by a stable position in the market, experience crises at least once every 50-60 years. For changing Russian conditions, the development stage can last a year and a half, and often several months. The main ones especially - A"3- 3 stories successful companies allowing the target orientation to highlight the following main features of the organization’s target orientation at various
In order to use personnel more effectively, personnel management must think through a system of career planning, formation of a personnel reserve, organization of training and promotion of personnel. It is in a situation of stability that staff begin to perceive career plans and plans for increasing remuneration as reasonable and real tools for planning their lives. At the stage of formation and intensive growth, such personnel tools seem unfounded and too distant.
Evolutionary processes also lead to certain expected changes in the behavior of existing competitors in the market. First, the intensity of competition is initially low, since rapid growth makes the competition win-win - everyone can grow. However, later, as market growth slows and incumbent firms increase production, competition becomes more intense. Secondly, on last stage During the growth phase, more aggressive competitors begin to pursue repositioning strategies that force them to compete directly with firms originally located in other strategic groups.
In the years following the Second World War, department stores' share of the retail trade declined and their profitability declined. Many then believed that department stores had entered a decline in their life cycle as retailers. Experts pointed to 1) increased competition between department stores, which caused an increase in costs, 2) increased competition from other types retail enterprises, especially discount stores, specialty store chains, and retail warehouse stores; and 3) heavy traffic, lack of parking, and urban degeneration
The biggest strategic mistake, says M. Porter, is the desire to chase all the rabbits, that is, to use all competitive strategies at the same time. In other words, according to M. Porter, a company that has not made a choice between strategies - to be a cost leader or to engage in differentiation, risks being stuck in the middle. Such companies try to achieve advantages based on both low cost and differentiation, but in fact they don't get anything. Poor performance results from the fact that a cost leader, a differentiator, or a firm with a focused strategy will have better position in the market to compete in any segment. The firm stuck in the middle will receive a significant share of the profits only if the industry situation is extremely favorable, or if all other firms are in a similar position. Rapid growth in the early stages of an industry's life cycle may allow such firms to obtain a good return on their investment, but as the industry matures and as competition becomes more intense, those firms that have not made a choice between existing alternative strategies , risk being forced out.
Main positive point economic growth - its impact on changes in the structure of production and consumption. With an intensive path, many countries are generally characterized by a general pattern and sequence of development on initial stage In the total volume of output and the structure of employment, the share of agricultural production is rapidly declining, the process of urbanization is underway, the volumes and share in the structure of the economy of industrial sectors are growing, with advanced dynamics, as noted, of progressive industries, then comes the era of services, which in some countries reaches half of GDP.
At the pre-monopoly stage of capitalism, there was an acceleration in population growth due to a decrease in mortality from infectious diseases(plague, cholera, smallpox). They claimed a huge number of human lives in the feudal era. Migration processes during this period occurred very intensively. An example is the colonization of America.
One of the most important indicators The rational structure of the herd is the correct ratio of individual sex and age groups of animals. Promotion specific gravity cows in a large herd cattle contributes to an increase in the intensity of reproduction and turnover of livestock, creates opportunities for a more rapid increase in production.
The stage of developed socialism is characterized by the presence of gigantic economic, scientific and technical potential, and the task is to ensure that it is used with maximum efficiency. This can only be achieved on the basis of IP. That's why the party modern stage communist construction aims at a decisive transition to predominantly intensive factors of economic growth. The main path to a qualitative shift in the productive forces, noted Yu. V. Andropov at the June (1983) Plenum of the CPSU Central Committee, is, of course, a transition to intensive
Microorganisms, once in a fresh, complete nutrient medium, do not immediately begin to reproduce. This period is called the lag phase - Phase I(Fig. 3.1). During this period, the culture seems to get used to new living conditions. Enzyme systems are activated, if necessary, new enzyme systems are synthesized, the cell prepares for the synthesis of nucleic acids and other compounds. The duration of this phase depends on the physiological characteristics of microorganisms, the composition of the nutrient medium and cultivation conditions. The smaller these differences are and the more seed, the shorter this phase.
II phase called the accelerated growth phase, it is characterized by the beginning of cell division, an increase in the total mass of the population and a constant increase in the growth rate of the culture; it usually doesn't last long.
This is followed by a logarithmic or exponential growth phase - III phase. During this period, the maximum growth rate of the crop is observed; the intervals between the appearance of the previous and subsequent generations are constant. The logarithm of the number of cells depends linearly on time.
Due to the intensive growth and reproduction of the crop, the supply of essential nutrients in the environment decreases. This is the main reason for the reduction in crop growth rate. In addition, metabolic products accumulate in the environment, which in a certain concentration can interfere with the normal course of biochemical metabolic processes. Sometimes so many cells are formed in the nutrient medium that there is not enough space, or rather, surface, for new generations of cells. The growth rate decreases, the number of cell divisions decreases, IV phase– phase of slowing down or decreasing the growth rate.
Rice. 3.1. Growth curve of microorganisms (dependence of the number of cells on the cultivation time): I, II, III, IV, V, VI, VII – growth phases
V phase called stationary (linear growth phase). The mass and number of all living cells reaches a maximum. The number of newly formed cells at this stage is equal to the number of cells that have died and autolyzed (destroyed by cellular enzymes).
At some point, this balance is disrupted, and the number of dead cells exceeds the growth. Coming VI phase– phase of accelerated death.
The cycle of growth and development of the population in a closed volume ends VII phase, characterized by the death and autolysis of microorganisms, which is called the death phase. At this stage, cell biomass decreases significantly, as the cell's reserve substances are exhausted.
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.
Bacteria growing on dense nutrient media form isolated round-shaped colonies with smooth or uneven edges (S- and R-forms), of varying consistency and color, depending on the pigment of the bacteria. Water-soluble pigments diffuse into the nutrient medium and color it, for example Pseudomonas aeruginosa ( Pseudomonas aeruginosa) colors the medium in Blue colour. Another group of pigments is insoluble in water, but soluble in organic solvents. So, the colonies wonderful wand"have a blood-red pigment that is soluble in alcohol. And finally, there are pigments that are insoluble neither in water nor in organic compounds.
The inherent properties of living matter are growth and development. Under development in a broad sense, one should understand the process of quantitative and qualitative changes leading to an increase in the complexity of the organization of a living system. During the development of multicellular animals, growth, differentiation of organs and tissues, and morphogenesis occur (the organism acquires characteristic forms inherent to it). These processes are closely interconnected and interdependent.
The development of an organism consists of 3 natural processes:
1. Growth process (weight, body length changes)
2. Actually differentiation - acquisition characteristic features tissues and organs.
3. Shaping - changing the proportions of the body.
One of the main features of the development of a child, in contrast to an adult, is height, those. a process characterized by a continuous increase in the size and mass of organs and the body as a whole. Moreover, in some organs (bones, lungs) growth is carried out mainly due to an increase in the number of cells, in others (muscles, nerve tissue) the processes of increasing the size of the cells themselves predominate. There are three periods of accelerated growth in children: up to 1 year, from 6 to 7 years, from 11 to 15 years. During the first year, the child’s body length increases by an average of 25 cm, and his weight increases by 6-7 kg. This stage of ontogenesis is often called the period of first extension. After each “leap” of growth, a period of intensive differentiation of organs and tissues begins, which is called the rounding period (on average from 1 year to 3 years). A new increase in growth rates is observed again at 6-7 years - the period of the second extension. Annual body growth at this time can be 7-10 cm. Then a slowdown in growth is observed again - the second rounding period (from 7 to 10-11 years). Finally, an increase in growth rates is observed during puberty - the third period of extension (from 11-12 to 15-16 years). In subsequent years, the growth rate decreases, and in women it stops at approximately 18-22 years, and in men at 20-25 years. Despite the changing periods of growth and maturation, these processes occur continuously for 20-25 years.
Features of development processes:
1. Continuity of development – development is continuous.
2. Heterochrony – different times in the development of individual organs and systems.
3. Harmony of development - organs must correspond to the requirements of the environment.
The growth and development of all organs and physiological systems of the body of children occurs unevenly and non-simultaneously, i.e. heterochronically (from the Greek heteros - other, chronos - time).
Doctrine of heterochrony was developed by P.K. Anokhin. He found that maturation different systems occurs unevenly, they are switched on step by step, depending on the needs of the body and its activity, providing a more adequate adaptation to different periods ontogeny.
First of all, those organs whose functioning is vital for the body develop and improve. For example, the heart functions already in the third week of prenatal development, and the kidneys form much later and come into effect only in the newborn child. In addition to heterochrony, A.A. Markosyan to general patterns ontogenesis attributed the formation and increase in reliability biological systems. Under reliability It is generally accepted to understand this level of regulation of processes in the body when their optimal course under normal conditions and the emergency mobilization of reserve capabilities under the influence of extreme factors are ensured, which guarantees adaptation to new conditions, followed by a rapid return of physiological processes to their original state. According to this concept, the entire developmental path from conception to the natural end requires a reserve of life opportunities. These backup capabilities ensure optimal flow of life processes under changing conditions external environment. For example, femur can withstand a load of 1500 kg, which is 30 times the normal load, a huge amount nerve cells(more than 15 billion) are considered as one of the possible factors of the reliability of the nervous system. The biological reliability of the body is achieved through several mechanisms: interchangeability of organs and structures (in blind people the sensitivity of the organs of hearing, smell, and touch increases significantly); duplication of many processes (removal of metabolic products from the body is carried out by the kidneys, lungs, skin, gastrointestinal tract), pairing of a number of organs (lungs, kidneys, auditory, visual analyzers, some endocrine glands); “cold reserve” (all organs and systems under normal conditions do not work at the limit of their capabilities, only 5-8% of the alveoli of the lungs are involved in breathing, not all capillaries are open and used in the blood circulation process). Thus, the harmony of development is characterized by the fact that at each age stage of ontogenesis functionality the bodies of children and adolescents meet the requirements imposed on them by the environment. The basis for the selection stages of human development features of morphological, physiological, mental development, the peculiarities of education, training in different stages child development, etc. All these schemes, in connection with the schemes that child development is a continuous process and there are no sharp boundaries between age periods, are conditional. However, for pedagogical purposes, in order to study the age-related anatomical and physiological characteristics of children of different ages, such classifications are very important.
I. Embryonic (prenatal).
In human ontogenesis there are two relatively independent stage: prenatal and postnatal. The first lasts 280 days or 10 lunar months and covers the period from the moment of conception to the birth of the child, the second begins with birth and ends with the death of a person.
II. Postembryonic, or postnatal - from birth to death.
1. Stage – infant 0-1 year.
a) newborns – 10-30 days
b) breastfeeding – up to one year.
2. Pre-school (nursery) – from 1 to 3 years.
3. Preschool – from 3 to 6-7 years.
4. Junior school age – from 6-11 girls, 6-13 boys
5. Adolescence (puberty) – 12-16 years old girls, 14-17 years old boys.
6. Youth age – from 17-20 years old girls, 18-21 years old boys.
7. Adult age – from 21-22 to women 55 years old, men 60 years old.
8. Elderly – up to 74 years old.
9. Senile - up to 90 years old.
10. Long-livers - from 90 years old.
Stage I. Infant (0-1 year)
The most characteristic feature of the first stage of child development is ongoing biological connection with mother , its inability to exist independently. The child feeds on mother's milk, is helpless, and needs constant care.
At the beginning of stage I, they distinguish neonatal period – the first 2-3 weeks of a child’s life. During this period, the child finds himself in new conditions of existence, adapts to environment. This adaptation occurs with great stress on all physiological functions. Fluctuations in body temperature reach 1.5-2 degrees due to imperfect thermoregulation mechanisms. Redness of the skin appears. Physiological weight loss is observed. A newborn can lose 100-400 g. If this period of adaptation to the environment goes well, then after 2-3 weeks the child’s rapid growth begins.
In the first year of life, body length increases by 1.5 times and body weight by 3 times. For example, a child at birth had a height of 50 cm, then by the end of the year the height will increase by 25 cm and reach 75 cm. If the weight of the newborn was 3-3.5 kg, then by the end of the year he will weigh 9-10 kg.
From the age of 6 months, baby teeth begin to grow. By the end of the year, the child has 8 baby teeth.
Tissue differentiation in a child of the first year of life is poorly expressed. Shaping is also imperfect. It has a relatively large head, long body, short arms and legs.
The imperfection of differentiation and morphogenesis also determines the imperfection of physiological functions. For the first 2-3 months, there is no control of the cerebral cortex over the skeletal muscles and the child’s movements are chaotic. Voluntary movements and motor skills develop gradually. At 3 months the child holds his head - a cervical curve has formed. By 6 months he can sit independently – thoracic curve. At 6-7 months he begins to crawl on all fours, at 9 months he begins to walk holding on to objects, at the age of one year he begins to walk independently - a lumbar curve is formed.
Breathing is frequent and shallow, ineffective for ventilation of the lungs.
Regulation of functions is mainly due to unconditioned reflexes, i.e. according to the principle of deviation. By the end of the first year of life, a child usually knows no more than 10 words.
The leading activity at the first stage of a child’s development is emotional communication with adults.
In the absence of emotional communication, the child lags behind in mental development.
Stage II – nursery. (1-3 years).
A characteristic feature of the second stage of child development is cessation of the biological connection with the mother and the formation of a second signal system of reality, i.e. speech system.
Stage I is biological birth child, and stage II is social birth of a child.
At stage II of development, growth rates slow down, and the processes of differentiation and morphogenesis intensify. The differentiation of analyzers is especially intensive. By the age of three, taste, smell and skin sensitivity become almost the same as in adults. The sense of smell can be even sharper. In the second year of life, the child begins to distinguish colors: first, the primary colors are distinguished - green, red, blue, and then mixed ones.
Thanks to the differentiation of muscle tissue, the locomotor act is formed. At 2 years old there is still no difference between walking and running. The child walks quickly and has short strides. At 3 years old, running and walking are differentiated, but they are still imperfect.
By the end of 2 years, the child already has all 20 baby teeth.
The processes of differentiation and formation in the brain are intense. The neurons of the cerebral cortex take on the shape of an adult; the cerebral hemispheres have all the grooves and convolutions. However, the frontal lobes are less developed compared to the other lobes.
The formation of a second signaling system is proceeding rapidly. By the end of the 2nd year of life, the child already knows about 400 words, and by the end of the 3rd year - about 1000. First, the child learns the names of objects, i.e. nouns, then actions of objects, i.e. verbs, then the names of the properties of objects and phenomena, i.e. adjectives, then prepositions and conjunctions. Then phrases begin to form from words, at first primitive and short.
The formation of the second signaling system occurs only in social environment, in the company of people. If a child is isolated from society, then the 2nd alarm system is not formed. Therefore, at the second stage of development, the child becomes social being .
At this stage active research activities child. Indicative reflex “What is it?” As a result of actions with an object, images of objects are created. That is, as a result of object-manipulative activity, images and imaginative thinking are formed. By the end of the stage, the first concepts are formed on the basis of images: doll, table, bed, etc.
Leading activities at the second stage of development – social communication and object-manipulative activities.
Table of contents of the topic "Respiration (aerobic, anaerobic). Catabolism in bacteria. Constructive metabolism (plastic metabolism). Growth of bacteria in culture.":1. Propionic acid fermentation. Butyric acid and acetone butyl fermentation. Homoacetate fermentation. Energy production by oxidative phosphorylation. Breath.
2. Catabolism of carbohydrates in bacteria. Glycolysis. Glycolytic oxidation pathway. The Embden-Meyerhof-Parnassus path. Pentose phosphate oxidation pathway. Warburg-Dickens-Horecker-Racker scheme.
3. Entner-Doudoroff pathway in bacteria. Krebs cycle. The tricarboxylic acid cycle in bacteria.
4. Catabolism of nitrogen-containing organic compounds by bacteria. Amino acids. Decarboxylation and deamination of amino acids by bacteria. Stickland mechanism.
5. Catabolism of fats and fatty acids by bacteria. Endogenous energy metabolism of bacteria.
6. Constructive metabolism (plastic metabolism). Carbon compounds for biosynthetic reactions of bacteria. Biosynthesis of amino acids and proteins by bacteria.
7. Biosynthesis of nucleotides and nucleic acids by bacteria.
8. Biosynthesis of oligosaccharides and polysaccharides by bacteria. Biosynthesis of lipids (fats) by bacteria.
9. Regulation of microbial metabolism. Allosteric proteins.
Actually under bacterial growth usually involve the coordinated replication of all bacterial components. Since the division of a bacterial cell leads to the formation of two individuals, their number grows exponentially: 2 0 -2 1 -2 2 -2 3 -..2 n. The quality of the nutrient medium and growing conditions have a regulatory effect on the growth of bacteria.
Cell Population Growth in a limited living space (periodic culture) can be divided into at least four phases(Figure 4-12).
Rice. 4-12. Bacterial culture growth.After being introduced into the environment, bacteria adapt to its conditions and multiply relatively slowly ( lag phase). Then comes exponential growth phase (exponential phase). Further, the environment is depleted, toxic metabolic products accumulate in it, which is manifested by a decrease in the rate of reproduction and a cessation of increase in the number of cells ( stationary phase).
Thus, growth in periodic culture obeys laws that are valid not only for unicellular, but also for multicellular organisms. Subsequently, the bacterial culture may die or be significantly reduced (die-off phase). Spore-forming species enter the sporulation stage; in non-spore-forming species, the formation of anabiotic forms is possible (see below). In some cases, a growth acceleration phase (the beginning of the exponential phase) and a growth deceleration phase (the transition to the stationary phase) are additionally distinguished.
Lag phase of bacterial growth corresponds to a period of physiological adaptation, including enzyme induction, synthesis and assembly of ribosomes. The duration of the phase depends mainly on the age of the inoculum of bacteria and the previous cultivation conditions. If the inoculum is taken from an old culture (in the stationary growth phase), then the bacteria need time to adapt to new conditions. If the sources of energy and carbon in the new environment differ from those available in the previous culture, then adaptation to new conditions may require the synthesis of new enzymes that were not previously needed.
Exponential phase of bacterial growth (logarithmic) is characterized maximum speed cell division. For a particular species of bacteria under specific growth conditions, the generation time (that is, the time required for the number of bacteria to double) is constant throughout the logarithmic phase, but varies among various types and strains, and also depends on the composition of the medium and cultivation conditions. The generation time on the optimal medium can be short (for E. coli 20 minutes) or long (for Mycobacterium tuberculosais 6 hours). In this phase, the maximum accumulation of bacterial metabolites (for example, toxins, bacteriocins) occurs in the medium.
Stationary phase of bacterial growth. During this period, the availability of essential nutrients becomes a limiting factor. A balance is established between cell growth and division and the process of cell death. Spore-forming bacteria (for example, the genera Bacillus and Clostridium) are able to enter the sporulation phase, which is activated when the bacteria are in conditions of limited nutrition. At a certain point, the ratio of dying, newly formed and resting cells becomes stable; such a state is known as the maximum stationary phase. The biomass of bacteria in the stationary phase is referred to as the “yield” or “biomass yield” (the difference between the maximum and initial biomass); or “economic coefficient”, if the increase in biomass is related to a unit of growth-limiting substrate.
Dieback phase (recession, lysis) includes a period of logarithmic death, which turns into a period of decreasing rate of bacterial death. The reasons for the death of bacteria in normal nutrient media are not completely clear. It is understandable that acids accumulate in the medium (during the growth of Escherichia, Lactobacillus). Sometimes bacteria are destroyed by their own enzymes (autolysis). The rate of death varies widely depending on the living conditions and characteristics of the microorganism (for example, enterobacteriaceae die off slowly, and bacilli die off quickly).