Biological adaptation (from Lat. Adaptatio - adaptation) - adaptation of a microorganism to external conditions in the process of evolution, including morphophysiological and behavioral components. Adaptation can ensure survival in a specific habitat, resistance to the effects of abiotic and biological factors, as well as success in competition with other species, populations, and individuals. Each species has its own ability to adapt, limited by physiology (individual adaptation).
Disadaptation - any violation of adaptation, adaptation of the body to the constantly changing conditions of the external or internal environment. A state of dynamic discrepancy between a living organism and the external environment, leading to a violation of physiological functioning, a change in forms of behavior, the development of pathological processes. A complete discrepancy between the body and the external conditions of its existence is incompatible with life. The degree of maladjustment is characterized by the level of disorganization of the functional systems of the body. Depending on the nature of the functioning, there are two forms of maladjustment: - non-pathological: maintaining homeostasis is possible with a mode of enhanced, but "normal" physiological functioning; - pathological: maintaining homeostasis is possible only during the transition to pathological functioning.
Adaptations of species within the same biocenosis are often closely related to each other. If the adaptation process in any species is not in equilibrium, then the entire biocenosis can evolve (sometimes with negative consequences) even in stable environmental conditions.
The main content of adaptation, according to T. Pilate, is the internal processes in the system, which ensure the preservation of its external functions in relation to the environment. If the structure of the system ensures its normal functioning in the given environmental conditions, then such a system should be considered adapted to these conditions. At this stage, dynamic equilibrium is established.
Examples of adaptation: in freshwater protozoa, the osmotic concentration of protoplasm is higher than that of the surrounding water. When water is absorbed, it is constantly desalinated. The disturbed osmotic balance is regulated by the activity of the contractile vacuole, which removes excess water from the body. Some protozoa are able, however, to adapt to life in saltier and even seawater. At the same time, the activity of the contractile vacuole in them slows down and may even completely stop, since under these conditions the excretion of water from the body would lead to an increase in the relative concentration of ions in the protoplasm and, in connection with this, to a violation of the osmotic balance in it. Thus, in this case, the adaptation mechanism is reduced to a direct physicochemical reaction of protoplasm. In other cases, the adaptation mechanism seems to be more complex and cannot always be immediately decomposed into elementary factors. Such, for example, are the adaptation of animals to temperature conditions (lengthening of mammalian fur under the influence of cold), to the phenomena of radiant energy (phototropism of plants); discoloration of the skin of cold-blooded, due to the reaction of pigment cells; seasonal dimorphism of the color of birds and mammals; change in their color depending on climatic and geographical conditions, etc. However, here, too, the adaptation mechanism can ultimately be reduced to physicochemical reactions of protoplasm. The phenomena of adaptation are closely related to the evolution of microorganisms and represent one of the most essential factors of acclimatization, struggle for existence and mimicry.
Adaptation of microorganisms, accommodation of microorganisms, their adaptation to the environment. Their structure, physiological properties and chemical composition depend both on the hereditary properties of a given species and on environmental influences. The latter cause the microorganism to change. Until recently, these changes were considered random and, according to the teachings of Conn, little significant for the main features of the microorganism, which were recognized as inviolable. However, over time, at first timidly, and then more and more decisively, the doctrine of the variability of microorganisms as a biological factor was put forward, and at present, changes in microorganisms are no longer considered only random, but are recognized as deeper. The nature of the variability of a microorganism depends on two factors: on the individual species resistance of a given microorganism and on the depth, scope and strength of the environment. Some types of microorganisms, such as the acid-resistant group, diphtheria and fungal forms, change less and adapt less well, while the enteric-typhoid, capsular, coccal, anaerobic groups undergo changes more easily. The adaptability of microorganisms primarily affects their relationship to oxygen and ambient temperature. It is known that anaerobes can be accustomed to both free oxygen and vice versa. The same must be said about the relation to the ambient temperature, as well as to the reaction of the environment, to the action of light and the chemical composition of the nutrient material. One condition must be met to detect this adaptation: the gradual impact of new factors. The slower and more gradual the new conditions act, the easier and more perfect the microorganism adapts. This adaptation goes in different directions. Environmental conditions force the microorganism to become less demanding in its physiological functions, to limit them to a minimum and pass into the stage of suspended animation ("latent microbism"), for which it forms spores, and it is surrounded by impenetrable mucous, calcareous and connective tissue capsules (cocci, tubes. sticks, etc.); or microorganisms undergo morphological changes, losing whole organs and parts that are especially sensitive to normal conditions (for example, trypanosomes, accustomed to arsenic, lose blepharoblasts (Verbitsky)), and thus new races of microorganisms are obtained. The formation of new races with new properties occurs especially easily when a microorganism meets new chemical substances in an organism in which it is accustomed to multiply freely. When harmful substances appear in such an environment, some of the microorganisms die, and the most resistant individuals survive and give the so-called “resistant” or “resistant” races (Enrlich). Such resistance has been proven in relation to various chemical compounds and alkaloids (arsenic, alcohol, quinine). - The adaptability of microorganisms can also go in the opposite direction - towards increasing their viability and acquiring greater activity. So, a little virulent microorganism, under the influence of a weakening of the body, begins to multiply rapidly and produce toxins that it did not have or had little before. An example of this is the numerous cases of so-called endogenous infections, when pneumococcus, under the influence of a cold, causes pneumonia or Bact. coli, under the influence of an error in the diet, causes dysentery-like disease. This "activation" of a microorganism is nothing more than its adaptation to new conditions. The phenomena of adaptation are particularly well studied and numerous where the microorganism meets the immune organism or immune environments. In addition to the above capsules, which serve as a protective layer for the microbe from the external environment, aggressins begin to be produced in the microorganism, which make it little accessible to phagocytes. The adaptability of microorganisms goes so far that they can become resistant even to immune sera. Bordet showed in 1895 how Vibrio cholerae can be accustomed to bacteriolytic serum. A number of authors have proven the ability to accustom agglutinating microorganisms to the fact that they cease to agglutinate. Conversely, nonaglutinable microorganisms can be converted into agglutinating microorganisms, for example, by passing through the body of animals and even with simple subcultures from medium to medium. Reconstructing their morphological and physiological features, microorganisms, depending on the soil on which they live, and depending on other microorganisms that multiply next to it, can acquire the features inherent in a neighbor and turn into a so-called "paramicrobe". Such a microorganism, as Rosenow proved, can acquire new properties obtained by it from cohabitation with a pathogenic microorganism, and retain them for a long time by inheritance. So, for example, streptococcus, isolated from meningitis caused by Weichselbaum's diplococcus, acquires the ability to give meningitis. It turns out, as it were, an imitation of another pathogen. This imitation is expressed either in the ability to cause the same disease or in the acquisition of new antigenic properties. So, Proteus, living in the body of a typhoid patient, begins to agglutinate with the patient's serum, although it is not the causative agent of the disease. From all the above facts, it is clear how important the phenomena of adaptation of microorganisms are for pathology and epidemiology.
Evolution of bacteria and its medical significance. Microorganisms on Earth originated about three billion years before the appearance of man. In 1822 E. Darwin proposed the theory of evolution, and 100 years later the Russian biochemist A. Oparin (1920) - the theory of the origin of biological life. In this system, bacteria have a very important place. The first self-replicating forms of biological life (protobionts) surrounded by a membrane were incapable of photosynthesis and received energy through simple, one-step abiogenic oxidative reactions. This lasted for about 1.0 billion years. The energy (electrochemical, thermal, photochemical) generated in these reactions was stored in certain molecules and used to carry out primitive processes. The formation of primary molecules and reactions laid the foundation for metabolic processes - anabolism and catabolism. The transition from protocell to prokaryotic cell took place in the interval of 2.5-3 billion years ago. There was no oxygen in the planet's atmosphere and the primary prokaryotes were anaerobes. The autotrophic CO 2 fixation pathway was the basis of primary productivity on the planet. The change from a reducing atmosphere to an oxygen one took place between the Middle and Late Precambrian (2.8 billion years ago). For comparison, the oxygen content in the planet's atmosphere 800 million years ago was about 1%, 400 million years ago it was already 10%, and now it is 21%. As the composition of the atmosphere changed, facultative phototrophic and heterotrophic anaerobes began to form, and later aerobic bacteria arose.
Bacteria were not only the primary accumulators of genes, but the object of their evolutionary improvement. The rate of evolution is the number of mutations per 100 amino acids of a particular protein molecule over 100 million years. It varies widely. This is the basis of the concept of a molecular clock, which declares that mutations gradually accumulate in the genome and form a new sequence for the further divergence of the species linearly with the time period of evolution. The diagram shown in Fig. 3. allows you to display the evolution of certain groups of bacteria and approximately establish the evolutionary time when a particular species (genus) diverged from a common ancestor.
The rate of evolution is constant and depends on many factors - the rate of metabolic processes, generation time, information flows, and selective pressure. For example, the divergence of the genus Salmonella and the genus Escherichia coli from a common ancestor occurred about 100-140 million years ago. Bacterial genomes have evolved over more than 50 billion generations, accumulating mutations and acquiring new genetic information through horizontal gene transfer without significant rearrangement of ancestral genes. During the year, the Salmonella genome acquired foreign genetic information of approximately 16 kb / million. years, and Escherichia coli - 22 kb / million years. Currently, their genomes differ by 25%. A significant part of the genome was acquired through horizontal transfer. In general, the bacterial genome varies in size from 0.6 to 9.4 Mb of information (on average, from 3 to 5 Mb). Some bacteria have two chromosomes (Leptospira interrogans serovar icterohemorrahgiae, Brucellae melitensis). The progressive evolution of bacteria took place in several interrelated directions - metabolic, morphological (structural-molecular), and ecological. In nature, there is a huge variety of microorganisms of which no more than 5-7% of them are currently known, and bacteria cultivated under artificial conditions make up about 1%. This means that we are just beginning to get to know the world of microbes.
Genome sequencing strategies. Each base pair of a genome is one bit of information. For example, the genome of Haemophilus influenzae contains 1,830,137, and the genome of Escherichia coli contains 4,639,221 bits of information. Comparative aspects of sequencing of bacterial genomes make it possible to determine the presence of common genes, regulatory mechanisms, to establish evolutionary intra and interspecific relationships and are the basis of structural and evolutionary genomics. A new science, bioinformatics, is engaged in mathematical analysis of the genomes of microorganisms. The subject of research is the sequences of fragments or complete genomes of bacteria using the developed computer programs and databases of information on nucleic acids and proteins.
Based on the analysis of the structure of genomes (sequencing) formed 36-40 large taxa (divisions). The members of each of them have a common ancestor, which at a certain stage diverged from another predecessor taxon. Some of the divisions include more species of known bacteria than others. This usually applies to those of them that are well cultivated in the laboratory. The largest number of bacterial species (from 40 to 80%) is described among taxa of proteobacteria, actinobacteria, gram-positive bacteria with a low G + C content. At the same time, in some departments, the cultivated representatives of bacteria are unknown. It should be noted that out of 36-40 divisions of the kingdom Bacteria, only representatives of 7 large taxa are capable of causing diseases in humans. The specialization and adaptation of these bacteria to the animal organism led to the formation of gene blocks that control pathogenicity factors (pathogenicity islands). They can be localized in the chromosome, plasmids and, possibly, in bacterial phages. Establishing the direction and order of evolution of microorganisms based on the variability of their genomes is a promising area of molecular epidemiology.
Bacteria are the oldest group of organisms currently existing on Earth. The first bacteria appeared, probably more than 3.5 billion years ago, and for almost a billion years were the only living things on our planet. Since these were the first representatives of living nature, their body had a primitive structure.
Over time, their structure has become more complex, but to this day bacteria are considered the most primitive unicellular organisms. Interestingly, some bacteria still retain the primitive features of their ancient ancestors. This is observed in bacteria that live in hot sulfur springs and anoxic silts at the bottom of reservoirs.
Most bacteria are colorless. Only a few are colored purple or green. But the colonies of many bacteria have a bright color, which is due to the release of a colored substance into the environment or pigmentation of cells.
The pioneer of the world of bacteria was Anthony Leeuwenhoek, a Dutch naturalist of the 17th century, who was the first to create a perfect magnifying glass microscope that magnifies objects 160-270 times.
Bacteria are classified as prokaryotes and are isolated into a separate kingdom - Bacteria.
Body shape
Bacteria are numerous and varied organisms. They vary in shape.
| Name of bacteria | Bacteria shape | Bacteria image |
| Cocchi | Spherical | |
| Bacillus |  | Rod-shaped |
| Vibrio | Comma curved | |
| Spirillum |  | Spiral |
| Streptococci |  | Cocci chain |
| Staphylococci |  | Bunches of cocci |
| Diplococci | Two round bacteria enclosed in one mucous capsule |
Modes of movement
Among bacteria, there are mobile and immobile forms. The mobile ones move due to wave-like contractions or with the help of flagella (twisted helical filaments), which consist of a special flagellin protein. There can be one or several flagella. They are located in some bacteria at one end of the cell, in others - on two or over the entire surface.
But the movement is inherent in many other bacteria in which flagella are absent. So, bacteria covered with mucus on the outside are capable of sliding movement.
Some aquatic and soil bacteria devoid of flagella have gas vacuoles in the cytoplasm. There can be 40-60 vacuoles in a cell. Each of them is filled with gas (presumably nitrogen). By regulating the amount of gas in the vacuoles, aquatic bacteria can submerge in the water column or rise to its surface, and soil bacteria can move in the capillaries of the soil.
Habitat
Due to the simplicity of organization and unpretentiousness, bacteria are widespread in nature. Bacteria are found everywhere: in a drop of even the purest spring water, in grains of soil, in the air, on rocks, in polar snows, desert sands, on the ocean floor, in oil extracted from great depths and even in hot springs with a temperature of about 80 ° C. They live on plants, fruits, in various animals and in humans in the intestines, mouth, on the limbs, on the surface of the body.
Bacteria are the smallest and most numerous living things. Due to their small size, they easily penetrate into any cracks, crevices, pores. They are very hardy and adapted to various conditions of existence. They tolerate drying, severe cold, heating up to 90 ° C, without losing their viability.
There is practically no place on Earth where bacteria would not be found, but in different quantities. The living conditions of bacteria are diverse. One of them needs oxygen in the air, others do not need it and are able to live in an oxygen-free environment.
In the air: bacteria rise up to 30 km into the upper atmosphere. and more.
There are especially many of them in the soil. One year of soil can contain hundreds of millions of bacteria.
In water: in the surface layers of water in open reservoirs. Beneficial aquatic bacteria mineralize organic residues.
In living organisms: pathogenic bacteria enter the body from the external environment, but only in favorable conditions cause disease. Symbiotic lives in the digestive organs, helping to break down and assimilate food, synthesize vitamins.
External structure
The bacterial cell is dressed in a special dense shell - the cell wall, which performs protective and supporting functions, and also gives the bacteria a permanent characteristic shape. The cell wall of a bacterium resembles the membrane of a plant cell. It is permeable: through it, nutrients freely pass into the cell, and metabolic products go out into the environment. Often on top of the cell wall, bacteria develop an additional protective layer of mucus - a capsule. The thickness of the capsule can be many times the diameter of the cell itself, but it can be very small. The capsule is not an obligatory part of the cell; it is formed depending on the conditions in which the bacteria enter. It prevents bacteria from drying out.
On the surface of some bacteria there are long flagella (one, two, or many) or short thin villi. The length of the flagella can be many times the size of the bacterial body. With the help of flagella and villi, bacteria move.
Internal structure
Inside the bacterial cell there is a dense, immobile cytoplasm. It has a layered structure, there are no vacuoles, therefore, various proteins (enzymes) and reserve nutrients are located in the very substance of the cytoplasm. Bacterial cells do not have a nucleus. In the central part of their cells, a substance is concentrated that carries hereditary information. Bacteria, - nucleic acid - DNA. But this substance is not formed into a nucleus.
The internal organization of a bacterial cell is complex and has its own specific features. The cytoplasm is separated from the cell wall by the cytoplasmic membrane. In the cytoplasm, a basic substance, or matrix, ribosomes and a small number of membrane structures that perform a variety of functions (analogs of mitochondria, endoplasmic reticulum, Golgi apparatus) are distinguished. The cytoplasm of bacterial cells often contains granules of various shapes and sizes. Granules can be composed of compounds that serve as a source of energy and carbon. Fat droplets are also found in the bacterial cell.
In the central part of the cell, a nuclear substance is localized - DNA, not delimited from the cytoplasm by a membrane. This is an analogue of the nucleus - a nucleoid. The nucleoid does not have a membrane, nucleolus and a set of chromosomes.
Meals
Bacteria have different ways of feeding. Among them are autotrophs and heterotrophs. Autotrophs are organisms that can independently form organic matter for their nutrition.
Plants need nitrogen, but they themselves cannot assimilate nitrogen from the air. Some bacteria combine nitrogen molecules in the air with other molecules to make substances available to plants.
These bacteria settle in the cells of young roots, which leads to the formation of thickenings called nodules on the roots. Such nodules are formed on the roots of plants of the legume family and some other plants.
The roots provide the bacteria with carbohydrates, and the bacteria provide the roots with nitrogen-containing substances that can be absorbed by the plant. Their cohabitation is mutually beneficial.
The roots of plants secrete many organic substances (sugars, amino acids, and others) that bacteria feed on. Therefore, a particularly large number of bacteria settle in the soil layer surrounding the roots. These bacteria convert dead plant residues into substances available to the plant. This layer of soil is called the rhizosphere.
There are several hypotheses about the penetration of nodule bacteria into the root tissue:
- through damage to the epidermal and crustal tissue;
- through root hairs;
- only through the young cell membrane;
- thanks to satellite bacteria that produce pectinolytic enzymes;
- by stimulating the synthesis of B-indoleacetic acid from tryptophan, which is always present in the root secretions of plants.
The process of introducing nodule bacteria into the root tissue consists of two phases:
- root hair infection;
- the process of nodule formation.
In most cases, the invading cell actively multiplies, forms the so-called infectious filaments, and already in the form of such filaments moves into the plant tissue. Nodule bacteria released from the infection thread continue to multiply in the host tissue.
Plant cells filled with rapidly multiplying cells of nodule bacteria begin to divide rapidly. The connection of a young nodule with the root of a legume plant is carried out thanks to the vascular-fibrous bundles. During the period of functioning, the nodules are usually dense. By the time of the manifestation of optimal activity, the nodules acquire a pink color (due to the pigment leghemoglobin). Only those bacteria that contain leghemoglobin are capable of fixing nitrogen.
Nodule bacteria create tens and hundreds of kilograms of nitrogen fertilizers per hectare of soil.
Metabolism
Bacteria differ from each other in their metabolism. In some, it goes with the participation of oxygen, in others - without its participation.
Most bacteria feed on ready-made organic matter. Only a few of them (blue-green, or cyanobacteria) are capable of creating organic substances from inorganic ones. They played an important role in the accumulation of oxygen in the Earth's atmosphere.
Bacteria absorb substances from the outside, tear their molecules apart, from these parts they collect their shell and replenish their contents (this is how they grow), and unnecessary molecules are thrown out. The shell and membrane of the bacterium allows it to absorb only the necessary substances.
If the shell and membrane of the bacteria were completely impermeable, no substances would enter the cell. If they were permeable to all substances, the contents of the cell would mix with the environment - the solution in which the bacterium lives. For the survival of bacteria, a shell is needed that allows the necessary substances to pass through, but not unnecessary ones.
The bacterium absorbs the nutrients nearby. What happens next? If it can move independently (by moving the flagellum or pushing back mucus), then it moves until it finds the necessary substances.
If it cannot move, then it waits until diffusion (the ability of molecules of one substance to penetrate into the midst of molecules of another substance) brings the necessary molecules to it.
Bacteria, in conjunction with other groups of microorganisms, do an enormous amount of chemical work. By transforming various compounds, they receive the energy and nutrients necessary for their life. Metabolic processes, methods of obtaining energy and the need for materials for building the substances of their body in bacteria are diverse.
Other bacteria satisfy all the requirements for carbon necessary for the synthesis of organic substances in the body at the expense of inorganic compounds. They are called autotrophs. Autotrophic bacteria are able to synthesize organic substances from inorganic ones. Among them are distinguished:
Chemosynthesis
The use of radiant energy is the most important, but not the only way to create organic matter from carbon dioxide and water. Bacteria are known that use not sunlight as an energy source for such synthesis, but the energy of chemical bonds occurring in the cells of organisms during the oxidation of certain inorganic compounds - hydrogen sulfide, sulfur, ammonia, hydrogen, nitric acid, ferrous compounds of iron and manganese. They use the organic matter formed with the use of this chemical energy to build the cells of their body. Therefore, this process is called chemosynthesis.
The most important group of chemosynthetic microorganisms are nitrifying bacteria. These bacteria live in the soil and carry out the oxidation of ammonia formed during the decay of organic residues to nitric acid. The latter, reacts with mineral compounds of the soil, turns into nitric acid salts. This process takes place in two phases.
Iron bacteria convert ferrous iron into oxide. The formed iron hydroxide settles and forms the so-called bog iron ore.
Some microorganisms exist by oxidizing molecular hydrogen, thus providing an autotrophic way of feeding.
A characteristic feature of hydrogen bacteria is the ability to switch to a heterotrophic lifestyle when they are provided with organic compounds and in the absence of hydrogen.
Thus, chemoautotrophs are typical autotrophs, since they independently synthesize the necessary organic compounds from inorganic substances, and do not take them ready-made from other organisms, like heterotrophs. Chemoautotrophic bacteria differ from phototrophic plants by their complete independence from light as an energy source.
Bacterial photosynthesis
Some pigment-containing sulfur bacteria (purple, green), containing specific pigments - bacteriochlorophylls, are capable of absorbing solar energy, with the help of which hydrogen sulfide in their organisms breaks down and releases hydrogen atoms to restore the corresponding compounds. This process has much in common with photosynthesis and differs only in that in purple and green bacteria, hydrogen sulfide is the donor of hydrogen (occasionally - carboxylic acids), and in green plants - water. In both cases, the elimination and transfer of hydrogen is carried out due to the energy of absorbed solar rays.
This bacterial photosynthesis, which occurs without the release of oxygen, is called photoreduction. Photoreduction of carbon dioxide is associated with the transfer of hydrogen not from water, but from hydrogen sulfide:
6СО 2 + 12Н 2 S + hv → С6Н 12 О 6 + 12S = 6Н 2 О
The biological significance of chemosynthesis and bacterial photosynthesis on a planetary scale is relatively small. Only chemosynthetic bacteria play an essential role in the sulfur cycle in nature. Absorbed by green plants in the form of sulfuric acid salts, sulfur is reduced and is part of protein molecules. Further, when dead plant and animal residues are destroyed by putrefactive bacteria, sulfur is released in the form of hydrogen sulfide, which is oxidized by sulfur bacteria to free sulfur (or sulfuric acid), which forms sulfites available for the plant in the soil. Chemo- and photoautotrophic bacteria are essential in the nitrogen and sulfur cycle.
Spore formation
Spores form inside the bacterial cell. In the process of sporulation, a bacterial cell undergoes a number of biochemical processes. The amount of free water in it decreases, the enzymatic activity decreases. This ensures the resistance of the spores to unfavorable environmental conditions (high temperature, high salt concentration, drying, etc.). Sporulation is characteristic of only a small group of bacteria.
Spores are not an essential stage in the life cycle of bacteria. Spore formation begins only with a lack of nutrients or the accumulation of metabolic products. Bacteria in the form of spores can be dormant for a long time. Bacterial spores can withstand prolonged boiling and very long freezing. With the onset of favorable conditions, the spore germinates and becomes viable. Bacterial spore is an adaptation to survival in adverse conditions.
Reproduction
Bacteria multiply by dividing one cell into two. Having reached a certain size, the bacterium divides into two identical bacteria. Then each of them begins to feed, grows, divides, and so on.
After cell elongation, a transverse septum is gradually formed, and then the daughter cells diverge; in many bacteria, under certain conditions, the cells after division remain linked into characteristic groups. In this case, depending on the direction of the division plane and the number of divisions, different shapes arise. Reproduction by budding occurs in bacteria as an exception.
Under favorable conditions, cell division in many bacteria occurs every 20-30 minutes. With such a rapid reproduction, the offspring of one bacterium in 5 days is able to form a mass that can fill all seas and oceans. A simple calculation shows that 72 generations can be formed in a day (720,000,000,000,000,000,000 cells). If translated into weight - 4720 tons. However, this does not happen in nature, since most bacteria quickly die under the influence of sunlight, during drying, lack of food, heating to 65-100 ° C, as a result of the struggle between species, etc.
The bacterium (1) that has absorbed enough food increases in size (2) and begins to prepare for reproduction (cell division). Its DNA (in a bacterium, the DNA molecule is closed in a ring) doubles (the bacterium produces a copy of this molecule). Both DNA molecules (3,4) turn out to be attached to the wall of the bacterium and, when the bacteria elongate, diverge to the sides (5,6). The nucleotide is divided first, then the cytoplasm.
After the divergence of two DNA molecules, a constriction appears on the bacteria, which gradually divides the bacterial body into two parts, each of which contains a DNA molecule (7).
It happens (in a hay stick), two bacteria stick together, and a bridge is formed between them (1,2).
Through the bridge, DNA is transported from one bacterium to another (3). Once in one bacterium, DNA molecules intertwine, stick together in some places (4), after which they exchange sections (5).
The role of bacteria in nature
The cycle
Bacteria are the most important link in the general circulation of substances in nature. Plants create complex organic substances from carbon dioxide, water and mineral salts of the soil. These substances return to the soil with dead fungi, plants and animal corpses. Bacteria break down complex substances into simple ones, which are used by plants again.
Bacteria destroy complex organic matter of dead plants and animal corpses, excretions of living organisms and various waste products. Feeding on these organic substances, saprophytic rotting bacteria turn them into humus. These are kind of orderlies of our planet. Thus, bacteria are actively involved in the cycle of substances in nature.
Soil formation
Since bacteria are widespread almost everywhere and are found in huge numbers, they largely determine the various processes that occur in nature. In autumn, the leaves of trees and shrubs fall, aerial shoots of grasses die off, old branches fall off, from time to time the trunks of old trees fall. All this gradually turns into humus. In 1 cm 3. The surface layer of forest soil contains hundreds of millions of saprophytic soil bacteria of several species. These bacteria convert humus into various minerals that can be absorbed from the soil by plant roots.
Some soil bacteria are able to absorb nitrogen from the air, using it in life processes. These nitrogen-fixing bacteria live independently or settle in the roots of legumes. Having penetrated the roots of legumes, these bacteria cause the growth of root cells and the formation of nodules on them.
These bacteria release nitrogen compounds that plants use. Bacteria receive carbohydrates and mineral salts from plants. Thus, there is a close relationship between the legume plant and the nodule bacteria, which is beneficial to both one and the other organism. This phenomenon is called symbiosis.
Thanks to their symbiosis with nodule bacteria, legumes enrich the soil with nitrogen, helping to increase the yield.
Distribution in nature
Microorganisms are ubiquitous. The only exceptions are craters of active volcanoes and small areas in the epicenters of exploded atomic bombs. Neither the low temperatures of Antarctica, nor boiling jets of geysers, nor saturated solutions of salts in salt pools, nor strong insolation of mountain peaks, nor severe irradiation of nuclear reactors interfere with the existence and development of microflora. All living things constantly interact with microorganisms, being often not only their repositories, but also distributors. Microorganisms are the aborigines of our planet, actively assimilating the most incredible natural substrates.
Soil microflora
The number of bacteria in the soil is extremely large - hundreds of millions and billions of individuals per gram. There are much more of them in the soil than in water and air. The total number of bacteria in soils varies. The number of bacteria depends on the type of soil, their condition, the depth of the layers.
On the surface of soil particles, microorganisms are located in small microcolonies (20-100 cells in each). They often develop in thick clots of organic matter, on living and dying plant roots, in thin capillaries, and inside lumps.
The microflora of the soil is very diverse. There are different physiological groups of bacteria: rotting bacteria, nitrifying, nitrogen-fixing, sulfur bacteria, etc. among them there are aerobes and anaerobes, spore and non-spore forms. Microflora is one of the factors of soil formation.
The area of development of microorganisms in the soil is the area adjacent to the roots of living plants. It is called the rhizosphere, and the totality of microorganisms contained in it is called the rhizosphere microflora.
Microflora of reservoirs
Water is a natural environment where microorganisms grow in large numbers. Most of them enter the water from the soil. A factor that determines the number of bacteria in water, the presence of nutrients in it. The cleanest are artesian wells and spring waters. Open reservoirs and rivers are very rich in bacteria. The greatest number of bacteria is found in the surface layers of the water, closer to the coast. With increasing distance from the coast and increasing depth, the number of bacteria decreases.
Pure water contains 100-200 bacteria in 1 ml., And polluted water - 100-300 thousand and more. There are many bacteria in the bottom sludge, especially in the surface layer, where bacteria form a film. This film contains many sulfur and iron bacteria, which oxidize hydrogen sulfide to sulfuric acid and thereby prevent fish from being killed. The silt contains more spore-bearing forms, while non-spore-bearing forms prevail in the water.
In terms of species composition, the microflora of water is similar to the microflora of soil, but there are also specific forms. Destroying various wastes that have got into the water, microorganisms gradually carry out the so-called biological purification of water.
Microflora of air
The microflora of the air is less abundant than the microflora of soil and water. Bacteria rise into the air with dust, can stay there for some time, and then settle to the surface of the earth and die from lack of nutrition or under the influence of ultraviolet rays. The number of microorganisms in the air depends on the geographic zone, terrain, season, dust pollution, etc. each speck of dust is a carrier of microorganisms. Most of all bacteria are in the air above industrial plants. The air in the countryside is cleaner. The cleanest air over forests, mountains, snowy spaces. The upper layers of the air contain fewer germs. There are many pigmented and spore-bearing bacteria in the microflora of the air, which are more resistant than others to ultraviolet rays.
Microflora of the human body
The human body, even a completely healthy one, is always a carrier of microflora. When a person's body comes into contact with air and soil, various microorganisms settle on clothes and skin, including pathogenic ones (tetanus sticks, gas gangrene, etc.). Most often, exposed parts of the human body are contaminated. Escherichia coli, staphylococci are found on the hands. There are over 100 types of microbes in the oral cavity. The mouth with its temperature, humidity, nutrient residues is an excellent environment for the development of microorganisms.
The stomach has an acidic reaction, so the bulk of the microorganisms in it dies. Starting in the small intestine, the reaction becomes alkaline, i.e. friendly to microbes. In the colon, the microflora is very diverse. Every adult excretes about 18 billion bacteria every day in excrement, i.e. more individuals than people on the globe.
Internal organs that do not connect with the external environment (brain, heart, liver, bladder, etc.) are usually free of microbes. Microbes enter these organs only during illness.
Bacteria in the Cycle
Microorganisms in general and bacteria in particular play an important role in biologically important cycles of substances on Earth, carrying out chemical transformations that are completely inaccessible to either plants or animals. Different stages of the cycle of elements are carried out by organisms of different types. The existence of each individual group of organisms depends on the chemical transformation of elements carried out by other groups.
The nitrogen cycle
The cyclic transformation of nitrogenous compounds plays a primary role in supplying the necessary forms of nitrogen to organisms of the biosphere for different nutritional needs. Over 90% of total nitrogen fixation is due to the metabolic activity of certain bacteria.
The carbon cycle
The biological transformation of organic carbon into carbon dioxide, accompanied by the reduction of molecular oxygen, requires the joint metabolic activity of various microorganisms. Many aerobic bacteria carry out the complete oxidation of organic matter. Under aerobic conditions, organic compounds are initially degraded by fermentation, and organic end products of fermentation are further oxidized as a result of anaerobic respiration, if there are inorganic hydrogen acceptors (nitrate, sulfate, or CO 2).
The sulfur cycle
Sulfur is available for living organisms mainly in the form of soluble sulfates or reduced organic sulfur compounds.
Iron cycle
In some freshwater bodies of water, reduced iron salts are contained in high concentrations. In such places, a specific bacterial microflora develops - iron bacteria that oxidize reduced iron. They participate in the formation of bog iron ores and water sources rich in iron salts.
Bacteria are the oldest organisms that appeared about 3.5 billion years ago in the Archean. For about 2.5 billion years, they dominated the Earth, forming the biosphere, participated in the formation of an oxygen atmosphere.
Bacteria are one of the simplest living organisms (other than viruses). They are believed to be the first organisms to appear on Earth.
The team of Richard Lensky, an evolutionary microbiologist known for his long-term evolutionary experiment, studied the genetic differences (accumulated mutations) between populations of bacteria that have adapted to five different temperature regimes over 2,000 generations. Despite the variety of possible ways of adaptation, most of the mutations turned out to be specific, that is, they arose in those and only those populations that developed under the same or under similar temperature conditions. However, most of these mutations later became entrenched in an ongoing long-term evolutionary experiment. Apparently, at different temperatures, different mutations turn out to be more useful than others (but rarely from useful ones become harmful) - and natural selection works precisely with these differences in relative utility, fixing earlier mutations that turned out to be more favorable under these conditions.
The Elements repeatedly talked about the work of Richard Lenski's laboratory, which has been experimenting with the evolution of bacteria for decades. These studies not only make it possible to better understand the patterns of adaptation of these microorganisms to the environment (which may be of practical importance, take at least antibiotic resistance), but also make it possible to see firsthand non-trivial evolutionary processes and their results, which is important for fundamental science (see. The early stages of adaptation are predictable, the later ones are random, "Elements", 03.03.2015; In a long-term evolutionary experiment, selection for "evolutionary prospects" was revealed, "Elements", 25.03.2011; The results of an evolutionary experiment of 40,000 generations long, "Elements" , 01.11.2009).
But, in addition to the well-known long-term evolutionary experiment (DEE) (see. E. coli Long-term Experimental Evolution Project), currently lasting for 50,000 generations, Richard Lenski's team also conducts shorter-term studies, which are "layouts" of the main experiment.
In a new work, the researchers studied the genetic basis of the adaptation of E. coli Escherichia coli to different temperatures for 2000 generations in several tens of lines. In this situation, one could expect both divergence due to stochastic processes - the emergence of mutations and genetic drift (see Genetic drift) - and parallel evolution, when different lineages would acquire similar adaptations in the same environment. At least for complex animals, in which individual development significantly complicates the path from genotype to phenotype, these two variants do not necessarily contradict each other: the same adaptation can occur on a different genetic basis. This plurality of permissible results (we emphasize that each of them turns out to be possible) is associated with the long-intriguing question of the predictability of evolution for scientists - or rather, the question is, at what level can we predict how a particular population will adapt to a changed in one way or another. environment (see DL Stern, V. Orgogozo, 2009. Is genetic evolution predictable?).
In the experiment, 30 separate lines of Escherichia coli, taken from a long-term experiment, developed over 2000 generations under five different temperature conditions, six lines each. Some of the bacteria were grown at optimal 37 ° C (let me remind you that normally these bacteria inhabit the intestines of warm-blooded animals) and "tolerant" 32 ° C, and some at extreme cold (20 ° C) and heat (42 ° C), located at the lower and upper boundaries of the zone of tolerance (see. The body's response to changes in environmental factors). In addition, another mode included an alternation of moderate and extreme conditions - the temperature fluctuated between 32 ° C and 42 ° C. A detailed diagram of the experiment is shown in Fig. 2A.
All bacterial populations increased their growth rate during the experiment, that is, their adaptability to the environment increased. Moreover, usually the evolved bacteria turned out to be more successful than the ancestral ones, not only in the environment in which they were grown, but also on others. But this did not always happen - for example, populations from 20, 32 and 37-degree environments at 42 ° C grew worse than their ancestors. However, these results were published a long time ago (see A. F. Bennett, R. E. Lenski, J. E. Mittler, 1992. Evolutionary adaptation to temperature. I. Fitness responses of Escherichia coli to changes in its thermal environment; J. A. Mongold, A. F. Bennett, R. E. Lenski, 1996. Evolutionary adaptation to temperature. IV. Adaptation of Escherichia coli at a niche boundary). And in a recent work, the authors understood the genetic "ins and outs" of temperature adaptations. To do this, they completely sequenced DNA from representatives of each population from the final, 2000th generation.
In total, over the entire period of the experiment, all studied lines accumulated 159 mutations (recall that the experiment uses the population E. coli, reproducing asexually, therefore evolutionary processes are studied by the accumulation of mutations), while each individual line has accumulated from two to eight mutations - interestingly, only one of these "extreme" populations grew not at the optimal 37 degrees, but at "moderate" 32- NS. But on average, the number of mutations accumulated by 37-degree bacteria is significantly less than that of all the others (but only if we consider them all together; when pairwise comparison of experimental variants, the differences in the number of accumulated mutations turn out to be insignificant - possibly due to the small number of populations in each from experience options). Such results are quite expected - after all, bacteria grew at an optimal temperature for them, in which, moreover, the common ancestors of the experimental lines developed for another 2000 generations (Fig. 2A). Thus, the bacteria were already very adapted to these conditions and they were acted upon by a cleansing selection - weeding out mutations that destroy already existing adaptations - rather than a driving one, leading to the formation of new adaptations. The detected mutations belonged to different types: they were synonymous and nonsynonymous nucleotide substitutions (see Mutations: nucleotide substitutions: types), deletions (loss of DNA sections), etc. Their distribution by types and individual populations is shown in Figure 2B. Three of the detected mutations can lead to hypermutability - an increased rate of mutation. Such mutations are often acquired in evolutionary experiments on bacteria, as they increase the chances of favorable mutations occurring. However, in this case, the populations carrying potential mutator genes did not show any significant excess of the number of obtained mutations over the expected one.
Next, scientists evaluated the similarity of mutations that appeared in different populations by calculating the Dyse similarity coefficient, also known as the Sorensen coefficient (S = 2 (X∩Y) / (X + Y), where X and Y are the number of mutated genes in the first and second compared group, and X∩Y is the number of genes mutated in both groups). In this case, only those mutations were taken into account that could be accurately attributed to a specific gene (for example, all large deletions were not taken into account). First, the coefficient of similarity for populations within each variant of the experiment turned out to be significantly higher than between different variants: 0.168 versus 0.042. At the same time, only the difference between the line cultivated at 42 ° C and cultivated at variable temperature turned out to be statistically insignificant (Fig. 3A). Secondly, it was possible to identify specific mutations that occur significantly more often (and sometimes are generally unique) for a particular temperature regime. In total, there were four of them - only the variable temperature regime did not have a specific gene (Fig. 3B).
But, apparently, adaptations are not limited to these four mutations. Since some of the other mutated genes also show a tendency to aggregation in one of the variants of the experiment. Interestingly, all genes, "specific" and suspected of this, belong to several functional groups: they affect the size and shape of cells ( mrdA, hslU), regulate metabolic pathways associated with the processing of nutrients ( nadR, iclR), and change the activity of the metabolic enzyme ( gltB) (see Fig.3B). Also among the "cold" populations there is a tendency to mutate genes associated with transcription and translation. Thus, we have before us a typical example of complex adaptation, involving different mechanisms - and therefore potentially multivariate. Fortunately, modern molecular genetic methods make it possible to isolate individual genes and traits involved in adaptation to a particular environmental factor, although a few decades ago, almost all evolutionists believed that it was impossible to unravel this tangle and the exact mechanisms of such complex adaptations were unknowable. ... Indeed, then one could only say something like: "Many genes participate in the response to selection, in each population - its own." Now we can tell which genes they are. And it turns out that, at least in some cases, this set of genes involved in adaptation turns out to be reproducible.
Interesting results were obtained by comparing the described experiment with the ongoing long-term evolutionary experiment. It turned out that bacteria from DEE over time accumulate mutations in the same genes as those adapting to different temperatures! On the one hand, they need to adapt not only to temperature - for example, there is not enough glucose in the environment of both experiments. On the other hand, where is the specificity of the adaptations here? Yes, the line cultivated at 37 ° С shows the greatest similarity with the DEE proceeding at the same temperature, but the rest acquire mutations, which subsequently turn out to be useful at other temperatures (Fig. 4).
The authors explain this paradox by the fact that different temperature regimes change the relative value of different mutations, but rarely make a useful mutation harmful - that is, for example, a mutation fixed in "cold" lines is more favorable under low temperatures than under optimal conditions. which increases its chance of fixing earlier. This is also supported by a direct assessment of the adaptive value of individual mutations. The researchers inserted them into the genome of ancestral bacteria and looked at how these modified organisms feel at different temperatures. None of the mutations showed significant differences in the positive effect on the growth rate under different temperature regimes, although pairwise comparisons revealed a weak tendency for the mutation to be more favorable in the variant of the experiment where it arose. This confirms the authors' interpretation: with a change in temperature, all fixed mutations remain favorable, but their relative usefulness changes and natural selection works with them: mutations that turned out to be more favorable under these conditions are fixed earlier.
This study allows us to emphasize once again that evolution can occur at the expense of seemingly weak, subtle differences. Not the presence of effective and ineffective ways, but small differences in the effectiveness of certain adaptations at different temperatures change the probability of their fixation by natural selection, which leads to different evolutionary paths.
At the end of the article, the authors emphasize that, given the wide range of adaptation possibilities, their results show unexpectedly high predictability of evolution. And they suggest that the presence of such specific traces of adaptation to specific environmental conditions can help, for example, in deciphering the evolutionary history of pathogenic microbes, tracing the history of the transition between different species, or even individual hosts (which will help to track the dynamics of diseases), as well as in forensic microbiology. helping to clarify the circumstances of death or the history of movements of individual objects (see RE Lenski, P. Keim, 2005.
The question of changing the nature of organisms under the influence of living conditions has been raised for a long time.
However, as Timiryazev points out, it was only in Lamarck's Philosophy of Zoology (1809) that the question of the origin of organisms was first elucidated not in passing, but with all the necessary breadth of coverage and fully armed with scientific knowledge of that time.
Lamarck attached tremendous importance to external conditions and exercise in changing the shape and organization of animals. Explaining the expediency of their structure, he assigned a significant role to the "inner feelings" and "aspirations" of animals. Fierce criticism of this provision led at one time to unreasonable denigration of the entire teachings of Lamarck.
Our great scientist Mechnikov highly appreciated the views of Lamarck. In his famous work "An Outline of the Origin of Species," he calls Lamarck's theory remarkable.
Mechnikov believed that science by the beginning of the 20th century. proved the heritability of the properties acquired by the organism: "The view expressed by him (ie, Lamarck) on the importance of adaptation of animals to environmental conditions and on the role of heredity in the transmission of acquired characters is fully recognized today." In his famous work "Historical Method in Biology" Timiryazev writes: "Deeply innovative thoughts, generously scattered in the pages of" Philosophy of Zoology ", remained obscured by an unsuccessful attempt to explain the expediency of the structure of animal organisms and shared its fate. We deliberately emphasize the words "animal organisms", because in relation to a plant, this theory of "aspirations", "inner feelings" that generate the corresponding organ, of course, did not find application, and here Lamarck remained a strict scientist who did not leave the soil of observable facts. "
The largest stage in the science of the development of the organic world was the emergence of the evolutionary doctrine of Darwin, which gave the correct basis for the theory of the development of plants and animals. Darwin materialistically explained the so-called expediency of the arrangement of forms and behavior of plants and animals, which is encountered at every step. Darwin attributed great importance in the formation of the forms of the animal and plant kingdom to natural and artificial selection.
As Timiryazev notes, Darwin interpreted the concept of natural selection broadly - metaphorically. This position should be emphasized, since later some researchers, who shared the concept of formal geneticists, tried to replace Darwinian concept of creative selection with a position that reduced selection to the role of a sieve.
Meanwhile, selection in the understanding of Darwin is the selection of living organisms that continue to live and change, as a rule, in the direction they have begun. Darwin has repeatedly pointed out that variability goes in the direction of selection. "Without selection and appropriate content, those breeds of animals and plant varieties that have been created by agricultural practice would never have appeared."
Thus, natural and artificial selection should be regarded as creators, creators of new forms of living beings. This view was adopted by Soviet biologists.
The evolutionary doctrine could not be developed by Darwin in all details. So, he essentially did not analyze the reasons giving rise to changes in the nature of living things, although he pointed out the large role of environmental conditions in their appearance. Towards the end of his life, Darwin wrote: "I am nevertheless ... convinced that changed conditions give impetus to variability ...".
Darwin appreciated Lamarck's work. In this regard, Engels writes: "Neither Darwin, nor his followers among natural scientists think about how to somehow belittle the great merits of Lamarck: after all, it was Darwin and his followers who were the first to once again raised him to the shield."
Speaking about the shortcomings of Darwin's teaching, Engels noted: “But Darwinism“ produces its transformations and differences out of nothing. Indeed, when Darwin talks about natural selection, he distracts from the reasons that caused changes in individuals, and treats, first of all, how such individual deviations gradually become signs of a certain race, variety or species ... However, the impetus to the study of the question of where these transformations and differences actually arise was, again, given by none other than Darwin. "
Michurin and Lysenko, who creatively developed Darwinism, filled in the gap just indicated in Darwin's teachings, marking the adaptive nature of the change in organisms.
Such outstanding Russian scientists as V. Kovalevsky, Timiryazev and Pavlov were inclined to this opinion, recognizing the direct influence of the conditions of existence of organisms on their hereditary nature.
Timiryazev wrote that heredity itself, ultimately, is an acquired property, and the only question is when exactly these or those changes occur, "The expediency of organic forms can be explained only by the historical process of their formation."
Michurin says: “Every organ, every property, every member, all internal and external parts of every organism are conditioned by the external environment of its existence. If the organization of plants is what it is, it is because each of its details performs a certain function, possible and necessary only under given conditions. If these conditions change, the function will become impossible or unnecessary, and the organ performing it will gradually atrophy. "
Lysenko has done a lot in the field of analyzing the causes that determine heredity and its variability. Heredity is, as it were, a concentrate of environmental conditions assimilated by plant organisms in a number of previous generations, ”Lysenko writes. “Changes in heredity are usually the result of the development of an organism in the external environment, which in one way or another does not correspond to natural needs, that is, its heredity. Changes in living conditions force the development of plant organisms to change. They are the root cause of the change in heredity.
Avakyan (1948) points out:
“If it is necessary to change certain stages of the organism's development, it is necessary to change the conditions for the completion of the process of this stage, providing the process with those conditions in the direction of which it is intended to change the heredity of the offspring of this organism.
From the facts brought to this system of views, the main position in the teaching of Acad. T. D. Lysenko that a change in the heredity of an organism always proceeds adequately (respectively) to the influence of external factors causing the change. By their nature, changes are always adaptive, but for the offspring of these organisms, they can be useful, harmful or indifferent, depending on the relationship of these changes to all living conditions in general. "
"The relative expediency, harmony of plants and animals in natural nature were created only by natural selection, that is, heredity, its variability and survival."
Lysenko develops and deepens the theory of Darwinism by revealing the causes of certain phenomena, the management of which is required by agricultural practice. This embodies the great principle of the unity of theory and practice.
The views of the Soviet school of Darwinists, as already indicated, must be opposed to the views of Weismann-Morgan. Completely rejecting the possibility of changing the nature of organisms under the influence of living conditions, Morganists reduce evolution to the appearance of random mutations. The ability to inherit certain traits is attributed to a special substance localized in the cell nucleus.
The session of VASKHNIL, held in August 1948, condemned the views of the Morganists and showed their inconsistency. The reactionary nature of the morganism, which asserts the existence of "internal factors" that control the development of the organism and act without the participation of the external environment, has become more obvious.
The thesis about the unknowability of the driving forces of evolution is incompatible with Marxist philosophical materialism, which proves, in the words of Comrade Stalin, “that the world and its regularities are completely cognizable, that our knowledge of the laws of nature, verified by experience and practice, is reliable knowledge that has the value of objective truths, that there are no unknowable things in the world, but only things that are not yet known, which will be revealed and cognized by the forces of science and practice. "
Darwin's fascination with the "theory" of Malthus and an attempt to use it to explain the evolutionary process must be recognized as erroneous. Already in his time F. Engels noted that the extinction of imperfect forms actually occurs without any Malthusianism.
Essentially speaking, Darwin's data refuted Malthus's "theory"; Marx wrote: "In the work of Darwin, for example, in the discussion of the reasons for the extinction of species, there is also a detailed - not to mention his basic principle - a natural-historical refutation of the Malthusian theory."
Revising Darwin's thesis on the role of overpopulation in the process of natural selection, which essentially contradicts evolutionary theory, Lysenko came to reject this thesis. Overpopulation in nature, as a rule, was not and cannot be. “Therefore, by Darwinian natural selection, I mean cumulatively acting factors - variability, heredity and survival ...
Finally, it should be noted that in Darwin's theory the problem of the species is not sufficiently developed.
Engels, assessing the meaning of the concept of a species, wrote: “But without the concept of a species, all science turned into nothing. All its branches needed the concept of a species as a basis: what would human anatomy and comparative anatomy, embryology, zoology, paleontology, botany, etc., be without the concept of a species? "
The fundamental flaw in the Darwinian concept of development was noted by Comrade Stalin, who wrote that “Darwinism rejects not only Cuvier's cataclysms, but also dialectically understood development, including revolution, while from the point of view of the dialectical method, evolution and revolution, quantitative and qualitative changes, are two necessary forms of the same movement. "
Michurin's biology, developed on the basis of dialectical materialism, rejects the idea of flat evolution proceeding without abrupt changes. Emphasizing this position, Lysenko points out that species are not abstractions, but really existing nodes (links) in the general biological chain.
Thus, the concept of a species has a twofold meaning. On the one hand, it denotes the qualitative certainty and relative stability of the species, on the other, the possibility of its abrupt transformation as a result of the accumulation of gradual changes.
The moments we have noted are colorfully revealed in one of Lysenko's works; he writes: “But Darwin's evolutionary theory proceeds from the recognition of only quantitative changes, only an increase or decrease, and loses sight of the obligatory nature and regularity of transformations, transitions from one qualitative state to another. And yet, without the transformation of one qualitative state of organic forms into another, there is no development, there is no transformation of some species into others, but there is only an increase or decrease in quantity, there is only what is usually called growth.
It is for this reason that the theory of Darwinism, which established the concept of development in biological science, only the concept of flat evolution could only explain the development of the organic world. But this explanation could not become an effective theory, a theoretical basis for practical transformation, for changing organic nature. "
“The old biological science, proceeding from the theory of flat evolutionism, from the recognition of only gradual quantitative transformations of some organic forms into others, some states into other states, could not reconcile its theoretical principles with the real and regular existence of species in nature. Therefore, even talented, advanced, progressive scientists with their theory of a gradual transition, the growth of one species into another, a new one, were forced, recognizing the species as reality in practice, in theory to consider them only a convention, only a service concept of taxonomy.
Trying to get out of this contradiction without departing from the position of flat evolutionism, Darwin, in his theory of the evolution of speciation, resorted to the reactionary Malthusian false doctrine of intraspecific overpopulation and intraspecific competition allegedly resulting from this as a driving force of evolution. "
By now, microbiologists have at their disposal a huge amount of material confirming the correctness of Michurin-Lysenko's teachings. Dwelling in this work only on the temperature adaptation of microorganisms, we can show many examples that speak of changes in the properties of microscopic creatures under the influence of the environment. So, in our recently published (1947) monograph "Ecological and geographical variability of soil bacteria", which summarizes the work for 1925-1945, it was shown that the climate favors the formation of temperature races in bacteria. Smaragdova (1941) established a similar fact in relation to the simplest soil.
Temperature adaptation of microorganisms, in particular the formation of thermophilic forms of microbes, provides much value for the study of changes in the hereditary properties of organisms under the influence of environments. This material is all the more important because many microorganisms, such as the predominant part of bacteria, lack a structurally formed nucleus, while others have it. Nevertheless, as can be seen from the material presented below, the stability of hereditary properties and their change do not depend on the height of organization of a particular microbe.
We have already noted that in a laboratory setting, although with certain efforts, it is still possible to change the position of the cardinal temperature points in microorganisms. Obviously, a similar phenomenon should occur in nature, where the influence of the environment leads to the appearance of a corresponding adaptive variability in microorganisms.
Based on the foregoing, it can be argued that the emergence of thermophilic forms of microbes occurs not as a result of unreasonable "mutations", but under the influence of appropriate environmental conditions. However, typical mesophilic microorganisms cannot immediately turn into thermophiles.
Of the experiments on the adaptation of mesophiles to thermophilia, the work of Dallinger (Dallinger, 1887) should be mentioned. This researcher succeeded, by gradually increasing the temperature of Flagellata cultivation, in seven years to raise the position of the maximum point of their development from 23 to 70 °.
Charles Darwin became very interested in Dallinger's works. In his letter to Dallinger, he wrote: “I did not know that you are engaged in changing lower organisms under the influence of changing living conditions and I have no doubt that your results will be extremely interesting and valuable. The fact that you mentioned that they live at different temperatures, but can gradually accustom themselves to much higher, is quite remarkable. He explains the existence of algae in hot springs. "
The work on accustoming bacteria to high temperatures was carried out by Dieudonne, who experimented with the anthrax bacillus Bad. fluorescens and Bad. prodigiosum. Dieudonne gradually raised the temperature at which the bacteria were grown and monitored their development. This researcher, after a series of inoculations, managed to increase the position of the maximum temperature point in bacteria by 4-5 °.
In a similar way, Tsiklinskaya (1898) received the race Bac. subtilis with a temperature maximum 8 ° higher than that of the original culture.
Gage and Stogton developed a more heat-resistant race, the Bact. coli, and Magun did the same for Bac. mycoides.
Krohn (1923) showed that Bac. thermophilus Negre, which had an optimum of 50 °, increased this point to 62.5 ° over two years of cultivation at elevated temperatures.
Works, very close in nature to those just noted, were carried out with bacteria and with mushrooms Ruzicka, Pfeiffer, Till, etc.
In the experiments of most researchers, the adaptation of microbes to elevated temperatures occurred very slowly. Often, when trying to isolate cultures that tolerate a relatively high temperature, non-viable forms were obtained that died after several passages. A similar phenomenon was observed, for example, in the experiments of Jahnke, who tried to obtain the thermophilic race Bac. mesentericus.
A gradual increase in temperature is sometimes not very effective in removing heat-resistant forms of microbes. So, Kasman and Rettger (Casman a. Rettger, 1933) using this method for a year could not achieve significant results in obtaining heat-resistant resinous bacteria. Therefore, some researchers have recommended the use of strong influences in order to induce in culture the appearance of a large number of cells that tolerate high temperatures. This technique, as not directly affecting the properties of living beings, of course, could not give tangible results. In particular, it was used by Burkey and Rugosa (Burkey a. Rugosa, 1940). In this case, the culture of the experimental microbe was usually subjected to sharp temperature fluctuations, the effects of salts, etc.
The opinion of Kluyver and Baars is sharply at odds with other researchers, who admit that many thermophiles are mutants that easily arise in nutrient laboratory media. This point of view was developed by the noted microbiologists on the basis of the study of Vibrio thermodesulfuricans, apparently derived from Vibrio desulfuricans. As already indicated, the opinion of Kluyver and Baars cannot be considered reasonable.
Recently, very detailed studies on the adaptation of mesophilic microorganisms (bacteria and yeast) to elevated temperatures were carried out by Imshenetskiy and Loginova (1944-1948). In their work, experimenters have tried to identify the conditions leading to a more rapid production of the desired forms of microbes. This information is extremely interesting, since in practice microorganisms with elevated temperatures of development are often needed. Such forms have usually been found by microbiologists in nature, but not always with success. Therefore, it is advisable to put on the agenda the issue of artificial breeding of microbial cultures with predetermined properties, i.e., the creation of a still practically absent line of work in microbiology.
According to the ideas developed by Imshenetsky, under the influence of suprooptimal temperatures, cells appear in culture that are able to develop better at elevated temperatures. If the properties of new cells are in tune with the external environment, then they turn out to be more viable than the original cultures.
Thus, the created environment contributes to a certain direction of the process of variability. Mesophilic microorganisms under appropriate conditions can be converted into thermophiles. It should be emphasized, however, once again that this process takes place with a certain difficulty, and the optimal conditions for its acceleration have not yet been clarified. Nevertheless, the facts noted allow us to assume the presence of a phylogenetic relationship between thermophilic and mesophilic microbes. Since a certain plasticity is inherent in all microbes, it becomes clear to us that there is a wide variety of physiological groups in thermophilic bacteria.
Quite remarkable is the fact that the reversion of thermophilic and thermotolerant forms of microbes into mesophilic forms is no less difficult. This was noted by the studies of Dieudonne (1895) and Golikova (1926), who worked with bacteria, Gilbert (1904), who dealt with thermotolerant mold, and Noak (1912), who experimented with thermophilic actinomycete.
Nevertheless, long-term cultivation of microbes at low temperatures reduces their maximum temperature and thermal resistance (Lowenstein, 1903; Mishustina, 1949, and others).
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Tests
666-01. How is a bacterial spore different from a free bacterium?
A) The spore has a denser shell than free bacteria.
B) Spore is a multicellular formation, and a free bacterium is unicellular.
C) Spore is less durable than free bacteria.
D) The spore feeds autotrophically, and the free bacteria feeds heterotrophically.
Answer
Answer
666-03. Indicate a case of symbiosis of a bacterium with another organism.
A) vibrio cholera and humans
B) salmonella and chicken
C) anthrax bacillus and sheep
D) Escherichia coli and humans
Answer
666-04. Nodule bacteria supply moth plants
A) organic matter of dead plants
B) nitrogen salts
B) nucleic acids
D) carbohydrates
Answer
666-05. Unfavorable conditions for the vital activity of bacteria are created when
A) pickling cabbage
B) canning mushrooms
C) cooking kefir
D) laying the silo
Answer
Answer
666-07. Anthrax bacteria can be stored for a long time in burial grounds in the form of
A) dispute
B) cysts
C) living cells
D) zoospores
Answer
Answer
666-09. What is characteristic of saprotrophic bacteria?
A) exist due to the supply of tissues of living organisms
C) use organic substances from the secretions of living organisms
Answer
666-10. Bacteria have existed on Earth for millions of years along with highly organized organisms, since
A) feed on ready-made organic substances
B) when unfavorable conditions occur, they form disputes
C) participate in the cycle of substances in nature
D) have a simple structure and microscopic size
Answer
666-11. Which of the following is correct?
A) bacteria multiply by meiosis
B) all bacteria are heterotrophs
C) bacteria adapt well to environmental conditions
D) some bacteria are eukaryotic organisms
Answer
666-12. The similarity of the vital activity of cyanobacteria and flowering plants is manifested in the ability to
A) heterotrophic nutrition
B) autotrophic nutrition
C) seed formation
D) double fertilization
Answer
666-13. Rotting bacteria living in the soil
A) form organic substances from inorganic
B) feed on organic matter of living organisms
C) contribute to the neutralization of poisons in the soil
D) decompose the dead remains of plants and animals to humus
Answer
666-14. What are the characteristics of putrefaction bacteria?
A) use ready-made organic substances of living organisms
B) synthesize organic substances from inorganic ones, using the energy of the sun
C) use organic matter of dead organisms
D) synthesize organic substances from inorganic ones, using the energy of chemical reactions
Answer
666-15. What bacteria are considered the "orderlies" of the planet?
A) acetic acid
B) nodule
C) decay
D) lactic acid
Answer
666-16. Dysentery amoeba, ciliate shoe, euglena green belong to one subkingdom because they have
A) general plan of the structure
B) a similar type of food
C) the same breeding methods
D) general habitat
Answer
666-17. What is the physiological process in unicellular animals associated with the absorption of gases by the cell?
A) food
B) selection
C) reproduction
D) breathing
