Problems of reproduction magazine archive. Reproduction problems
BACTERIA
a large group of unicellular microorganisms characterized by the absence of a cell nucleus surrounded by a membrane. At the same time, the genetic material of the bacterium (deoxyribonucleic acid, or DNA) occupies a very specific place in the cell - a zone called the nucleoid. Organisms with such a cell structure are called prokaryotes (“prenuclear”), in contrast to all others - eukaryotes (“true nuclear”), whose DNA is located in the nucleus surrounded by a shell. Bacteria, previously considered microscopic plants, are now classified into the independent kingdom Monera - one of five in the current classification system, along with plants, animals, fungi and protists.
Fossil evidence. Bacteria are probably the oldest known group of organisms. Layered stone structures - stromatolites - dated in some cases to the beginning of the Archeozoic (Archean), i.e. arose 3.5 billion years ago, - the result of the vital activity of bacteria, usually photosynthesizing, the so-called. blue-green algae. Similar structures (bacterial films impregnated with carbonates) are still formed today, mainly off the coast of Australia, the Bahamas, in the California and Persian Gulfs, but they are relatively rare and do not reach large sizes, because herbivorous organisms, such as gastropods, feed on them. Nowadays, stromatolites grow mainly where these animals are absent due to high salinity of water or for other reasons, but before the emergence of herbivorous forms during the evolution, they could reach enormous sizes, constituting an essential element of oceanic shallow water, comparable to modern coral reefs. In some ancient rocks, tiny charred spheres have been found, which are also believed to be the remains of bacteria. The first nuclear ones, i.e. eukaryotic, cells evolved from bacteria approximately 1.4 billion years ago.
Ecology. Bacteria are abundant in the soil, at the bottom of lakes and oceans - wherever organic matter accumulates. They live in the cold, when the thermometer is just above zero, and in hot acidic springs with temperatures above 90 ° C. Some bacteria tolerate very high salinity; in particular, they are the only organisms found in the Dead Sea. In the atmosphere, they are present in water droplets, and their abundance there usually correlates with the dustiness of the air. Thus, in cities, rainwater contains much more bacteria than in rural areas. There are few of them in the cold air of high mountains and polar regions, however, they are found even in the lower layer of the stratosphere at an altitude of 8 km. The digestive tract of animals is densely populated with bacteria (usually harmless). Experiments have shown that they are not necessary for the life of most species, although they can synthesize some vitamins. However, in ruminants (cows, antelopes, sheep) and many termites, they are involved in the digestion of plant food. Additionally, the immune system of an animal raised under sterile conditions does not develop normally due to lack of bacterial stimulation. The normal bacterial flora of the intestines is also important for suppressing harmful microorganisms that enter there.
STRUCTURE AND LIFE ACTIVITY OF BACTERIA
Bacteria are much smaller than the cells of multicellular plants and animals. Their thickness is usually 0.5-2.0 microns, and their length is 1.0-8.0 microns. Some forms are barely visible at the resolution of standard light microscopes (approximately 0.3 microns), but species are also known with a length of more than 10 microns and a width that also goes beyond the specified limits, and a number of very thin bacteria can exceed 50 microns in length. On the surface corresponding to the point marked with a pencil, a quarter of a million medium-sized representatives of this kingdom will fit.
Structure. Based on their morphological features, the following groups of bacteria are distinguished: cocci (more or less spherical), bacilli (rods or cylinders with rounded ends), spirilla (rigid spirals) and spirochetes (thin and flexible hair-like forms). Some authors tend to combine the last two groups into one - spirilla. Prokaryotes differ from eukaryotes mainly in the absence of a formed nucleus and the typical presence of only one chromosome - a very long circular DNA molecule attached at one point to the cell membrane. Prokaryotes also do not have membrane-enclosed intracellular organelles called mitochondria and chloroplasts. In eukaryotes, mitochondria produce energy during respiration, and photosynthesis occurs in chloroplasts (see also CELL). In prokaryotes, the entire cell (and primarily the cell membrane) takes on the function of a mitochondrion, and in photosynthetic forms, it also takes on the function of a chloroplast. Like eukaryotes, inside bacteria there are small nucleoprotein structures - ribosomes, necessary for protein synthesis, but they are not associated with any membranes. With very few exceptions, bacteria are unable to synthesize sterols, important components of eukaryotic cell membranes. Outside the cell membrane, most bacteria are covered with a cell wall, somewhat reminiscent of the cellulose wall of plant cells, but consisting of other polymers (they include not only carbohydrates, but also amino acids and bacteria-specific substances). This membrane prevents the bacterial cell from bursting when water enters it through osmosis. On top of the cell wall is often a protective mucous capsule. Many bacteria are equipped with flagella, with which they actively swim. Bacterial flagella are structured simpler and somewhat differently than similar structures of eukaryotes.
"TYPICAL" BACTERIAL CELL and its basic structures.
Sensory functions and behavior. Many bacteria have chemical receptors that detect changes in the acidity of the environment and the concentration of various substances, such as sugars, amino acids, oxygen and carbon dioxide. Each substance has its own type of such “taste” receptors, and the loss of one of them as a result of mutation leads to partial “taste blindness”. Many motile bacteria also respond to temperature fluctuations, and photosynthetic species respond to changes in light intensity. Some bacteria perceive the direction of magnetic field lines, including the Earth's magnetic field, with the help of particles of magnetite (magnetic iron ore - Fe3O4) present in their cells. In water, bacteria use this ability to swim along lines of force in search of a favorable environment. Conditioned reflexes in bacteria are unknown, but they do have a certain kind of primitive memory. While swimming, they compare the perceived intensity of the stimulus with its previous value, i.e. determine whether it has become larger or smaller, and, based on this, maintain the direction of movement or change it.
Reproduction and genetics. Bacteria reproduce asexually: the DNA in their cell is replicated (doubled), the cell divides in two, and each daughter cell receives one copy of the parent DNA. Bacterial DNA can also be transferred between non-dividing cells. At the same time, their fusion (as in eukaryotes) does not occur, the number of individuals does not increase, and usually only a small part of the genome (the complete set of genes) is transferred to another cell, in contrast to the “real” sexual process, in which the descendant receives a complete set of genes from each parent. This DNA transfer can occur in three ways. During transformation, the bacterium absorbs “naked” DNA from the environment, which got there during the destruction of other bacteria or was deliberately “slipped” by the experimenter. The process is called transformation because in the early stages of its study the main attention was paid to the transformation (transformation) of harmless organisms into virulent ones in this way. DNA fragments can also be transferred from bacteria to bacteria by special viruses - bacteriophages. This is called transduction. A process reminiscent of fertilization and called conjugation is also known: bacteria are connected to each other by temporary tubular projections (copulatory fimbriae), through which DNA passes from a “male” cell to a “female” one. Sometimes bacteria contain very small additional chromosomes - plasmids, which can also be transferred from individual to individual. If the plasmids contain genes that cause resistance to antibiotics, they speak of infectious resistance. It is important from a medical point of view because it can spread between different species and even genera of bacteria, as a result of which the entire bacterial flora of, say, the intestines becomes resistant to the action of certain drugs.
METABOLISM
Partly due to the small size of bacteria, their metabolic rate is much higher than that of eukaryotes. Under the most favorable conditions, some bacteria can double their total mass and number approximately every 20 minutes. This is explained by the fact that a number of their most important enzyme systems function at a very high speed. Thus, a rabbit needs a matter of minutes to synthesize a protein molecule, while bacteria take seconds. However, in a natural environment, for example in soil, most bacteria are “on a starvation diet”, so if their cells divide, it is not every 20 minutes, but once every few days.
Nutrition. Bacteria are autotrophs and heterotrophs. Autotrophs (“self-feeding”) do not need substances produced by other organisms. They use carbon dioxide (CO2) as the main or only source of carbon. By incorporating CO2 and other inorganic substances, particularly ammonia (NH3), nitrates (NO-3) and various sulfur compounds, in complex chemical reactions, they synthesize all the biochemical products they need. Heterotrophs (“feeding on others”) use organic (carbon-containing) substances synthesized by other organisms, in particular sugars, as the main source of carbon (some species also need CO2). When oxidized, these compounds supply energy and molecules necessary for cell growth and functioning. In this sense, heterotrophic bacteria, which include the vast majority of prokaryotes, are similar to humans.
Main sources of energy. If mainly light energy (photons) is used for the formation (synthesis) of cellular components, then the process is called photosynthesis, and species capable of it are called phototrophs. Phototrophic bacteria are divided into photoheterotrophs and photoautotrophs depending on which compounds - organic or inorganic - serve as their main source of carbon. Photoautotrophic cyanobacteria (blue-green algae), like green plants, break down water molecules (H2O) using light energy. This releases free oxygen (1/2O2) and produces hydrogen (2H+), which can be said to convert carbon dioxide (CO2) into carbohydrates. Green and purple sulfur bacteria use light energy to break down other inorganic molecules, such as hydrogen sulfide (H2S), rather than water. The result also produces hydrogen, which reduces carbon dioxide, but no oxygen is released. This type of photosynthesis is called anoxygenic. Photoheterotrophic bacteria, such as purple nonsulfur bacteria, use light energy to produce hydrogen from organic substances, in particular isopropanol, but their source can also be H2 gas. If the main source of energy in the cell is the oxidation of chemicals, the bacteria are called chemoheterotrophs or chemoautotrophs, depending on whether the molecules serve as the main source of carbon - organic or inorganic. For the former, organic matter provides both energy and carbon. Chemoautotrophs obtain energy from the oxidation of inorganic substances, such as hydrogen (to water: 2H4 + O2 to 2H2O), iron (Fe2+ to Fe3+) or sulfur (2S + 3O2 + 2H2O to 2SO42- + 4H+), and carbon from CO2. These organisms are also called chemolithotrophs, thereby emphasizing that they “feed” on rocks.
Breath. Cellular respiration is the process of releasing chemical energy stored in “food” molecules for its further use in vital reactions. Respiration can be aerobic and anaerobic. In the first case, it requires oxygen. It is needed for the work of the so-called. electron transport system: electrons move from one molecule to another (energy is released) and ultimately join oxygen along with hydrogen ions - water is formed. Anaerobic organisms do not need oxygen, and for some species of this group it is even poisonous. The electrons released during respiration attach to other inorganic acceptors, such as nitrate, sulfate or carbonate, or (in one form of such respiration - fermentation) to a specific organic molecule, in particular glucose. See also METABOLISM.
CLASSIFICATION
In most organisms, a species is considered to be a reproductively isolated group of individuals. In a broad sense, this means that representatives of a given species can produce fertile offspring by mating only with their own kind, but not with individuals of other species. Thus, the genes of a particular species, as a rule, do not extend beyond its boundaries. However, in bacteria, gene exchange can occur between individuals not only of different species, but also of different genera, so whether it is legitimate to apply the usual concepts of evolutionary origin and kinship here is not entirely clear. Due to this and other difficulties, there is no generally accepted classification of bacteria yet. Below is one of the widely used variants.
KINGDOM OF MONERA
Phylum Gracilicutes (thin-walled gram-negative bacteria)
Class Scotobacteria (non-photosynthetic forms, such as myxobacteria) Class Anoxyphotobacteria (non-oxygen-producing photosynthetic forms, such as purple sulfur bacteria) Class Oxyphotobacteria (oxygen-producing photosynthetic forms, such as cyanobacteria)
Phylum Firmicutes (thick-walled gram-positive bacteria)
Class Firmibacteria (hard-celled forms, such as clostridia)
Class Thallobacteria (branched forms, e.g. actinomycetes)
Phylum Tenericutes (Gram-negative bacteria without a cell wall)
Class Mollicutes (soft-celled forms, such as mycoplasmas)
Phylum Mendosicutes (bacteria with defective cell walls)
Class Archaebacteria (ancient forms, e.g. methane-forming)
Domains. Recent biochemical studies have shown that all prokaryotes are clearly divided into two categories: a small group of archaebacteria (Archaebacteria - "ancient bacteria") and all the rest, called eubacteria (Eubacteria - "true bacteria"). It is believed that archaebacteria, compared to eubacteria, are more primitive and closer to the common ancestor of prokaryotes and eukaryotes. They differ from other bacteria in several significant features, including the composition of ribosomal RNA (rRNA) molecules involved in protein synthesis, the chemical structure of lipids (fat-like substances) and the presence in the cell wall of some other substances instead of the protein-carbohydrate polymer murein. In the above classification system, archaebacteria are considered only one of the types of the same kingdom, which unites all eubacteria. However, according to some biologists, the differences between archaebacteria and eubacteria are so profound that it is more correct to consider archaebacteria within Monera as a special subkingdom. Recently, an even more radical proposal has appeared. Molecular analysis has revealed such significant differences in gene structure between these two groups of prokaryotes that some consider their presence within the same kingdom of organisms to be illogical. In this regard, it is proposed to create a taxonomic category (taxon) of an even higher rank, calling it a domain, and divide all living things into three domains - Eucarya (eukaryotes), Archaea (archaebacteria) and Bacteria (current eubacteria).
ECOLOGY
The two most important ecological functions of bacteria are nitrogen fixation and mineralization of organic residues.
Nitrogen fixation. The binding of molecular nitrogen (N2) to form ammonia (NH3) is called nitrogen fixation, and the oxidation of the latter to nitrite (NO-2) and nitrate (NO-3) is called nitrification. These are vital processes for the biosphere, since plants need nitrogen, but they can only absorb its bound forms. Currently, approximately 90% (approx. 90 million tons) of the annual amount of such “fixed” nitrogen is provided by bacteria. The rest is produced by chemical plants or occurs during lightning strikes. Nitrogen in the air, which is approx. 80% of the atmosphere is bound mainly by the gram-negative genus Rhizobium and cyanobacteria. Rhizobium species enter into symbiosis with approximately 14,000 species of leguminous plants (family Leguminosae), which include, for example, clover, alfalfa, soybeans and peas. These bacteria live in the so-called. nodules - swellings formed on the roots in their presence. Bacteria obtain organic substances (nutrition) from the plant, and in return supply the host with fixed nitrogen. Over the course of a year, up to 225 kg of nitrogen per hectare is fixed in this way. Non-legume plants, such as alder, also enter into symbiosis with other nitrogen-fixing bacteria. Cyanobacteria photosynthesize, like green plants, releasing oxygen. Many of them are also capable of fixing atmospheric nitrogen, which is then consumed by plants and ultimately animals. These prokaryotes serve as an important source of fixed nitrogen in the soil in general and rice paddies in the East in particular, as well as its main supplier for ocean ecosystems.
Mineralization. This is the name given to the decomposition of organic residues into carbon dioxide (CO2), water (H2O) and mineral salts. From a chemical point of view, this process is equivalent to combustion, so it requires large amounts of oxygen. The top layer of soil contains from 100,000 to 1 billion bacteria per 1 g, i.e. approximately 2 tons per hectare. Typically, all organic residues, once in the ground, are quickly oxidized by bacteria and fungi. More resistant to decomposition is a brownish organic substance called humic acid, which is formed mainly from lignin contained in wood. It accumulates in the soil and improves its properties.
BACTERIA AND INDUSTRY
Given the variety of chemical reactions bacteria catalyze, it is not surprising that they are widely used in manufacturing, in some cases since ancient times. Prokaryotes share the glory of such microscopic human assistants with fungi, primarily yeast, which provide most of the processes of alcoholic fermentation, for example, in the production of wine and beer. Now that it has become possible to introduce useful genes into bacteria, causing them to synthesize valuable substances such as insulin, the industrial application of these living laboratories has received a new powerful incentive. See also GENETIC ENGINEERING.
Food industry. Currently, bacteria are used by this industry mainly for the production of cheeses, other fermented milk products and vinegar. The main chemical reactions here are the formation of acids. Thus, when producing vinegar, bacteria of the genus Acetobacter oxidize the ethyl alcohol contained in cider or other liquids to acetic acid. Similar processes occur when cabbage is sauerkraut: anaerobic bacteria ferment the sugars contained in the leaves of this plant into lactic acid, as well as acetic acid and various alcohols.
Ore leaching. Bacteria are used for leaching of low-grade ores, i.e. converting them into a solution of salts of valuable metals, primarily copper (Cu) and uranium (U). An example is the processing of chalcopyrite, or copper pyrite (CuFeS2). Heaps of this ore are periodically watered with water, which contains chemolithotrophic bacteria of the genus Thiobacillus. During their life activity, they oxidize sulfur (S), forming soluble copper and iron sulfates: CuFeS2 + 4O2 in CuSO4 + FeSO4. Such technologies greatly simplify the extraction of valuable metals from ores; in principle, they are equivalent to the processes that occur in nature during the weathering of rocks.
Waste recycling. Bacteria also serve to convert waste materials, such as sewage, into less hazardous or even useful products. Wastewater is one of the most pressing problems of modern humanity. Their complete mineralization requires huge amounts of oxygen, and in ordinary reservoirs where it is customary to dump this waste, there is no longer enough oxygen to “neutralize” it. The solution lies in additional aeration of wastewater in special pools (aeration tanks): as a result, mineralizing bacteria have enough oxygen to completely decompose organic matter, and in the most favorable cases, drinking water becomes one of the final products of the process. The insoluble sediment remaining along the way can be subjected to anaerobic fermentation. To ensure that such water treatment plants take up as little space and money as possible, a good knowledge of bacteriology is necessary.
Other uses. Other important areas of industrial application of bacteria include, for example, flax lobe, i.e. separation of its spinning fibers from other parts of the plant, as well as the production of antibiotics, in particular streptomycin (bacteria of the genus Streptomyces).
COMBATING BACTERIA IN INDUSTRY
Bacteria are not only beneficial; The fight against their mass reproduction, for example in food products or in the water systems of pulp and paper mills, has become a whole area of activity. Food spoils under the influence of bacteria, fungi and its own enzymes that cause autolysis ("self-digestion"), unless they are inactivated by heat or other means. Since bacteria are the main cause of spoilage, developing efficient food storage systems requires knowledge of the tolerance limits of these microorganisms. One of the most common technologies is pasteurization of milk, which kills bacteria that cause, for example, tuberculosis and brucellosis. The milk is kept at 61-63°C for 30 minutes or at 72-73°C for only 15 seconds. This does not impair the taste of the product, but inactivates pathogenic bacteria. Wine, beer and fruit juices can also be pasteurized. The benefits of storing food in the cold have long been known. Low temperatures do not kill bacteria, but they do prevent them from growing and reproducing. True, when frozen, for example, to -25 ° C, the number of bacteria decreases after a few months, but a large number of these microorganisms still survive. At temperatures just below zero, bacteria continue to multiply, but very slowly. Their viable cultures can be stored almost indefinitely after lyophilization (freeze-drying) in a protein-containing medium, such as blood serum. Other known methods of storing food include drying (drying and smoking), adding large amounts of salt or sugar, which is physiologically equivalent to dehydration, and pickling, i.e. placing in a concentrated acid solution. When the acidity of the environment corresponds to pH 4 and below, the vital activity of bacteria is usually greatly inhibited or stopped.
BACTERIA AND DISEASES
STUDYING BACTERIA
Many bacteria are easy to grow in so-called. culture medium, which may include meat broth, partially digested protein, salts, dextrose, whole blood, its serum and other components. The concentration of bacteria in such conditions usually reaches about a billion per cubic centimeter, causing the environment to become cloudy. To study bacteria, it is necessary to be able to obtain their pure cultures, or clones, which are the offspring of a single cell. This is necessary, for example, to determine what type of bacteria infected the patient and what antibiotic this type is sensitive to. Microbiological samples, such as throat or wound swabs, blood samples, water samples or other materials, are highly diluted and applied to the surface of a semi-solid medium: on it, round colonies develop from individual cells. The hardening agent for the culture medium is usually agar, a polysaccharide obtained from certain seaweeds that is not digestible by almost any type of bacteria. Agar media is used in the form of “shoals”, i.e. inclined surfaces formed in test tubes standing at a large angle when the molten culture medium solidifies, or in the form of thin layers in glass Petri dishes - flat round vessels, closed with a lid of the same shape, but slightly larger in diameter. Usually, within a day, the bacterial cell manages to multiply so much that it forms a colony that is easily visible to the naked eye. It can be transferred to another environment for further study. All culture media must be sterile before starting to grow bacteria, and in the future measures should be taken to prevent the settlement of unwanted microorganisms on them. To examine bacteria grown in this way, heat a thin wire loop in a flame, touch it first to a colony or smear, and then to a drop of water applied to a glass slide. Having evenly distributed the taken material in this water, the glass is dried and quickly passed over the burner flame two or three times (the side with the bacteria should be facing up): as a result, the microorganisms, without being damaged, are firmly attached to the substrate. Dye is dripped onto the surface of the preparation, then the glass is washed in water and dried again. Now you can examine the sample under a microscope. Pure cultures of bacteria are identified mainly by their biochemical characteristics, i.e. determine whether they form gas or acids from certain sugars, whether they are able to digest protein (liquefy gelatin), whether they require oxygen for growth, etc. They also check whether they are stained with specific dyes. Sensitivity to certain drugs, such as antibiotics, can be determined by placing small disks of filter paper soaked in these substances on a surface infested with bacteria. If any chemical compound kills bacteria, a bacteria-free zone is formed around the corresponding disk.
Collier's Encyclopedia. - Open Society. 2000 .
Which do not have a core. Most bacteria are heterotrophs, but there are also autotrophs. They reproduce by division. When unfavorable conditions occur, some bacteria form spores.
Bacteria can only be seen through a microscope, which is why they are called microorganisms. Microorganisms are studied by the science of microbiology. The branch of microbiology that studies bacteria is called bacteriology.
The first to see and describe bacteria was the Dutch naturalist Anthony van Leeuwen Hoek (1632-1723). He learned to grind glass and make lenses. Leeuwenhoek made more than 400 microscopes and opened the world of microscopic organisms- bacteria and protists.
When we hear about bacteria, we most often imagine a sore throat or gums, despite the fact that only a small part of bacteria cause disease. Most of these organisms perform other important functions.
We begin to come into contact with bacteria from the first hours of life. Many of them live permanently on the surface skin person. There are even more of them on the teeth, gums, tongue and walls oral cavity. In mouth There are more bacteria than people on Earth! But the largest number of them lives in the intestines - up to 5 kg in an adult.
Bacteria are found everywhere: in water, soil, air, in plant tissues, in the bodies of animals and humans. They live where they find enough food, moisture and favorable temperatures (10-40 ° C). Most of them require oxygen. There are also bacteria that live in hot springs (with a temperature of 60-90 ° C), extremely salty bodies of water, in volcanic vents, deep in the oceans where sunlight does not penetrate. Even in the coldest regions (Antarctica) and on the highest mountain peaks, bacteria live.
Different numbers of bacteria are found in different places. There are fewer of them in the air, especially in natural conditions. And in crowded places, such as cinemas, train stations, and classrooms, there are much more of them. Therefore, it is necessary to ventilate the premises frequently.
In river waters, especially near large cities, there can be a lot of bacteria - up to several hundred thousand per 1 mm3. Therefore, you should not drink raw water from open reservoirs. There are a lot of bacteria in the water of the seas and oceans.
There are even more bacteria in the soil - up to 100 million per 1 g of humus (fertile soil layer).
Bacteria are very small organisms. The largest bacteria can be seen under a light microscope.
To get to know the smallest ones, an electron microscope is required (Fig. 7).
Most of the bacteria that inhabit our home and our body are in the form of balls, sticks and spirals. Spherical bacteria are called cocci, rod-shaped bacteria are called bacilli, and spiral-shaped bacteria are called spirilla (Fig. 9). Some bacteria form chains, located close to each other.
Consider the structure of bacterial cells in Figure 10. It includes cytoplasm surrounded by a cytoplasmic membrane and cell membrane(cell wall). The shell gives the bacterium a certain shape and serves as protection from unfavorable conditions.
Additional protection for many bacteria will be provided by the mucus layer located on the outside of the shell. The surface of the bacterial cell is covered with numerous villi, which are hollow outgrowths of the cytoplasmic membrane. Some bacteria have one or more filamentous flagella.
The main difference between bacteria is the absence of a nucleus, i.e. they are prokaryotes.
It is on this basis that they are separated into a separate kingdom. The nuclear material of bacteria is the bacterial chromosome: it carries hereditary information.
Most bacteria are heterotrophs. They consume ready-made organic substances. Their food is living and dead organisms, human food products, wastewater, etc.
Saprotrophs
Some heterotrophic bacteria use organic substances from dead bodies or secretions of living organisms. These are saprotrophs (from the Greek sapros - rotten and trophos - nutrition).
There are also autotrophic bacteria. They are capable of forming organic substances from inorganic ones (carbon dioxide, water, hydrogen sulfide, etc.). Autotrophic photosynthetic bacteria have bacterial chlorophyll in their cells, with which they form organic substances under the influence of solar energy.
Cyanobacteria
An example of autotrophic bacteria is cyanobacteria. They make their own food from carbon dioxide and water when exposed to sunlight. At the same time, oxygen is released, enriching it with habitat.
Bacteria reproduce by division. In this case, from one mother cell two daughter cells are formed, similar to the mother one. Under favorable conditions (sufficient nutrition, humidity and temperature from 10 to 30 ° C), bacteria can divide every 20-30 minutes, so their number increases very quickly. Material from the site
If bacteria are cultivated (grown) on a nutrient medium under favorable conditions, they multiply very quickly and form colonies of up to 4 billion cells. Colonies of bacteria of certain species have characteristic outlines and colors (Fig. 8). By the type of colonies, you can determine the presence of certain bacteria in a particular material.
Some bacteria move using flagella. The base of the flagellum rotates, and it seems to be screwed into the medium, ensuring the movement of the bacterium. Most bacteria move passively: some with the help of air currents, others with the flow of water. This is how they are distributed.
Under unfavorable conditions (lack of food, moisture, sudden temperature fluctuations), bacteria can turn into spores. The cytoplasm near the bacterial chromosome becomes denser. A very strong shell is formed around it. Spores formed in this way can exist for hundreds of years (Fig. 11).
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