Do bacteria have DNA? Genetic material of bacteria. Bacteria dna, bacteria dna in smear

Bacteria are the oldest group of organisms currently existing on Earth. The first bacteria probably appeared more than 3.5 billion years ago and for almost a billion years they were the only living creatures on our planet. Since these were the first representatives of living nature, their body had a primitive structure.

Over time, their structure became more complex, but to this day bacteria are considered the most primitive single-celled organisms. It is interesting that some bacteria still retain the primitive features of their ancient ancestors. This is observed in bacteria living in hot sulfur springs and anoxic mud at the bottom of reservoirs.

Most bacteria are colorless. Only a few are purple or green. But the colonies of many bacteria have a bright color, which is caused by the release of a colored substance into the environment or pigmentation of cells.

The discoverer of the world of bacteria was Antony Leeuwenhoek, a Dutch naturalist of the 17th century, who first created a perfect magnifying microscope that magnifies objects 160-270 times.

Bacteria are classified as prokaryotes and are classified into a separate kingdom - Bacteria.

Body Shape

Bacteria are numerous and diverse organisms. They vary in shape.

Name of the bacterium	Bacteria shape	Bacteria image
Cocci		Ball-shaped
Bacillus		Rod-shaped
Vibrio		Comma-shaped
Spirillum		Spiral
Streptococci		Chain of cocci
Staphylococcus		Clusters of cocci
Diplococcus		Two round bacteria enclosed in one mucous capsule

Methods of transportation

Among bacteria there are mobile and immobile forms. Motiles move due to wave-like contractions or with the help of flagella (twisted helical threads), which consist of a special protein called flagellin. There may be one or more flagella. In some bacteria they are located at one end of the cell, in others - at two or over the entire surface.

But movement is also inherent in many other bacteria that lack flagella. Thus, bacteria covered on the outside with mucus are capable of gliding movement.

Some aquatic and soil bacteria lacking flagella have gas vacuoles in the cytoplasm. There may 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 sink into the water column or rise to its surface, and soil bacteria can move in the soil capillaries.

Habitat

Due to their 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 snow, desert sands, on the ocean floor, in oil extracted from great depths, and even in the water of hot springs with a temperature of about 80ºC. They live on plants, fruits, various animals and in humans in the intestines, oral cavity, limbs, and on the surface of the body.

Bacteria are the smallest and most numerous living creatures. Due to their small size, they easily penetrate into any cracks, crevices, or pores. Very hardy and adapted to various living conditions. They tolerate drying, extreme cold, and heating up to 90ºC without losing their viability.

There is practically no place on Earth where bacteria are not found, but in varying quantities. The living conditions of bacteria are varied. Some of them require atmospheric oxygen, others do not need it and are able to live in an oxygen-free environment.

In the air: bacteria rise to the upper atmosphere up to 30 km. and more.

There are especially many of them in the soil. 1 g 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 under favorable conditions cause diseases. Symbiotic live in the digestive organs, helping to break down and absorb food, and synthesize vitamins.

External structure

The bacterial cell is covered with a special dense shell - a cell wall, which performs protective and supporting functions, and also gives the bacterium a permanent, characteristic shape. The cell wall of a bacterium resembles the wall of a plant cell. It is permeable: through it, nutrients freely pass into the cell, and metabolic products exit into the environment. Often, bacteria produce an additional protective layer of mucus on top of the cell wall - a capsule. The thickness of the capsule can be many times greater than the diameter of the cell itself, but it can also be very small. The capsule is not an essential part of the cell; it is formed depending on the conditions in which the bacteria find themselves. It protects the 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 greater than the size of the body of the bacterium. Bacteria move with the help of flagella and villi.

Internal structure

Inside the bacterial cell there is dense, immobile cytoplasm. It has a layered structure, there are no vacuoles, therefore various proteins (enzymes) and reserve nutrients are located in the substance of the cytoplasm itself. Bacterial cells do not have a nucleus. A substance carrying hereditary information is concentrated in the central part of their cell. 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 characteristics. The cytoplasm is separated from the cell wall by the cytoplasmic membrane. In the cytoplasm there is a main substance, or matrix, ribosomes and a small number of membrane structures that perform a variety of functions (analogues of mitochondria, endoplasmic reticulum, Golgi apparatus). The cytoplasm of bacterial cells often contains granules of various shapes and sizes. The granules may be composed of compounds that serve as a source of energy and carbon. Droplets of fat are also found in the bacterial cell.

In the central part of the cell, the nuclear substance is localized - DNA, which is not delimited from the cytoplasm by a membrane. This is an analogue of the nucleus - a nucleoid. The nucleoid does not have a membrane, a nucleolus, or a set of chromosomes.

Eating methods

Bacteria have different feeding methods. Among them there are autotrophs and heterotrophs. Autotrophs are organisms that are capable of independently producing organic substances for their nutrition.

Plants need nitrogen, but cannot absorb nitrogen from the air themselves. Some bacteria combine nitrogen molecules in the air with other molecules, resulting in substances that are available to plants.

These bacteria settle in the cells of young roots, which leads to the formation of thickenings on the roots, called nodules. Such nodules form on the roots of plants of the legume family and some other plants.

The roots provide carbohydrates to the bacteria, and the bacteria to the roots provide nitrogen-containing substances that can be absorbed by the plant. Their cohabitation is mutually beneficial.

Plant roots secrete a lot of organic substances (sugars, amino acids and others) that bacteria feed on. Therefore, especially many bacteria settle in the soil layer surrounding the roots. These bacteria convert dead plant debris into plant-available substances. This layer of soil is called the rhizosphere.

There are several hypotheses about the penetration of nodule bacteria into root tissue:

• through damage to epidermal and cortex tissue;
• through root hairs;
• only through the young cell membrane;
• thanks to companion bacteria producing pectinolytic enzymes;
• due to stimulation of the synthesis of B-indoleacetic acid from tryptophan, always present in plant root secretions.

The process of introduction of nodule bacteria into root tissue consists of two phases:

• infection of root hairs;
• process of nodule formation.

In most cases, the invading cell actively multiplies, forms so-called infection threads and, in the form of such threads, moves into the plant tissue. Nodule bacteria emerging from the infection thread continue to multiply in the host tissue.

Plant cells filled with rapidly multiplying cells of nodule bacteria begin to rapidly divide. The connection of a young nodule with the root of a legume plant is carried out thanks to vascular-fibrous bundles. During the period of functioning, the nodules are usually dense. By the time optimal activity occurs, the nodules acquire a pink color (thanks to the leghemoglobin pigment). Only those bacteria that contain leghemoglobin are capable of fixing nitrogen.

Nodule bacteria create tens and hundreds of kilograms of nitrogen fertilizer per hectare of soil.

Metabolism

Bacteria differ from each other in their metabolism. In some it occurs with the participation of oxygen, in others - without it.

Most bacteria feed on ready-made organic substances. 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 into pieces, assemble their shell from these parts and replenish their contents (this is how they grow), and throw unnecessary molecules out. The shell and membrane of the bacterium allows it to absorb only the necessary substances.

If the shell and membrane of a bacterium 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 medium - the solution in which the bacterium lives. To survive, bacteria need a shell that allows necessary substances to pass through, but not unnecessary substances.

The bacterium absorbs nutrients located near it. What happens next? If it can move independently (by moving a flagellum or pushing mucus back), 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 thicket of molecules of another substance) brings the necessary molecules to it.

Bacteria, together with other groups of microorganisms, perform enormous chemical work. By converting 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 bodies are diverse in bacteria.

Other bacteria satisfy all their needs 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 capable of synthesizing organic substances from inorganic ones. Among them are:

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 using 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 oxidize ammonia formed during the decay of organic residues to nitric acid. The latter reacts with mineral compounds of the soil, turning into salts of nitric acid. This process takes place in two phases.

Iron bacteria convert ferrous iron into oxide iron. The resulting iron hydroxide settles and forms the so-called bog iron ore.

Some microorganisms exist due to the oxidation of molecular hydrogen, thereby providing an autotrophic method of nutrition.

A characteristic feature of hydrogen bacteria is the ability to switch to a heterotrophic lifestyle when provided with organic compounds and 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 in their complete independence from light as an energy source.

Bacterial photosynthesis

Some pigment-containing sulfur bacteria (purple, green), containing specific pigments - bacteriochlorophylls, are able to absorb solar energy, with the help of which hydrogen sulfide in their bodies is broken 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 the hydrogen donor is hydrogen sulfide (occasionally carboxylic acids), and in green plants it is water. In both of them, the separation 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 a significant role in the process of sulfur cycling in nature. Absorbed by green plants in the form of sulfuric acid salts, sulfur is reduced and becomes part of protein molecules. Further, when dead plant and animal remains 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), forming sulfites in the soil that are accessible to plants. Chemo- and photoautotrophic bacteria are essential in the nitrogen and sulfur cycle.

Sporulation

Spores form inside the bacterial cell. During the process of sporulation, the bacterial cell undergoes a number of biochemical processes. The amount of free water in it decreases and 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 an optional stage in the life cycle of bacteria. Sporulation begins only with a lack of nutrients or accumulation of metabolic products. Bacteria in the form of spores can remain dormant for a long time. Bacterial spores can withstand prolonged boiling and very long freezing. When favorable conditions occur, the spore germinates and becomes viable. Bacterial spores are an adaptation to survive in unfavorable conditions.

Reproduction

Bacteria reproduce 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 gradually forms, and then the daughter cells separate; In many bacteria, under certain conditions, after dividing, cells remain connected in 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 as an exception in bacteria.

Under favorable conditions, cell division in many bacteria occurs every 20-30 minutes. With such rapid reproduction, the offspring of one bacterium in 5 days is capable of forming a mass that can fill all seas and oceans. A simple calculation shows that 72 generations (720,000,000,000,000,000,000 cells) can be formed per day. If converted into weight - 4720 tons. However, this does not happen in nature, since most bacteria quickly die under the influence of sunlight, drying, lack of food, heating to 65-100ºC, as a result of struggle between species, etc.

The bacterium (1), having 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) find themselves attached to the wall of the bacterium and, as the bacterium elongates, move apart (5,6). First the nucleotide divides, then the cytoplasm.

After the divergence of two DNA molecules, a constriction appears on the bacterium, which gradually divides the body of the bacterium into two parts, each of which contains a DNA molecule (7).

It happens (in Bacillus subtilis) that two bacteria stick together and a bridge is formed between them (1,2).

The jumper transports DNA from one bacterium to another (3). Once in one bacterium, DNA molecules intertwine, stick together in some places (4), and then exchange sections (5).

The role of bacteria in nature

Gyre

Bacteria are the most important link in the general cycle of substances in nature. Plants create complex organic substances from carbon dioxide, water and mineral salts in 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 then used by plants.

Bacteria destroy complex organic substances of dead plants and animal corpses, excretions of living organisms and various wastes. Feeding on these organic substances, saprophytic bacteria of decay turn them into humus. These are a kind of orderlies of our planet. Thus, bacteria actively participate in the cycle of substances in nature.

Soil formation

Since bacteria are distributed almost everywhere and occur in huge numbers, they largely determine various processes occurring in nature. In autumn, the leaves of trees and shrubs fall, above-ground shoots of grasses die, old branches fall off, and from time to time the trunks of old trees fall. All this gradually turns into humus. In 1 cm3. 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 vital processes. These nitrogen-fixing bacteria live independently or settle in the roots of legume plants. Having penetrated the roots of legumes, these bacteria cause the growth of root cells and the formation of nodules on them.

These bacteria produce nitrogen compounds that plants use. Bacteria obtain 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 symbiosis with nodule bacteria, leguminous plants enrich the soil with nitrogen, helping to increase yield.

Distribution in nature

Microorganisms are ubiquitous. The only exceptions are the craters of active volcanoes and small areas at the epicenters of exploded atomic bombs. Neither the low temperatures of Antarctica, nor the boiling streams of geysers, nor saturated salt solutions in salt pools, nor the strong insolation of mountain peaks, nor the harsh irradiation of nuclear reactors interfere with the existence and development of microflora. All living beings constantly interact with microorganisms, often being not only their repositories, but also their distributors. Microorganisms are natives of our planet, actively exploring 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 soil than in water and air. The total number of bacteria in soils changes. The number of bacteria depends on the type of soil, their condition, and the depth of the layers.

On the surface of soil particles, microorganisms are located in small microcolonies (20-100 cells each). They often develop in the thickness of clots of organic matter, on living and dying plant roots, in thin capillaries and inside lumps.

The soil microflora is very diverse. Here there are different physiological groups of bacteria: putrefaction bacteria, nitrifying bacteria, nitrogen-fixing bacteria, sulfur bacteria, etc. among them there are aerobes and anaerobes, spore and non-spore forms. Microflora is one of the factors in soil formation.

The area of ​​development of microorganisms in the soil is the zone 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 develop in large numbers. The bulk of them enters the water from the soil. A factor that determines the number of bacteria in water and the presence of nutrients in it. The cleanest waters are from artesian wells and springs. Open reservoirs and rivers are very rich in bacteria. The largest number of bacteria is found in the surface layers of water, closer to the shore. As you move away from the shore and increase in depth, the number of bacteria decreases.

Clean water contains 100-200 bacteria per ml, and polluted water contains 100-300 thousand or more. There are many bacteria in the bottom sludge, especially in the surface layer, where the bacteria form a film. This film contains a lot of sulfur and iron bacteria, which oxidize hydrogen sulfide to sulfuric acid and thereby prevent fish from dying. There are more spore-bearing forms in silt, while non-spore-bearing forms predominate in water.

In terms of species composition, the microflora of water is similar to the microflora of soil, but there are also specific forms. By destroying various waste that gets into the water, microorganisms gradually carry out the so-called biological purification of water.

Air microflora

The microflora of the air is less numerous than the microflora of soil and water. Bacteria rise into the air with dust, can remain there for some time, and then settle on 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 geographical zone, terrain, time of year, dust pollution, etc. each speck of dust is a carrier of microorganisms. Most bacteria are in the air above industrial enterprises. The air in rural areas is cleaner. The cleanest air is over forests, mountains, and snowy areas. The upper layers of air contain fewer microbes. The air microflora contains many pigmented and spore-bearing bacteria, 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 the human body comes into contact with air and soil, various microorganisms, including pathogenic ones (tetanus bacilli, gas gangrene, etc.), settle on clothing and skin. The most frequently exposed parts of the human body are contaminated. E. coli and staphylococci are found on the hands. There are over 100 types of microbes in the oral cavity. The mouth, with its temperature, humidity, and nutrient residues, is an excellent environment for the development of microorganisms.

The stomach has an acidic reaction, so the majority of microorganisms in it die. Starting from the small intestine, the reaction becomes alkaline, i.e. favorable for microbes. The microflora in the large intestines is very diverse. Each adult excretes about 18 billion bacteria daily in excrement, i.e. more individuals than people on the globe.

Internal organs that are not connected to the external environment (brain, heart, liver, bladder, etc.) are usually free of microbes. Microbes enter these organs only during illness.

Bacteria in the cycle of substances

Microorganisms in general and bacteria in particular play a large role in the 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.

Nitrogen cycle

The cyclic transformation of nitrogenous compounds plays a primary role in supplying the necessary forms of nitrogen to organisms of the biosphere with different nutritional needs. Over 90% of total nitrogen fixation is due to the metabolic activity of certain bacteria.

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 complete oxidation of organic substances. Under aerobic conditions, organic compounds are initially broken down by fermentation, and the organic end products of fermentation are further oxidized by anaerobic respiration if inorganic hydrogen acceptors (nitrate, sulfate, or CO 2 ) are present.

Sulfur cycle

Sulfur is available to living organisms mainly in the form of soluble sulfates or reduced organic sulfur compounds.

Iron cycle

Some freshwater bodies contain high concentrations of reduced iron salts. In such places, a specific bacterial microflora develops - iron bacteria, which oxidize reduced iron. They participate in the formation of bog iron ores and water sources rich in iron salts.

Bacteria are the most ancient organisms, appearing about 3.5 billion years ago in the Archean. For about 2.5 billion years they dominated the Earth, forming the biosphere, and participated in the formation of the oxygen atmosphere.

Bacteria are one of the most simply structured living organisms (except viruses). They are believed to be the first organisms to appear on Earth.

GENETICS OF BACTERIA

The purpose of the lecture: to familiarize students with the basics of bacterial genetics and the basic methods of gene diagnostics.

Lecture outline

1. Features of the organization of the nuclear apparatus of bacteria.

2. Composition of the bacterial genome.

3. Variability of bacteria.

4. Recombinations in bacteria and their features.

5. Gene diagnostics.

6. Classification of bacteria.

1. Features of the morphological organization of the nuclear apparatus of bacteria:

- does not have a nuclear membrane or nucleolus; is called a nucleoid;

- DNA is the carrier of genetic information. If in eukaryotes the DNA is linear, then in most bacteria it is circular, and one strand is fixed on the cytoplasmic membrane. If you unwind the DNA, its length will be hundreds of times greater than the length of the cell. Bacterial DNA is supercoiled.

- a bacterial cell contains one chromosome, i.e. bacteria are haploid organisms.

2. Biochemical features.

- Bacterial DNA has the same composition as eukaryotic DNA.

- In bacteria, the DNA may contain minor bases, the presence of which protects the DNA from the action of its own endonucleases.

- in the genome of pathogenic bacteria there are DNA sections that differ from the main genome in composition G-C nucleotide base pairs. These areas are responsible for the synthesis of pathogenicity factors—pathogenicity islands.

- Bacterial DNA does not contain histones, and their role is played by polyamines. The bacterial genome is represented by structures that are capable of

offline replication. There are two such structures: chromosomes, in which all vital information is encoded (a bacterial chromosome contains up to 3 thousand different genes), and plasmids.

Plasmids are DNA that are circular in nature. Plasmids in a cell can be in one of two alternative states: free or integrated with the chromosome.

Plasmids encode additional genetic information that is not vital for the cell, but the presence of this information gives it certain selective advantages. Plasmids include:

Structural genes; -genes responsible for their own replication of the plasmid.

Some plasmids have genes that ensure the transmissibility of the plasmid - tra genes.

According to the coded attribute they distinguish:

- R plasmids encode bacterial drug resistance;

- F (sex) plasmids - determine the cell’s ability to be a donor of genetic information;

- Col plasmid - encodes the synthesis of bacteriocins;

- plasmids responsible for the synthesis of virulence factors(Ent-, Hly-)

and other plasmids.

The bacterial genome includes mobile genetic elements: IS elements (insertion sequences), transposons and integrons. They are found both as part of the bacterial chromosome and as part of plasmids. Their replication is an integral part of chromosome and plasmid replication.

IS elements are short (2000) nucleotide sequences. A distinctive feature of IS elements is the presence of inverted repeats at the ends, which are recognized by the transposase. They do not carry structural genes; are the same in bacteria of different species, genera, and it is even believed that they are the same in prokaryotes and eukaryotes. IS elements can move both along a chromosome and between chromosomes. They contain 2 genes: the 1st encodes the synthesis of transposase; this enzyme ensures the process of exclusion of the IS element from the chromosome and its integration into the new chromosome locus. The 2nd gene encodes the synthesis of a repressor, which regulates the entire movement process.

Transposons are segments of DNA that have the same properties as the IS element, but have structural genes.

Integrons are mobile genetic elements; they contain a gene encoding antibiotic resistance. Integrons are a system for capturing small DNA elements called gene cassettes through site-specific recombination and their expression.

The meaning of mobile elements.

Moving along the DNA of a cell or between the DNA of different cells, they cause:

- inactivation of genes of those sections of DNA where they, having moved, are integrated;

- damage to genetic material;

- integration of the plasmid into the chromosome;

- distribution of a gene in a bacterial population.

Bacteria, like all living beings, are characterized by variability. Variation in eukaryotes occurs vertically, in bacteria - both vertically and horizontally.

There are two types of variability: - phenotypic - genotypic.

Phenotypic variability manifests itself in the form of modifications - this is a change in the properties of the cell under the influence of external influences.

Modifications can be long-term or short-term. Modification changes affect the vast majority of cells in the population.

Genotypic is mutation or recombination. Mutations can be spontaneous or induced.

Recombination is the interaction between two genomes with different genotypes, which leads to the formation of a genome that combines the genes of the donor and recipient. During the process of recombination, bacteria are conventionally divided into donor cells, which transfer genetic material, and recipient cells, which receive it. Recombination in bacteria is considered to be analogous to sexual reproduction.

Features of recombination in bacteria:

- there is no meiosis. It is not a zygote that is formed, but a merazigote.

- always directed from the donor to the recipient.

- the amount of genetic material in a recombinant is always more than one. The recombinant contains all the genetic information of the recipient and part

donor genetic information.

In eukaryotes, there is only one mechanism of recombination - meiosis; In bacteria, there are three types of recombination:

1) Transformation is the exchange of genetic information using pure DNA.

2) Transduction is a method of transferring genetic information using phages.

3) Conjugation is a method of transferring genetic information when cytoplasmic bridges are formed between two bacteria. During conjugation

Almost the entire genome can pass into the recipient cell.

Genetic methods are used for practical purposes both to detect a microbe in the material under study without isolating a pure culture, and to determine the taxonomic position of the microbe and carry out intraspecific identification.

Genome sequencing– determination of the sequence of DNA nucleotide pairs.

Restriction analysis- this method is based on the use of restriction enzymes - these are endonucleases that cleave the DNA molecule only in certain places. If DNA isolated from a specific material is treated with a certain restriction enzyme, this will lead to the formation of a strictly defined number of DNA fragments of fixed sizes.

Ribotyping– allows you to determine the type of bacteria. The sequence of nucleotide bases in operons encoding rRNA is characterized by the presence of both conserved regions, which have a similar structure in different bacteria, and variable sequences, which are genus- and species-specific and are markers for genetic identification.

Molecular hybridization– used in gene systematics. This method allows us to determine the degree of similarity between different DNAs.

PCR is used to detect genes or corresponding nucleotide sequences that encode either a species or another trait.

The PCR method is based on the principle of complementarity and allows you to increase (amplify) the amount of the DNA sample being tested. This method has extremely high sensitivity and theoretically allows even single DNA molecules to be detected in the material under study.

Types of PCR:

- Real-time PCR; makes it possible to determine the number of DNA fragments present in the material, i.e. carry out quantitative analysis;

- multiplex PCR – the advantage is that 2–4 or more pairs of primers can be introduced into the reaction mixture. They are characteristic of various pathogens.

- reverse transcription PCR – allows for copying the RNA of pathogens.

DNA chips are the latest technologies for hybridization methods of molecular genetic analysis. They are carriers of known oligonucleotides (less than 20 bases each), complementary to sections of the genome (or genomes) under study and occupying a specific site (cell). If there are fragments of the desired DNA in the test sample, they hybridize (join according to the principle of complementarity) with the nucleotide sequences located on the chip.

Classification of bacteria.

The basic taxonomic unit of bacteria is the species. To designate species in bacteria, double (binary) nomenclature is used

A species in bacteria is a collection of related bacteria that have similar biological properties and have a common origin. Currently, there are 3 approaches to classifying bacteria:

1. Routine classification.

It forms the basis of the guide to bacteria edited by Bergey.

2. Numerical taxonomy.

3. Gene systematics.

Conclusion: students are familiar with the basics of bacterial genetics and the basic methods of gene diagnostics.

DNA-containing viruses either have their own replication enzymes (in the capsid), or their genome encodes information about the synthesis of viral enzymes that ensure the replication of viral nucleic acid. The amount of these enzymes varies when applied to different viruses. For example, the genome of the bacterial T4 virus encodes information about the synthesis of about 30 viral enzymes. Further, the genome of large viruses encodes nucleases that destroy the DNA of the host cell, as well as proteins, the effect of which on the cellular RNA polymerase is accompanied by the fact that “the RNA polymerase treated in this way transcribes different viral genes at different stages of viral infection. In contrast, small DNA viruses are more dependent on host cell enzymes. For example, DNA synthesis of adenoviruses is ensured by cellular enzymes.[...]

Bacterial DNA is a high-polymer compound consisting of a large number of nucleotides - polynucleotides with a molecular weight of about 4 million. A DNA molecule is a chain of nucleotides, where their arrangement has a certain sequence. The sequence of nitrogenous bases encodes the genetic information of each species. Violation of this sequence is possible due to natural mutations or under the influence of mutagenic factors. In this case, the microorganism gains or loses some property. His characteristics change hereditarily, that is, a new form of the microorganism appears. In all microorganisms - prokaryotes and eukaryotes - the carriers of genetic information are nucleic acids - DNA and RNA. Only some viruses are an exception: they do not have DNA, and hereditary information is recorded or reflected only in RNA.[...]

In bacterial cells, the total number of DNA bases contains 32-65 mol.% guanine and cytosine.[...]

Nucleus of a bacterial cell. Approximately 1-2% of the dry mass of microorganisms is DNA, which contains the genetic information of the organism. Most microorganisms have an area (or several areas) in which the bulk of DNA is concentrated, having a specific structure (or organelle) and called the nucleus. The nucleus (or nuclear substance) is associated with a cytoplasmic membrane, regardless of whether it is surrounded by elementary membranes (as in amoeba) or without them (as in bacteria and blue-green algae). The nuclear substance is activated during the reproduction period and with the onset of age-related changes associated with cell aging.[...]

The DNA segment (gene) that is intended for molecular cloning must have the ability to replicate when transferred into a bacterial cell, i.e., be a replicon. However, he does not have such an ability. Therefore, to ensure the transfer and detection of cloned genes in cells, they are combined with so-called genetic vectors. The latter must have at least two properties. First, the vectors must be capable of replicating in cells, and in multiple copies. Secondly, they must provide the ability to select cells containing the vector, i.e., have a marker that can be used to counter-select cells containing the vector along with the cloned gene (recombinant DNA molecules). Plasmids and phages meet these requirements. Plasmids are good vectors because they are replicons and can contain genes for resistance to any antibiotic, which allows selection of bacteria for resistance to this antibiotic and, therefore, easy detection of recombinant DNA molecules. [...]

In bacteria, DNA is packed less tightly, unlike true nuclei; A nucleoid does not have a membrane, a nucleolus, or a set of chromosomes. Bacterial DNA is not associated with the main proteins - histones - and is located in the nucleoid in the form of a bundle of fibrils.[...]

The use of recombinant DNA techniques to produce biological agents for pollution control is in its early stages, but one technique that may prove useful in the foreseeable future is genetic probing. The selection of organisms capable of transforming a new compound is often based on the ability to use the substance as a growth substrate. If growth is weak or the substrate is only metabolized, then selection methods will be unsuitable for identifying degradative ability. Therefore, it would be useful to develop genetic probing to identify specific sequences in plasmids and chromosomes, this is necessary to determine the catabolic potential, even if this potential is not expressed. Such probes are designed for TOL plasmids. The method can identify one bacterial colony containing a TOL plasmid among 106 Escherichia coli colonies. Such a powerful tool will be of great value in isolating hidden catabolic functions.[...]

The development of an elegant technique for “cloning” DNA to produce large numbers of exact copies of specific DNA fragments (Fig. 13.4) has recently opened new horizons in the study of the structure, organization and function of the genome. If you cleave double-stranded DIC with one of the “restriction” enzymes (one of the nucleases), which specifically recognize and cleave short sequences of nucleotides (4-6 pairs), then highly reproducible DNA fragments appear. The ends of two DNA strands are usually displaced relative to each other due to the specificity of the cutting sites of a double-stranded molecule, the strands of which are complementary in base composition. The DNA is usually inserted into a plasmid gene important for breeding, such as an antibiotic resistance gene, which allows bacteria containing the plasmid to grow in the presence of the antibiotic.[...]

In bacteria, replication produces many copies of plasmids, and in this way large quantities of embedded DNA fragments can be “grown” and then simply isolated again by digestion with the same restriction enzyme and separation of the resulting products by gel electrophoresis. The use of this method of DNA recombination revolutionized the study of genes.[...]

It was recently discovered that low-intensity rays with a wavelength of 320-400 nm (a region close to the visible light zone) have a mutagenic effect on bacterial DNA viruses. The possible effect of radiation in this wavelength range on plant viruses has not yet been discovered.[...]

The curves of the dependence of reassociation on COT obtained for bacterial DNA are devoid of kinks, and DIC of eukaryotes reassociates according to a different type (Fig. 13.2). At low DNA concentrations and a short incubation time, a significant proportion of single-stranded DNA is re-atured, and with an increase in COT, an additional amount of double-stranded molecules is formed, so that a two-phase curve is obtained. Rapid reaturation at low COT values ​​shows that some sequences in eukaryotes are repeated many times, i.e., up to 10,000 times or more. [...]

The absence of CXC can also be imitated in cases where the DNA of the test phages does not contain sites recognized by the restriction enzyme existing in the strain under study. This phenomenon represents one of the variants of evolutionary adaptive changes in bacterial viruses designed to help them overcome the CXC barrier. The effect of selection pressure in this particular case is expressed in a statistically significant decrease in the number or even complete elimination in the phage DNA of nucleotide sequences that are the substrate of restriction enzymes characteristic of the host cells of the bacterial virus.[...]

Lindegren described the possible stages of the formation of a bacteriophage from prophage DNA, suggesting that the prophage arises as a fragment of foreign bacterial DNA that accidentally entered the cell, which in the early stages divides synchronously with bacterial DNA. The next important stage in the development of the virus would be such a change in the prophage, as a result of which its reproduction, independent of the DNA of the host cell, became possible; as a result the prophage would be used. all available nucleotides, thereby disrupting the growth of the host cell. Finally, at some later stage, a protective protein shell could form and other proteins would arise, which would ensure the survival of the DNA outside the host body and the effective infection of new cells. The separated fragment of bacterial DNA initially apparently encoded proteins adapted to bacterial functions. Very significant changes in DNA are necessary for objects as complex and specialized as, say, the T2 phage of E. coli, which also contain bases that are absent in bacterial DIC, to arise. [...]

The genetic information of bacteria is not limited to the DNA located in the nucleoid of the bacterial cell. As already noted in previous sections of the book, extrachromosomal elements, collectively called plasmids, also serve as carriers of hereditary properties. Unlike DNA nuclear equivalents, nucleoids, which are the organelles of a bacterial cell, plasmids are independent genetic elements. The loss of plasmids or their acquisition does not affect the biology of the cell (the acquisition of plasmids has a positive effect only on the population as a whole, increasing the viability of the species). Transmissible plasmids include those that initiate donor properties in host cells. At the same time, the latter receive a new quality - the ability to conjugate with recipient cells and give them their plasmids. Recipient cells, acquiring plasmids during conjugation, themselves turn into donors.[...]

The absence of adsorption does not exhaust the variety of interaction options between bacterial viruses and microbial cells. They illustrate only one side of this phenomenon, namely the manifestation of cellular protective mechanisms that phenotypically (according to the criterion of lack of growth) imitate restriction. However, there is another variant of cell-bacteriophage interaction that can mimic the absence of CXC. Examples of such mechanisms are the synthesis of inhibitors and methylases encoded by phage genes that protect viral DNA from the action of type II restriction enzymes.[...]

The mechanism of the disinfecting effect of chlorine is associated with metabolic disorders of the bacterial cell during the process of water disinfection. At the same time, an effect on the enzymatic activity of bacteria was revealed, in particular, on dehydrogenases that catalyze redox reactions in the bacterial cell. A. M. Skidalskaya (1969) studied the effect of chlorine on the process of decarboxylation of bacterial amino acids, which occurs in the presence of strictly specific decarboxylase enzymes, and also determined the nucleotide composition of Escherichia coli DNA after completion of the disinfection process at various levels of bactericidal effect.[ . ..]

T-group bacteriophages have the shape of drumsticks measuring 100 x 25 nm. Their genome is represented by DNA. They are virulent phages, because after they infect bacterial cells, the latter are lysed, releasing a large number of newly synthesized phage particles. [...]

Bacterial plasmids are genetic structures located in the cytoplasm and representing DNA molecules ranging in size from 2250 to 400,000 nitrogen base pairs. They exist separately from chromosomes in quantities from one to several tens of copies per bacterial cell.[...]

Strain Pseu.dom.onas vug1 ae ri. pka8eoIso1a has a plasmid 150 thousand bp long, which can replicate autonomously or can be integrated into the bacterial chromosome. Subsequent imprecise excision produced a family of plasmids ranging in length from 35 to 270 kb, some of which contained large segments of chromosomal DNA.[...]

During evolution, bacteria developed the ability to synthesize so-called restriction enzymes (endonucleases), which became part of the cellular (bacterial) restriction-modification system. In bacteria, restriction-modification systems are an intracellular immune system for protecting against foreign DNA. Unlike higher organisms, in which the recognition and destruction of viruses, bacteria and other pathogens occurs extracellularly, in bacteria, protection from foreign DNA (DNA of plants and animals in whose bodies they live) occurs intracellularly, i.e. when foreign DNA penetrates into the cytoplasm of bacteria. In order to protect themselves, bacteria have also evolved the ability to “tag” their own DNA with methylation bases on certain sequences. For this reason, foreign DNA, due to the absence of methyl groups on the same sequences, is melted (cut) into fragments by various bacterial restriction enzymes, and then degraded by bacterial exonucleases to nucleotides. We can say that in this way bacteria protect themselves from the DNA of plants and animals, in whose bodies they live temporarily (as pathogens) or permanently (as saprophytes).[...]

The hereditary properties of bacteria or individual characteristics are encoded in units of heredity - genes, linearly located in the chromosome along the DNA strand. Consequently, a gene is a fragment of a DNA strand. Each characteristic corresponds to a specific gene, and often to an even smaller piece of DNA - a codon. In other words, the DNA strand contains information about all the properties of bacteria in a linear order. However, bacteria have one more feature. The nuclei of eukaryotes usually contain several chromosomes, the number of them in the nucleus is constant in each species. The bacterial nucleoid contains only one ring of a DNA strand, i.e. one chromosome. However, the sum of the hereditary characteristics of a bacterial cell is not exhausted by the store of information contained in one chromosome or in a ring-shaped closed double-stranded DNA helix. Plasmids contain DNA, which also carries genetic information transmitted from the mother cell to the daughter cell.[...]

Mutations are changes in the gene apparatus of a cell, which are accompanied by changes in the characteristics controlled by these genes. There are macro- and microdamage to DNA, leading to changes in the properties of the cell. Macro changes, namely: loss of a section of DNA (division), movement of a separate section (translocation) or rotation of a certain section of the molecule by 180° (inversion) are observed relatively rarely in bacteria. Microdamages, or point mutations, i.e., are much more typical for them. qualitative changes in individual genes, for example, replacement of a pair of nitrogenous bases. Mutations can be direct and inverse, or reverse. Direct mutations are mutations in wild-type organisms, for example, loss of the ability to independently synthesize growth factors, i.e., a transition from proto- to auxotrophy. Back mutations represent a return, or reversion, to the wild type. The ability to revert is characteristic of point mutations. As a result of mutations, such important characteristics as the ability to independently synthesize amino acids and vitamins (auxotrophic mutants) and the ability to form enzymes change. These mutations are called biochemical. Mutations leading to changes in sensitivity to antibiotics and other antimicrobial substances are also well known. Based on their origin, mutations are divided into spontaneous and induced. Spontaneous occur spontaneously without human intervention and are random in nature. The frequency of such mutations is very low and ranges from 1 X 10"4 to 1 X 10-10. Induced ones occur when microorganisms are exposed to physical or chemical mutagenic factors. Physical factors that have a mutagenic effect include ultraviolet and ionizing radiation, as well as temperature. A number of compounds are chemical mutagens, and among them the most active are the so-called supermutagens. Under natural conditions and in experiments, changes in the composition of bacterial populations can occur as a result of the action of two factors - mutations and autoselection, which occurs as a result of the adaptation of some mutants to environmental conditions. This process is obviously observed in an environment where the predominant food source is a synthetic substance, for example, a surfactant or caprolactam.[...]

A single E. coli cell is surrounded by a three-layer cell membrane about 40 nm thick, which is a “bag” or “envelope” containing cellular contents in the form of approximately 2 x 10 16 g of protein, 6 x 10 16 g of DNA and 2 x 10 14 g of RNA (mainly ribosomal RNA). About 2000 different proteins are synthesized in a bacterial cell, most of which are found in the cytoplasm. The concentration of some proteins is 10“® M, while others are on the order of 2 x 10“4 M (from 10 to 200,000 molecules per cell). [...]

In single-celled organisms, sexual reproduction occurs in several forms. Conjugation is also found in ciliates, in which during this process a transfer of nuclei occurs from one individual to another, followed by division of the latter.[...]

Bacteria: prokaryotes (“prenuclear”) single-celled organisms. Their cells do not have a nucleus separated from the cytoplasm. However, the genetic program, like that of all living organisms, is encoded as a sequence of nucleotides in DNA and carries information about the structure of proteins. Bacterial cells do not contain organelles such as chloroplasts (specialized for photosynthesis) and mitochondria (specialized for cellular respiration and ATP synthesis). These biochemical processes occur in bacteria in the cytoplasm.[...]

Extremely small cell sizes are a characteristic, but not the main feature of bacteria. All bacteria are represented by a special type of cell that lacks a true nucleus surrounded by a nuclear membrane. An analogue of the nucleus in bacteria is the nucleoid - DNA-containing plasma, not delimited from the cytoplasm by a membrane. In addition, bacterial cells are characterized by the absence of mitochondria, chloroplasts, as well as the special structure and composition of membrane structures and cell walls. Organisms whose cells lack a true nucleus are called prokaryotes (prenuclear) or protocytes (i.e., organisms with a primitive cell organization).[...]

Mycoplasma cells are oval in shape and their size is about 0.1-0.25 nm in diameter (Fig. 43). They are characterized by the presence of a thin outer plasma membrane (thickness - about 8 nm), which surrounds the cytoplasm containing a DNA molecule sufficient to encode about 800 different proteins, RNA of different types, ribosomes with a diameter of about 20 nm. Their cytoplasm contains various inclusions in the form of proteins, lipid granules and other compounds. Due to insufficient cell rigidity, mycoplasma membranes pass through bacterial filters.[...]

It has been established that on ribosomes the binding of activated amino acids occurs and their placement into a polypeptide chain in accordance with the genetic information received from the nucleus through messenger RNA (mRNA), which reads the corresponding information from the DNA and transmits it to the ribosomes. A number of proteins are synthesized on isolated ribosomes and the inclusion of labeled amino acids in them is noted. The role of the matrix in protein synthesis is performed by mRNA, which is attached to the ribosome. On the surface of the latter, an interaction occurs between a complex of amino acids, transfer RNA carrying the next amino acid, and the nucleotide sequence of messenger RNA, which functions on the ribosome once and, after the synthesis of the polypeptide chain, disintegrates, and the newly synthesized protein accumulates in the ribosomes. In a bacterial cell, with a regeneration period of 90 minutes, the rate of mRNA turnover reaches 4-6 seconds.[...]

Cytoplasm is a colloidal solution, the dispersed phase of which is complex protein compounds and substances similar to fats, and the dispersion medium is water. Some forms of bacteria contain inclusions in the cytoplasm - droplets of fat, sulfur, glycogen, etc. The permanent components of bacterial cells are special outgrowths of the cytoplasmic membrane - mesosomes, which contain enzymatic redox systems. In these formations, processes mainly associated with the respiration of bacteria take place. In small inclusions - ribosomes containing ribonucleic acid, protein biosynthesis occurs. Most types of bacteria do not have a separate nucleus. The nuclear substance, represented by DNA, is not separated from the cytoplasm and forms a nucleoid. The transportation of substances necessary for the life of the cell and the removal of metabolic products is carried out through special channels and cavities, separated from the cytoplasm by a membrane having the same structure as the cytoplasmic one. This structural formation is called the endoplasmic reticulum (reticulum).[...]

An idea of ​​the variability and heredity of bacteria cannot be formed without knowledge of some provisions of the molecular genetics of the prokaryotic cell. The processes of adaptation of microbial cultures to changing environmental conditions are based on variability and heredity, which are sections of bacterial genetics. When presenting the cytology of a bacterial cell, the structure of DNA and RNA and their role in the life of the cell were already considered. The characteristic structure of DNA is preserved in each species and is passed on to offspring from generation to generation, like other characteristics. Bacterial DNA is a double-stranded helix that closes into a ring. The ringed strand of bacterial DNA, located in the nucleoid, does not contain protein. This DNA ring corresponds to the chromosome of a eukaryotic cell. It is known that the chromosome of eukaryotic cells, in addition to DNA, always contains a protein component. It follows that the concept of a chromosome in eukaryotes is somewhat different from the concept of a bacterial chromosome. The strand of DNA that makes up the bacterial chromosome, of course, differs from species to species. The sugar phosphate component of DNA is the same in all types of bacteria; the arrangement of nitrogenous bases and their combination, on the contrary, differ among different species.[...]

The increasing indiscriminate use of antibiotics in livestock, which are used in low doses as growth promoters and also as a preventive measure against stress-related gastrointestinal disorders in farmed animals, is leading to the increasing prevalence of R-factor antibiotic resistance in microbial populations. , transmitted from one bacterial cell to another during conjugation. Transfer occurs through a plasmid, which is a circular extrachromosomal DNA capable of replication.[...]

In contrast to virulent phages, so-called moderate-acting phages, or simply moderate phages, are known. A typical representative of such phages is phage X, which has also been and is being used as an experimental model to clarify many issues in molecular genetics. Phage X has two important properties. Like virulent phages, it can infect bacterial cells, reproduce vegetatively, producing hundreds of copies in cells, and lyse cells releasing mature phage particles. However, the DNA of this phage can be included in the bacterial chromosome, turning into a prophage. In this case, the so-called lysogenization of bacteria occurs, and bacteria containing the prophage are called lysogenic. Lysogenic bacterial cells can possess a prophage for an indefinitely long time without lysing. Lysis with the release of new phage particles is observed after exposure of lysogenic bacteria to any factor, for example, UV radiation, which induces the development of a prophage into a phage. The study of lysogenic bacteria made it possible to obtain a number of new data on the role of different proteins in the action of phage genes.[...]

The chloroplast genome of a number of higher plants consists of 120 genes. The chloroplast genome is very similar to the bacterial genome in both organization and function. The human mitochondrial genome probably lacks introns, but introns are found in the DNA of the chloroplasts of some higher plants, as well as in the DNA of mitochondria of fungi. It is believed that the chloroplast genomes of higher plants remain unchanged for approximately several million years. It is possible that such antiquity is also characteristic of the mitochondrial genomes of mammals, including humans.[...]

Modern diagrams illustrating the work of genes are built on the basis of a logical analysis of experimental data obtained using biochemical and genetic methods. The use of subtle electron microscopic methods allows one to literally see the work of the hereditary apparatus of the cell. Recently, electron microscopic images have been obtained, which show how on the bacterial DNA matrix, in those areas where molecules of RNA polymerase (an enzyme that catalyzes the transcription of DNA into RNA) are attached to the DNA, the synthesis of mRNA molecules occurs. The mRNA strands, located perpendicular to the linear DNA molecule, move along the matrix and increase in length. As the RNA strands lengthen, ribosomes are attached to them, which, in turn, moving along the RNA strand towards DNA, lead to protein synthesis.[...]

Transduction is the transfer of genetic material from a donor bacterium to a recipient bacterium using a phage. The phenomenon of transduction was first discovered in 1951 by Lederberg and his colleagues in Salmonella typhimurium. Nowadays a distinction is made between nonspecific and specific transduction. With nonspecific transduction, phage can transfer any trait from a donor bacterium to a recipient bacterium. Transfer is carried out only by temperate (non-virulent) phages. Temperate phages are capable of infecting bacteria, but do not reproduce in them and do not cause lysis, but are included in the DNA of the bacterial cell and in this non-infectious state in the form of a so-called prophage are transmitted from cell to cell during reproduction. Bacterial cultures containing a prophage are called lysogenic. In these cultures, with a low frequency (in one of 102 - 105 cells), spontaneous reproduction of the phage is observed and cell lysis occurs with the release of phage particles, detected with the help of indicator bacteria for which such a phage is virulent.[...]

The experiments were carried out on a three-chamber cell, consisting of a central working chamber and two electrode chambers. 750 mg of cotton wool was placed in a working chamber measuring 25 X 7 X 37 mm (length X width X height), separated from the electrode chambers by cellophane membranes. Through it, the initial solution of the substances under study was fed from bottom to top at a constant speed. The content of compounds in the initial solutions supplied to the working chamber (C0) and in the solutions leaving the chamber (Ci) was monitored by the absorption maxima of proteins and nucleic acids in the wavenumber range (35.5-38) X 103 cm-1 using a Specord UV-VIS UV spectrophotometer. The electrode chambers were filled with granular activated carbon and distilled water was passed through them in a separate flow.

MORPHOLOGY OF BACTERIA

Bacteria– microscopic, usually unicellular organisms of plant nature (microflora); Certain types of bacteria are characterized by a certain morphology with sufficient constancy. There are three main forms of bacteria - spherical or oval (cocci), rods (bacillus) and spiral.

Cocci divided into pairs - diplococci(Neisseria); tetracocci, arranged in groups of 4 in the shape of squares; packet-forming cocci, or sarcins, located on “floors”; streptococci, arranged in chains; staphylococci, forming shapeless clusters, somewhat reminiscent of bunches of grapes.

Sticks. Among the sticks there are single, randomly arranged bacteria (enterobacteriaceae), diplobacillus, located in pairs (along one line), and streptobacilli, forming chains (anthrax bacilli).

Spiral shaped bacteria divided into two groups - vibrios and bacteria similar in shape, the curvature of the body of which does not exceed a quarter turn of the spiral (Campylobacter), and spirochetes and spirilla, having bends equal to one or several turns of the spiral (the causative agent of syphilis).

Any bacterium is made up of three components: surface structures, cell membrane, cytoplasm.

The surface structures of bacteria are capsules, flagella and microvilli.

Capsules surround the cell membrane of many bacteria, including pathogenic ones. The capsules lack the ordered organization characteristic of the bacterial cell wall. There are microcapsules, which are detected only by electron microscopy in the form of a layer of mucopolysaccharide microfibrils) and macrocapsules (detected by light microscopy).

Most bacterial capsules consist of complex polysaccharides. They are detected by staining according to Burri-Gins, or using the Neufeld swelling reaction. Capsules may include nitrogen-containing compounds, such as those of pneumococci (composed of polysaccharides, glucosamine and glucuronic acid), but may not contain nitrogen, such as leuconostoc capsules (consisting of dextrin, levulan, fructosan and other polymerized monosaccharides).

The capsules of some bacteria (Bacillus anthracis) consist of polysaccharides and polypeptides formed by monomers of D-glutamic acid, which protects the bacterium from proteolytic enzymes of phagocytes.

Flagella present in many bacteria and provide mobility. The flagellum is a spirally curved filament driven into rotation by a “motor” located at the point of its attachment to the membrane. In different bacteria, the thickness of the flagella varies from 12 to 18 nm, and the length can reach 20 µm.

Bacterial flagella consist of a protein (flagellin) and are built from its subunits with a relatively low molecular weight. The filaments of the flagella are driven by a membrane hinge-like basal hook, secured by a basal body, which consists of one pair of rings in gram-positive bacteria and two pairs of rings in gram-negative bacteria. The rings act as a “drive disk” and a “bearing” on the inner surface of the peptidoglycan layer. The entire structure performs the function of a chemomechanical converter (flagellin motor).

Location.

Peritrichous. Flagella are located over the entire surface of the cell wall (bacteria of the Enterobacteriaceae and Bacillaceae families).

Monotrichs. One thick flagellum at one end (vibrios).

Polytrichs. Bundle of 2-50 flagella, visible as single.

Polar flagella are attached to one or both ends of the bacterium. Lophotrichs- a bundle of flagella at one end of a bacterium (Pseudomonas). Amphitrichy– bipolarly located bundles (Spirillum).

Microvilli(pili, fimbriae) are protein hairs (from 10 to several thousand) 3-25 nm thick and up to 12 microns long.

A. Ordinary drank. Many Gram-negative bacteria have long, thin pili (fimbriae) that begin on the cytoplasmic membrane and penetrate the cell wall. They are formed by proteins of the same type, the molecules of which form a helical thread. Their main function is the attachment of bacteria to substrates, such as mucosal surfaces, which is an important factor in colonization and infection. In addition, increasing the surface area of ​​the bacterial cell gives it additional advantages in utilizing environmental nutrients.

B. F-drank(fertility factor) – special formations involved in the conjugation of bacteria. They look like hollow protein tubes 0.5-10 microns long. Their formation is encoded by plasmids.

Cell membrane Most bacteria consist of a cell wall and an underlying cytoplasmic membrane.

The bacterial cell wall is thin, elastic and rigid, and may be completely absent in some bacteria (for example, L-forms and mycoplasmas). The cell wall protects bacteria from external influences, gives them a characteristic shape, and transports nutrients and releases metabolites through it. On its surface there are various receptors for bacteriophages, bacteriocins and various chemicals. The CS maintains the constancy of the internal environment and withstands significant pressure from the inside (for example, the partial pressure of intracellular substances of gram-positive bacteria can reach 30 atmospheres). The structure and composition of the elements of the CS determine the ability to perceive dyes, i.e. their tinctorial properties. One of the basic principles of bacterial differentiation is the ability to perceive and retain the coloring complex of gentian violet with iodine inside the cell, or lose it after treatment with alcohol (Gram stain). Accordingly, gram-positive (colored violet-purple) and gram-negative (red) are distinguished.

The main component of bacterial CS is peptidoglycan (murein). Peptidoglycan is relatively more abundant in Gram-positive bacteria: the proportion of the murein network, which is approximately 40 layers thick, accounts for 30–70% of the dry mass of the CM. Gram-negative bacteria contain only 1-2 layers of murein, which makes up about 10% of the dry mass of the CS.

Peptidoglycan is represented by polymer molecules consisting of repeating disaccharide groups, the formation of which involves N-acetylglucosamine andN-acetylmuramic acid, the latter binds disaccharides with oligopeptides (out of 20 known amino acids in the CS of bacteria, only 4 were found - glutamic acid, glycine, lysine and alanine). Bacterial CS also includes unique amino acids, such as diaminopimelic and D-isomers of glutamic acid and alanine. Lysozyme hydrolyzes peptidoglycan by cleaving the glycosidic bonds between N-acetylglucosamine and N-acetylmuramic acid.

Peptidoglycan cross-linking involves the formation of a peptide bond between the terminal residue of a peptide side chain (usually D-alanine) with the penultimate residue of the adjacent side chain (L-lysine or diaminopimelic acid).

Gram-positive bacteria have a simply organized but powerful CS, consisting mainly of multiple layers of peptidoglycan, including unique teichoic acid polymers– chains of 8-50 glycerol or ribitol residues, interconnected by phosphate bridges.

Gram-negative bacteria have a thinner (compared to gram-positive bacteria) CS, which includes a bimolecular layer of peptidoglycan and does not contain teichoic acid.

On top of the peptidoglycan layer is an additional, or outer, membrane. Its thickness exceeds the size of a peptidoglycan monolayer.

Components of the outer membrane: phospholipid bilayer, proteins, polysaccharides and LPS, arranged in a mosaic pattern.

Phospholipid bilayer attached to peptidoglycan by lipoproteins crossing the periplasmic space.

Squirrels, including porins, forming transmembrane channels, are involved in the transport of ions and hydrophilic compounds from the external environment to the periplasm.

LPS formed from a lipid part (lipid A), a polysaccharide-rich core and polysaccharide side chains. The polysaccharide part of LPS has immunogenic properties and is called O-Ag. The lipid part is heat stable and is responsible for the biological effects of endotoxin.

Autolysins. Bacterial CSs contain autolysins, enzymes that dissolve the peptidoglycan layer. Their activity is necessary for the processes of cell growth, cell division, sporulation, and achieving a state of competence during transformation.

Cytoplasmic membrane(otherwise the cellular or plasma membrane) is a physical, osmotic and metabolic barrier between the internal contents of a bacterial cell and the external environment. CPM has a complex three-layer structure and is characterized by pronounced selective permeability. In some bacteria, between the CPM and the CS there is a periplasmic space - a cavity filled with enzymes (ribonucleases, phosphatases, penicillinases, etc.); in gram-negative bacteria, enzymes are freely poured into the environment. The bacterial CPM consists of proteins, lipids, carbohydrates and RNA.

Squirrels CPM is divided into structural And functional. The latter include enzymes involved in synthetic reactions on the membrane surface, redox processes, as well as some special enzymes (for example, permeases).

The center is located bacterial electron transport system, providing energy needs.

Mesosomes – complex invaginations of the CPM, the functions of which have not yet been fully established. They are known to be associated with the nucleoid and are related to cell division and sporulation.

Removal of the CS, which protects the adjacent CPM, leads to lysis of bacteria or to the formation of protoplasts and spheroplasts, differing in origin (from gram-positive or gram-negative bacteria, respectively), as well as in osmotic stability. Being in an isotonic environment, bacteria lacking CS are able to absorb O 2 and release CO 2, as well as multiply.

L-forms. Under the influence of certain external factors, bacteria are able to lose CS, forming L-forms (named after the D. Lister Institute, where they were first isolated). Such transformation can be spontaneous (for example, in chlamydia) or induced (for example, under the influence of antibiotics). Highlight stable and unstableL-forms. The former are not capable of reversion, while the latter revert to their original forms after removing the causative factor.

Representatives of the mycoplasma group (class Mollicutes) do not have cell walls.

Cytoplasm bacteria - a matrix for the implementation of vital reactions - is separated from the CS by a cytoplasmic membrane. The cytoplasm of most bacteria contains DNA, ribosomes, and storage granules; the rest of the space is occupied by the colloidal phase, its main components are soluble enzymes and RNA (matrix and transfer RNA). Bacteria lack various organelles characteristic of eukaryotic cells, and their functions are performed by the bacterial CPM.

DNA. A bacterial cell does not have a nuclear membrane. DNA is concentrated in the cytoplasm in the form of a coil called a nucleoid, or genophore.

Genophore bacteria is represented by a double helical circular covalently closed supercoiled DNA molecule, constituting 2-3% of the dry mass of the cell (more than 10% by volume). The length of the molecule contour varies from 0.25 to 3 mm. The bacterial DNA superhelix does not contain histones. The amount of genetic information encoded in the genephore varies between species (for example, the Escherichia coli genome encodes approximately 4,000 different polypeptides).

Plasmids. In bacteria, an additional DNA molecule may be present in the form of extrachromosomal elements or integrated into the genophore. Such inclusions are called plasmids (respectively episomal or integrated). Episomal DNA is also characterized by a ring shape, but the episome is smaller in size than the bacterial chromosome. Plasmids carry a number of different genes and often determine the virulence of bacteria, but the information contained in plasmids is not absolutely necessary for the bacterial cell.

Ribosomes bacteria are complex globular formations consisting of various RNA molecules and many associated proteins. The entire formation functions as a locus of protein synthesis.

70 Sribosomes. The diameter of bacterial ribosomes is about 20 nm. Sedimentation coefficient – ​​70S (Svedberg units). Bacterial ribosomes consist of two subunits with a sedimentation coefficient of 50S for one and 30S for the other. The joining of subunits occurs before protein synthesis begins. Depending on the intensity of growth, a bacterial cell can contain from 5,000 to 50,000 ribosomes.

Bacteriostatic antibiotics (streptomycin, tetracycline, chloramphenicol) inhibit protein synthesis, blocking some metabolic processes occurring in bacterial ribosomes.

Spare pellets contain a temporary excess of metabolites. The presence and number of granules vary depending on the type of bacteria and their metabolic activity. Polysaccharides (starch, glycogen, granulosa), fats (triglycerides, similar to the fats of higher animals, are stored in yeast of the genus Candida; waxes - in mycobacteria and nocardia; polymers of β-hydroxybutyric acid - for example in the cells of Bacillus megaterium), can be stored in the form of granules. polyphosphates (for example, volutin, first discovered in Spirillum volutans), sulfur (in bacteria that oxidize sulfide to sulfate), proteins - for example, protoxin (in Bacillus thuringiensis and related species).

The main secret of organic life lies in the ability to reproduce and transmit hereditary information from previous generations to descendants through a fairly simple mechanism of self-copying the DNA macromolecule of each living cell. Each one, regardless of whether the organism consists of a large number of cells or whether we are talking about the DNA that is found in the cells of bacteria, these single-celled simple organisms that are not always capable of gathering even into a large colony.

Like all representatives of organic life, the hereditary (genetic) information of bacteria is stored in their DNA. What is genetic information? What structure stores hereditary information?

1. Genetic information is a specific sequence of nucleotides. There is no other secret in the kernel. By copying this sequence, the cell synthesizes a wide variety of proteins. They also solve all other issues of the body, from organizational issues to supplying the cell with building materials.
2. The DNA macromolecule consists of four nucleic bases (adenine, guanine, thymine and cytosine), united into a double helix by the sugar deoxyribose and phosphoric acid residues. It is the nucleic bases that encode the sequence of protein assembly, regardless of whether there is a formed nucleus in the cell or not.

The deoxyribonucleic acid of bacteria has the same structure as the molecules that store the hereditary information of all other living beings on the planet. Just like all other organic cells, bacteria form chromosomes from DNA. But this does not mean that there are no other differences.

The fundamental difference between a bacterium is that it does not have a cell nucleus, the hereditary information of a bacterium is not collected in the cell nucleus, it is simply a ring molecule that is stuck to one of the walls of the cytoplasmic membrane.

However, the fact that there is no core does not prevent active processes of replication and translation using this keeper of hereditary information. To understand how information is transferred, you need to understand what chromosomes, genes and the cell nucleus are.

1. A gene is a section of a macromolecule on which a sequence of nucleotides is written that allows the assembly of one specific type of protein. There is no other information in the genes.
2. A chromosome is a combination of a DNA strand with histone proteins that structure it and give it a certain shape before the cell begins to divide. In the phase when division does not occur, there are no chromosomes as such in the cell (or in the nucleus, if we are talking about nuclear eukaryotes).
3. The cell nucleus is a cellular structure that contains hereditary information structured into a chromosome when the cell prepares to divide. It initiates the division process itself. It is important to remember that bacteria do not have a cell nucleus.

If in a eukaryotic cell, during division, separate structures are used, specially formed for the convenience of division, then how does bacteria multiply in conditions of unformed, apparent chaos in the absence of a cell nucleus?

Deoxyribonucleic acid of a bacterial cell

Although the bacterial DNA molecule is depicted as a rather voluminous circular structure located in the center of the cell, it is in fact a rather compact formation localized in limited areas of the cytoplasm.

Due to the absence of a nuclear membrane that would separate the assembled bacterial macromolecule from other cellular structures, the genetic apparatus of nuclear-free organisms cannot be associated with the genetic apparatus of eukaryotes, therefore the genetic apparatus of prokaryotes was called nucleoid.

Characteristic features of a nucleoid:

1. DNA containing several thousand genes.
2. Genes are arranged linearly and are called chromosomes. The chromosome of a bacterium is a linear collection of its genes.
3. The macromolecule is also folded by proteins similar to eukaryotic histones.

The nucleoid is attached to the cytoplasmic membrane at the points where replication begins and ends (self-copying).

It has been established experimentally that a nucleoid and a chromosome are not the same thing. An increase in the number of chromosomes (linear genes) is evidence that bacteria are actively dividing. One nucleoid can consist of one chromosome or several copies of it. Thus, during the division period, Azotobacter replicates to 20-25 chromosomes (nucleoid copies).

Copy process

In theoretical designs developed by microbiologists in those years when it was very difficult or practically impossible to study complex molecular processes experimentally, copying deoxyribonucleic acid can be carried out in three ways:

1. Conservative, in which the parent double helix does not unwind and the daughter double helix is ​​formed entirely from new material.
2. Dispersive, in which the parent macromolecule breaks up into fragments, and daughter ones are formed on the nucleotide sequences of these fragments as on templates.
3. Semi-conservative. According to this model, the double helix unwinds and each strand of the helix serves as a template for daughter DNA. A so-called hybrid of an old macromolecule and a chain created from new components is formed.

When in 1957 a way was found to monitor the processes occurring in bacterial DNA during its replication, it was found that deoxyribonucleic acid replicates in a semi-conservative way, that is, through unwinding and the use of unwinding regions as templates for the synthesis of new macromolecules.

The process of bacterial DNA replication itself is very similar to the DNA replication of other organic mechanisms. It happens according to the following scheme:

1. DNA helicases unwind and break the double helix by moving along the sugar-phosphate backbone of deoxyribonucleic acid.
2. Polymerase enzymes catalyze the addition of complementary nucleic bases to single-stranded fragments of deoxyribonucleic acid.

After replication, all the main parts of the cell are duplicated: organelles, cytoplasmic membrane, cell wall, and the bacterial cell splits in two.

Issues

In addition to the purely scientific interest in the study of bacterial DNA, the mechanism of replication and transmission of hereditary information from one cell to another is also of exceptional practical importance.

It is a widely known fact that bacteria very quickly adapt when exposed to antibiotics and begin to produce certain antibody proteins that block the destructive effect of antibiotics on the bacterial cell. In subsequent generations of bacteria, this resistance to a specific group of antibacterial drugs is maintained.

Moreover, through horizontal gene transfer (not through division, but through the simple contact of one bacterium with another), such genetic information is also transferred, making an increasing number of bacterial species resistant to antibiotics.

The study of these properties of bacteria, the determination of how an extraneous gene is included in the general structure of deoxyribonucleic acid, is what modern microbiology deals with.