home-Tops-What is the analogue of the nucleus in bacterial cells. Bacterial cell composition and cytoplasmic functions

What is the analogue of the nucleus in bacterial cells. Bacterial cell composition and cytoplasmic functions

The concept of “cytoplasm” is complex, and when translated from Greek it means “cell contents”. Modern science understands the cytoplasm as a complex dynamic physicochemical system contained within the plasma membrane. That is, all the intracellular contents of prokaryotes, excluding the chromosome, are considered the cytoplasm of the bacterial cell.

The cytoplasm of a prokaryotic cell has 2 layers of restriction:

  • cytoplasmic membrane (CPM);
  • cell wall.

The layers that limit the cytoplasm in bacteria have different functions and properties.

Bacterial cell wall

The outer covering layer of prokaryotes, the cell wall, is a dense shell and performs a number of functions:

  • protection from external influences;
  • giving the microorganism a characteristic shape.

In fact, the cell wall of microorganisms is a kind of exoskeleton. This structure is justified - after all, the intracellular osmotic pressure can be tens of times higher than the external pressure, and without the protection of a dense cell wall, the bacterium will simply burst.

A dense cell wall is characteristic only of bacterial and plant cells - an animal cell has a soft shell.

The bacterial cell wall, which limits the contents of the cell, has a thickness of 0.01 to 0.04 microns, and the thickness of the wall increases during the life of the microorganism. Despite the density of the cell membrane, it is permeable. Nutrients pass inside without hindrance, and waste products are removed from it.

Cytoplasmic membrane

Between the cytoplasm and the cell wall is the CPM - the cytoplasmic membrane. In a bacterial cell it performs a number of functions:

  • regulates the intake of nutrients and the removal of waste products;
  • synthesizes compounds for the cell wall;
  • controls the activity of a number of enzymes located on it.

The cytoplasmic membrane is so strong that a bacterial cell can exist for some time even without a cell wall.

Intracellular composition of the microorganism

Studies using an electron microscope have revealed a very complex structure of the intracellular substance.

The cytoplasm of any bacterial cell contains a large amount of water, it contains various organic and inorganic compounds - vital structures and organelles. Thus, in the cytosol (cytoplasmic matrix), the intracellular fluid, ribosomes, plastids and a supply of nutrients are located.

All intracellular contents are divided into three groups:

  • hyaloplasm (cytosol or matrix of the cytoplasm);
  • organelles are essential parts of a bacterial cell;
  • inclusions are optional parts.

The cytoplasmic matrix is ​​not an aqueous solution, but a gel with varying viscosity. The aggregate state of hyaloplasm - gel-sol (higher or lower degree of viscosity) is in dynamic equilibrium and depends on external conditions.

The hyaloplasm of a bacterial organism includes the following structures:

  • inorganic substances;
  • metabolites of organic origin;
  • biopolymers (proteins, polysaccharides).

The main purpose of hyaloplasm is to unite all existing inclusions and ensure stable chemical interaction between them.

Intracellular organelles of prokaryotes are microstructural plasmatic compounds responsible for life-support functions and are present in almost all bacterial cells. Organelles are divided into two large groups:

  • mandatory - are vital for the functioning of the body;
  • optional – not of great importance for operation; microorganisms of even the same strain can differ in the set of these organelles.

Obligatory organelles

The organelles necessary for cell functioning include:

  • nucleoid (bacterial chromosome) – is a circular double-stranded DNA molecule;
  • ribosomes (responsible for protein synthesis) - similar to the ribosomes of cells that have a nucleus; can move freely in the cytoplasm or be associated with the CPM;
  • cytoplasmic membrane (CPM);
  • mesosomes are responsible for energy metabolism and participate in the process of cell division; are the result of invagination of the cytoplasmic membrane.

In the central part of the bacterial space there is an analogue of the eukaryotic nucleus - the nucleoid (DNA of the microorganism). In the case of eukaryotes, DNA is located only in the nucleus, but in bacteria, DNA can be concentrated in one place or dispersed in several places (plasmids).

Other differences between the bacterial chromosome and eukaryotic nuclei are:

  • more loose packaging;
  • absence of organelles characteristic of the nucleus - nucleoli, membranes and others;
  • have no connection with histones - the main proteins.

As an analogue of the eukaryotic nucleus, the bacterial chromosome is a primitive form in terms of the organization of nuclear matter.

Optional organelles of prokaryotes

Optional bacterial organelles do not have a significant effect on the functional abilities of the bacterial organism. A characteristic feature of prokaryotes is the manifestation of dissociation, as a result of which morphotypes (morphovars) are formed - strains of microorganisms of the same species that have morphological differences.

As a result, in a bacterial colony differences appear not only in morphological characteristics, but also in physiological, biochemical, and genetic ones. The main differences between morphovars and each other are precisely in the composition of optional organelles.

Optional organelles include:

  • plasmids - carriers of genetic information, similar to the bacterial chromosome, but much smaller in size and with the possibility of the presence of several copies in the body;
  • inclusions containing nutrients (for example, volutin); may be a characteristic feature of a particular type of microorganism.

Optional bacterial organelles are not a permanent feature of a given species—many inclusions are sources of carbon or energy. Under favorable conditions, the microorganism forms a similar reserve in the intracellular space, which is consumed when unfavorable conditions occur.

Inclusions containing nutrients belong to the granular type of compounds. According to their composition they can be divided into:

  • polysaccharides – granulosa (starch), glycogen;
  • volutin (metachromatin granules) – contains polymetaphosphate;
  • fat drops;
  • drops of sulfur.

It is the inclusion of low molecular weight formations that leads to the emergence of different values ​​of osmotic pressure of the bacterial cytoplasm and the external environment.

The substance of the intracellular space of a living bacterium is in constant motion (this is called cyclosis), thereby moving the substances and organelles contained in it.

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 bacteriumBacteria shapeBacteria image
Cocci Ball-shaped
BacillusRod-shaped
Vibrio Comma-shaped
SpirillumSpiral
StreptococciChain of cocci
StaphylococcusClusters 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 can form 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.

BACTERIA

BACTERIA, simple unicellular microscopic organisms belonging to the kingdom Prokaryotae (prokaryotes). They do not have a clearly defined nucleus; most of them lack CHLOROPHYLL. Many of them are mobile and swim using whip-like flagella. They reproduce primarily by division. Under unfavorable conditions, many of them are able to be preserved inside spores, which have high resistance due to dense protective shells. They are divided into AEROBIC AND ANAEROBIC. Although pathogenic bacteria are the cause of most human diseases, many of them are harmless or even beneficial to humans, since they form an important link in the FOOD CHAIN; for example, they contribute to the processing of plant and animal tissues, the conversion of nitrogen and sulfur into AMINO ACIDS and other compounds that can be used by plants and animals. Some bacteria contain chlorophyll and participate in PHOTOSYNTHESIS. see also ARCHAEBACTERIA, EUBACTERIA, PROKARYOTES.

Bacteria exist in three main forms and types: spherical (A), called cocci, rod-shaped (bacillus, B) and spiral (spirilla, C). Cocci occur in the form of lumps (staphylococci, 1), pairs of two (diplococci, 2) or chains (streptococci, 3). Unlike cocci, which are unable to move, bacilli move freely; some of them, called peritrichia, are equipped with many flagella (4) and can swim, and monotrichium forms (5, see in the figure below) have only one flagellum. Bacilli can also form spores (6) in order to survive a period of unfavorable conditions SPIRILLA can have a corkscrew shape, such as the spirochete Leplospira (7), or can be slightly curved, with flagella, such as Spirillum (8). Images are given with a magnification of x 5000

Bacteria do not have a nucleus; instead they have a nucleoid (1), a single loop of DNA. It contains genes, chemically encoded programs that determine the structure of the bacterium. On average, bacteria have 3,000 genes (compared to 100,000 in humans). The cytoplasm (2) also contains glycogen granules (food) (3) and ribosomes (4), which give the cytoplasm a granular appearance and serve to produce protein. In many bacteria, it also contains tiny genetic elements called plasmids. Most bacteria, but not all, have rigid protective cell walls (B). They come in two main types. The first type has one thick (10-50 nm) layers. Bacteria with this cell type are called Gram-positive because they stain bright purple using Gram dye. Gram-negative bacteria have been shown to have thinner walls (1) with an additional layer of proteins and lipids on the outside (2). This type of cell does not stain purple. This difference in properties is used in medicine. The body's defense cells recognize bacteria precisely by their walls. The cell membrane (3) surrounds the cytoplasm. It is only a few molecules of proteins and lipids thick and is a barrier through which a living cell controls the entry and exit of various substances. Some bacteria move (C) using flagella (1), which are rotated by a hook (2). The energy for movement is provided by the flow of protons through the cell membrane (3), which DRIVES a disk of protein molecules (4) located in the membrane into motion. A rod (5) connects this protein “rotor” to the hook via another disc (6), which seals the cell wall.

Before the development of effective sanitation systems and the discovery of antibiotics, epidemics of serious diseases caused by bacteria swept through Europe again and again. The symptoms of many bacterial diseases are caused by the action of toxic proteins (called toxins) that are produced by bacteria. The botulinum toxin, produced by the bacterium Clostridium botulinum (which causes food poisoning), is one of the most powerful poisons known today. The tetanus toxin, produced by the related Clostridium tetani (1), infects deep and contaminated wounds. When a nerve impulse (2) causes tension in a muscle cell, the toxin blocks the relaxing part of the signal and the muscles remain tense (this is why the disease is called tetanus). In developed countries, most killer bacteria are now under control, tuberculosis is rare and diphtheria is not a serious problem. However, in developing countries, bacterial diseases are still taking their toll.


Scientific and technical encyclopedic dictionary.

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    - (from the Greek bakteria stick). Microscopic single-celled organisms, mostly rod-shaped. Dictionary of foreign words included in the Russian language. Chudinov A.N., 1910. BACTERIA Greek, from bakteria, stick. Genus of fireweeds... ... Dictionary of foreign words of the Russian language

    Modern encyclopedia

    bacteria- microorganisms with a prokaryotic type of cell structure, i.e. there is no nuclear envelope, no real nucleus; die from exposure to sunlight; have a sense of smell. cocci are spherical bacteria. diplococci. micrococci. streptococci. staphylococcus... ... Ideographic Dictionary of the Russian Language

    Bacteria- (from the Greek bakterion rod), a group of microscopic predominantly single-celled organisms. They have a cell wall, but do not have a clearly defined nucleus. They reproduce by division. According to the shape of the cells, bacteria can be spherical (cocci),... ... Illustrated Encyclopedic Dictionary

    Bacteria- (from the Greek bakterion rod), a group of microscopic unicellular organisms. Based on the type of respiration they are divided into aerobic and anaerobic, and based on the type of nutrition into autotrophic and heterotrophic. Participate in the cycle of substances in nature, performing the function... ... Ecological dictionary

All living organisms on Earth are divided into two groups: prokaryotes and eukaryotes.

  • Eukaryotes are plants, animals and fungi.
  • Prokaryotes are bacteria (including cyanobacteria, also known as blue-green algae).

Main difference

Prokaryotes do not have a nucleus, circular DNA (circular chromosome) is located directly in the cytoplasm (this section of the cytoplasm is called the nucleoid).


Eukaryotes have a formed nucleus(hereditary information [DNA] is separated from the cytoplasm by the nuclear envelope).

Additional Differences

1) Since prokaryotes do not have a nucleus, then there is no mitosis/meiosis. Bacteria reproduce by dividing in two ("direct" division, as opposed to "indirect" division - mitosis).


2) In prokaryotes, ribosomes are small (70S), and in eukaryotes they are large (80S).

3) Eukaryotes have many organelles: mitochondria, endoplasmic reticulum, cell center, etc. Instead of membrane organelles, prokaryotes have mesosomes - outgrowths of the plasma membrane, similar to mitochondrial cristae.


4) A prokaryotic cell is much smaller than a eukaryotic cell: 10 times in diameter, 1000 times in volume.

Similarities

The cells of all living organisms (all kingdoms of living nature) contain a plasma membrane, cytoplasm and ribosomes.

Choose three correct answers out of six and write down the numbers under which they are indicated. The similarity between animal cells and bacteria is that they have
1) ribosomes
2) cytoplasm
3) glycocalyx
4) mitochondria
5) decorated core
6) cytoplasmic membrane

Answer

1. Establish a correspondence between the characteristic of an organism and the kingdom for which it is characteristic: 1) fungi, 2) bacteria
A) DNA is closed in the form of a ring
B) according to the method of nutrition - autotrophs or heterotrophs
B) cells have a formed nucleus
D) DNA has a linear structure
D) the cell wall contains chitin
E) nuclear substance is located in the cytoplasm

Answer


2. Establish a correspondence between the characteristics of organisms and the kingdoms for which they are characteristic: 1) Fungi, 2) Bacteria. Write numbers 1 and 2 in the order corresponding to the letters.
A) formation of mycorrhiza with the roots of higher plants
B) formation of a cell wall from chitin
B) body in the form of mycelium
D) reproduction by spores
D) ability for chemosynthesis
E) location of circular DNA in the nucleoid

Answer


Choose three options. How do fungi differ from bacteria?
1) constitute a group of nuclear organisms (eukaryotes)
2) belong to heterotrophic organisms
3) reproduce by spores
4) unicellular and multicellular organisms
5) when breathing, they use air oxygen
6) participate in the cycle of substances in the ecosystem

Answer


1. Establish a correspondence between the characteristics of a cell and the type of organization of this cell: 1) prokaryotic, 2) eukaryotic
A) the cell center participates in the formation of the division spindle
B) there are lysosomes in the cytoplasm
B) the chromosome is formed by circular DNA
D) there are no membrane organelles
D) the cell divides by mitosis
E) the membrane forms mesosomes

Answer


2. Establish a correspondence between the characteristics of the cell and its type: 1) prokaryotic, 2) eukaryotic
A) there are no membrane organelles
B) there is a cell wall made of murein
C) hereditary material is represented by a nucleoid
D) contains only small ribosomes
D) hereditary material is represented by linear DNA
E) cellular respiration occurs in mitochondria

Answer


3. Establish a correspondence between the trait and the group of organisms: 1) Prokaryotes, 2) Eukaryotes. Write numbers 1 and 2 in the order corresponding to the letters.
A) absence of a nucleus
B) the presence of mitochondria
B) lack of EPS
D) presence of the Golgi apparatus
D) the presence of lysosomes
E) linear chromosomes consisting of DNA and protein

Answer


4. Establish a correspondence between organelles and the cells that have them: 1) prokaryotic, 2) eukaryotic. Write numbers 1 and 2 in the order corresponding to the letters.
A) Golgi apparatus
B) lysosomes
B) mesosomes
D) mitochondria
D) nucleoid
E) EPS

Answer


5. Establish a correspondence between cells and their characteristics: 1) prokaryotic, 2) eukaryotic. Write numbers 1 and 2 in the order corresponding to the letters.
A) DNA molecule is circular
B) absorption of substances by phago- and pinocytosis
B) form gametes
D) ribosomes are small
D) there are membrane organelles
E) characterized by direct division

Answer


FORMED 6. Establish a correspondence between cells and their characteristics: 1) prokaryotic, 2) eukaryotic. Write numbers 1 and 2 in the order corresponding to the letters.
1) the presence of a separate core
2) formation of spores to endure unfavorable environmental conditions

3) the location of hereditary material only in closed DNA

4) division by meiosis
5) ability for phagocytosis

Choose three options. Bacteria, unlike cap mushrooms,
1) unicellular organisms
2) multicellular organisms
3) have ribosomes in cells
4) do not have mitochondria
5) prenuclear organisms
6) do not have cytoplasm

Answer


1. Choose three options. Prokaryotic cells are different from eukaryotic cells
1) the presence of a nucleoid in the cytoplasm
2) the presence of ribosomes in the cytoplasm
3) ATP synthesis in mitochondria
4) the presence of the endoplasmic reticulum
5) absence of a morphologically distinct nucleus
6) the presence of invaginations of the plasma membrane, performing the function of membrane organelles

Answer


2. Select three options. A bacterial cell is classified as a prokaryotic cell because it
1) does not have a shell-covered core
2) has cytoplasm
3) has one DNA molecule immersed in the cytoplasm
4) has an outer plasma membrane
5) does not have mitochondria
6) has ribosomes where protein biosynthesis occurs

Answer


3. Select three options. Why are bacteria classified as prokaryotes?
1) contain a nucleus in the cell, separated from the cytoplasm
2) consist of many differentiated cells
3) have one ring chromosome
4) do not have a cell center, Golgi complex and mitochondria
5) do not have a nucleus isolated from the cytoplasm
6) have cytoplasm and plasma membrane

Answer


4. Select three options. Prokaryotic cells are different from eukaryotic cells
1) the presence of ribosomes
2) absence of mitochondria
3) lack of a formalized core
4) the presence of a plasma membrane
5) lack of organelles of movement
6) the presence of one ring chromosome

Answer


5. Select three options. A prokaryotic cell is characterized by the presence
1) ribosomes
2) mitochondria
3) decorated core
4) plasma membrane
5) endoplasmic reticulum
6) one circular DNA

Answer


COLLECTING 6:

A) absence of membrane organelles

B) absence of ribosomes in the cytoplasm

C) the formation of two or more chromosomes of a linear structure

Choose three options. The cells of eukaryotic organisms, unlike prokaryotic organisms, have
1) cytoplasm
2) core covered with shell
3) DNA molecules
4) mitochondria
5) dense shell
6) endoplasmic reticulum

Answer


Choose one, the most correct option. CHOOSE THE INCORRECT STATEMENT. Bacteria do not have
1) sex cells
2) meiosis and fertilization
3) mitochondria and cell center
4) cytoplasm and nuclear substance

Answer


Analyze the table. Fill in the blank cells of the table using the concepts and terms given in the list.
1) mitosis, meiosis
2) enduring unfavorable environmental conditions
3) transfer of information about the primary structure of the protein
4) double-membrane organelles
5) rough endoplasmic reticulum
6) small ribosomes

Answer


Answer



Choose three correct answers out of six and write down the numbers under which they are indicated. In the process of evolution, organisms of different kingdoms were formed. What signs are characteristic of the kingdom, the representative of which is depicted in the figure.
1) the cell wall consists mainly of murein
2) chromatin is contained in the nucleolus
3) well developed endoplasmic reticulum
4) there are no mitochondria
5) hereditary information is contained in a circular DNA molecule
6) digestion occurs in lysosomes

Answer



1. All the signs listed below, except two, are NOT used to describe the cell shown in the picture. Identify two characteristics that “drop out” from the general list and write down the numbers under which they are indicated in the table.
1) Presence of mitochondria
2) Presence of circular DNA
3) Presence of ribosomes
4) Availability of a core
5) The presence of a light peephole

Answer



2. All but two of the terms listed below are used to describe the cell shown in the figure. Identify two terms that “drop out” from the general list and write down the numbers under which they are indicated.
1) closed DNA molecule
2) mesosoma
3) membrane organelles
4) cell center
5) nucleoid

Answer



3. All of the characteristics listed below, except two, are used to describe the cell shown in the figure. Identify two terms that “drop out” from the general list and write down the numbers under which they are indicated.
1) division by mitosis
2) the presence of a cell wall made of murein
3) the presence of a nucleoid
4) absence of membrane organelles
5) absorption of substances by phago- and pinocytosis

Answer



4. All but two of the terms listed below are used to describe the cell shown in the figure. Identify two terms that “drop out” from the general list and write down the numbers under which they are indicated.
1) closed DNA
2) mitosis
3) gametes
4) ribosomes
5) nucleoid

Answer



5. All of the signs listed below, except two, can be used to describe the cell shown in the figure. Identify two characteristics that “drop out” from the general list and write down the numbers under which they are indicated.
1) there is a cell membrane
2) there is a Golgi apparatus
3) there are several linear chromosomes
4) there are ribosomes
5) there is a cell wall

Answer



6 Sat. All of the characteristics listed below, except two, can be used to describe the cell shown in the figure. Identify two characteristics that “drop out” from the general list and write down the numbers under which they are indicated.
1) have linear chromosomes
2) binary fission is characteristic
3) has an endoplasmic reticulum
4) forms a spore
5) contains small ribosomes

Answer

COLLECTING 7:
1) plasmid
2) respiration in mitochondria
3) division in two

1. All of the listed characteristics, except two, are used to describe a prokaryotic cell. Identify two characteristics that “fall out” from the general list and write down the numbers under which they are indicated.
1) The absence of a formal core in it
2) Presence of cytoplasm
3) Presence of a cell membrane
4) Presence of mitochondria
5) Presence of endoplasmic reticulum

Answer


2. All of the signs listed below, except two, characterize the structure of a bacterial cell. Identify two characteristics that “drop out” from the general list and write down the numbers under which they are indicated.
1) lack of a formalized kernel
2) the presence of lysosomes
3) the presence of a dense shell
4) absence of mitochondria
5) absence of ribosomes

Answer


3. The concepts listed below, except two, are used to characterize prokaryotes. Identify two concepts that “fall out” from the general list and write down the numbers under which they are indicated.
1) mitosis
2) dispute
3) gamete
4) nucleoid
5) mesosoma

Answer


4. All but two of the terms below are used to describe the structure of a bacterial cell. Identify two terms that “drop out” from the general list and write down the numbers under which they are indicated.
1) immobile cytoplasm
2) circular DNA molecule
3) small (70S) ribosomes
4) ability to phagocytose
5) presence of EPS

Answer


Establish a correspondence between the trait and the kingdom: 1) bacteria, 2) plants. Write numbers 1 and 2 in the correct order.
A) all representatives of prokaryotes
B) all representatives of eukaryotes
B) can be divided in half
D) there are tissues and organs
D) there are photos and chemosynthetics
E) chemosynthetics are not found

Answer


Establish a correspondence between the characteristics of organisms and their kingdom: 1) bacteria, 2) plants. Write numbers 1 and 2 in the correct order.
A) various representatives are capable of photosynthesis and chemosynthesis
B) in terrestrial ecosystems they surpass all other groups in biomass
B) cells divide by mitosis and meiosis
D) have plastids
D) cell walls usually do not contain cellulose
E) lack mitochondria

Answer


Choose one, the most correct option. In prokaryotic cells, oxidation reactions occur at
1) ribosomes in the cytoplasm
2) invaginations of the plasma membrane
3) cell membranes
4) circular DNA molecule

Answer



All but two of the following characteristics can be used to describe the cell shown in the figure. Identify two characteristics that “drop out” from the general list and write down the numbers under which they are indicated.
1) has a nucleus in which DNA molecules are located
2) the area where DNA is located in the cytoplasm is called a nucleoid
3) DNA molecules are circular
4) DNA molecules are associated with proteins
5) various membrane organelles are located in the cytoplasm

Answer


Choose three correct answers out of six and write down the numbers under which they are indicated. The similarity between bacteria and plants is that they
1) prokaryotic organisms
2) form spores under unfavorable conditions
3) have a cell body
4) among them there are autotrophs
5) have irritability
6) capable of vegetative reproduction

Answer


Choose three correct answers out of six and write down the numbers under which they are indicated in the table. The similarity between bacterial and plant cells is that they have
1) ribosomes
2) plasma membrane
3) decorated core
4) cell wall
5) vacuoles with cell sap
6) mitochondria

Answer


Choose three correct answers out of six and write down the numbers under which they are indicated. Bacteria, like fungi,
1) constitute a special kingdom
2) are only single-celled organisms
3) reproduce using spores
4) are decomposers in the ecosystem
5) can enter into symbiosis
6) absorb substances from the soil using hyphae

Answer


Choose three correct answers out of six and write down the numbers under which they are indicated. Bacteria, unlike lower plants,
1) according to the type of nutrition they are chemotrophs
2) during reproduction they form zoospores
3) do not have membrane organelles
4) have a thallus (thallus)
5) under unfavorable conditions they form spores
6) synthesize polypeptides on ribosomes

Answer



Match the characteristics and types of cells shown in the figure. Write numbers 1 and 2 in the order corresponding to the letters.
A) have mesosomes
B) osmotrophic method of nutrition
B) divide by mitosis
D) have a developed EPS
D) form spores under unfavorable conditions
E) have a murein shell

Answer


All but two of the following characteristics can be used to describe prokaryotic DNA. Identify two characteristics that fall out of the general list and write down the numbers under which they are indicated.
1) contains adenine, guanine, uracil and cytosine
2) consists of two circuits
3) has a linear structure
4) not associated with structural proteins
5) lies in the cytoplasm

Answer


Establish a correspondence between the characteristics and organisms: 1) yeast, 2) E. coli. Write numbers 1 and 2 in the order corresponding to the letters.
A) the genome is represented by one circular DNA molecule
B) the cell is covered with a murein membrane
B) divides by mitosis
D) produces ethanol under anaerobic conditions
D) has flagella
E) does not have membrane organelles

Answer


© D.V. Pozdnyakov, 2009-2019

In electron microscopy of ultrathin sections, the cytoplasmic membrane is a three-layer membrane (2 dark layers 2.5 nm thick are separated by a light intermediate one). In structure, it is similar to the plasmalemma of animal cells and consists of a double layer of phospholipids with embedded surface and integral proteins, as if penetrating through the structure of the membrane. With excessive growth (compared to the growth of the cell wall), the cytoplasmic membrane forms invaginates - invaginations in the form of complex twisted membrane structures, called mesosomes. Less complexly twisted structures are called intracytoplasmic membranes.

Cytoplasm

The cytoplasm consists of soluble proteins, ribonucleic acids, inclusions and numerous small granules - ribosomes, responsible for the synthesis (translation) of proteins. Bacterial ribosomes have a size of about 20 nm and a sedimentation coefficient of 70S, in contrast to the 80S ribosomes characteristic of eukaryotic cells. Ribosomal RNAs (rRNAs) are conserved elements of bacteria (the “molecular clock” of evolution). 16S rRNA is part of the small ribosomal subunit, and 23S rRNA is part of the large ribosomal subunit. The study of 16S rRNA is the basis of gene systematics, allowing one to assess the degree of relatedness of organisms.
The cytoplasm contains various inclusions in the form of glycogen granules, polysaccharides, beta-hydroxybutyric acid and polyphosphates (volutin). They are reserve substances for the nutrition and energy needs of bacteria. Volutin has an affinity for basic dyes and is easily detected using special staining methods (for example, Neisser) in the form of metachromatic granules. The characteristic arrangement of volutin granules is revealed in the diphtheria bacillus in the form of intensely stained cell poles.

Nucleoid

Nucleoid is the equivalent of a nucleus in bacteria. It is located in the central zone of bacteria in the form of double-stranded DNA, closed in a ring and tightly packed like a ball. The nucleus of bacteria, unlike eukaryotes, does not have a nuclear envelope, nucleolus and basic proteins (histones). Typically, a bacterial cell contains one chromosome, represented by a DNA molecule closed in a ring.
In addition to the nucleoid, represented by one chromosome, the bacterial cell contains extrachromosomal factors of heredity - plasmids, which are covalently closed rings of DNA.

Capsule, microcapsule, mucus

The capsule is a mucous structure more than 0.2 microns thick, firmly associated with the bacterial cell wall and having clearly defined external boundaries. The capsule is visible in imprint smears from pathological material. In pure bacterial cultures, the capsule is formed less frequently. It is detected by special methods of staining a smear (for example, according to Burri-Gins), which create a negative contrast of the substances of the capsule: ink creates a dark background around the capsule. The capsule consists of polysaccharides (exopolysaccharides), sometimes of polypeptides, for example, in the anthrax bacillus it consists of polymers of D-glutamic acid. The capsule is hydrophilic and prevents phagocytosis of bacteria. The capsule is antigenic: antibodies against the capsule cause its enlargement (capsule swelling reaction).
Many bacteria form a microcapsule - a mucous formation less than 0.2 microns thick, detectable only by electron microscopy. One should distinguish from the capsule mucoid exopolysaccharides, which do not have clear boundaries. Mucus is soluble in water.
Bacterial exopolysaccharides are involved in adhesion (sticking to substrates); they are also called glycocalyx. Besides synthesis
exopolysaccharides by bacteria, there is another mechanism for their formation: through the action of extracellular enzymes of bacteria on disaccharides. As a result, dextrans and levans are formed.

Flagella

Bacterial flagella determine the motility of the bacterial cell. Flagella are thin filaments originating from the cytoplasmic membrane and are longer than the cell itself. The thickness of the flagella is 12-20 nm, length 3-15 µm. They consist of 3 parts: a spiral filament, a hook and a basal body containing a rod with special disks (1 pair of disks in gram-positive bacteria and 2 pairs of disks in gram-negative bacteria). Flagella are attached to the cytoplasmic membrane and cell wall by discs. This creates the effect of an electric motor with a motor rod that rotates the flagellum. Flagella consist of a protein - flagellin (from flagellum - flagellum); is an H antigen. Flagellin subunits are twisted in a spiral.
The number of flagella in bacteria of various species varies from one (monotrich) in Vibrio cholerae to tens and hundreds of flagella extending along the perimeter of the bacterium (peritrich) in Escherichia coli, Proteus, etc. Lophotrichs have a bundle of flagella at one end of the cell. Amphitrichy has one flagellum or a bundle of flagella at opposite ends of the cell.

Drank

Pili (fimbriae, villi) are thread-like formations, thinner and shorter (3-10 nm x 0.3-10 µm) than flagella. Pili extend from the cell surface and consist of the protein pilin, which has antigenic activity. There are pili responsible for adhesion, that is, for attaching bacteria to the affected cell, as well as pili responsible for nutrition, water-salt metabolism and sexual (F-pili), or conjugation pili. Pili are numerous - several hundred per cell. However, there are usually 1-3 sex pili per cell: they are formed by so-called “male” donor cells containing transmissible plasmids (F-, R-, Col-plasmids). A distinctive feature of the sex pili is the interaction with special “male” spherical bacteriophages, which are intensively adsorbed on the sex pili.

Controversy

Spores are a peculiar form of resting firmicute bacteria, i.e. bacteria
with a gram-positive type of cell wall structure. Spores are formed under unfavorable conditions for the existence of bacteria (drying, nutrient deficiency, etc.. One spore (endospore) is formed inside the bacterial cell. The formation of spores contributes to the preservation of the species and is not a method of reproduction, like fungi. Spore-forming bacteria of the genus Bacillus have spores, not exceeding the diameter of the cell. Bacteria in which the size of the spore exceeds the diameter of the cell are called clostridia, for example, bacteria of the genus Clostridium (lat. Clostridium - spindle). The spores are acid-fast, therefore they are stained red using the Aujeszky method or the Ziehl-Neelsen method, and the vegetative cell in blue.

The shape of the spores can be oval, spherical; location in the cell is terminal, i.e. at the end of the stick (in the causative agent of tetanus), subterminal - closer to the end of the stick (in the causative agents of botulinum, gas gangrene) and central (in the anthrax bacillus). The spore persists for a long time due to the presence of a multilayer shell, calcium dipicolinate, low water content and sluggish metabolic processes. Under favorable conditions, spores germinate, going through three successive stages: activation, initiation, germination.



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