We cannot even imagine how many microorganisms constantly surround us. By grabbing the handrail on the bus, you have already planted about a hundred thousand bacteria on your hand, going into a public toilet, you, again, have rewarded yourself with these microorganisms. Bacteria always and everywhere accompany a person. But there is no need to react negatively to this word, because bacteria are not only pathogenic, but also useful for the body.
Scientists were very surprised when they realized that some bacteria have retained their appearance for about a billion years. Such microorganisms have even been compared with a Volkswagen car - the appearance of one of their models has not changed for 40 years, having an ideal shape.
Bacteria were one of the first to appear on Earth, so they can deservedly be called long-livers. An interesting fact is that these cells do not have a formed nucleus, therefore, to this day, they attract a lot of attention to their structure.
Bacteria are microscopic organisms of plant origin. The structure of a bacterial cell (table, diagrams exist for clarity in understanding the types of these cells) depends on its purpose.
These cells are ubiquitous as they multiply rapidly. There is scientific evidence that in literally six hours, one cell can produce offspring of 250 thousand bacteria. These single-celled organisms come in many varieties that vary in shape.
Bacteria are very tenacious organisms, their spores can retain the ability to live for 30-40 years. These spores are transferred with the breath of the wind, the current of water and in other ways. Viability is maintained up to a temperature of 100 degrees and with a slight frost. And yet, what structure does a bacterial cell have? The table describes the main components of bacteria, the functions of other organelles are outlined below.
They are pathogenic in nature. Cocci are divided into groups depending on their location to each other:
Rods that form spores are subdivided into clostridia and bacilli. These bacteria are short and very short in size. The end sections of the sticks are rounded, thickened or cut off. Depending on the location of bacteria, several groups are distinguished: mono-, diplo- and streptobacteria.
These microscopic cells are of two types:
Filamentous bacteria. There are two groups of such forms:
The structural features of a bacterial cell are that in the course of its existence it is capable of changing forms, but at the same time polymorphism is not inherited. Various factors act on the cell in the course of metabolism in the body, as a result of which there are quantitative changes in its appearance. But as soon as the action from the outside ceases, the cell will take on its former image. What are the structural features of a bacterial cell, you can identify when examining it with a microscope.
The shell gives and maintains the shape of the cell, protects the internal components from damage. Due to incomplete permeability, not all substances can enter the cell, which facilitates the exchange of low and high molecular weight structures between the external environment and the cell itself. Also, various chemical reactions take place in the wall. With the help of an electron microscope, it is not difficult to study what detailed structure a bacterial cell has.
The shell base contains the murein polymer. Gram-positive bacteria have a single-layer skeleton composed of murein. There are polysaccharide and lipoprotein complexes, phosphates. In gram-negative cells, the murein skeleton has many layers. The outer layer adjacent to the cell wall is the cytoplasmic membrane. It also has certain layers containing proteins with lipids. The main function of the cytoplasmic membrane is to control the penetration of substances into the cell and their excretion (osmotic barrier). This is a very important function for cells, as it protects cells.
The living semi-liquid substance that fills the cell cavity is called the cytoplasm. A large amount of protein, a supply of nutrients (fats and fat-like substances) contains a bacterial cell. A photo taken during examination under a microscope clearly shows the constituent parts inside the cytoplasm. The main structure includes ribosomes located in a chaotic order and in large numbers. Also in the composition there are mesosomes containing enzymes of a redox nature. Due to them, the cell draws energy. The nucleus is presented in the form of a nuclear substance located in chromatin bodies.
Ribosomes are composed of subunits (2) and are nucleoproteins. Connecting with each other, these constituent elements form polysomes or polyribosomes. The main task of these inclusions is protein synthesis based on genetic information. The sedimentation rate is 70S.
Genetic material (DNA) is found in the unformed nucleus (nucleoid). This nucleus is located in several places in the cytoplasm, being a loose membrane. Bacteria with such a nucleus are called prokaryotes. The apparatus of the nucleus is devoid of a membrane, nucleolus and a set of chromosomes. And deoxyribonucleic acid is located in it by fibril bundles. The diagram of the structure of a bacterial cell demonstrates in detail the structure of the nuclear apparatus.
Under some conditions, bacteria can develop mucous membranes. As a result, the formation of a capsule occurs. If mucus is very strong, then the bacteria turn into zoogley (total mucous mass).
The structure of a bacterial cell has a peculiarity - it is the presence of a protective capsule consisting of polysaccharides or glycoproteins. Sometimes these capsules are composed of polypeptides or fiber. It sits on top of the cell wall. In terms of thickness, the capsule can be either thick or thin. Its formation occurs due to the conditions in which the cell falls. The main property of the capsule is to protect the bacteria from drying out.
In addition to the protective capsule, the structure of the bacterial cell provides for its motor ability.
Flagella are additional elements that move the cell. They are presented in the form of threads of different lengths, which are composed of flagellin. It is a protein that has the ability to contract.
The composition of the flagellum is three-component (thread, hook, basal body). Depending on the attachment and location, several groups of motile bacteria were identified:
There are many interesting facts about bacteria. So, it has long been proven that a mobile phone contains a huge amount of these cells, even on the toilet seat there are fewer of them. Other bacteria allow us to live a high-quality life - to eat, to perform certain activities, to free our body from the breakdown products of nutrients without any problems. Bacteria are truly diverse, their functions are multifaceted, but one should not forget about their pathological effect on the body, so it is important to monitor our own hygiene and cleanliness around us.
From the point of view of modern science, prokaryotes have a primitive structure. But it is precisely this "simplicity" that helps them survive in the most unexpected conditions. For example, in hydrogen sulfide sources or at nuclear test sites. Scientists have calculated that the total mass of all terrestrial microorganisms is 550 billion tons.
Bacteria are unicellular... But this does not mean that bacterial cells pass before the cells of animals or plants. Microbiology already has knowledge of hundreds of thousands of microbial species. Nevertheless, representatives of science discover new types and features of them every day.
It is not surprising that for the full development of the Earth's surface, microorganisms have to take various forms:
The size of bacteria is measured in nanometers and micrometers. Their average value is 0.8 microns. But among them there are giant prokaryotes, reaching 125 microns and more. The real giants among the midgets are the spirochetes 250 microns long. Now compare with them the size of the smallest prokaryotic cell: mycoplasmas "grow" quite a bit and reach 0.1-0.15 microns in diameter.
It is worth saying that giant bacteria do not so easily survive in the environment. They find it difficult to find enough nutrients for themselves to successfully fulfill their function. But on the other hand, they are not easy prey for bacteria-predators, which feed on their counterparts - single-celled microorganisms, "flowing around" and eating them.
Under unfavorable environmental conditions, bacteria form a capsule. The microcapsule fits snugly against the wall. It can only be seen with an electron microscope. The macrocapsule is often formed by pathogenic microbes (pneumococci). In Klebsiella pneumonia, a macrocapsule is always found.
The capsule-like membrane is a formation loosely attached to the cell wall. Thanks to bacterial enzymes, the capsule-like shell is covered with carbohydrates (exopolysaccharides) of the external environment, which ensures the adhesion of bacteria with different surfaces, even completely smooth ones. For example, streptococci, entering the human body, are capable of sticking to teeth and heart valves.
The functions of the capsule are diverse:
They provide immersion and ascent. In the soil, the bacterial cell moves along the soil channels.
The entire contents of a cell, with the exception of the nucleus and the cell wall, are called cytoplasm. The liquid, structureless phase of the cytoplasm (matrix) contains ribosomes, membrane systems, mitochondria, plastids and other structures, as well as reserve nutrients. The cytoplasm has an extremely complex, fine structure (layered, granular). Many interesting details of the cell structure have been revealed with the help of an electron microscope.
The outer lipoprotein layer of the protoplast of bacteria, which has special physical and chemical properties, is called the cytoplasmic membrane. All vital structures and organelles are located inside the cytoplasm. The cytoplasmic membrane plays a very important role - it regulates the entry of substances into the cell and the excretion of metabolic products. Through the membrane, nutrients can enter the cell as a result of an active biochemical process involving enzymes.
In addition, synthesis of some constituent parts of the cell occurs in the membrane, mainly the components of the cell wall and capsule. Finally, the cytoplasmic membrane contains the most important enzymes (biological catalysts). The ordered arrangement of enzymes on membranes allows you to regulate their activity and prevent the destruction of some enzymes by others. Ribosomes are associated with the membrane - structural particles on which protein is synthesized. The membrane consists of lipoproteins. It is strong enough and can provide the temporary existence of a cell without a shell. The cytoplasmic membrane accounts for up to 20% of the dry mass of the cell.
In electronic photographs of thin sections of bacteria, the cytoplasmic membrane appears as a continuous strand about 75A thick, consisting of a light layer (lipids) enclosed between two darker ones (proteins). Each layer is 20-30A wide. Such a membrane is called elementary.
The cytoplasm of bacterial cells often contains granules of various shapes and sizes. However, their presence cannot be considered as some kind of permanent sign of a microorganism, usually it is largely associated with the physical and chemical conditions of the environment.
Many cytoplasmic inclusions are composed of compounds that serve as a source of energy and carbon. These storage substances are formed when the body is supplied with sufficient nutrients, and, conversely, are used when the body is placed in conditions that are less favorable in terms of nutrition.
In many bacteria, granules are composed of starch or other polysaccharides - glycogen and granulose. In some bacteria, when grown in a medium rich in sugars, fat droplets are found inside the cell. Another widespread type of granular inclusions is volutin (metachromatin granules). These granules are composed of polymetaphosphate (storage substance containing phosphoric acid residues). Polymetaphosphate serves as a source of phosphate groups and energy for the body. Bacteria are more likely to accumulate volutin in unusual feeding conditions, such as in a sulfur-free environment. Sulfur droplets are found in the cytoplasm of some sulfuric bacteria.
There is a connection between the plasma membrane and the cell wall in the form of desmoses - bridges. The cytoplasmic membrane often gives invagination - invagination into the cell. These invaginations in the cytoplasm form special membrane structures called mesosomes.
Some types of mesosomes are bodies separated from the cytoplasm by their own membrane. Numerous vesicles and tubules are packed inside such membrane sacs. These structures perform a wide variety of functions in bacteria. Some of these structures are analogs of mitochondria.
Others perform the functions of the endoplasmic reticulum or the Golgi apparatus. The photosynthetic apparatus of bacteria is also formed by invagination of the cytoplasmic membrane. After invagination of the cytoplasm, the membrane continues to grow and forms stacks, which, by analogy with plant chloroplast granules, are called thylakoid stacks. In these membranes, which often fill most of the cytoplasm of a bacterial cell, pigments (bacteriochlorophyll, carotenoids) and enzymes (cytochromes) that carry out the process of photosynthesis are localized.
Bacteria do not have such a nucleus as in higher organisms (eukaryotes), but have its analogue - the "nuclear equivalent" - the nucleoid, which is an evolutionarily more primitive form of organization of nuclear matter. It consists of one closed in a ring double-stranded DNA strand with a length of 1.1-1.6 nm, which is considered as a single bacterial chromosome, or genophore. The nucleoid in prokaryotes is not delimited from the rest of the cell by a membrane - it does not have a nuclear envelope.
The structure of the nucleoid includes RNA polymerase, basic proteins and no histones; the chromosome is fixed on the cytoplasmic membrane, and in gram-positive bacteria - on the mesosomes. The bacterial chromosome replicates in a polyconservative way: the parental DNA double helix unwinds and a new complementary strand is assembled on the template of each polynucleotide chain. The nucleoid does not have a mitotic apparatus, and the divergence of daughter nuclei is provided by the growth of the cytoplasmic membrane.
The bacterial nucleus is a differentiated structure. Depending on the stage of development of the cell, the nucleoid can be discrete (discontinuous) and consist of separate fragments. This is due to the fact that the division of a bacterial cell in time occurs after the completion of the replication cycle of the DNA molecule and the formation of daughter chromosomes.
The nucleoid contains the bulk of the genetic information of the bacterial cell. In addition to the nucleoid, extrachromosomal genetic elements - plasmids, represented by small circular DNA molecules capable of autonomous replication, were found in the cells of many bacteria.
Plasmids are self-contained, coiled, double-stranded DNA molecules. Their mass is much less than the mass of a nucleotide. Despite the fact that hereditary information is encoded in the DNA of plasmids, they are not vital and necessary for the bacterial cell.
The cytoplasm of bacteria contains ribosomes - protein-synthesizing particles with a diameter of 200A. There are more than a thousand of them in a cell. Ribosomes are made up of RNA and protein. In bacteria, many ribosomes are located freely in the cytoplasm, some of them may be associated with membranes.
Ribosomes are the centers of protein synthesis in the cell. Moreover, they often join together, forming aggregates called polyribosomes or polysomes.
Inclusions are metabolic products of nuclear and non-nuclear cells. They represent a supply of nutrients: glycogen, starch, sulfur, polyphosphate (valutin), etc. Inclusions often, when colored, acquire a different appearance than the color of the dye. Values can be used to diagnose diphtheria bacillus.
Since a bacterium is a prokaryotic microorganism, many organelles are always absent in bacterial cells, which are inherent in eukaryotic organisms:
It is also worth remembering that bacteria do not have a cell wall, therefore, processes such as pinocytosis and phagocytosis cannot proceed.
As a special microorganism, bacteria are adapted to exist in conditions where oxygen may be absent. And the very same breathing in them occurs due to the mesosomes. It is also very interesting that green organisms are able to photosynthesize in exactly the same way as plants. But it is important to take into account the fact that in plants the process of photosynthesis occurs in chloroplasts, and in bacteria, on membranes.
Reproduction in a bacterial cell occurs in the most primitive way. A mature cell divides in two, they reach maturity after a while, and this process is repeated. In favorable conditions, a change of 70-80 generations can occur per day. It is important to remember that bacteria, due to their structure, do not have access to such methods of reproduction as mitosis and meiosis. They are inherent only in eukaryotic cells.
Spore formation is known to be one of several ways fungi and plants reproduce. But bacteria also know how to form spores, which is inherent in few of their species. They have this ability in order to survive particularly adverse conditions that can be dangerous to their lives.
Such species are known that are able to survive even in space. This can not be repeated by any living organisms. Bacteria became the progenitors of life on Earth due to their simplicity of structure. But the fact that they exist to this day shows how important they are for the world around us. With their help, people can get as close as possible to the answer to the question of the origin of life on Earth, constantly studying bacteria and learning something new.
Staphylococcus aureus (Staphylococcus aureus) is a common bacteria that affects about 30 percent of all people. In some people, it is part of the microbiome (microflora) and is found both inside the body and on the skin or mouth. While there are harmless strains of Staphylococcus aureus, others, such as Methicillin-resistant Staphylococcus aureus, pose serious health problems, including skin infections, cardiovascular disease, meningitis, and digestive diseases.
Researchers at Vanderbilt University found that staphylococcus bacteria prefer human blood over animal blood. These bacteria are partial to iron, which is found in hemoglobin found in red blood cells. Staphylococcus aureus tears apart blood cells to get to the iron inside them. It is believed that genetic variations in hemoglobin may make some people more desirable to Staphylococcus bacteria than others.
The researchers found that bacteria in the atmosphere may play a role in the production of rain and other forms of rainfall. This process begins when bacteria from plants are blown into the atmosphere. At a height, ice forms around them and they begin to grow. Once the frozen bacteria reach a certain growth threshold, the ice begins to melt and returns to the ground in the form of rain. The bacteria of the species Psuedomonas syringae have even been found in the center of large hail particles. They produce a special protein in cell membranes that allows them to bind water in a unique way, promoting ice formation.
Researchers have found that certain strains of acne-causing bacteria may actually help prevent acne. The bacteria that causes acne, Propionibacterium acnes, lives in the pores of our skin. When these bacteria provoke an immune response, the area on the skin swells and pimples form.
However, certain strains of bacteria have been found to be less likely to cause acne. These strains may be the reason why people with healthy skin rarely get acne. By studying genes from strains of Propionibacterium acnes collected from people with acne and healthy skin, the researchers identified a strain that was common on clear skin and rarely found on skin with acne. Future research will include attempts to develop a drug that only kills the acne-causing strains of the bacteria Propionibacterium acnes.
Who would have thought that brushing your teeth regularly could help prevent heart disease? Previous studies have found a link between gum disease and cardiovascular disease. Now scientists have found a specific link between these diseases.
Both bacteria and humans are thought to produce certain types of proteins called stress proteins. These proteins are formed when cells experience various types of stressful conditions. When a person has a gum infection, the cells of the immune system start attacking the bacteria. Bacteria produce stress proteins when attacked, and white blood cells also attack stress proteins.
The problem is that white blood cells cannot differentiate between stress proteins produced by bacteria and those produced by the body. As a result, the cells of the immune system also attack the stress proteins produced by the body, which causes the accumulation of white blood cells in the arteries and leads to atherosclerosis. A calcified heart is the leading cause of cardiovascular disease.
Did you know that spending time in the garden or gardening can help you learn better? According to the researchers, the soil bacterium Mycobacterium vaccae can improve learning in mammals.
Probably, these bacteria enter our body by swallowing or through breathing. According to scientists, the bacterium Mycobacterium vaccae improves learning by stimulating the growth of neurons in the brain, which leads to an increase in serotonin levels and a decrease in anxiety.
The study was carried out using mice fed with live bacteria, Mycobacterium vaccae. The results showed that mice that ate the bacteria moved the maze much faster and with less anxiety than mice that did not eat the bacteria. Scientists suggest that Mycobacterium vaccae plays a role in improving new challenges and reducing stress levels.
Researchers at Argonne National Laboratory have found that the bacterium Bacillus subtilis has the ability to rotate very small gears. These bacteria are aerobic, meaning they need oxygen to grow and develop. When they are placed in a solution with microbubbles of air, bacteria float in the teeth of the gear and cause it to turn in a specific direction.
It takes several hundred bacteria working in unison to start the gear spinning. It was also found that bacteria can turn several gears connected to each other. The researchers were able to control the speed at which the bacteria turned the gears by adjusting the amount of oxygen in the solution. The decrease in the amount of oxygen led to a slowdown in bacteria. Removing oxygen causes them to stop moving completely.
The structural components of a cell are the bacterial membrane, which consists of a cell wall, a cytoplasmic membrane, and sometimes a capsule; cytoplasm; ribosomes; various cytoplasmic inclusions; nucleoid (nucleus). In addition, some types of bacteria have spores, flagella, cilia (pili, fimbria) (Fig. 2).
Cell wall obligatory formation of bacteria of most species. Its structure depends on the type and belonging.
bacteria to groups differentiated by Gram staining. The mass of the cell wall is about 20% of the dry mass of the entire cell, the thickness is from 15 to 80 nm.
Rice. 3. Diagram of the structure of a bacterial cell
1 - capsule; 2 - cell wall; 3 - cytoplasmic membrane; 4 - cytoplasm; 5 - mesosomes; 6 - ribosomes; 7 - nucleoid; 8 - intracytoplasmic membrane formations; 9 - fatty drops; 10 - polysaccharide granules; 11 - polyphosphate granules; 12 - sulfur inclusions; 13 - flagella; 14 - basal body
The cell wall has pores up to 1 nm in diameter, therefore it is a semipermeable membrane through which nutrients penetrate and metabolic products are released.
These substances can penetrate into the microbial cell only after preliminary hydrolytic cleavage by specific enzymes secreted by bacteria into the external environment.
The chemical composition of the cell wall is not uniform, but it is constant for a certain type of bacteria, which is used for identification. The cell wall contains nitrogenous compounds, lipids, cellulose, polysaccharides, and pectin substances.
The most important chemical component of the cell wall is the complex polysaccharide peptide. It is also called peptidoglycan, glycopeptide, murein (from lat. murus - wall).
Murein is a structural polymer composed of glycan molecules formed by acetylglucosamine and acetylmuramic acid. Its synthesis is carried out in the cytoplasm at the level of the cytoplasmic membrane.
Peptidoglycan of the cell wall of various types has a specific amino acid composition and, depending on this, a certain chemotype, which is taken into account when identifying lactic acid and other bacteria.
In the cell wall of gram-negative bacteria, peptidoglycan is represented by one layer, while in the wall of gram-positive bacteria it forms several layers.
In 1884, Gram proposed a tissue staining method that was used to stain prokaryotic cells. If, during Gram staining, the fixed cells are treated with an alcohol solution of crystal violet paint, and then with a solution of iodine, then these substances form a stable colored complex with murein.
In goam-positive microorganisms, the colored violet complex does not dissolve under the influence of ethanol and, accordingly, does not fade; when stained with fuchsin (red paint), the cells remain stained dark violet.
In gram-negative microorganisms, gentian violet is dissolved in ethanol and washed out with water, and when stained with fuchsin, the cell turns red.
The ability of microorganisms to stain with analytical dyes and, according to the Gram method, is called tinctorial properties . They must be studied in young (18-24 hour) cultures, since some gram-positive bacteria in old cultures lose their ability to stain positively according to the Gram method.
The significance of peptidoglycan lies in the fact that thanks to it the cell wall has rigidity, i.e. elasticity, and is the protective framework of the bacterial cell.
When peptidoglycan is destroyed, for example, under the action of lysozyme, the cell wall loses its rigidity and collapses. The content of the cell (cytoplasm), together with the cytoplasmic membrane, takes on a spherical shape, that is, it becomes a protoplast (spheroplast).
Many synthesizing and destructive enzymes are associated with the cell wall. Cell wall components are synthesized in the cytoplasmic membrane and then transported to the cell wall.
Cytoplasmic membrane is located under the cell wall and fits snugly to its inner surface. It is a semi-permeable membrane that surrounds the cytoplasm and the inner contents of the protoplast cell. The cytoplasmic membrane is the thickened outer layer of the cytoplasm.
The cytoplasmic membrane is the main barrier between the cytoplasm and the environment, violation of its integrity leads to cell death. It contains proteins (50-75%), lipids (15-45%), in many species - carbohydrates (1-19%).
The main lipid component of the membrane is phospho- and glycolipids.
The cytoplasmic membrane, with the help of enzymes localized in it, performs various functions: synthesizes membrane lipids - components of the cell wall; membrane enzymes - selectively transfer various organic and inorganic molecules and ions through the membrane, the membrane participates in the transformation of cellular energy, as well as in the replication of chromosomes, in the transfer of electrochemical energy and electrons.
Thus, the cytoplasmic membrane provides selective entry into the cell and removal from it of various substances and ions.
Derivatives of the cytoplasmic membrane are mesosomes . These are spherical structures formed when the membrane is twisted into a curl. They are located on both sides - at the site of the formation of the cell septum or next to the zone of localization of nuclear DNA.
Mesosomes are functionally equivalent to the mitochondria of cells of higher organisms. They are involved in the redox reactions of bacteria, play an important role in the synthesis of organic substances, in the formation of the cell wall.
Capsule is a derivative of the outer layer of cell clumps and is a mucous membrane that surrounds one or more microbial cells. Its thickness can reach 10 microns, which is many times greater than the thickness of the bacteria itself.
The capsule has a protective function. The chemical composition of the capsule of bacteria is different. In most cases, it consists of complex polysaccharides, mucopolysaccharides, and sometimes polypeptides.
Capsule formation is usually a specific feature. However, the appearance of the microcapsule often depends on the culture conditions of the bacteria.
Cytoplasm- a complex colloidal system with a large amount of water (80-85%), in which proteins, carbohydrates, lipids, as well as mineral compounds and other substances are dispersed.
The cytoplasm is the content of a cell surrounded by a cytoplasmic membrane. It is divided into two functional parts.
One part of the cytoplasm is in the state of a sol (solution), has a homogeneous structure and contains a set of soluble ribonucleic acids, enzyme proteins and metabolic products.
The other part is represented by ribosomes, inclusions of various chemical nature, genetic apparatus, and other intracytoplasmic structures.
Ribosomes Are submicroscopic granules, which are spherical nucleoprotein particles with a diameter of 10 to 20 nm, a molecular weight of about 2-4 million.
Ribosomes of prokaryotes consist of 60% RNA (ribonucleic acid) located in the center, and 40 % the protein that covers the outside of the nucleic acid.
Cytoplasmic inclusions are metabolic products, as well as reserve products, due to which the cell lives in conditions of a lack of nutrients.
The genetic material of prokaryotes consists of a double strand of deoxyribonucleic acid (DNA) of a compact structure located in the central part of the cytoplasm and not separated from it by a membrane. The structure of the DNA of bacteria does not differ from the DNA of eukaryotes, but since it is not separated from the cytoplasm by a membrane, the genetic material is called nucleoid or genophore... Nuclear structures are spherical or horseshoe-shaped.
Controversy bacteria are dormant, not multiplying their form. They are formed inside the cell, they are round or oval formations. Spores are formed mainly by gram-positive bacteria, rod-shaped with aerobic and anaerobic respiration in old cultures, as well as in unfavorable environmental conditions (lack of nutrients and moisture, accumulation of metabolic products in the environment, changes in pH and temperature of cultivation, presence or absence of atmospheric oxygen, etc. etc.) can switch to an alternative development program, resulting in disputes. In this case, one spore is formed in the cell. This indicates that sporulation in bacteria is an adaptation for the preservation of a species (individual) and is not a way of their reproduction. The process of sporulation occurs, as a rule, in the external environment for 18-24 hours.
A mature spore is approximately 0.1 of the maternal cell volume. Spores in different bacteria differ in shape, size, and location in the cell.
Microorganisms in which the diameter of the spore does not exceed the width of the vegetative cell are called bacilli, bacteria that have spores, the diameter of which is 1.5-2 times larger than the cell diameter, are called clostridia.
Inside the microbial cell, the spore can be located in the middle - central position, at the end - terminal position and between the center and the end of the cell - subterminal position.
Flagella bacteria are locomotor organs (organs of movement), with the help of which bacteria can move at a speed of up to 50-60 microns / s. At the same time, in 1 s, bacteria overlap their body length by 50-100 times. The length of the flagella exceeds the length of bacteria by 5-6 times. The thickness of the flagella is on average 12-30 nm.
The number of flagella, their size and location are constant for certain types of prokaryotes and therefore are taken into account when identifying them.
Depending on the number and location of flagella, bacteria are subdivided into monotrichs (monopolar monotrichs) - cells with one flagellum at one end, lophotrichs (monopolar polytriches) - a bundle of flagella is located at one of the ends, amphitrichs (bipolar polytrichs) - flagella are located on each of poles, peritriches - flagella are located over the entire surface of the cell (Fig. 4) and atrichs - bacteria devoid of flagella.
The nature of the movement of bacteria depends on the number of flagella, age, culture characteristics, temperature, the presence of various chemicals and other factors. Monotrichs have the greatest mobility.
Flagella are more often found in rod-shaped bacteria, they are not vital cell structures, since there are flagella-free variants of motile bacterial species.
Bacteria are the oldest organism on earth, and also the simplest in structure. It consists of just one cell, which can only be seen and studied under a microscope. A characteristic feature of bacteria is the absence of a nucleus, which is why bacteria are classified as prokaryotes.
Some species form small groups of cells, such clusters may be surrounded by a capsule (sheath). The size, shape and color of bacteria are highly dependent on their environment.
In shape, bacteria differ into: rod-shaped (bacilli), spherical (cocci) and crimped (spirilla). There are also modified ones - cubic, C-shaped, star-shaped. Their sizes range from 1 to 10 microns. Certain types of bacteria can actively move with the help of flagella. The latter are sometimes twice the size of the bacteria itself.
Types of forms of bacteria
For the movement of bacteria, flagella are used, the number of which is different - one, a pair, a bundle of flagella. The location of the flagella is also different - on one side of the cell, on the sides, or evenly distributed over the entire plane. Also, one of the methods of movement is sliding thanks to the mucus that is covered with prokaryotes. Most have vacuoles inside the cytoplasm. Adjusting the gas capacity in vacuoles helps them move up or down in the liquid, as well as move along the air channels of the soil.
Scientists have discovered more than 10 thousand varieties of bacteria, but according to the assumptions of scientific researchers, there are more than a million species of them in the world. The general characteristics of bacteria makes it possible to determine their role in the biosphere, as well as to study the structure, types and classification of the bacterial kingdom.
The simplicity of structure and the speed of adaptation to environmental conditions helped bacteria to spread over a wide range of our planet. They exist everywhere: water, soil, air, living organisms - all this is the most acceptable habitat for prokaryotes.
The bacteria were found both at the South Pole and in geysers. They are found on the ocean floor, as well as in the upper layers of the Earth's air shell. Bacteria live everywhere, but their number depends on favorable conditions. For example, a large number of bacterial species live in open water bodies, as well as soil.
The bacterial cell differs not only in that it does not have a nucleus, but also in the absence of mitochondria and plastids. The DNA of this prokaryote is located in a special nuclear zone and looks like a nucleoid closed in a ring. In a bacterium, the cell structure consists of a cell wall, a capsule, a capsule-like membrane, flagella, pili, and a cytoplasmic membrane. The internal structure is formed by the cytoplasm, granules, mesosomes, ribosomes, plasmids, inclusions and nucleoid.
The bacterial cell wall serves as a defense and support. Substances can freely flow through it due to their permeability. This shell contains pectin and hemicellulose. Some bacteria secrete a special mucus that can help protect against drying out. The mucus forms a capsule - a polysaccharide in chemical composition. In this form, the bacterium is able to tolerate even very high temperatures. It also performs other functions, such as sticking to any surfaces.
On the surface of the bacterial cell there are thin protein fibers - they drank. There may be a large number of them. Pili helps the cell transfer genetic material, and also provides adhesion to other cells.
There is a three-layer cytoplasmic membrane under the wall plane. It guarantees the transport of substances, and also has a significant role in the formation of spores.
The cytoplasm of bacteria is 75 percent produced from water. Cytoplasm composition:
Metabolism in prokaryotes is possible with or without oxygen. Most of them feed on ready-made organic nutrients. Very few species are capable of synthesizing organic substances from inorganic ones on their own. These are blue-green bacteria and cyanobacteria, which have played a significant role in the formation of the atmosphere and its saturation with oxygen.
Under conditions favorable for reproduction, it is carried out by budding or vegetatively. Asexual reproduction occurs in the following sequence:
With this method of reproduction, there is no exchange of genetic information, so all daughter cells will be an exact copy of the mother's.
The process of reproduction of bacteria in unfavorable conditions is more interesting. Scientists learned about the ability of bacteria to reproduce sexually relatively recently - in 1946. Bacteria have no division into female and germ cells. But their DNA is heterosexual. Two such cells, when approaching each other, form a channel for the transfer of DNA, an exchange of sites occurs - recombination. The process is quite lengthy, the result of which is two completely new individuals.
Most bacteria are very difficult to see under a microscope, as they do not have their own color. Few varieties are purple or green due to their bacteriochlorophyll and bacteriopurpurin content. Although, if we consider some colonies of bacteria, it becomes clear that they release colored substances into the habitat and acquire a bright color. In order to study prokaryotes in more detail, they are stained.
The classification of bacteria can be based on indicators such as:
Symbiont bacteria live in collaboration with other organisms.
Saprophyte bacteria live on already dead organisms, products and organic waste. They contribute to the processes of decay and fermentation.
Rotting removes corpses and other organic waste from nature. Without the decay process, there would be no circulation of substances in nature. So what is the role of bacteria in the cycle of substances?
Putrefaction bacteria are an assistant in the process of breaking down protein compounds, as well as fats and other compounds containing nitrogen. After carrying out a complex chemical reaction, they break the bonds between the molecules of organic organisms and capture protein molecules, amino acids. By splitting, the molecules release ammonia, hydrogen sulfide and other harmful substances. They are poisonous and can cause poisoning in humans and animals.
Putrefaction bacteria multiply rapidly in favorable conditions. Since these are not only beneficial bacteria, but also harmful ones, in order to prevent premature rotting in products, people have learned to process them: dry, pickle, salt, smoke. All of these treatments kill bacteria and prevent them from multiplying.
Fermentation bacteria are able to break down carbohydrates with the help of enzymes. People noticed this ability in ancient times and use such bacteria for the manufacture of lactic acid products, vinegars, and other food products to this day.
Bacteria, working in conjunction with other organisms, do a very important chemical job. It is very important to know what types of bacteria there are and what benefits or harm they bring to nature.
Above, we have already noted the great importance of many types of bacteria (in the processes of decay and various types of fermentation), i.e. fulfilling a sanitary role on Earth.
Bacteria also play a huge role in the cycle of carbon, oxygen, hydrogen, nitrogen, phosphorus, sulfur, calcium and other elements. Many types of bacteria contribute to the active fixation of atmospheric nitrogen and convert it into an organic form, contributing to an increase in soil fertility. Of particular importance are those bacteria that decompose cellulose, which is the main source of carbon for the life of soil microorganisms.
Sulfate-reducing bacteria are involved in the formation of oil and hydrogen sulfide in therapeutic muds, soils and seas. Thus, the layer of water saturated with hydrogen sulfide in the Black Sea is the result of the vital activity of sulfate-reducing bacteria. The activity of these bacteria in soils leads to the formation of soda and soda salinization of the soil. Sulfate-reducing bacteria convert nutrients in rice paddy soils into a form that becomes available to the roots of the crop. These bacteria can corrode metal structures underground and underwater.
Thanks to the vital activity of bacteria, the soil is freed from many products and harmful organisms and is saturated with valuable nutrients. Bactericidal preparations are successfully used to combat many types of insect pests (corn moth, etc.).
Many types of bacteria are used in various industries for the production of acetone, ethyl and butyl alcohols, acetic acid, enzymes, hormones, vitamins, antibiotics, protein-vitamin preparations, etc.
Without bacteria, processes are impossible for tanning leather, drying tobacco leaves, producing silk, rubber, processing cocoa, coffee, soaking hemp, flax and other bast fiber plants, pickling cabbage, cleaning waste water, leaching metals, etc.
The required organelles are: nuclear apparatus, cytoplasm, cytoplasmic membrane.
Optional(minor) structural elements are: cell wall, capsule, spores, drank, flagella.
1.In the center of the bacterial cell is nucleoid- nuclear formation, represented most often by one annular chromosome. Consists of a double-stranded DNA strand. The nucleoid is not separated from the cytoplasm by the nuclear membrane.
2.Cytoplasm- a complex colloidal system containing various inclusions of metabolic origin (grains of volutin, glycogen, granulosis, etc.), ribosomes and other elements of the protein synthesizing system, plasmids (extra-nucleoid DNA), mesosomes(formed as a result of invagination of the cytoplasmic membrane into the cytoplasm, participate in energy metabolism, sporulation, formation of the intercellular septum during division).
3.Cytoplasmic membrane limits the cytoplasm from the outside, has a three-layer structure and performs a number of important functions - barrier (creates and maintains osmotic pressure), energy (contains many enzyme systems - respiratory, redox, carries out the transfer of electrons), transport (transfer of various substances into the cell and from the cage).
4.Cell wall- inherent in most bacteria (except for mycoplasmas, acholeplasmas and some other microorganisms that do not have a true cell wall). It has a number of functions, first of all, it provides mechanical protection and a constant shape of cells; antigenic properties of bacteria are largely associated with its presence. In the composition - two main layers, of which the outer one is more plastic, the inner one is rigid.
The main chemical compound of the cell wall, which is specific only to bacteria peptidoglycan(mureic acids). The structure and chemical composition of the bacterial cell wall determines the important for taxonomy trait of bacteria - relation to Gram staining... In accordance with it, two large groups are distinguished - gram-positive (“gram +”) and gram-negative (“gram -”) bacteria. The wall of gram-positive bacteria after Gram staining retains the iodine complex with gentian violet(colored in blue-violet color), gram-negative bacteria lose this complex and the corresponding color after treatment and are colored pink due to additional staining with magenta.
Features of the cell wall of gram-positive bacteria.
A powerful, thick, easily organized cell wall, which is dominated by peptidoglycan and teichoic acids, no lipopolysaccharides (LPS), and often no diaminopimelic acid.
Features of the cell wall of gram-negative bacteria.
The cell wall is much thinner than that of gram-positive bacteria, contains LPS, lipoproteins, phospholipids, diaminopimelic acid. The structure is more complicated - there is an outer membrane, so the cell wall is three-layered.
When gram-positive bacteria are treated with enzymes that destroy peptidoglycan, structures completely devoid of the cell wall appear - protoplasts... Treatment of gram-negative bacteria with lysozyme destroys only the peptidoglycan layer without completely destroying the outer membrane; such structures are called spheroplasts... Protoplasts and spheroplasts have a spherical shape (this property is associated with osmotic pressure and is characteristic of all cellless forms of bacteria).
L-forms of bacteria.
Under the influence of a number of factors that adversely affect the bacterial cell (antibiotics, enzymes, antibodies, etc.), occurs L- transformation bacteria, leading to permanent or temporary loss of the cell wall. L-transformation is not only a form of variability, but also adaptation of bacteria to unfavorable conditions of existence. As a result of changes in antigenic properties (loss of O- and K-antigens), a decrease in virulence and other factors, L-forms acquire the ability to stay for a long time ( persist) in the host's body, maintaining a sluggish current infectious process. The loss of the cell wall makes the L-form insensitive to antibiotics, antibodies and various chemotherapy drugs, the point of application of which is the bacterial cell wall. Unstable L-shape capable reverse into the classic (original) forms of bacteria with a cell wall. There are also stable L-forms of bacteria, the absence of a cell wall and the inability to reverse them into classical forms of bacteria are genetically fixed. In a number of ways, they very much resemble mycoplasmas and others. mollicuts- bacteria in which the cell wall is absent as a taxonomic feature. Microorganisms belonging to mycoplasmas are the smallest prokaryotes, do not have a cell wall and, like all bacterial wallless structures, have a spherical shape.
To the surface structures of bacteria(optional, like the cell wall) include capsule, flagella, microvilli.
Capsule or a mucous layer surrounds the shell of a number of bacteria. Allocate microcapsule detected by electron microscopy in the form of a layer of microfibrils, and macrocapsule detected by light microscopy. The capsule is a protective structure (primarily from drying out), in a number of microbes it is a pathogenic factor, prevents phagocytosis, inhibits the first stages of defense reactions - recognition and absorption. Have saprophytes capsules are formed in the external environment, in pathogens - more often in the host's body. There are a number of methods for coloring capsules, depending on their chemical composition. The capsule often consists of polysaccharides (the most common color is according to Ginsu), less often from polypeptides.
Flagella. Motile bacteria can be gliding (moving on a hard surface as a result of wave-like contractions) or floating, moving due to filamentous, spirally curved proteins ( flagelline by chemical composition) formations - flagella.
According to the location and number of flagella, a number of forms of bacteria are distinguished.
1.Monotrichs have one polar flagellum.
2. Lophotrichs - have a polarly located bundle of flagella.
3.Amphitrichs - have flagella at diametrically opposite poles.
4. Peritrixes - have flagella along the entire perimeter of the bacterial cell.
The ability for purposeful movement (chemotaxis, aerotaxis, phototaxis) in bacteria is genetically determined.
Fimbriae or cilia- short filaments surrounding a bacterial cell in large numbers, with the help of which bacteria are fixed to substrates (for example, to the surface of mucous membranes). Thus, the fimbriae are factors of adhesion and colonization.
F- drank (fertility factor)- apparatus conjugation of bacteria, are found in small quantities in the form of thin proteinaceous villi.
Endospores and sporulation.
Spore formation- a method of preserving certain types of bacteria in adverse environmental conditions. Endospores are formed in the cytoplasm, are cells with low metabolic activity and high resistance ( resistance) to drying, the action of chemical factors, high temperature and other undesirable environmental factors. Light microscopy often uses a spore detection method. by Ozheshko... High resistance is associated with a high content of calcium salt of dipicolinic acid in the shell of a dispute. The location and size of spores in different microorganisms is different, which has differential diagnostic (taxonomic) significance. The main phases of the "life cycle" of spores sporulation(includes the preparatory stage, the pre-dispute stage, the formation of the shell, maturation and dormancy) and germination ending in the formation of a vegetative form. The process of sporulation is genetically determined.
Non-cultivated forms of bacteria.
In many species of gram-negative bacteria that do not form spores, there is a special adaptive state - uncultivated forms. They have low metabolic activity and do not actively reproduce, i.e. do not form colonies on solid nutrient media, are not detected during sowing. They are highly resistant and can remain viable for several years. They are not detected by classical bacteriological methods, they are detected only using genetic methods ( polymerase chain reaction - PCR).
