Bacter. the cell is surrounded by an outer membrane, cat. consists of a capsule, a capsule-like shell and a cell wall. Tinctorial properties depend on their composition. There are capsules: micro- and macrocapsules.
Microcapsules are microfibrils of mucopodisaccharides, cat. Closely adjacent to the cell wall.
Macrocapsules are a pronounced mucous layer that covers the cell wall on the outside. It consists of polysaccharides. Macrocapsule in a few types of pathogenic microorganisms - pneumococci
Capsule-like shell - lipid-polysaccharide formation, loosely associated with the cell surface, can be released into the environment
Capsule functions: protective, adhesive. Pathogenic and adhesive properties may be associated with it. Capsule – Buri-Gins stain
Flagella - located on the surface of cells. The composition includes flagelin protein (Socrates protein). Flagella are attached to the basal body (a system of several disks embedded in the cytoplasmic membrane and CS)
Monotrichs - 1 flagellum at one of the poles
Amphitrichy - flagella at both poles
Lophotrichous - a bundle of flagella
Peritrichous - over the entire surface.
They have antigenic properties.
Function – locomotor
Pili are thin hollow threads of protein nature, covered. Cell surface. Not completed locomotor function
Pili of the 1st general type ensure adhesion of bacteria to certain cells of the host body
Type 2 pili (sexual pili ) are involved in the conjugation of bacteria
8.Disputes and sporulation. Chemical composition and functional significance of the dispute. Detection methods. Pathogenic representatives
Disputes are a form of preservation of the hereditary information of a bacterial cell under unfavorable conditions external environment. Pathogenic representatives include bacillus and clostridium. Identified by Peshkov and Ozheshko staining. The difference is in the size of the spores.
The spores are located: centrally, subterminally or terminally.
Sporulation process:
A sporogenic zone is formed around the bacterial cell (i.e., a dense area of cytoplasm with a nucleoid inside)
Then a prospore is formed by separating the sporogenic zone from the rest of the cytoplasm (i.e. by ingrowth of the cytoplasm)
Formation of the cortex (composed of peptidoglycan)
The outer side of the membrane is covered with a dense capsule consisting of proteins, lipids, dipicolinic acid (determining heat resistance)
Then the vegetative part of the cell dies, and the spore can persist in the external environment for months and years (i.e., low water content, increased calcium concentration)
Under favorable conditions, the spore swells, enzymes are activated, metabolism starts - a vegetative cell is formed
Spores are a taxonomic character
23. Mutations, their classifications. Mutagens physical, chemical, biological. Molecular mechanism of mutation (deletion, duplication, inversion). Reparations and their meaning. The role of mutations. Mutations are changes in the primary structure of DNA, which are expressed in a hereditarily fixed loss or change of any characteristic. They can be classified by origin, the nature of changes in the primary structure, Phenotypic consequences for the mutated bacterial cell. By origin they are divided into spontaneous and induced The former constitute a natural background, the value of which varies depending on the type of mutation and the type of microbial population. Mutations occur as a result of the erroneous inclusion in the synthesized daughter chain of one nitrogenous base of another non-complementary one present in the parent chain. The reason for changes in the natural background may be insertional mutations that occur when Is sequences, transposons and plasmids are inserted into the chromosome of a microbial cell. In this case, the phenotype of the mutation depends on the location of their integration: if it occurs near the promoter, then the functions of the regulatory gene are disrupted, and near the structural gene, the synthesis of the product encoded in it is disrupted. Induced mutations- obtained in experiments under the influence of any mutagens. According to the number of mutated genes: Genetic and chromosomal. The former affect one gene and are most often point-specific, the latter extend to several genes. Spot– replacement or insertion of a pair of nitrogenous bases in DNA, which leads to a change in one codon, as a result of which, instead of one AK, another is encoded, or a meaningless codon is formed that does not encode any of the AKs (nonsense mutation). Mutations with insertions or deletions of 1 pair of nitrogenous bases lead to changes in all subsequent codons - frameshift mutations. A microorganism carrying a point mutation in 1 gene may experience a secondary mutation in the same gene, resulting in the restoration of the wild phenotype, while the primary mutation is called direct, and the secondary mutation is called reverse. With true reversion, not only the phenotype, but also the genotype is restored. Restoration of one phenotype can occur as a result of suppression, i.e. suppression of the mutant phenotype, which is expressed in the correction of the mutational change. With extragenic suppression, secondary mutations that suppress the expression of the primary mutational change are localized in suppressor genes encoding t-RNA synthesis Chromosomal mutations– large rearrangements in individual DNA fragments, resulting from the loss of fewer or more nucleotides (deletion), or a rotation of a DNA section by 180 degrees. (inversion), or repetition of a DNA fragment (duplication). One of the mechanisms for the formation of chromosomal mutations is associated with the movement of Is sequences and transposons from one DNA section to another or from replicon to replicon. According to phenotypic consequences they are divided into: neutral, conditionally lethal, lethal Neutral- phenotypically do not manifest themselves as changes in characteristics, since they do not noticeably affect the functional activity of the synthesized enzyme. Conditionally lethal- lead to a change, but not to a loss of the functional activity of the enzyme. Lethal- complete loss of the ability to synthesize vital enzymes. Most often they occur with extensive deletions involving a group of genes. In the phenotype they manifest themselves in the form of loss or changes in morphological and biochemical characteristics (flagella, pili. Capsules, the ability to ferment carbohydrates. Synthesize AAs, vitamins. Mutants that require certain AAs, nitrogenous bases are called. Aucostrophic. To mutagens include chemical substances or physical factors (UV rays, radiation) that cause pre-mutation damage in a separate DNA fragment, which turns into mutation as a result of errors in the work of repair enzymes or during the repair process. The action of some leads to changes in the primary structure of DNA by replacing base pairs. When exposed to nitrous acid, which causes deamination of nitrogenous bases, cytosine is converted into uracil, and adenine into hypoxanthine. Other mutagens, such as acridine dyes, directly complex with DNA, causing base loss or insertion. The third nitroso-containing mutagens have multiple effects, causing high frequency mutations, for which they are called supermutagens. Of the physical factors for inducing mutations, UV irradiation is most often used, which leads to the formation of thymine dimers in DNA, i.e. strong bonds between neighboring thymines in the same chain, which interfere with the work of DNAase, disrupting the process of DNA replication. Mtagens do not have a specific effect, since they can cause changes in any gene contained in the genome of a microbial cell. Some chemotherapy drugs are also mutagenic. A\B are not mutagenic, but when affecting the metabolism of NK bacteria, some can cause premutational damage. Cell genome(DNA) is not a passive target exposed to mutagenic factors; they have special systems that repair damage to the genetic material. These systems are reparations, and the process of restoring the cellular genome itself is reparation. The ability of bacterial cells to repair determines the relative stability of their DNA. Repair of damaged DNA is carried out by enzymes, the formation of which is controlled by special genes. F-and enzymes - establishing the location of DNA damage, cutting it out, synthesizing damaged fragments on the matrix of the preserved DNA strand. One of the systems that repairs DNA damage caused by UV rays is called the photoreactivation system. Enzymes act in the presence of visible light and cleave thymine dimers, converting them into monomeric forms. The activity of another system is ensured by enzymes that act in the absence of visible light - the dark repair system, which is divided into pre-replicative and post-replicative. The process of pre-replicative repair: 1. Detection and cutting of the damaged DNA fragment by endonuclease; 2. Removal of the excised fragment by DNA polymerase Ι; 3. Synthesis of nucleotides according to the template of the second preserved strand either by DNA polymerase Ι or DNA polymerase ΙΙΙ; 4. Linking of the restorative DNA fragment with the main strand, carried out by ligase. Mutants that have lost the ability for dark repair are repaired by the post-replicative repair system through recombinations. SOS repair is an inducible process that occurs during multiple changes in DNA; it has several activation systems. Low and medium systems - occur quickly, with a high one, chromosome destruction is observed, plasmid amplification is observed, the transition of an integrative phage infection to a productive one - cell death occurs, but markers for the bacterial population are saved. Repair systems are capable of repairing damage to the cellular genome caused by radiation. Defects in these systems are the causes of a number of diseases.
24. Genetic recombination in bacteria. Transformation. Transduction. Conjugation. Their role in the evolution of microorganisms. Genetic recombination is determined by the method of reproduction and patterns of transmission of genetic material. In eukaryotic cells, they are carried out during the processes that accompany sexual reproduction through the reciprocal (mutual) exchange of chromosome fragments. With this exchange, 2 recombinant chromosomes are formed from 2 recombining parental chromosomes. Prokaryotes do not reproduce sexually. Recombination in them occurs as a result of intragenomic rearrangements, which consist in changing the localization of genes within the chromosome, or when part of the donor's DNA penetrates into the recipient cell. The latter leads to the formation of an incomplete zygote - a merozygote, in which only one recombination is formed. Recombinations are divided into legal and illegal. Legal recombination requires the presence of extended, complementary DNA sections in recombining molecules. It occurs only between closely related species of microorganisms . Illegal– does not require the presence of extended, complementary sections of DNA; it occurs with the participation of IS elements, which have “sticky ends”, ensuring their rapid integration into the bacterial chromosome. Of practical importance are programmed intragenomic recombinations, in which only a change in the localization of existing genes occurs, which play an important role in changing the antigenic structure of microorganisms and effectively resist factors immune system. Genetic recombination occurs through the participation of a number of enzymes. There are special rec genes that determine the recombination ability of bacteria. The transfer of genetic material (chromosomal genes) from one bacteria to another occurs through transformation, transduction and conjugation, and plasmid genes through transduction and conjugation. Transformation- direct transfer of the donor's genetic material to the recipient cell. It was first reproduced in experiments with an avirulent noncapsular strain of pneumococcus, which acquired virulent properties. The transformation phenomenon is reproduced in experiments with various pathogenic and non-pathogenic bacteria: streptococci, meningococci. Only one gene is usually transferred from donor DNA to the recipient cell; this is due to the extent of the transforming DNA fragment that can penetrate into the recipient cell (including one or more linked genes). Transformation occurs effectively in experiments with bacteria of the same species having different genotypes. Not everyone is susceptible to the transformative action of DNA. And only part of the cells of the bacterial population. Cells capable of accepting donor DNA competent. The state of competence occurs during a certain period of bacterial culture growth, coinciding with the end of the logarithmic phase. As a result, the cell wall becomes permeable to high-polymer DNA fragments. This is due to the fact that the transformed DNA fragment binds to the protein, forming a transfosome, in which it is transferred to the bacterial cell. Transformation phases: 1. Adsorption of donor DNA on the recipient cell.2. penetration of DNA into the recipient cell; 3. Connection of DNA with a homologous region of the recipient chromosome, followed by recombination. After penetration into the cell, the transforming DNA despirals. Then the physical inclusion of 2 strands of the donor’s DNA occurs in the recipient’s genome Transduction- transfer of genetic material from one bacteria to another using phages. They are divided into nonspecific, specific and abortive transductions. Nonspecific- occurs during the process of phage reproduction at the moment of assembly of phage particles into their head along with phage DNA, when any DNA fragment of the donor bacterium can penetrate, and the phage can lose part of its genome and become defective. During non-specific transduction in the cell of the recipient strain, along with phage DNA, any donor genes can be transferred, for example, genes that control the ability to synthesize AA, purines, pyrimidines, a/b resistance genes. Thus, during non-specific transduction, transducing phages are only a carrier of genetic material from one bacteria to others, since the phage DNA itself does not participate in the formation of recombinants. Specific transduction characterized by the ability of a phage to transfer certain genes from donor bacteria to recipient bacteria, this is due to the fact that the formation of a transducing phage occurs by separating the prophage from the bacterial chromosome along with genes located on the chromosome of the donor cell next to the prophage. When transducing phages interact with cells of the recipient strain, the gene of the donor bacterium is inserted together with the DNA of the defective phage into the chromosome of the recipient bacterium. Abortive transduction- with it, the DNA fragment of the donor bacterium brought by the phage is not included in the chromosome of the recipient bacterium, but is located in its cytoplasm and can function in this form. During the division of a bacterial cell, a transduced donor DNA fragment can be transferred to only one of the 2 daughter cells, i.e. inherited unilineally and is ultimately lost in offspring. Conjugation- transfer of genetic material from a donor cell to a recipient cell when they are crossed. The donors of genetic material are cells carrying the F-plasmid (sex factor). Bacterial cells that do not have an F-plasmid are not capable of being genetic donors; they are recipients of genetic material and are designated F¯ cells. When crossing an F¯ cell with an F⁺, the sex factor is transmitted regardless of the donor chromosome with a high frequency - all recipient cells receive the sex factor and become F¯ cells. The most important property of the F-plasmid is the ability to insert into certain areas of the bacterial chromosome and become part of it. In some cases, the F plasmid is released from the chromosome, capturing the bacterial genes linked to it. The first stage is the attachment of the donor cell to the recipient cell using the sex villi, then a conjugation bridge is formed between both cells, through which F-factor and other plasmids located in the cytoplasm of the donor bacterium can be transferred from the donor cell to the recipient cell. autonomous state. To transfer a bacterial chromosome, a break in one of the DNA strands is required, which occurs at the site of inclusion of the F-plasmid with the participation of endonuclease, i.e. During conjugation, only one strand of donor DNA is transferred, and the 2nd, remaining complementary, strand is completed in the recipient cell.
25. Microbiological foundations of genetic engineering and biotechnology. Construction of genetically engineered strains with specified properties, their use in the production of vaccines. The development of molecular genetics has become a powerful stimulus for research devoted to the study of the molecular genetic basis of pathogenicity and immunogenicity, the mechanisms of formation of new biological variants of pathogenic and opportunistic microorganisms, and the spread of antibiotic-resistant strains against the backdrop of an expanding arsenal of chemotherapeutic agents. Achievements of genetic engineering make it possible to create new genetic elements from nucleotide sequences that carry specified information, methods for their transfer into pro- and eukaryotic cells. New genetic elements are recombinant DNA molecules that include 2 components: vector-carrier and cloned “foreign” DNA. The vector must have the properties of a replicon and ensure replication of the newly created recombinant molecule. Therefore, replicons such as plasmids, temperate phages, and animal viruses that have a circular closed DNA structure are used as vectors. Cloned DNA is a DNA fragment carrying the necessary gene that controls the synthesis of the desired product. Various technological methods have now been developed for creating recombinant molecules, for example, processing isolated vector DNA molecules and DNA carrying the desired gene with restriction enzymes that attack the taken DNA molecules in a strictly defined area. Some restriction enzymes cleave DNA molecules by forming single-stranded ends that are complementary to each other (sticky ends). Stages: 1. Cutting the DNA molecule using restriction endonucleases; 2. Treatment of the resulting linear molecules with the enzyme polynucleotide ligase, which cross-links 2 different molecules into one recombinant one; 3. Introduction of recombinant molecules by transformation into E.coΙİ cells.
Villi or drank(fimbria from the English fimbria - fringe), - thin hollow filaments of a protein nature, thinner and shorter (3-10 nm x 0.3-10 microns) than flagella. The pili extend from the cell surface and are composed of the protein pilin. They have antigenic activity. In my own way functional purpose pili are divided into several types.
Type 1 pili, or general type - common pili - pili responsible for adhesion, i.e. for the attachment of bacteria to the affected cell. They begin at the CPM and penetrate the cell wall. Their number is large - from several hundred to several thousand per bacterial cell. Bacterial and eukaryotic cells are negatively charged, but surface microvilli reduce the charge of the bacterium and reduce the electrostatic repulsive forces. In addition, increasing the surface area of the bacterial cell gives it additional advantages in utilization nutrients environment.
Type 2 pili (sexual, F-pili, conjugative - sex pili) are involved in the conjugation of bacteria, ensuring the transfer of part of the genetic material from the donor cell to the recipient cell. They are present only in donor bacteria in limited quantities (1-4 per cell), longer (0.5-10 µm). Distinctive feature genital pili is the interaction with special “male” spherical bacteriophages, which are intensively adsorbed on the genital pili.
Flagella and pili of bacteria. Electron microscopy. (Atlas of medical microbiology, virology and immunology / Edited by A.A. Vorobyov, A.S. Bykov - M.: Medical news agency, 2003.-236 p.).
Escherichia coli. Electron microscopy. Adsorption of phage ms2 onto f-pili. x100000. “Avakyan A.A., Kats L.N., Pavlova I.B. Atlas of the anatomy of bacteria pathogenic to humans and animals. M "Medicine". - 1972. - 183 p. "
The bacterial organism is represented by one single cell. The forms of bacteria are varied. The structure of bacteria differs from the structure of animal and plant cells.
The cell lacks a nucleus, mitochondria and plastids. The carrier of hereditary information DNA is located in the center of the cell in a folded form. Microorganisms that do not have a true nucleus are classified as prokaryotes. All bacteria are prokaryotes.
It is estimated that there are over a million species of these amazing organisms on earth. To date, about 10 thousand species have been described.
A bacterial cell has a wall, a cytoplasmic membrane, cytoplasm with inclusions and a nucleotide. Of the additional structures, some cells have flagella, pili (a mechanism for adhesion and retention on the surface) and a capsule. Under unfavorable conditions, some bacterial cells are capable of forming spores. The average size of bacteria is 0.5-5 microns.
External structure of bacteria
Rice. 1. The structure of a bacterial cell.
Cell wall
- The cell wall of a bacterial cell is its protection and support. It gives the microorganism its own specific shape.
- The cell wall is permeable. Through it, nutrients pass in and metabolic products pass out.
- Some types of bacteria produce special mucus that resembles a capsule that protects them from drying out.
- Some cells have flagella (one or more) or villi that help them move.
- Bacterial cells that appear pink when stained with Gram stain ( gram-negative), the cell wall is thinner and multilayered. Enzymes that help break down nutrients are released.
- Bacteria that appear violet on Gram staining ( gram-positive), the cell wall is thick. Nutrients that enter the cell are broken down in the periplasmic space (the space between the cell wall and the cytoplasmic membrane) by hydrolytic enzymes.
- There are numerous receptors on the surface of the cell wall. Cell killers - phages, colicins and chemical compounds - are attached to them.
- Wall lipoproteins in some types of bacteria are antigens called toxins.
- With long-term treatment with antibiotics and for a number of other reasons, some cells lose their membranes, but retain the ability to reproduce. They acquire a rounded shape - L-shape and can persist in the human body for a long time (cocci or tuberculosis bacilli). Unstable L-forms have the ability to return to their original form (reversion).
Rice. 2. The photo shows the structure of the bacterial wall of gram-negative bacteria (left) and gram-positive bacteria (right).
Capsule
Under unfavorable environmental conditions, bacteria form a capsule. The microcapsule adheres tightly to the wall. It can only be seen in an electron microscope. The macrocapsule is often formed by pathogenic microbes (pneumococci). In Klebsiella pneumoniae, the macrocapsule is always found.
Rice. 3. In the photo is pneumococcus. Arrows indicate the capsule (electronogram of an ultrathin section).
Capsule-like shell
The capsule-like shell is a formation loosely associated with the cell wall. Thanks to bacterial enzymes, the capsule-like shell is covered with carbohydrates (exopolysaccharides) from the external environment, which ensures the adhesion of bacteria to different surfaces, even completely smooth ones.
For example, streptococci, when entering the human body, are able to stick to teeth and heart valves.
The functions of the capsule are varied:
- protection from aggressive environmental conditions,
- ensuring adhesion (sticking) to human cells,
- Possessing antigenic properties, the capsule has a toxic effect when introduced into a living organism.
Rice. 4. Streptococci are capable of sticking to tooth enamel and, together with other microbes, cause caries.
Rice. 5. The photo shows damage to the mitral valve due to rheumatism. The cause is streptococci.
Flagella
- Some bacterial cells have flagella (one or more) or villi that help them move. The flagella contain the contractile protein flagellin.
- The number of flagella can be different - one, a bundle of flagella, flagella at different ends of the cell or over the entire surface.
- Movement (random or rotational) is carried out as a result of the rotational movement of the flagella.
- The antigenic properties of flagella have a toxic effect in disease.
- Bacteria that do not have flagella, when covered with mucus, are able to glide. Aquatic bacteria contain 40-60 vacuoles filled with nitrogen.
They provide diving and ascent. In the soil, the bacterial cell moves through soil channels.
Rice. 6. Scheme of attachment and operation of the flagellum.
Rice. 7. In the photo different types flagellar microbes.
Rice. 8. The photo shows different types of flagellated microbes.
Drank
- Pili (villi, fimbriae) cover the surface of bacterial cells. The villus is a helically twisted thin hollow thread of protein nature.
- General type drank provide adhesion (sticking) to host cells. Their number is huge and ranges from several hundred to several thousand. From the moment of attachment, any .
- Sexual drank facilitate the transfer of genetic material from the donor to the recipient. Their number is from 1 to 4 per cell.
Rice. 9. The photo shows E. coli. Flagella and pili are visible. The photo was taken using a tunneling microscope (STM).
Rice. 10. The photo shows numerous pili (fimbriae) of cocci.
Rice. 11. The photo shows a bacterial cell with fimbriae.
Cytoplasmic membrane
- The cytoplasmic membrane is located under the cell wall and is a lipoprotein (up to 30% lipids and up to 70% proteins).
- Different bacterial cells have different membrane lipid compositions.
- Membrane proteins perform many functions. Functional proteins are enzymes due to which the synthesis of its various components, etc. occurs on the cytoplasmic membrane.
- The cytoplasmic membrane consists of 3 layers. The double phospholipid layer is permeated with globulins, which ensure the transport of substances into the bacterial cell. If its function is disrupted, the cell dies.
- The cytoplasmic membrane takes part in sporulation.
Rice. 12. The photo clearly shows a thin cell wall (CW), a cytoplasmic membrane (CPM) and a nucleotide in the center (the bacterium Neisseria catarrhalis).
Internal structure of bacteria
Rice. 13. The photo shows the structure of a bacterial cell. The structure of a bacterial cell differs from the structure of animal and plant cells - the cell lacks a nucleus, mitochondria and plastids.
Cytoplasm
The cytoplasm is 75% water, the remaining 25% is mineral compounds, proteins, RNA and DNA. The cytoplasm is always dense and motionless. It contains enzymes, some pigments, sugars, amino acids, a supply of nutrients, ribosomes, mesosomes, granules and all sorts of other inclusions. In the center of the cell, a substance is concentrated that carries hereditary information - the nucleoid.
Granules
The granules are made up of compounds that are a source of energy and carbon.
Mesosomes
Mesosomes are cell derivatives. Have different shapes- concentric membranes, vesicles, tubes, loops, etc. Mesosomes have a connection with the nucleoid. Participation in cell division and sporulation is their main purpose.
Nucleoid
A nucleoid is an analogue of a nucleus. It is located in the center of the cell. It contains DNA, the carrier of hereditary information in a folded form. Unwound DNA reaches a length of 1 mm. The nuclear substance of a bacterial cell does not have a membrane, a nucleolus or a set of chromosomes, and does not divide by mitosis. Before dividing, the nucleotide is doubled. During division, the number of nucleotides increases to 4.
Rice. 14. The photo shows a section of a bacterial cell. A nucleotide is visible in the central part.
Plasmids
Plasmids are autonomous molecules coiled into a ring of double-stranded DNA. Their mass is significantly 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.
Rice. 15. The photo shows a bacterial plasmid. The photo was taken using an electron microscope.
Ribosomes
Ribosomes of a bacterial cell are involved in the synthesis of protein from amino acids. The ribosomes of bacterial cells are not united into the endoplasmic reticulum, like those of cells with a nucleus. It is ribosomes that often become the “target” for many antibacterial drugs.
Inclusions
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 painted, take on a different appearance than the color of the dye. You can diagnose by currency.
Shapes of bacteria
The shape of a bacterial cell and its size are of great importance in their identification (recognition). The most common shapes are spherical, rod-shaped and convoluted.
Table 1. Main forms of bacteria.
Globular bacteria
The spherical bacteria are called cocci (from the Greek coccus - grain). They are arranged one by one, two by two (diplococci), in packets, in chains, and like bunches of grapes. This location depends on the method of cell division. The most harmful microbes are staphylococci and streptococci.
Rice. 16. In the photo there are micrococci. The bacteria are round, smooth, and white, yellow and red in color. In nature, micrococci are ubiquitous. They live in different cavities of the human body.
Rice. 17. The photo shows diplococcus bacteria - Streptococcus pneumoniae.
Rice. 18. The photo shows Sarcina bacteria. Coccoid bacteria cluster together in packets.
Rice. 19. The photo shows streptococcus bacteria (from the Greek “streptos” - chain).
Arranged in chains. They are causative agents of a number of diseases.
Rice. 20. In the photo, the bacteria are “golden” staphylococci. Arranged like “bunches of grapes”. The clusters are golden in color. They are causative agents of a number of diseases.
Rod-shaped bacteria
Rod-shaped bacteria that form spores are called bacilli. They have a cylindrical shape. The most a prominent representative of this group is the bacillus. The bacilli include plague and hemophilus influenzae. The ends of rod-shaped bacteria may be pointed, rounded, chopped off, flared, or split. The shape of the sticks themselves can be regular or irregular. They can be arranged one at a time, two at a time, or form chains. Some bacilli are called coccobacilli because they have a round shape. But, nevertheless, their length exceeds their width.
Diplobacillus are double rods. Anthrax bacilli form long threads (chains).
The formation of spores changes the shape of the bacilli. In the center of the bacilli, spores form in butyric acid bacteria, giving them the appearance of a spindle. In tetanus bacilli - at the ends of the bacilli, giving them the appearance of drumsticks.
Rice. 21. The photo shows a rod-shaped bacterial cell. Multiple flagella are visible. The photo was taken using an electron microscope. Negative.
Rice. 24. In butyric acid bacilli, spores are formed in the center, giving them the appearance of a spindle. In tetanus sticks - at the ends, giving them the appearance of drumsticks.
Twisted bacteria
No more than one whorl has a cell bend. Several (two, three or more) are campylobacters. Spirochetes have a peculiar appearance, which is reflected in their name - “spira” - bend and “hate” - mane. Leptospira (“leptos” - narrow and “spera” - gyrus) are long filaments with closely spaced curls. Bacteria resemble a twisted spiral.
Rice. 27. In the photo, a spiral-shaped bacterial cell is the causative agent of “rat bite disease.”
Rice. 28. In the photo, Leptospira bacteria are the causative agents of many diseases.
Rice. 29. In the photo, Leptospira bacteria are the causative agents of many diseases.
Club-shaped
Corynebacteria, the causative agents of diphtheria and listeriosis, have a club-shaped form. This shape of the bacterium is given by the arrangement of metachromatic grains at its poles.
Rice. 30. The photo shows corynebacteria.
Read more about bacteria in the articles:
Bacteria have lived on planet Earth for more than 3.5 billion years. During this time they learned a lot and adapted to a lot. The total mass of bacteria is enormous. It is about 500 billion tons. Bacteria have mastered almost all known biochemical processes. The forms of bacteria are varied. The structure of bacteria has become quite complex over millions of years, but even today they are considered the most simply structured single-celled organisms.
On the cell surface of many prokaryotes there are structures that determine the ability of a cell to move in a liquid environment. This - flagella . Their number, size, location, as a rule, are characteristics that are constant for a particular species, and therefore are taken into account in the taxonomy of prokaryotes. However, evidence is accumulating that the number and location of flagella in the same species can be largely determined by culture conditions and stage life cycle, and, therefore, the taxonomic significance of this character should not be overestimated.
If the flagella are located at the poles or in the polar region of the cell, they are said to be polar or subpolar location, if along the lateral surface, they talk about lateral location.
Flagella are long shoots, which extend from one (monotrichs, lophotrichs) or both (amphitrichs) poles of the bacterial cell or are distributed over its entire surface (peritrichs). Like fimbriae, flagella consist of polymerized or tightly folded protein subunits that give them toughness spiral shape and cause serological differences different types bacteria.
In some spirochetes, for example Treponema pallidum and Borrelia burgdorferi, longitudinally located flagella are collected into an axial filament. Thanks to this formation, which spirals around the cell, spirochetes can actively move using rotational movements. Some bacteria can move along the substrate without visible motor structures.
Depending on the number of flagella and their location on the cell surface, they are distinguished:
- monopolar monotrichs (one flagellum attached to one pole of the cell;
- monopolar polytrichs (a bundle of flagella is located at one pole of the cell), bipolar polytrichs (a bundle of flagella at each pole;
- peritrichous (numerous flagella located over the entire surface of the cell or along its lateral surface.
In the latter case, the number of flagella can reach 1000 per cell.
The usual thickness of the flagellum is 10-20 nm, length - from 3 to 15 microns. In some bacteria, the length of the flagellum can be an order of magnitude greater than the diameter of the cell. As a rule, polar flagella are thicker than peritrichous flagella.
The flagellum is a relatively rigid spiral, usually twisted counterclockwise. The flagellum also rotates counterclockwise with a frequency of 40 to 60 rps, which causes the cell to rotate, but in the opposite direction. Since the cell is much more massive than the flagellum, it rotates at a much lower speed - about 12-14 rpm. Rotational movement The flagellum is also converted into translational movement of the cell, the speed of which in a liquid medium for different types of bacteria ranges from 16 to 100 μm/s.
Studying the structure of the flagellum under an electron microscope revealed that it consists of three parts. The main mass of the flagellum is a long spiral thread (fibril), which at the surface of the cell wall turns into a thickened curved structure - hook. The thread is attached with a hook to the basal body, embedded in the CPM and the cell wall. The protein subunits are arranged in the form of a spiral, inside which there is a hollow channel. The flagella grows from the distal end, where the subunits enter through the internal channel. In some species, the outside of the flagellum is additionally covered with a sheath of a special chemical structure or which is a continuation of the cell wall and, probably, built from the same material.
The surface structures of a bacterial cell also include fimbriae (pili, cilia, villi) - hard, straight, hollow filaments of the pilin protein, localized on the CS. Fimbriae are shorter and thinner than flagella: their diameter is 3–20 nm, length 0.2–10.0 µm.
Fimbriae are an optional cellular structure, since bacteria grow and reproduce well without them. Unlike flagella, fimbriae do not perform a motor function and are found in motile and immobile forms. According to their functional purpose, fimbriae are divided into 2 types. The term "fimbriae" is more often used to refer to the common pili, and the term "pili" to refer to the sex pili.
Fimbriae 1 (general) type found in most bacteria. They cover the entire surface of the cell and are located peritrichially or polarly. The number of fimbriae is large - from several hundred to several thousand per bacterial cell. The synthesis of fimbriae is controlled by the bacterial chromosome; the loss of fimbriae leads to their new synthesis.
Covering the entire cell, fimbriae create a fleecy surface. Sometimes the fimbriae merge into lumps, giving the cell an untidy appearance; in other cases, the surface of the cells is covered with a felt-like cover, consisting of plexuses of thin filaments.
Drank 2 types(synonyms: conjugative, sexual, sex pili) are formed only by male donor cells containing transmissible plasmids (F, R, Col), in limited quantities (1–4 per cell), and have terminal swellings.
Functions of fimbriae.
Fimbriae of both types:
- They have antigenic activity.
- Bacteriophages (specific bacterial viruses) are adsorbed on them.
- Adhesive function: ensure the attachment of bacteria to the cells of the mucous membranes of the host body and to other substrates (cells of plants, fungi, inorganic particles and organic residues).
- Mechanical protection of the bacterial cell. They give bacteria the property of hydrophobicity and promote the union of cells into groups.
- They increase the absorption surface of bacterial cells, participate in nutrition processes, water-salt metabolism and in the transport of metabolites.
Sex pili: F-pili provide conjugation - the transfer of part of the genetic material from the donor cell to the recipient cell.
Pili are extracellular protein structures, which perform a wide variety of functions, including DNA exchange, adhesion and biofilm formation by prokaryotic cells
Many adhesive pili are assembled via the chaperone-Usher-protein system. Assembly occurs on the outer membrane with the participation of the Usher protein, which forms a pore through which the pili subunits pass, and the periplasmic chaperone, which promotes their twisting and passage through the pore
Flagella are external structures of the cell that serve as propellers to enable its movement.
In prokaryotes, flagella consist of multiple segments, each of which is formed during the assembly of protein subunits
Two types of appendage structures extend from the surface of a prokaryotic cell, drank And flagella. Pili are thread-like oligomers of proteins present on the cell surface. There are different types of saws. For example, F pili are involved in cell conjugation and DNA transfer. When these appendage structures were first discovered, they were called “fimbria” (Latin fimbria - thread, fiber). Their presence correlated with the ability of E. coli to agglutinate red blood cells.
Later to designate fibrillar structures ( F-drank), associated with the process of transfer of genetic material between organisms during conjugation, the term pili (or pilus) (Latin pilus - hair) was proposed. Since then, the term has become a general term to describe all types of villous adnexal structures, and is used along with the term fimbria.
Cell interaction bacteria with other prokaryotic and eukaryotic cells with the participation of villi often serves as an important stage in the colonization of the epithelium, the penetration of microbes into host cells, the exchange of DNA and the formation of biofilms. Pili can serve as receptors for bacteriophages. The main function of most pili is to provide structural support for the positioning of specific molecules involved in cell adhesion. The adhesive subunits of the villi (adhesins) are minor components of the tips, but the major structural subunits can also function as adhesins.
Often adhesive pili are important factors in the colonization of host organisms by microbes. For example, in urinary tract infections with pathogenic E. coli bacteria, cells attach to the bladder epithelium using type I pili. This type of pili is present in many Gram-negative microorganisms. They are complex structures consisting of a thick body connected to a thin fibrillar end. At the end there are FimH adhesin molecules that bind to mannose residues on the surface of host cells.
Two types of pili in prokaryotic cells.P-pili are shorter than F-pili and are involved in cell adhesion.
F-pili are involved in conjugation and DNA transfer between cells.
Photos courtesy of Matt Chapman (left) and Ron Scarry (right), Department of Biology, University of Sydney.
Assembly pili is a complex process that involves the structural proteins that make up the body of the pili and additional proteins that facilitate the assembly of subunits on the cell surface. All structural components, necessary for the process of pili assembly on the surface of gram-negative microorganisms, must be translocated through the cytoplasmic membrane into the periplasm and further through the outer membrane. Two specific proteins are involved in completing the assembly process: a chaperone present in the periplasm and an outer membrane transport protein called the Usher protein.
The processes in which these proteins function provide biogenesis more than 30 various types villous structures. As shown in the figure below, chaperone complexes with subunits are formed in the periplasm and interact with the Usher protein at the outer membrane, where the chaperone is released. In this case, interactive surfaces open on the subunits, which ensures their further assembly into pili. Studies of type I and P pili have shown that adhesin-chaperone complexes (PapDG or FimCH) have a high affinity for the Usher protein, and adhesins are the initial subunits that assemble into pili.
Enabling remaining subunits is partly determined by the kinetics of formation of a complex with the chaperone on the Usher protein. In addition to functioning as an assembly platform, the Usher protein likely plays other roles in pilus assembly. According to electron microscopy data high resolution, PapС Usher has the form of ring complexes with a diameter of 15 nm, which in the middle have a pore 2 nm in size. After cleavage from the chaperone, which occurs on the Usher protein, the subunits are incorporated into the growing pili structure, which is believed to be extruded through the central pore of the complex in the form of a thick linear fibril consisting of a single subunit.
Majority microorganisms has motility, and this is often achieved by long structural appendages called flagella. In gram-positive and gram-negative bacteria, flagella are collected on the surface of cells. When there is one flagellum at the cell pole, this arrangement is called monotrichial (or polar). If the flagella are located around the cell, then this arrangement is called peritrichial.
If on one pole of the cell There is a group of flagella, then they speak of their lophotrichial arrangement (from the Latin “tuft”). bacteria differ from these structures of eukaryotic cells, which consist of microtubules and associated proteins and are surrounded by a plasma membrane.
Flagella can be of different lengths, but their diameter is usually 20 nm. They are not visible in a light microscope unless the preparations are first treated with reagents that increase the diameter of the flagella. The figure below shows that flagella are composed of three distinct domains: the filament, the hook, and the basal body. The flagellum filament consists of repeating structures of flagellin proteins. Flagellins are highly conserved bacterial proteins, suggesting that cell movement involving flagella is characteristic of primitive forms of living organisms. At the point where the flagellum attaches to the cell there is a basal body, which is complex structure consisting of many proteins.
Filament flagellum connects to the basal body via a hook. In Gram-negative bacteria, the basal body extends through the outer membrane, the cell wall proteoglycan, and the cytoplasmic membrane. The flagellum is connected to the outer membrane through an L-ring. Two pairs of rings, S-M and P, promote attachment of the flagellum to the cytoplasmic membrane and to the cell wall, respectively. Each ring consists of many membrane proteins. There are two Mot proteins on the cytoplasmic membrane, which act as motors that drive the flagella. Another set of proteins is embedded in the cytoplasmic membrane and performs a reverse function in relation to the flagellum motors. Since Gram-positive organisms lack an outer membrane, they have only S-M rings.
IN formation and assembly of flagella filaments Several dozen different genes are involved. Their activity is strictly regulated according to the order of the assembly process. Thus, the genes involved in the assembly of the basal body and hook are expressed first, and then comes the turn of the genes responsible for the formation of flagellum subunits. Expression of flagellin subunits does not occur until hook assembly is complete. At this point, a transcriptional suppressor exits through the hook channel, and thus the suppression of flagellin expression is released. Flagellin subunits are exported through the flagellum and added to its growing end.
Such mechanism ensures filament assembly only after the formation of the hook structure. This structure is also relevant to other protein secretory systems.
System chemotaxis determines the presence of nutritional components and then determines the direction of rotation of the flagellum. In the absence of nutritional components, the flagella rotate clockwise, which causes the cell to rotate. The movement of a cell towards or away from molecules of a chemical compound is called chemotaxis. In this section we will consider the movement of a prokaryotic cell in the presence of an attractant, which is a nutrient product.
In order to provide the cell with such movement, rigid flagellum should rotate like a propeller, due to the energy supplied by the proton motive force. The cell's movement consists of a series of straight runs followed by rapid, erratic turns. When the flagella rotate counterclockwise, the cell moves in a straight line, and when it rotates clockwise, the cell makes turns. Since the cell takes random positions as a result of rotations, one would think that the overall result of the movement would be zero. However, the frequency of runs is regulated according to the availability of the nutrient component: longer runs are characteristic of the movement of the cell towards the food source, and the number of turns increases as the cell moves away from it.
Although the direction of individual runs is still random, the overall result is the movement of the cell towards the attractant.
Signal Transmission Pathways chemotaxis in prokaryotes are characterized by an extremely conservative nature. The only known organism whose genome lacks chemotaxis genes is Mycoplasma. The following conserved chemotaxis proteins are found in almost all prokaryotes: CheR, CheA, CheY, CheW, and CheB. Through a complex cascade of events, including phosphorylation and methylation, these proteins provide a complex, coordinated and highly flexible cell response to the presence of attractants and repellents in environment. We describe how these events occur in E. coli cells.
Present in the environment attractants or repellents bind to receptors located on the cytoplasmic membrane. CheA kinase, also located in the cytoplasmic membrane, interacts with these receptors. This kinase phosphorylates CheY, which then binds to the flagellar motor, causing the flagellum to switch its direction of rotation and cause the cell to turn. The phosphatase CheZ removes the phosphate group from CheY. At a low attractant concentration, autophosphorylation of CheA occurs, the phosphate group is transferred to CheY, and the latter migrates to the flagellum motor, changing the pattern of cell movement to turn.
Chemotaxis system characterized by another level of complexity that allows the cell to constantly adapt to the conditions existing in the environment. As the cell moves along the concentration gradient of chemical compounds, the cell can respond to small fluctuations that occur. Such short-term memory is ensured by methylation of membrane receptors. CheR methylates membrane receptors, and CheB removes methyl groups.