It is customary to consider unicellular organisms, the size of which does not exceed 0.1 mm. Representatives of this large group may have different cellular organization, morphological features and metabolic capabilities, that is, the main feature that unites them is size. The term "microorganism" itself is not endowed with a taxonomic sense. Microbes belong to a variety of taxonomic units, and other representatives of these units can be multicellular and reach large sizes.
As a result of the gradual accumulation of factual material about microbes, it became necessary to introduce rules for their description and systematization.
The classification of microorganisms is characterized by the presence of the following taxa: domain, phylum, class, order, family, genus, species. In microbiology, scientists use the binomial system of object characteristics, that is, the nomenclature includes the names of the genus and species.
Most microorganisms are characterized by an extremely primitive and universal structure, therefore, their division into taxa cannot be carried out only on the basis of morphological features. Functional features, molecular biological data, and patterns of biochemical processes, etc., are used as criteria.
To identify an unknown microorganism, studies are carried out to study the following properties:
The systematics and classification of microorganisms related to prokaryotes is carried out using the Bergey's Guide to the Systematics of Bacteria. And the identification is carried out using the Burgey determinant.
To determine the taxonomic affiliation of an organism, several methods of classifying microorganisms are used.
With a formal numerical classification, all features are considered equally significant. That is, the presence or absence of a particular feature is taken into account.
Morphophysiological classification involves the study of the totality of morphological properties and features of the course of metabolic processes. In this case, it is endowed with meaning and significance of a particular property of an object. The placement of a microorganism in one or another and the assignment of a name depend primarily on the type of cellular organization, the morphology of cells and colonies, as well as the nature of growth.
Accounting for functional characteristics provides for the possibility of using various nutrients by microorganisms. Also important is the dependence on certain physical and chemical factors of the environment, and in particular the ways of obtaining energy. There are microbes that require chemotaxonomic studies to identify them. Pathogenic microorganisms require serodiagnosis. A qualifier is used to interpret the results of the above tests.
In molecular genetic classification, the structure of the molecules of the most important biopolymers is analyzed.
Nowadays, the identification of a specific microscopic organism begins with the isolation of its pure culture and analysis of the nucleotide sequence of 16S rRNA. Thus, the place of the microbe on the phylogenetic tree is determined, and the subsequent specification by genus and species is carried out using traditional microbiological methods. The coincidence value equal to 90% allows you to determine the generic affiliation, and 97% - species.
An even clearer differentiation of microorganisms by genus and species is possible using polyphyletic (polyphase) taxonomy, when the determination of nucleotide sequences is combined with the use of information at various levels, up to ecological. That is, a search for groups of similar strains is carried out first, followed by determining the phylogenetic positions of these groups, fixing the differences between the groups and their nearest neighbors, and collecting data to differentiate the groups.
This domain includes three groups where there are microscopic organisms. We are talking about algae, protozoa and fungi.
Algae are unicellular, colonial or multicellular phototrophs that carry out oxygenic photosynthesis. The development of a molecular genetic classification of microorganisms belonging to this group has not yet been completed. Therefore, at the moment, algae are classified in practice based on the composition of pigments and reserve substances, the structure of the cell wall, the presence of mobility and the method of reproduction.
Typical representatives of this group are unicellular organisms belonging to dinoflagellates, diatoms, euglenoids and green algae. All algae are characterized by the formation of chlorophyll and various forms of carotenoids, but the ability to synthesize other forms of chlorophylls and phycobilins in the representatives of the group manifests itself in different ways.
The combination of these or those pigments causes the staining of cells in different colors. They can be green, brown, red, golden. Cell pigmentation is a species characteristic.
Diatoms are unicellular planktonic forms that have the appearance of a silicon bivalve shell. Some representatives are capable of movement by the type of sliding. Reproduction is both asexual and sexual.
The habitats of unicellular organisms are freshwater reservoirs. They move with the help of flagella. There is no cell wall. Able to grow in the dark due to the process of oxidation of organic substances.
Dinoflagellates have a special structure of the cell wall, it consists of cellulose. These planktonic unicellular algae have two lateral flagella.
For microscopic representatives, habitats are fresh and marine water bodies, soil and the surface of various terrestrial objects. There are non-motile species, and some are capable of locomotion using flagella. Just like dinoflagellates, green microalgae have a cellulose cell wall. The storage of starch in cells is characteristic. Reproduction is carried out both asexually and sexually.
The basic principles for the classification of microorganisms belonging to the protozoa are based on morphological characteristics that vary greatly among representatives of this group.
They can lead a stationary lifestyle or move around with the help of various devices: flagella, cilia and pseudopods. Within the taxonomic group of protozoa, there are several more groups.
Amoebas carry out nutrition by endocytosis, move with the help of pseudopods, the essence of reproduction lies in the primitive in two. Most amoebas are free-living aquatic forms, but there are also those that cause diseases in humans and animals.
Infusoria cells have two different nuclei, asexual reproduction consists in transverse division. There are representatives for which sexual reproduction is characteristic. A coordinated system of cilia takes part in the movement. Endocytosis is carried out by capturing food in a special oral cavity, and the remains are excreted through an opening at the posterior end. In nature, ciliates live in water bodies polluted with organic substances, as well as in the rumen of ruminants.
Flagellates are characterized by the presence of flagella. The absorption of dissolved nutrients is carried out by the entire surface of the CPM. Division occurs only in the longitudinal direction. Among flagellates, there are both free-living and symbiotic species. The main symbionts of humans and animals are trypanosomes (cause sleeping sickness), leishmania (cause difficult-to-heal ulcers), giardia (lead to intestinal disorders).
Of all the protozoa, sporozoans have the most complex life cycle. The most famous representative of sporozoans is the malarial Plasmodium.
The classification of microorganisms according to classifies representatives of this group as heterotrophs. Most are characterized by the formation of mycelium. Respiration is usually aerobic. But there are also facultative anaerobes that can switch to alcoholic fermentation. Reproduction methods are vegetative, asexual and sexual. It is this feature that serves as a criterion for further
If we talk about the importance of representatives of this group, then the combined non-taxonomic group of yeasts is of the greatest interest here. This includes mushrooms that do not have a mycelial growth stage. There are many facultative anaerobes among yeasts. However, there are also pathogenic species.
The morphology and classification of prokaryotic microorganisms unite them into two domains: bacteria and archaea, whose representatives have many significant differences. Archaea do not have peptidoglycan (murein) cell walls typical of bacteria. They are characterized by the presence of another heteropolysaccharide - pseudomurein, in which there is no N-acetylmuramic acid.
Archaea are divided into three phyla.
The principles of classification of microorganisms that unite microbes in this domain are based on the structural features of the cell membrane, and in particular the content of peptidoglycan in it. At the moment there are 23 phylums in the domain.
Bacteria are an important link in the cycle of substances in nature. The essence of their significance in this global process is the decomposition of plant and animal remains, the purification of water bodies polluted with organic matter, and the modification of inorganic compounds. Without them, the existence of life on Earth would be impossible. These microorganisms live everywhere, their habitat can be soil, water, air, human body, animals and plants.
According to the shape of the cells, the presence of devices for movement, the articulation of cells among themselves, this domain is carried out within the subsequent classification of microorganisms. Microbiology considers the following types of bacteria based on the shape of the cells: round, rod-shaped, filamentous, convoluted, spiral. According to the type of movement, bacteria can be immobile, flagellated, or move due to the secretion of mucus. Based on the method of articulation of cells with each other, bacteria can be isolated, linked in the form of pairs, granules, and branching forms are also found.
There are many pathogenic microorganisms among rod-shaped bacteria (causative agents of diphtheria, tuberculosis, typhoid fever, anthrax); protozoa (malarial plasmodium, toxoplasma, leishmania, giardia, trichomonas, some pathogenic amoeba), actinomycetes, mycobacteria (causative agents of tuberculosis, leprosy), molds and yeast-like fungi (causative agents of mycoses, candidiasis). Mushrooms can cause all kinds of skin lesions, for example, different types of lichen (with the exception of herpes zoster, in which the virus is involved). Some yeasts, being permanent inhabitants of the skin, do not have a detrimental effect under normal immune system conditions. However, if the activity of immunity decreases, then they cause the appearance of seborrheic dermatitis.
The epidemiological danger of microorganisms is a criterion for combining all pathogenic microbes into four groups corresponding to four risk categories. Thus, the pathogenicity groups of microorganisms, the classification of which is given below, are of the greatest interest to microbiologists, since they directly affect the life and health of the population.
The safest, the 4th pathogenicity group, includes microbes that do not pose a threat to the health of an individual (or the risk of this threat is negligible). That is, the risk of infection is very small.
The 3rd group is characterized by a moderate risk of infection for an individual, a low risk for society as a whole. Such pathogens could theoretically cause disease, and even if they do, there are proven effective treatments, as well as a set of preventive measures that can prevent the spread of infection.
The 2nd pathogenicity group includes microorganisms that pose a high risk for the individual, but low for society as a whole. In this case, the pathogen can cause severe disease in humans, but it does not spread from one infected person to another. Effective methods of treatment and prevention are available.
The 1st pathogenicity group is characterized by a high risk for both the individual and society as a whole. A pathogen that causes severe disease in a human or animal can be easily transmitted in a variety of ways. Effective treatments and preventive measures are usually not available.
Pathogenic microorganisms, the classification of which determines their belonging to one or another pathogenicity group, cause great damage to the health of society only if they belong to the 1st or 2nd group.
Lecture No. 5 Morphology and systematics of microorganisms. Prokaryotes (bacteria and actinomycetes).
1 Morphology and systematics of microorganisms. The morphology of microorganisms studies their appearance, shape and structural features, the ability to move, spore formation, and methods of reproduction. Morphological features play an important role in the recognition and classification of microorganisms. Since ancient times, the living world has been divided into two kingdoms: the kingdom of plants and the kingdom of animals. When the world of microorganisms was discovered, they were separated into a separate kingdom. Thus, until the 19th century, the whole world of living organisms was divided into three kingdoms. At the beginning, the classification of microorganisms was based on morphological characteristics, since a person knew nothing more about them. By the end of the 19th century, many species had been described; different scientists, mainly botanists, divided microorganisms into groups accepted for the classification of plants. In 1897, for the systematics of microbes, they began to use, along with morphological, and physiological signs. As it turned out later, for a scientifically based classification, some signs alone are not enough. Therefore, a set of features is used:
Morphological (cell shape, size, mobility, reproduction, sporulation, Gram stain);
Cultural (character of growth on liquid and solid nutrient media);
Physiological and biochemical (nature of accumulated products);
Genotypic (physical and chemical properties of DNA).
Genosystematics allows you to determine the type of microorganisms not by similarity, but by kinship. It has been established that the nucleotide composition of total DNA does not change during the development of microorganisms under different conditions. S- and R-forms are identical in DNA composition. Microorganisms have also been found that have a similar nucleotide composition of DNA, although they belong to different systematic groups: Escherichia coli and some corynebacteria. This indicates that the systematics (taxonomy) of microbes should take into account different characters.
Until recently, all living beings of the cellular structure, depending on the relationship of the nucleus and organelles with the cytoplasm, the composition of the cell wall and other features, were divided into two groups (kingdoms):
1.1 Prokaryotes-prenuclear (classified - organisms that do not have a clearly defined nucleus, represented by a DNA molecule in the form of a ring; the cell wall includes peptidoglycan (murein) and teichoic acids; ribosomes have sedimentation constants of 70; energy centers of the cell are located in mesosomes and there are no organelles ).
1.2 Nuclear eukaryotes (with a clearly defined nucleus separated from the cytoplasm by a membrane; peptidoglycan and teichoic acids are absent in the cell wall; cytoplasmic ribosomes are larger; sedimentation constant is 80; energy processes are carried out in mitochondria; there is a Golgi complex from organelles, etc.).
Later it turned out that among microorganisms there are also non-cellular forms-viruses, and therefore a third group (kingdom) was identified - vira.
To designate microorganisms, a double (binary) nomenclature is adopted, which includes the name of the genus and species. The generic name is written with a capital letter (capital), the species name (even derived from a surname) is written with a lowercase (small). For example, anthrax bacillus is called Bacillus anthracis, Escherichia coli is called Escherichia coli, black aspergillus is called Aspergillus niger.
The basic (lower) taxonomic unit is the species. Species are grouped into genera, genera into families, families into orders, orders into classes, classes into divisions, and divisions into kingdoms.
A species is a collection of individuals of the same genotype with a pronounced phenotypic similarity.
Culture - microorganisms obtained from an animal, human, plant or environmental substrate and grown on a nutrient medium. Pure cultures consist of individuals of the same species (the offspring obtained from one cell is a clone).
A strain is a culture of the same species, isolated from different habitats and characterized by minor changes in properties. For example, E. coli isolated from the human body, cattle, water bodies, soil, can be of different strains.
2 Prokaryotes (bacteria and actinomycetes). Bacteria (prokaryotes) are a large group of microorganisms (about 1600 species), most of which are unicellular. Shape and size of bacteria. The main forms of bacteria are spherical, rod-shaped and convoluted. Spherical bacteria - cocci have the usual shape of a ball, there are flattened, oval or bean-shaped. Cocci can be in the form of single cells - monococci (micrococci) or connected in various combinations: in pairs - diplococci, four cells - tetracocci, in the form of more or less long chains - streptococci, and also in the form of clusters of a cubic shape (in the form of packages) of eight cells arranged in two tiers, one above the other, are sarcins. There are clusters of irregular shape, resembling bunches of grapes - staphylococci. Rod-shaped bacteria can be single or connected in pairs - diplobacteria, chains of three to four or more cells - streptobacteria. The ratios between the length and thickness of the sticks are very different. Curved, or curved, bacteria vary in length, thickness, and degree of curvature. Sticks slightly curved in the form of a comma are called vibrios, sticks with one or more corkscrew curls are called spirilla, and thin sticks with numerous curls are called spirochetes. Thanks to the use of an electron microscope to study microorganisms in natural substrates, bacteria were found that have a special shape of cells: a closed or open ring (toroids); with outgrowths (prostekami); worm-shaped - long with curved very thin ends; and also in the form of a hexagonal star.
Bacteria are very small, ranging from tenths of a micrometer (µm) to a few micrometers. On average, the body size of most bacteria is 0.5-1 microns, and the average length of rod-shaped bacteria is 2-5 microns. There are bacteria whose sizes are much larger than the average, and some are on the verge of visibility in ordinary optical microscopes. The body shape of bacteria, as well as their size, can vary depending on age and growth conditions. However, under certain, relatively stable conditions, bacteria retain their size and shape inherent in this species. The mass of a bacterial cell is very small, approximately 4-10-1:! G.
The structure of a bacterial cell . The cell of prokaryotic organisms, which include bacteria, has the fundamental features of the ultrastructure. The cell wall (shell) is an important structural element of most bacteria. The cell wall accounts for 5 to 20% of the dry matter of the cell. It has elasticity, serves as a mechanical barrier between the protoplast and the environment, gives the cell a certain shape. The cell wall contains a heteropolymer compound specific for prokaryotic cells - peptidoglycan (murein), which is absent in the cell walls of eukaryotic organisms. According to the staining method proposed by the Danish physicist H. Gram (1884), bacteria are divided into two groups: gram-positive and gram-negative. Gram-positive cells retain the dye, while Gram-negative cells do not, due to differences in the chemical composition and ultrastructure of their cell walls. Gram-positive bacteria have thicker, amorphous cell walls, they contain a large amount of murein (from 50 to 90% of the dry mass of the cell wall) and teichoic acids. The cell walls of gram-negative bacteria are thinner, layered, they contain a lot of lipids, little murein (5-10%) and no teichoic acids.
The cell wall of bacteria is often covered with mucus. The mucous layer may be thin, barely visible, but may be significant, may form a capsule. Often the capsule is much larger than the bacterial cell. The mucus of the cell walls is sometimes so strong that the capsules of individual cells merge into mucous masses (zoogels) in which bacterial cells are interspersed. Mucous substances formed by some bacteria are not retained in the form of a compact mass around the cell wall, but diffuse into the environment. When rapidly multiplying in liquid substrates, mucus-forming bacteria can turn them into a continuous slimy mass. This phenomenon is sometimes observed in sugar beet extracts in the production of sugar. In a short time, sugar syrup can turn into a viscous slimy mass. Meat, sausages, cottage cheese are subjected to mucus; the viscosity of milk, brines, pickled vegetables, beer, wine is observed. The intensity of mucus formation and the chemical composition of mucus depend on the type of bacteria and cultivation conditions. The capsule has useful properties, mucus protects cells from adverse conditions - in many bacteria, mucus formation increases under such conditions. The capsule protects the cell from mechanical damage and drying out, creates an additional osmotic barrier, serves as an obstacle to the penetration of phages, antibodies, and sometimes it is a source of reserve nutrients. The cytoplasmic membrane separates the contents of the cell from the cell wall. This is a mandatory structure of any cell. If the integrity of the cytoplasmic membrane is violated, the cell loses its viability. The cytoplasmic membrane accounts for 8-15% of the dry matter of the cell. The membrane contains up to 70-90% of cell lipids, its thickness is 7-10 nm 1 . On sections of cells in an electron microscope, it is visible in the form of a three-layer structure - one lipid layer and two protein layers adjacent to it on both sides. The cytoplasmic membrane in places protrudes into the cell, forming all kinds of membrane structures. It contains various enzymes; it is semi-permeable, plays an important role in the exchange of substances between the cell and the environment. The cytoplasm of a bacterial cell is a semi-liquid, viscous, colloidal system. In some places, it is permeated with membrane structures - mesosomes, which originated from the cytoplasmic membrane and retained their connection with it. Mesosomes perform various functions; in them and in the cytoplasmic membrane associated with them there are enzymes involved in energy processes - in supplying the cell with energy. Well-developed mesosomes are found only in Gram-positive bacteria; in Gram-negative bacteria, they are poorly developed and have a simpler structure. The cytoplasm contains ribosomes, a nuclear apparatus and various inclusions. Ribosomes are scattered in the cytoplasm in the form of 20–30 nm granules; Ribosomes are about 60% ribonucleic acid (RNA) and 40% protein. Ribosomes are responsible for cell protein synthesis. In a bacterial cell, depending on its age and living conditions, there may or may not be 5-50 thousand ribosomes. The nuclear apparatus of bacteria is called the nucleoid. Electron microscopy of ultrathin sections of bacterial cells made it possible to establish that the carrier of the cell's genetic information is the deoxyribonucleic acid (DNA) molecule. DNA has the form of a double helical strand closed in a ring; it is also called the "bacterial chromosome". It is located in a certain area of the cytoplasm, but is not separated from it by its own membrane.
Cytoplasmic inclusion bacterial cells are diverse, mainly these are reserve nutrients that are deposited in cells when they develop in conditions of excess nutrients in the environment, and are consumed when cells fall into starvation conditions. Polysaccharides are deposited in bacterial cells: glycogen, a starch-like granulose substance, which are used as a source of carbon and energy. Lipids are found in cells in the form of granules and droplets. Fat is a good source of carbon and energy. Many bacteria accumulate polyphosphates; they are contained in volutin granules and are used by cells as a source of phosphorus and energy. Molecular sulfur is deposited in the cells of sulfur bacteria.
Mobility of bacteria . Globular bacteria are usually immobile. Rod-shaped bacteria are both mobile and non-motile. Curved and spiral bacteria are mobile. Some bacteria move by sliding. The movement of most bacteria is carried out using flagella. Flagella are thin, spirally twisted filaments of a protein nature that can carry out rotational movements. The length of the flagella is different, and the thickness is so small (10-20 nm) that they can be seen in a light microscope only after special processing of the cell. The presence, number, and location of flagella are constant features for the species and are of diagnostic value. Bacteria with one flagellum at the end of the cell are called monotrichous; with a bundle of flagella - lofotrichs ", with a bundle of flagella at both ends of the cell - amphitrichous; bacteria in which flagella are located on the entire surface of the cell are called peritrichous. The speed of movement of bacteria is high: in a second a cell with flagella can travel a distance of 20-50 times more than the length of its body.Under unfavorable conditions of life, with aging of the cell, with mechanical action, mobility may be lost.In addition to the flagella, on the surface of some bacteria there are a large number of filamentous formations, much thinner and shorter than the flagella - fimbriae (or pili) .
Reproduction of bacteria. Prokaryotic cells are characterized by simple cell division in two. Cell division begins, as a rule, some time after the division of the nucleoid. Rod-shaped bacteria divide across, spherical shapes in different planes. Depending on the orientation of the fission plane and their number, various forms arise: single cocci, paired, chains, in the form of packages, clusters. A feature of the reproduction of bacteria is the speed of the process. The rate of division depends on the type of bacteria, cultivation conditions: some species divide every 15-20 minutes, others - after 5-10 hours. With this division, the number of bacterial cells per day reaches a huge amount. This is often observed in food products: rapid souring of milk due to the development of lactic acid bacteria, rapid spoilage of meat and fish due to the development of putrefactive bacteria, etc.
Sporulation. Spores in bacteria are usually formed under unfavorable conditions of development: with a lack of nutrients, changes in temperature, pH, with the accumulation of metabolic products above a certain level. Rod-shaped bacteria have the ability to form spores. Each cell produces only one spore (endospore).
Sporulation is a complex process, several stages are distinguished in it: first, a restructuring of the genetic apparatus of the cell is observed, and the morphology of the nucleoid changes. DNA synthesis stops in the cell. The nuclear DNA is pulled out as a strand, which is then split; part of it is concentrated at one of the poles of the cell. This part of the cell is called the sporogenous zone. In the sporogenous zone, the cytoplasm becomes denser, then this area is separated from the rest of the cellular contents by a septum (septum). The cut-off area is covered by the membrane of the mother cell, the so-called prospore is formed. A prospore is a structure located inside the mother cell, from which it is separated by two membranes: outer and inner. A cortical layer (cortex) is formed between the membranes, similar in chemical composition to the cell wall of a vegetative cell. In addition to peptidoglycan, the cortex contains dipicolinic acid (C 7 H 8 O 4 Mg), which is absent in vegetative cells. Subsequently, a spore shell is formed on top of the prospore, consisting of several layers. The number, thickness and structure of the layers are different in different types of bacteria. The surface of the outer shell can be smooth or with outgrowths of different lengths and shapes. On top of the spore shell, a thin cover is often formed that surrounds the spore in the form of a sheath, the exosporium.
Spores are usually round or oval in shape. The diameter of the spores of some bacteria exceeds the width of the cell, as a result of which the shape of the spore-bearing cells changes. The cell takes the form of a spindle (clostridium) , if the spore is located in its center, or the shape of a drumstick (plectridium) when the spore is near the end of the cell.
After maturation of the spore, the mother cell dies, its shell is destroyed, and the spore is released. The spore formation process takes several hours.
The presence of a dense, impermeable membrane in bacterial spores, a low water content in it, a large amount of lipids, as well as the presence calcium and dipicolinic acid determine the high resistance of spores to environmental factors. Spores can survive for hundreds or even thousands of years. For example, viable spores have been isolated from the corpses of mammoths and Egyptian mummies, which are thousands of years old. Spores are resistant to high temperatures: in a dry state, they die after heating at 165-170 ° C for 1.5-2 hours, and with superheated steam (in an autoclave) - at 121 ° C for 15-30 minutes.
Under favorable conditions, the spore germinates into a vegetative cell; this process usually takes several hours.
The germinating spore begins to actively absorb water, its enzymes are activated, and biochemical processes leading to growth are intensified. During spore germination, the cortex turns into the cell wall of a young vegetative cell; dipicolinic acid and calcium are released into the external environment. The outer shell of the spore is torn, through the gaps the "sprout" of a new cell comes out, from which a vegetative bacterial cell is then formed.
Food spoilage is caused only by vegetative cells. Knowledge of the factors that contribute to the formation of spores in bacteria, and the factors that cause them to grow into vegetative cells, is important in choosing a method for processing products in order to prevent their microbial spoilage.
The above information characterizes mainly the so-called true bacteria. There are others, more or less different from them, which include the following.
Filamentous (filamentous bacteria). These are multicellular organisms in the form of threads of various lengths, with a diameter of 1 to 7 microns, mobile or attached to the substrate. Mostly filaments with a slimy sheath. They may contain magnesium oxide or iron oxides. They live in water bodies, are found in the soil.
Myxobacteria. These are rod-shaped bacteria that move by sliding. They form fruiting bodies - clusters of cells enclosed in mucus. Cells in the fruiting bodies go into a resting state - myxospores. These bacteria live in the soil, on various plant debris.
Budding and stalk bacteria reproduce by budding, forming stalks, or both. There are species with outgrowths - prostheca. They live in soil and water bodies.
Actinomycetes. Bacteria are branched. Some are slightly branched sticks (see Fig. 2, e), others are in the form of thin branching filaments that form a unicellular mycelium. Mycelial actinomycetes, called "radiant fungi", reproduce by spores that develop on the aerial branches of the mycelium. Actinomycetes are colored; they are widely distributed in nature. They are also found on food products and can cause spoilage. The product acquires a characteristic earthy odour. Many actinomycetes produce antibiotics. There are species that are pathogenic to humans and animals.
Mycoplasmas. Organisms without a cell wall are covered only by a three-layer membrane. The cells are very small, sometimes ultramicroscopic in size (about 200 nm), pleomorphic (of various shapes) - from coccoid to filamentous. Some cause diseases in humans, animals, plants.
Fundamentals of taxonomy of bacteria Modern bacterial classification systems are essentially artificial, combining bacteria into certain groups based on their similarity in terms of a complex of morphological, physiological, biochemical and genotypic characters. For this purpose, Bergi's guide to the definition of bacteria (1974, 8th edition and 1984 - 9th edition). According to the 8th edition, all prokaryotes are divided into two divisions - cyanobacteria and bacteria. The first section - cyanobacteria (blue-green algae) - are phototrophic microorganisms. The second section is bacteria. This department is divided into 19 groups. The 17th group includes actinomycetes. According to the 9th edition, the kingdom of prokaryotes is divided into four sections depending on the presence or absence of a cell wall and its chemical composition: the first section includes thin-skinned groups of bacteria, gram-negative, phototrophic and cyanobacteria; in the 2nd department - hard-skinned, groups of bacteria are included that are positive for Gram stain; the third section includes mycoplasmas - bacteria that do not have a cell wall; the fourth section includes methane-forming and archaebacteria (a special group of bacteria that lives in extreme environmental conditions and is one of the oldest forms of life).
The morphology of microorganisms is a science that studies their shape, structure, methods of movement and reproduction.
The microbes most commonly found in food preparation are divided into bacteria, molds, yeasts and viruses. Most microbes are single-celled organisms measured in micrometers - microns (1/1000 mm) and nanometers - nm (1/1000 microns).
bacteria.
Bacteria are unicellular, the most studied microorganisms with a size of 0.4-10 microns. Bacteria are spherical, rod-shaped, and convoluted in shape (Fig. 1). The spherical bacteria are called cocci.
Depending on the size and location of the cells, there are micrococci (single cells), diplococci (a group of two cells), streptococci (in the form of a chain of cells), staphylococci (clusters of cells in the form of a grape bunch). The size of the cells of spherical bacteria is 0.2-2.5 microns.
Rod-shaped bacteria are found in the form of single rods, as well as in the form of double and connected in a chain.
A variety of cell shapes are distinguished by convoluted bacteria, which have different lengths and thicknesses. These include vibrios, spirilla, spirochetes.
The length of rod-shaped and convoluted bacteria is from 1 to 5 microns.
The size and shape of bacteria can vary depending on various environmental factors.
The structure of a bacterial cell.
The cell is separated from the external environment by a dense membrane - the cell wall. The cell wall accounts for 5 to 20% of the dry matter of the cell. The cell wall is the frame of the cell, gives it a certain shape, protects it from adverse external influences, and participates in the metabolism of the cell with the environment.
The outer layer of the shell in many bacteria can be mucilaginous, forming a protective cover - a capsule.
The main part of the cell is the cytoplasm - a transparent, semi-liquid viscous protein mass impregnated with cell sap. The cytoplasm protects the cell from mechanical damage and drying out. The cytoplasm contains reserve nutrients (grains of starch, fat droplets, glycogen, protein) and other cellular structures. In the cytoplasm are membrane structures - mesosomes. Mesosomes contain enzymes. The cytoplasm contains the nuclear apparatus of a bacterial cell, which is called the nucleoid. It is a double helix of DNA in the form of a closed ring.
Some bacteria have flagella. Flagella are thin, spirally twisted filaments. With the help of flagella, some types of bacteria can actively move. Spherical bacteria (cocci) are immobile. Some types of rod-shaped bacteria are mobile and all are convoluted. Bacteria can move with the help of cilia.
The cytoplasmic membrane separates the contents of the cell from the cell wall. It is semi-permeable and plays an important role in the exchange of substances between the cell and the external environment.
The cytoplasm also contains ribosomes and various inclusions. Ribosomes in the cytoplasm are presented in the form of small granules. They are about half made up of ribonucleic acid (RNA) and protein. RNA is involved in protein synthesis.
Reproduction. Bacteria reproduce asexually, mainly by simple cell division into two.
Reproduction occurs under favorable conditions. A characteristic feature of bacterial reproduction is the speed of the process. The duration of bacteria reproduction is from 30 minutes to several hours. The names of microorganisms consist of two Latin words, the first means genus, the second - species.
Some rod-shaped bacteria form spores under unfavorable conditions (condensed cytoplasm covered with a dense membrane). Spores do not need nutrition, are not able to reproduce, but retain their viability at high temperatures, drying, freezing for several months (botulinum bacillus) or even many years (anthrax bacillus). Spores die during sterilization (heating to 120°C for 29 minutes). Under favorable conditions, they germinate into a normal (vegetative) bacterial cell. Spore-forming bacteria are called bacilli.
Mushrooms make up a large group of organisms that are isolated in a separate kingdom Mycota (Mycota). Mushrooms are widely distributed in nature. Fungi are eukaryotes. The kingdom of fungi includes microscopic filamentous fungi (molds).
Structure. Mold cells have the form of elongated intertwining threads - hyphae 1 - 15 microns thick, forming the mold body - mycelium (mycelium), consisting of one or many cells. Fruiting bodies develop on the surface of the mycelium, in which spores ripen.
Structure. Cells of microscopic fungi have an elongated shape and are called hyphae. Intertwining, filamentous hyphae form the body of the fungus in the form of cotton wool, fluff and other similar formations, which is called mycelium, or mycelium. The mycelium consists of two parts: the upper fruit-bearing and the lower, which serves to attach to the nutrient medium - the substrate - and feed the fungus. Mushrooms are visible to the naked eye.
Mycelial cells have a cell wall that has protective properties. The cell wall also determines the shape of the cell. Inside the cell is filled with cytoplasm, which contains nuclei, ribosomes, mitochondria and vacuoles.
The nuclei regulate the process of metabolism, reproduction and transmission of hereditary traits. Ribosomes are the center of protein synthesis, and energy processes take place in mitochondria. Vacuoles are round cavities filled with cell sap, where reserve nutrients (glycogen, fat, volutin) are deposited.
Reproduction. Microscopic fungi reproduce mainly in two ways: asexually (vegetatively) and sexually.
During asexual reproduction, spores are formed.
In sexual reproduction, two adjacent cells first fuse. Then the process of reproduction proceeds in different types of mushrooms in different ways. Some form a cell called a zygote, which then germinates. In other fungi, a fruiting body is formed, inside which bags (asci) with spores develop. Once in favorable conditions, the spores ripen, the bag is torn. Fungal spores are very resistant to external influences, they can remain viable for several years.
Microscopic fungi require oxygen for their development, that is, they are aerobes and multiply only when air is available! The optimal conditions for their reproduction are a temperature of 25-35 ° C and a relative humidity of 70-80%.
In terms of structure, mold cells differ from bacterial cells in that they have one or more nuclei and vacuoles (cavities filled with cell fluid).
Yeasts are eukaryotic microorganisms. They constitute a large group of unicellular, immobile microorganisms that are widely distributed in nature. Most yeasts belong to the class of fungi - ascomycetes. In shape, yeasts are round, oval, ovoid and elongated. The sizes of yeast cells are from 2 to 12 microns.
Yeasts are widely distributed in nature. They are able to break down (ferment) sugars into alcohol and carbon dioxide.
Cell structure. Yeast cells are separated from the external environment by a cell wall. It protects the cell from adverse influences and determines its shape. Under the cell wall is the cytoplasmic membrane, which plays an important role in metabolism. The cell is filled with cytoplasm, which contains the nucleus, mitochondria, ribosomes, vacuoles.
The nucleus is surrounded by a double membrane. The functions of the nucleus are the regulation of metabolic processes and other chemical processes in the cell, the transmission of hereditary traits.
Mitochondria are small particles of various shapes. Energy processes take place in them and energy is stored.
Ribosomes are the smallest bodies that are the center of protein synthesis. Vacuoles are vesicles filled with cell sap. Inside the vacuoles are spare substances - fats, carbohydrates (glycogen), volutin.
Reproduction. Yeast, under favorable conditions, reproduces in two ways: asexually, or vegetatively (budding), and sexually (sporulation).
Vegetative propagation proceeds as follows. First, a small tubercle is formed on the original (mother) cell - a kidney, which increases in size as it grows. At the same time, the nucleus is divided into two parts. One of the nuclei with a part of the cytoplasm and other elements of the cell passes into a young (daughter) cell.
As the daughter cell grows, the constriction that connects it to the mother cell narrows, thus, the daughter cell, as it were, laces off, and then breaks off and separates from the mother cell. This process takes several hours.
Sporulation can also occur by the fusion of two vegetative cells with the formation of a zygote, in which spores are then formed, germinating into vegetative cells. They then reproduce by budding.
Viruses are very small microorganisms, ranging from 35 to 125 nanometers, so they can only be detected with an electron microscope.
In shape, viruses are round, spiral, as well as in the form of rods and polyhedrons. They have a simple structure and different chemical composition.
Viruses do not have a cellular structure. They are resistant to drying and low temperatures. Their destruction occurs when heated to 60-80 °C.
Viruses cause a number of serious diseases: smallpox, measles, poliomyelitis, influenza, etc. Penetrating into the host cells, the virus multiplies, causing their death.
Questions for self-control
1. Bacteria. Structure. Classification. Reproduction.
2. Mushrooms. Structure. Classification. Reproduction.
3. Yeast. Structure. Classification. Reproduction.
4. Viruses. Structure. Classification. Reproduction.
The vast majority of bacteria are unicellular. According to the shape of the cells, they can be round (cocci), rod-shaped (bacilli, clostridia, pseudomonads), convoluted (vibrios, spirilla, spirochetes), less often - stellate, tetrahedral, cubic, C- or O-shaped. The shape determines such abilities of bacteria as attachment to the surface, mobility, absorption of nutrients. It has been noted, for example, that oligotrophs, that is, bacteria living at a low nutrient content in the environment, tend to increase the surface-to-volume ratio, for example, through the formation of outgrowths (the so-called prostek).
Of the mandatory cellular structures, three are distinguished: * nucleoid * ribosomes * cytoplasmic membrane (CPM)
On the outer side of the CPM there are several layers (cell wall, capsule, mucous membrane), called the cell membrane, as well as surface structures (flagella, villi). CPM and cytoplasm are combined together in the concept of protoplast.
2. Genetics of viruses. Viruses pathogenic to humans have two main properties - heredity and variability, the study of which is the subject of a special scientific discipline - the genetics of viruses. The population structure of viruses and the nature of the processes occurring in them are determined by the following factors. High population, which increases the likelihood of mutations that can be picked up by natural selection when the conditions for the existence of viruses change. Rapid generational change makes it possible to study the variability of viruses not only in the experiment, but also to observe their natural evolution in nature. Haploidy and asexual reproduction determine: genetic purity of the population (absence of hybrids); the impossibility of maintaining reserves of variability due to diploidy; immediate entry of mutants under the control of selection.
Small genome capacity and lack of repetitive genes. The functional integrity of all genes is necessary for the implementation of the infectious cycle.
A slight change in one of them can cause a lethal or conditionally lethal effect for the virus.
Continuity in the dynamics of the epidemic process, since a prerequisite for conservation in nature is the transfer to new sensitive hosts. Virus populations well adapted to external conditions and do not undergo significant changes for a long time. When conditions change for the survival of the population, it becomes necessary rearrangement of the hereditary structure to adapt to the new environment. Such a restructuring is possible only if there is a population of altered genes in the general gene pool. Gene pool of viral populations is created and replenished from four main sources: internal factors: mutations, recombinations. External: inclusion in the genome of the genetic material of the host cell (the appearance of genomes containing new material), Phenotypic mixing (enrichment of the gene pool due to the receipt of genes from other viral populations).
3. Causative agents of cholera. Taxonomy. Characteristic. Microbiological diagnostics. Specific prevention and treatment. Family vibrionaceae, genus vibrio, view V. cholerae. Cholera is an ancient anthroponosis; since the time of Hippocrates it has been known as "magi mara" - "great pestilence". It took millions of lives. quarantine infection.
Morphology. Gram (-), slightly curved rods (comma-shaped, spores and capsules (except for the Bengal strain) do not form; Bengal strain forms a capsule in the body. Obligate aerobes. Monotrichous, the length of the flagellum can be 2-3 times the length of the soma, which causes a high mobility. cultural properties. They grow well on simple nutrient media with an alkaline reaction (pH 8.5 - 9.5). On the 1% peptone water forms a delicate film (aerobic). On the alkaline agar- more often smooth transparent colonies with a bluish tint, less often (in the process of dissociation) - rough and folded colonies. biochemical properties. In laboratory practice, it is used biochemical classification according to Heiberg(for the whole genus Vibrio). There are 8 groups, the causative agents of cholera belong to 1st group(mannose k, sucrose k, arabinose -). They form indole. Antigenic structure:(1) common vido specific H-AG - flagella (2) supposedly specific O-AG - somatic According to O-AG, 80 serogroups are distinguished; V. cholerae, el-tor - serogroup 01 (02 causes enteritis, gastroenteritis). O1-AG consists of fractions A, B and C, their combinations form serovars. 3 serovar : Inaba (AC), Ogawa (AB) (main pathogens), Gikoshima (ABC) (intermediate). Bengal strain - serovar 0-139. Pathogenic factors:(1) flagella- active promotion of bacteria to enterocytes in the mucus layer; (2) adhesiveness- drank; (3) capsule in the Bengal strain; (4) toxins: 1 type - endotoxin(O-AG), 2 types - exoenterotoxin- cholerogen, the main symptom; identical in all three pathogens. 2 subunits: B - non-toxic, promotes toxin adhesion to enterocytes; A - the toxin itself, penetrates into enterocytes, where it activates AC, which leads to the accumulation of cAMP, which enhances the secretion of water, sodium and chlorine from cells and disrupts potassium absorption; 3 types - thermostable toxin, affects sodium-potassium ATPase; as a result - diarrhea, severe dehydration of the body; (5) neuraminidase- promotes adhesion of vibrios on enterocytes and penetration into the cell; Disease.A source- sick, vibriocarrier. Storage tank- hydrobionts. Route of infection- alimentary, when drinking contaminated water (vegetables, hydrobionts, etc.). Main clinical forms- cholera enteritis, gastroenteritis. Incubation period- several hours - 6 days. First symptom- diarrhea, Second symptom- profuse repeated vomiting with a fountain, dehydration, demineralization of the body, muscle weakness, dizziness, hoarseness, a sharp loss of skin turgor. Microbiological diagnostics: (1) express methods: for the determination of AG pathogens: RIF, RNGA according to Knight, the method of vibrio immobilization using O-cholera serum; accounting in a dark-field and phase-contrast microscope. (2) main method - bacteriological.(3) additional- serological: determination of vibriocidal antibodies in the patient's serum using bacteriolysis reaction (for convalescents). (4) genetic- the use of molecular genetic probes to the genes of tox+ pathogens of the toxin. Treatment. First of all - the restoration of water-salt metabolism, and then - the use of antibiotics, chemotherapy. Restoration of water-salt metabolism should be carried out by introducing saline solutions per os or intravenously: KCl, NaCl, NaHCO3, glucose, etc. The volume of fluid injected and withdrawn must be strictly controlled. Prevention. 6-month immunity, do not prevent the Bengal strain. 1) corpuscular cholera vaccine inactivated from V. cholerae, V. el-tor; 2) chemical cholera vaccine - mono (contains cholerogen-anatoxin and O-AG of serovar Inaba); 3) chemical cholera vaccine - bi (serovars Ogawa, Inaba).
1. Principles of classification of bacteria. For bacteria the following taxonomic categories are recommended: class, department, order, family, genus, species. The species name corresponds to the binary nomenclature, i.e. it consists of two words. For example, the causative agent of syphilis is written as Treponema pallidum. The first word is the name of the genus and is written with a capital letter, the second word denotes the species and is written with a lowercase letter. When a species is mentioned again, the generic name is abbreviated to the initial letter, for example: T.pallidum. bacteria belong to prokaryotes, i.e., pre-nuclear organisms, since they have a primitive nucleus without a shell, nucleolus, histones, and there are no highly organized organelles in the cytoplasm Bacteria are divided into 2 domains:« bacteria" and "Archaea". In the domain "bacteria» the following bacteria can be distinguished:
1) bacteria with a thin cell wall, gram (-);
2) bacteria with a thick cell wall, gram(+);
3) bact. without CS (class Mollicutes - mycoplasmas)
archaebacteria do not contain peptidoglycan in the cell wall. They have special ribosomes and ribosomal RNA (rRNA). Among thin-walled gram (-) eubacteria distinguish:
Spherical forms, or cocci (gonococci, meningococci, veillonella);
Convoluted forms - spirochetes and spirilla;
Rod-shaped forms, including rickettsiae.
To thick-walled gram(+) eubacteria include:
Spherical shapes, or cocci (staphylococci, streptococci, pneumococci);
Rod-shaped forms, as well as actinomycetes (branching, filamentous bacteria), corynebacteria (club-shaped bacteria), mycobacteria and bifidobacteria.
Thin-walled gram(-) bacteria: Meningococci, gonococci, Veillonella, Rods, Vibrios, Campylobacter, Helicobacter, Spirilla, Spirochetes, Rickettsia, Chlamydia.
Thick-walled gram(+) bacteria: Pneumococci, Streptococci, Staphylococci, Rods, Bacilli, Clostridia, Corynebacteria, Mycobacteria, Bifidobacteria, Actinomycetes.
2. Mechanisms of drug resistance of pathogens of infectious diseases. Ways to overcome it. Antibiotic resistance is the resistance of microbes to antimicrobial chemotherapy drugs. Bacteria should be considered resistant if they are not neutralized by such drug concentrations that are actually created in the macroorganism. Resistance can be natural and acquired.
Natural sustainability. Some microbial species are naturally resistant to certain families of antibiotics, either as a result of the lack of an appropriate target (for example, mycoplasmas do not have a cell wall, so they are not sensitive to all drugs acting at this level), or as a result of bacterial impermeability to a given drug (for example, gram-negative microbes less permeable to large molecular compounds than gram-positive bacteria, since their outer membrane has "small" pores).
Acquired resilience. The acquisition of resistance is a biological pattern associated with the adaptation of microorganisms to environmental conditions. It is, although to varying degrees, true for all bacteria and all antibiotics. Not only bacteria, but also other microbes adapt to chemotherapy drugs - from eukaryotic forms (protozoa, fungi) to viruses. The problem of the formation and spread of drug resistance in microbes is especially significant for nosocomial infections caused by the so-called "hospital strains", which, as a rule, have multiple resistance to antibiotics (the so-called polyresistance).
Genetic basis of acquired resistance. Antibiotic resistance is determined and maintained by resistance genes (r-genes) and the conditions that promote their spread in microbial populations. Acquired drug resistance can arise and spread in a population of bacteria as a result of:
Mutations in the chromosome of a bacterial cell, followed by selection (i.e., selection) of mutants. Selection is especially easy in the presence of antibiotics, since under these conditions the mutants gain an advantage over other cells in the population that are sensitive to the drug. Mutations occur regardless of the use of the antibiotic, i.e. the drug itself does not affect the frequency of mutations and is not their cause, but serves as a selection factor. Further, resistant cells give birth and can be transferred to the body of the next host (human or animal), forming and spreading resistant strains. Mutations can be: 1) single (if the mutation occurred in one cell, as a result of which altered proteins are synthesized in it) and 2) multiple (a series of mutations, as a result of which not one, but a whole set of proteins changes, for example, penicillin-binding proteins in penicillin-resistant pneumococcus);
Transfer of transmissible resistance plasmids (R-plasmids). Resistance plasmids (transmissible) usually encode cross-resistance to several families of antibiotics. For the first time, such multiple resistance was described by Japanese researchers in relation to intestinal bacteria. It has now been shown to occur in other groups of bacteria. Some plasmids can be transferred between bacteria of different species, so the same resistance gene can be found in bacteria that are taxonomically distant from each other. For example, beta-lactamase, encoded by plasmid TEM-1, is widely distributed in Gram-negative bacteria and occurs in Escherichia coli and other intestinal bacteria, as well as in penicillin-resistant gonococcus and ampicillin-resistant Haemophilus influenzae;
Transfer of transposons carrying r-genes (or migrating genetic sequences). Transposons can migrate from a chromosome to a plasmid and vice versa, as well as from a plasmid to another plasmid. Thus, resistance genes can be passed on to daughter cells or by recombination to other recipient bacteria.
Implementation of acquired stability. Changes in the genome of bacteria lead to the fact that some properties of the bacterial cell also change, as a result of which it becomes resistant to antibacterial drugs. Typically, the antimicrobial effect of the drug is carried out in this way: the agent must bind to the bacterium and pass through its membrane, then it must be delivered to the site of action, after which the drug interacts with intracellular targets. The realization of acquired drug resistance is possible at each of the following stages:
target modification. The target enzyme can be so changed that its functions are not disturbed, but the ability to bind to the chemotherapy drug (affinity) is sharply reduced or a “bypass” of metabolism can be turned on, i.e. another enzyme is activated in the cell that is not affected by this drug .
"inaccessibility" of the target due to a decrease in the permeability of the cell wall and cell membranes or the "effluco-mechanism" when the cell, as it were, "pushes" the antibiotic out of itself.
inactivation drug with bacterial enzymes. Some bacteria are able to produce specific enzymes that render drugs inactive (eg, beta-lactamases, aminoglycoside-modifying enzymes, chloramphenicol acetyltransferase). Beta-lactamases are enzymes that break down the beta-lactam ring to form inactive compounds. The genes encoding these enzymes are widely distributed among bacteria and can be either in the chromosome or in the plasmid.
To combat the inactivating effect of beta-lactamases, substances are used - inhibitors (for example, clavulanic acid, sulbactam, tazobactam). These substances contain a beta-lactam ring in their composition and are able to bind to beta-lactamases, preventing their destructive effect on beta-lactams. At the same time, the intrinsic antibacterial activity of such inhibitors is low. Clavulanic acid inhibits most known beta-lactamases. It is combined with penicillins: amoxicillin, ticarcillin, piperacillin.
It is almost impossible to prevent the development of antibiotic resistance in bacteria, but it is necessary to use antimicrobial drugs in such a way as not to contribute to the development and spread of resistance (in particular, use antibiotics strictly according to indications, avoid their use for prophylactic purposes, after 10-15 days of antibiotic therapy change the drug, use narrow-spectrum drugs if possible, limit the use of antibiotics in veterinary medicine and do not use them as a growth factor).
The morphology of microorganisms is a science that studies their shape, structure, methods of reproduction and movement.
This science is quite extensive and deals with the study of many issues. Despite the fact that all microorganisms are invisible to human eyes, they still exist and are both “good” for the body and bad.
Microbes can be found in all spheres of manifestation of life: in water, soil, air, as well as in other organisms.
For the first time, the famous scientist Levenguk, who was engaged in the manufacture of the first lenses, made it possible to magnify objects up to two hundred times, learned about bacteria. And what he saw completely amazed him. The scientist learned that microbes are everywhere, and they are all different from each other. Thus, Leeuwenhoek became the discoverer of microorganisms.
Louis Pasteur began to deal with such a question as the morphology of microorganisms, and found out that they not only have a different structure and shape, but also differ in the ways of movement and reproduction. He found that some are for the human body, and some, on the contrary, are useful. He also discovered that microbes such as yeast can lead to fermentation processes.
The morphology of organisms has enabled many scientists to invent various vaccines that help to cope with deadly human diseases.
Microorganisms are considered the smallest representatives that live on planet Earth. Most often they are single-celled, and they can only be seen with a very powerful microscope.
The size of this life form is measured in micrometers and nanometers. There are a huge number of them in nature, so they have significant differences in structure, modes of existence and movement.
According to the established, they are divided into non-cellular, unicellular and multicellular. At the same time, they are divided into the following categories: fungi, yeast, phages, bacteria and viruses.
When studying such a topic as the morphology of microorganisms, much attention should be paid to bacteria. Most often they are single-celled organisms (although there are exceptions) and have quite a variety of sizes. Some of them reach 500 microns.
There are several types of bacteria that differ in their shape. These include rod-shaped, spherical and convoluted organisms. Let's take a closer look at each type.
In medicine they are called "cocci". Most often they are round in shape, although sometimes oval and bean-shaped microorganisms are also found. They can be located not only singly, but also in pairs, in the form of chains or vines.
Many of them have a negative effect on the human body. For example, streptococci cause allergies, and staphylococci cause the formation of purulent and inflammatory processes.
Rod-shaped bacteria are considered the most common. These include microorganisms that lead to tuberculosis, typhoid fever, dysentery.
Some types of sticks form spores under poor environmental conditions. These bacteria are called bacilli.
The formation of spores is a very interesting and complex process, since the cell itself of this type is very different from the usual bacillus. Each spore has a dense and strong shell, while possessing a negligible amount of water. Such a cell does not need nutrients at all, it stops moving and multiplying. At the same time, spores can be in terrible conditions for life, such as too high or low temperatures. But as soon as the environment favorable for them comes, they immediately begin their vital activity.
Curled bacteria most often occur in the form of commas or whorls. Typically, such microorganisms cause diseases such as syphilis and cholera.
Many bacteria are able to move, and they do this with the help of flagella of various shapes and lengths.
Bacteria reproduce by dividing. This process is very fast (every fifteen to twenty minutes). The fastest reproduction can be seen on food products and in other environments that are highly nutritious.
Viruses can be attributed to a special group of microorganisms that do not have a cellular structure. Such life forms are extremely small, so they can only be seen under an electron microscope. Some types of viruses can only consist of proteins and nucleic acids.
Every person at least once in his life faced with diseases caused by these microorganisms. This includes influenza, hepatitis, measles and many other diseases.
This group of microorganisms is also special. Mushrooms do not contain chlorophyll, and also do not synthesize organic substances. They need ready-made food. That is why mushrooms are most often found on fertile soils or on food products.
Mushrooms have different ways of reproduction. This includes not only asexual and sexual methods, but also vegetative.
Yeasts are unicellular, immobile organisms that have a wide variety of shapes. There are both round and oval species, as well as rod-shaped and crescent-shaped.
This type of microorganism is quite widespread. They can be found on plants, in the soil, and also in foodstuffs that spoil. Some of them are able to convert sugars into carbon dioxide and ethyl alcohol. This process is called fermentation. It is in great demand in the food industry.
It is worth considering that bacteria are the first form of life that appeared on our planet. Their main feature is the structure of the cell. Unlike eukaryotes (cells containing a nucleus), prokaryotes (bacteria) do not contain a nucleus.
Such microorganisms live in all spheres of life and directly affect human life as well.
Scientists also classify bacteria according to the principle of usefulness. There are beneficial species and harmful ones. Useful ones are involved in the process of photosynthesis, have a positive effect on the human digestive system, and are also very often used in industry.
The study of the morphology of microorganisms gives a general idea of their existence, and also makes it possible to find out their benefits and harms in certain situations.
A standard bacterial cell consists of the following components:
Plasma membrane. This cell element is no different from the eukaryotic membrane.
The mesosome is a special component with the help of which it is possible to attach hereditary material to the cell.
Nucleotide. It is an incompletely formed nucleus. It contains all the chromosomes.
Ribosomes are special organelles that occupy about forty percent of the cell space.
In addition to the elements listed above, the prokaryotic cell also includes: a capsule, a cell wall and a mucous membrane. Many bacteria are able to move independently and cling to surfaces. They do this with the help of special flagella and villi.
A virus is a special organism that does not have a cellular structure. Each of its particles consists of a shell, as well as of information located in the center of the core.
But the structure is more complicated than that of other microorganisms. Their cells also include nuclei and vacuoles. In structure, they are very similar to plants, but have a different shape. They look like long and branching threads called hyphae. Usually such hyphae form mycelium.
Yeast cells contain all the elements of eukaryotes, but in addition, they also have other components. Their uniqueness lies in the fact that they have the qualities of both animals and plants.
The morphology and physiology of microorganisms allow us to understand the main stages of their life. Bacteria, just like more complex life forms, synthesize lipids, fats and carbohydrates. But at the same time, the processes occurring in their cells are different.
Scientists distinguish two types of eukaryotes: autotrophs and heterotrophs.
The first type is capable of synthesizing organic substances from inorganic compounds, while the second type produces transformation processes of organic components.
There are also saprophytes. They feed on the synthesized substances of dead organisms.
The morphology of the structure of microorganisms is a rather important component of the study of the life of bacteria. However, in addition to the structure of the cell, it is also worth considering the types of metabolism. The construct type has been discussed above. There is also an energy exchange.
Scientists distinguish the following types of energy production:
Photosynthesis. This procedure can be carried out both in the presence of oxygen and without it.
Fermentation. This energetic reaction occurs due to the detachment of molecules that transfer phosphoric acid to ADP.
Breath. Microorganisms can breathe not only with oxygen, but also with the help of organic and mineral compounds.
There are several ways of transferring hereditary information by prokaryotes (the morphology and systematics of microorganisms are also described in this article). Let's consider each of them in detail:
conjugation - a method of transferring hereditary information from one microorganism to another only by their direct contact;
transformation - a type of transfer during which donors share information with recipients;
transduction - a method of direct transmission of hereditary material using phages.
For the most accurate study of the structure of prokaryotes, methods such as microscopy and staining are used.
Morphologies of microorganisms are produced by electron and light microscopes. Experts have developed several methods for the most accurate results.
The morphological method of research allows using a microscope to examine the structure of the cell, as well as its mobility and ability to reproduce.
The physiological method allows us to consider the reaction of microorganisms to various stimuli, as well as the ability to adapt to various conditions.
With the help of the cultural method, it is possible to conduct studies of a microorganism in a nutrient medium. This technique allows you to identify the ability to grow and reproduce.
The morphology of microorganisms (microbiology) is a very important science that studies bacteria and other unicellular organisms. Do not think that bacteria cause only harm to nature and the human body. This is far from true. Without them, life on planet Earth would be impossible.
