Structure and classification of bacteria. The structure of microorganisms. Location and number of flagella

In accordance with the eighth edition of Berger's Guide to Bacteria, all bacteria are divided into 19 groups. The division is based on some important properties of bacteria: the shape of their cell, their relationship to oxygen, the formation of spores, Gram staining*, characteristics of reproduction, type of nutrition, etc. The following groups are important for the food industry.

* Gram stain is an important diagnostic sign for identifying microorganisms, revealing profound differences in the structure and composition of their cell wall. Thus, gram-positive organisms are painted violet (initial color), gram-negative organisms are red-brown (secondary color, since the primary color is not preserved when processed in an alcohol solution).

Microorganisms that stain positive for Gram have little protein and polysaccharides in their cell walls. These include yeast, cocci and rod bacteria, many that form spores or do not form them (for example, lactic acid bacteria), etc.

In microorganisms that stain negatively for Gram, the cell wall contains compounds of fatty and protein substances, carbohydrates and phosphates. These include non-spore-forming cocci and bacteria (including acetic acid), bacteria of the Escherichia coli group, etc.

1. Gram-negative aerobic rods and cocci. Among these bacteria, the Pseudomonas family is important - straight or curved rods with polarly arranged flagella. Incapable of fermentation, respiratory metabolism, strict anaerobes (cannot reproduce in the presence of oxygen), form the enzyme catalase, and some oxidase. They reproduce on food products in the form of translucent colonies, sometimes in the form of mucus.

Causes a change in the color of the product - greening or browning. They reproduce in the temperature range of 4-43 °C, are cold-resistant, and spoil food products.

2. Gram-negative facultative anaerobic rods and cocci. This includes families of great importance for food quality and human health.

Family Enterobacteriaceae (Enterobacteriaceae)- small rods, motile (peritrichous) or immobile, not forming spores, aerobes or facultative anaerobes. Metabolism is respiratory or fermentative. When glucose and other carbohydrates are fermented, acid and gas are formed (not for everyone). They form the enzyme catalase or oxidase. Enterobacteriaceae are inhabitants of the gastrointestinal tract of humans and animals. According to biochemical characteristics, enterobacteria are divided into two large subsections. The first includes three genera: Escherichia, Salmonella and Shigella, the second - the genus Proteus.

Escherichia- straight small rods, single or paired, mobile (peritrichous) or immobile. They grow well on simple nutrient media. They ferment glucose and other carbohydrates to form organic acids.

Salmonella- rods, usually mobile (peritrichs). Most bacteria grow on synthetic media and ferment some sugars to produce gas. Causes food poisoning and infectious diseases in humans.

Shigella- motionless rods without capsules, growing well on nutrient media. They ferment glucose and other carbohydrates to form acid, but do not produce gas. Causes dysentery.

Proteus- straight small rods, coccoid or irregular in shape. Depending on environmental conditions, the shape of cells changes. There are cells connected in pairs or chains. The cells are motile (peritrichous); at a temperature of 37 °C, motility is often absent. They do not form capsules. Ferment carbohydrates and form indole. Temperature limits for growth are 10-43 °C.

Family Vibrioaceae (Vibrioaceae)- straight and curved rods, usually movable, polar flagella. Fermentative and respiratory metabolism. Oxidase is produced by facultative anaerobes. Usually found in fresh and sea water, sometimes in fish or humans.

This family includes three genera - Vibrio, Zymomonas and Flavobacterium.

Vibrio- short small rods that do not form spores, straight or curved, mobile. Found in the digestive tract of humans and animals, some species are pathogenic to humans and fish. Causes cholera disease.

For the growth of Zymomonas and Flavobacterium bacteria, the optimal temperature is below 30 °C. They are widely distributed in soil, fresh and marine waters. Flavobacteria are commonly found on vegetables during processing and in dairy products. Some are pests of fermentation industries.

3. Gram-positive cocci. This group includes three families of bacteria, differing in oxygen requirements and cell arrangement.

Family Micrococcacee (Micrococcus)- small spherical cells; When multiplying, they divide in two or three directions, forming irregular groups, tetrads (groups of 4 cells) or packets. They do not form spores, are mobile or immobile, the metabolism is respiratory or fermentative. They grow in the presence of 5% table salt, many can withstand concentrations of up to 10-15%. Catalase is formed. Aerobes or facultative anaerobes. The optimal development temperature is 25-30 °C. They are common inhabitants of soil and fresh water. Often found in human and animal excrement. In the Micrococcacee family, the genus Staphylococcus is of greatest importance, as it produces toxins.

Staphylococcus- cells are spherical in shape, small, located singly and in pairs, as well as in irregular clusters. Motile, do not form spores. Metabolism is respiratory and fermentative. Thanks to the formation of extracellular enzymes, they can break down many organic substances - proteins and fats. Most strains grow in the presence of 15% table salt. Usually sensitive to heat. They produce toxins, so many strains (coagulase-positive, for example Staphylococcus aureus) are pathogenic.

Family Streptococcaceae (streptococci)- cells of spherical or oval shape, in pairs or chains of various lengths or in tetrads. Motile, do not form spores. Facultative anaerobes. Metabolism is fermentative. Acids are formed from carbohydrates.

Three genera are of greatest importance: Streptococcus, Leuconostocus and Pediococcus.

Streptococcus- ferment glucose to form mainly lactic acid. Cells in pairs, chains. Catalase is not formed. Rarely mobile.

Leuconostok- ferment glucose to form lactic acid and other products. Cells divide in one plane, and pairs of cells and chains are formed. Catalase is not formed. Many are pests in the production of sugar, soft drinks, etc.

Pediococcus- found in the form of single cells, in pairs and tetrads or chains. They are immobile, do not form spores, have a fermentative metabolism.

Lactic acid is formed from glucose and other sugars. Anaerobes, but can grow in the presence of small amounts of oxygen. Catalase is not usually produced. Gelatin is not liquefied. Pediococci are saprophytes and are found in fermenting plant materials. They are pests of brewing production and are less common in milk and dairy products. Some are resistant to table salt and develop at a 15% concentration in the environment.

4. Rods and cocci that form endospores. Among the bacteria of this group, several genera belonging to the Bacilliaceae family are of greatest importance for the food industry.

Family Bacilliaceae (Bacilliaceae)- rod-shaped cells form endospores, which are more resistant to heat and other unfavorable environmental factors. Most representatives are gram-positive, motile or immobile, aerobes or anaerobes.

Two genera are of greatest importance in this family: Bacillus and Clostridium.

Genus Bacillus- small mobile rods, flagella usually at the end of the cell. They form heat-resistant spores. Most species produce catalase. Strict aerobes or facultative anaerobes. Individual species of the genus Bacillus differ in the shape of the cells, the position of the spore in the center of the cell or at the end, as well as in biochemical characteristics.

Among the representatives of this genus there are putrefactive bacteria - saprophytes that cause protein hydrolysis - Bacillus subtilis (bacillus subtilis), which form very heat-resistant spores.

The same genus includes pathogenic bacteria that cause food poisoning (Bacillus cereus), as well as pathogenic Bacillus anthracis, which causes an acute infectious disease of animals that is transmitted to humans - anthrax.

Genus Clostridium- rods, usually mobile (peritrichs), sometimes immobile. They form spores of various shapes (from oval to spherical), which usually inflate the cell. Mesophilic clostridia live in soil, dust, air, water, and sediments of reservoirs. They cause putrefactive processes, butyric acid fermentation, ferment sugars, and some species fix atmospheric nitrogen. Most strains are strict anaerobes, although some can grow in the presence of atmospheric oxygen. Catalase is not usually produced. Typically gram-positive.

The genus Clostridium includes bacteria with various properties. Some of them are mesophiles and constantly contaminate food products. Some clostridia are thermophiles, form heat-resistant spores, and cause spoilage of canned food.

Some species of clostridia, such as Clostridium botulinum, produce toxins and cause food poisoning. Two species of the genus Clostridium are pathogenic. Clostridium tetani causes tetanus in humans. Clostridium perfringens causes food poisoning when it enters the gastrointestinal tract, and gas gangrene when it enters wounds.

5. Gram-positive rods that do not form spores. Bacteria are rod-shaped or filamentous, motile or immobile, forming catalase or incapable of it.

Family Lactobacillaceae (lactobacillus). Bacteria of this family are straight or curved rods, usually single or in chains. The main part is motionless. Anaerobes or facultative anaerobes. They have complex nutritional requirements for organic matter. Capable of fermenting sugars. Catalase is not formed. Bacteria of the genus Lactobacillus (lactic acid bacteria) are rods, often forming chains. Mobility is rare. Metabolism is fermentative. Some representatives of this genus are strict anaerobes, others can grow with access to atmospheric oxygen. Ferment sugars. Temperature limits for growth are 5-53 °C, optimal temperature is 30-40 °C. Acid-resistant: grows at pH 5.0 and below.

The species differ in the type of lactic acid fermentation. In homofermentative species, the main waste product is lactic acid. This includes the bacteria Lactobacillus bulgaricus (Bulgaricus bacillus), used to produce curdled milk, Lactobacillus casei, used in the production of cheese, etc.

Rice. 5. The structure of actinomycetes: a - branching hyphae (threads); b - part of the hyphae with spores; c - rods with lateral outgrowths.

In heterofermentative bacteria, as a result of glucose fermentation, 50% of the final products are lactic acid, the rest is carbon dioxide and acids.

6. Actinomycetes and related microorganisms.

This group includes bacteria that differ in cell shape and properties.

Genus Corynebacterium- gram-positive, immobile rods of irregular shape that do not form spores and catalase. Among them, pathogenic species that produce toxin are known - these are the causative agents of diphtheria, as well as those that cause diseases of plants and animals. They are distinguished by “clicking” division. This also includes organisms that cause propionic acid fermentation - propionic acid bacteria.

Actinomycetes are of great importance - immobile single-celled organisms with the ability to branch. Some actinomycetes form mycelium from thin filaments, others (non-mycelial) exist in the form of individual cells of irregular shape, sometimes coccoid (Fig. 5).

Actinomycetes are widespread in soil, water and food and cause spoilage, manifested by an earthy odor.

Concept of microorganisms

Microorganisms- these are organisms invisible to the naked eye due to their small size.

The size criterion is the only one that unites them.

Otherwise, the world of microorganisms is even more diverse than the world of macroorganisms.

According to modern taxonomy, microorganisms to 3 kingdoms:

• Vira - viruses;
• Eucariotae - protozoa and fungi;
• Procariotae - true bacteria, rickettsia, chlamydia, mycoplasma, spirochetes, actinomycetes.

Just like for plants and animals, the name of microorganisms is used binary nomenclature, i.e., generic and specific name.

If researchers cannot determine species affiliation and only genus affiliation is determined, then the term species is used. Most often this occurs when identifying microorganisms that have non-traditional nutritional needs or living conditions. Genus name usually either based on the morphological characteristic of the corresponding microorganism (Staphylococcus, Vibrio, Mycobacterium), or is derived from the name of the author who discovered or studied the pathogen (Neisseria, Shigella, Escherichia, Rickettsia, Gardnerella).

Species name often associated with the name of the main disease caused by this microorganism (Vibrio cholerae - cholera, Shigella dysenteriae - dysentery, Mycobacterium tuberculosis - tuberculosis) or with the main habitat (Escherihia coli - E. coli).

In addition, in Russian-language medical literature it is possible to use the corresponding Russified name of bacteria (instead of Staphylococcus epidermidis - epidermal staphylococcus; Staphylococcus aureus - Staphylococcus aureus, etc.).

Kingdom of prokaryotes

includes the department of cyanobacteria and the department of eubacteria, which, in turn, divided intoorders:

• bacteria themselves (divisions Gracilicutes, Firmicutes, Tenericutes, Mendosicutes);
• actinomycetes;
• spirochetes;
• rickettsia;
• chlamydia.

Orders are divided into groups.

Prokaryotes differ from eukaryotes because Dont Have:

• morphologically formed nucleus (no nuclear membrane and no nucleolus), its equivalent is a nucleoid, or genophore, which is a closed circular double-stranded DNA molecule attached at one point to the cytoplasmic membrane; by analogy with eukaryotes, this molecule is called a chromosomal bacterium;
• Golgi reticular apparatus;
• endoplasmic reticulum;
• mitochondria.

There is also a number of signs or organelles, characteristic of many, but not all prokaryotes, which allow distinguish them from eukaryotes:

• numerous invaginations of the cytoplasmic membrane, which are called mesosomes, they are associated with the nucleoid and are involved in cell division, sporulation and respiration of the bacterial cell;
• a specific component of the cell wall is murein; its chemical structure is peptidoglycan (diaminopiemic acid);
• Plasmids are autonomously replicating circular molecules of double-stranded DNA with a molecular weight lower than that of a bacterial chromosome. They are located along with the nucleoid in the cytoplasm, although they can be integrated into it, and carry hereditary information that is not vital for the microbial cell, but provides it with certain selective advantages in the environment.

Most famous:

F-plasmids providing conjugative transfer

between bacteria;

R-plasmids are drug resistance plasmids that ensure the circulation among bacteria of genes that determine resistance to chemotherapeutic agents used to treat various diseases.

Bacteria

Prokaryotic, predominantly unicellular microorganisms that can also form associations (groups) of similar cells, characterized by cellular, but not organismal, similarities.

Basic taxonomic criteria,allowing to classify bacterial strains into one group or another:

• morphology of microbial cells (cocci, rods, convoluted);
• relation to Gram staining - tinctorial properties (gram-positive and gram-negative);
• type of biological oxidation - aerobes, facultative anaerobes, obligate anaerobes;
• ability to form spores.

Further differentiation of groups into families, genera and species, which are the main taxonomic category, is carried out based on the study of biochemical properties. This principle forms the basis for the classification of bacteria given in special manuals - determinants of bacteria.

View is an evolutionarily established set of individuals having a single genotype, which under standard conditions is manifested by similar morphological, physiological, and biochemical characteristics.

For pathogenic bacteria, the definition of “species” is supplemented by the ability to cause certain nosological forms of diseases.

Exists intraspecific differentiation of bacteriaonoptions:

• according to biological properties - biovars or biotypes;
• biochemical activity - enzyme digesters;
• antigenic structure - serovars or serots;
• sensitivity to bacteriophages - phagevars or phagetypes;
• antibiotic resistance - resistant products.

In microbiology, special terms are widely used - culture, strain, clone.

Culture is a collection of bacteria visible to the eye on nutrient media.

Cultures can be pure (a set of bacteria of one species) or mixed (a set of bacteria of 2 or more species).

Strain is a collection of bacteria of the same species isolated from different sources or from the same source at different times.

Strains may differ in some characteristics that do not go beyond the characteristics of the species. Clone is a collection of bacteria that are the offspring of one cell.

Bacteria are prokaryotic microorganisms with a cellular structure. Their sizes range from 0.1 to 30 microns. Germs are extremely common. They live in soil, air, water, snow and even hot springs, on the body of animals, as well as inside living organisms, including the human body.

The distribution of bacteria into species takes into account several criteria, among which the shape of microorganisms and their spatial distribution are most often taken into account. So, according to the shape of the cells, bacteria are divided into:

Coca - micro-, diplo-, strepto-, staphylococci, as well as sarcina;

Rod-shaped - monobacteria, diplobacteria and streptobacteria;

The convoluted species are vibrios and spirochetes.

Bergey's determinant systematizes all known bacteria according to the most widely used principles of bacterial identification in practical bacteriology, based on differences in the structure of the cell wall and the relationship to Gram staining. The description of bacteria is given by groups (sections), which include families, genera and species; in some cases, groups include classes and orders. Bacteria pathogenic to humans are included in a small number of groups.

The key identifies four main categories of bacteria -

Gracillicutes [from lat. gracilis, graceful, thin, + cutis, skin] - species with a thin cell wall, staining gram negative;

firmicutes [from lat. flrmus, strong, + cutis, skin] - bacteria with a thick cell wall, staining gram-positive;

Tenericutes [from Lat. tener, tender, + cutis, skin] - bacteria lacking a cell wall(mycoplasmas and other representatives of the class Mollicutes)

Mendosicutes [from Lat. mendosus, irregular, + cutis, skin] - archaebacteria (methane- and sulfate-reducing, halophilic, thermophilic and archaebacteria lacking a cell wall).

Group 2 of the Bergey determinant. Aerobic and microaerophilic motile convoluted and curved gram-negative bacteria. Species pathogenic to humans are included in the genera Campylobacter and Helicobacters Spirillum.

Group 3 of the Bergey determinant. Non-motile (rarely motile) gram-negative bacteria. Does not contain pathogenic species.

Group 4 of the Bergey determinant. Gram-negative aerobic and microaerophilic rods and cocci. Species pathogenic to humans are included in the families Legionellaceae, Neisseriaceae and Pseudomonada-ceae; the group also includes pathogenic and opportunistic bacteria of the genera Acinetobacter, Afipia, Alcaligenes, Bordetella, Brucella, Flavobacterium, Francisella, Kingella and Moraxella.

Group 5 of the Bergey determinant. Facultatively anaerobic gram-negative rods. The group is formed by three families - Enterobacteriaceae, Vibrionaceae and Pasteurellaceae, each of which includes pathogenic species, as well as pathogenic and opportunistic bacteria of the genera Calymmobaterium, Cardiobacterium, Eikenetta, Gardnerella and Streptobacillus.

Group 6 of the Bergey determinant. Gram-negative anaerobic straight, curved and spiral bacteria. Pathogenic and opportunistic species are included in the genera Bacteroides, Fusobacterium, Porphoromonas and Prevotelta.

Group 7 of the Bergey determinant. Bacteria performing dissimilatory reduction of sulfate or sulfur Does not include pathogenic species.

Group 8 of the Bergey determinant. Anaerobic gram-negative cocci. Includes opportunistic bacteria of the genus Veillonella.

Group 9 of the Bergey determinant. Rickettsia and chlamydia. Three families - Rickettsiaceae, Bartonellaceae and Chlamydiaceae, each of which contains species pathogenic to humans.

Groups 10 and 11 of Bergey's determinant include anoxy- and oxygenic phototrophic bacteria that are not pathogenic to humans.

Group 12 of the Bergey determinant. Aerobic chemolithotrophic bacteria and related organisms. Combines iron-sulphur- and manganese-oxidizing and nitrifying bacteria that do not cause damage to humans.

Groups 13 and 14 of Bergey's determinant include budding and/or protruding bacteria and sheath-forming bacteria. They are represented by free-living species that are not pathogenic to humans;

Groups 15 and 16 of Bergey's determinant combine gliding bacteria that do not form fruiting bodies and those that form them. The groups do not include species pathogenic to humans.

Group 17 of the Bergey determinant. Gram-positive cocci. Includes opportunistic species of the genera Enterococcus Leuconostoc, Peptococcus, Peptostreptococcus, Sarcina, Staphylococcus, Stomatococcus, Streptococcus.

Group 18 of the Bergey determinant. Spore-forming gram-positive rods and cocci. Includes pathogenic and opportunistic bacilli of the genera Clostridium and Bacillus.

Group 19 of the Bergey determinant. Spore-forming gram-positive rods of regular shape. Including opportunistic species of the genera Erysipelothrix and Listeria.

Group 20 of the Bergey determinant. Spore-forming gram-positive rods of irregular shape. The group includes pathogenic and opportunistic species of the genera Actinomyces, Corynebacterium Gardnerella, Mobiluncus, etc.

Group 21 of the Bergey determinant. Mycobacteria. Includes the only genus Mycobacterium, which combines pathogenic and opportunistic species.

Groups 22-29. Actinomycetes. Among numerous species, only nocardioform actinomycetes (group 22) of the genera Gordona, Nocardia, Rhodococcus, Tsukamurella, Jonesia, Oerskovi and Terrabacter are capable of causing lesions in humans.

Group 30 of the Bergey determinant. Mycoplasmas. Species included in the genus Acholeplasma, Mycoplasma and Ureaplasma are pathogenic to humans.

The remaining groups of Bergey's determinant - methanogenic bacteria (31), sulfate-reducing bacteria (32 extremely halophilic aerobic archaebacteria (33), archaebacteria lacking cell walls (34), extreme thermophiles and hyperthermophiles that metabolize sulfur (35) - do not contain species pathogenic to humans.

Microorganisms (microbes) are single-celled organisms smaller than 0.1 mm in size that cannot be seen with the naked eye. These include bacteria, microalgae, some lower filamentous fungi, yeast, and protozoa (Fig. 1). Microbiology studies them.

Rice. 1. Microbiology objects.

In Fig. 2. You can see some representatives of single-celled protozoa. Sometimes the objects of this science include the most primitive organisms on Earth - viruses that do not have a cellular structure and are complexes of nucleic acids (genetic material) and protein. More often they are isolated into a completely separate field of study (Virology), since microbiology is rather aimed at the study of microscopic single-celled organisms.

Rice. 2. Individual representatives of unicellular eukaryotes (protozoa).

The sciences of algology and mycology, which study algae and fungi, respectively, are separate disciplines that overlap with microbiology in the study of microscopic living objects. Bacteriology is a true branch of microbiology. This science deals exclusively with the study of prokaryotic microorganisms (Fig. 3).

Rice. 3. Scheme of a prokaryotic cell.

Unlike eukaryotes, which include all multicellular organisms, as well as protozoa, microscopic algae and fungi, prokaryotes do not have a formed nucleus containing genetic material and real organelles (permanent specialized structures of the cell).

Prokaryotes include true bacteria and archaea, which according to modern classification are designated as domains (superkingdoms) Archaea and Eubacteria (Fig. 4).

Rice. 4. Domains of modern biological classification.

Structural features of bacteria

Bacteria are an important link in the cycle of substances in nature; they decompose plant and animal residues, clean bodies of water contaminated with organic matter, and modify inorganic compounds. Without them, life on earth could not exist. These microorganisms are distributed everywhere, in soil, water, air, animal and plant organisms.

Bacteria differ in the following morphological features:

1. Cell shape (round, rod-shaped, filamentous, convoluted, spiral, as well as various transitional options and star-shaped configuration).
2. The presence of devices for movement (immobile, flagellated, due to the secretion of mucus).
3. Articulation of cells with each other (isolated, linked in the form of pairs, granules, branching forms).

Among the structures formed by round bacteria (cocci), there are cells that are in pairs after division and then break up into single formations (micrococci) or remain together all the time (diplococci). A quadratic structure of four cells is formed by tetracocci, a chain by streptococci, a granule of 8-64 units by sarcina, and clusters by staphylococci.

Rod-shaped bacteria are represented by a variety of shapes due to the great variability in the length (0.1-15 µm) and thickness (0.1-2 µm) of the cell. The shape of the latter also depends on the ability of bacteria to form spores - structures with a thick shell that allows microorganisms to survive unfavorable conditions. Cells with this ability are called bacilli, and those without such properties are simply called rod-shaped bacteria.

Special modifications of rod-shaped bacteria are filamentous (elongated) forms, chains and branching structures. The latter is formed by actinomycetes at a certain stage of development. “Curved” rods are called crimped bacteria, among which vibrios are isolated; spirilla having two bends (15-20 µm); spirochetes that resemble wavy lines. Their cell lengths are 1-3, 15-20 and 20-30 µm, respectively. In Fig. Figures 5 and 6 show the main morphological forms of bacteria, as well as the types of spore arrangement in the cell.

Rice. 5. Basic forms of bacteria.

Rice. 6. Bacteria according to the type of spore location in the cell. 1, 4 – in the center; 2, 3, 5 – end location; 6 – from the side.

The main cellular structures of bacteria: nucleoid (genetic material), ribosomes intended for protein synthesis, cytoplasmic membrane (part of the cell membrane), which in many representatives is additionally protected from above, capsule and mucous sheath (Fig. 7).

Rice. 7. Scheme of a bacterial cell.

According to the classification of bacteria, there are more than 20 types. For example, extremely thermophilic (high temperature lovers) Aquificae, anaerobic rod-shaped bacteria Bacteroidetes. However, the most dominant phylum, which includes diverse representatives, is Actinobacteria. It includes bifidobacteria, lactobacilli, and actinomycetes. The uniqueness of the latter lies in the ability to form mycelium at a certain stage of development.

In common parlance this is called mycelium. Indeed, the branching cells of actinomycetes resemble fungal hyphae. Despite this feature, actinomycetes are classified as bacteria, since they are prokaryotes. Naturally, their cells are less similar in structure to fungi.

Actinomycetes (Fig. 8) are slow-growing bacteria, and therefore do not have the ability to compete for readily available substrates. They are capable of decomposing substances that other microorganisms cannot use as a carbon source, in particular petroleum hydrocarbons. Therefore, actinomycetes are intensively studied in the field of biotechnology.

Some representatives concentrate in areas of oil fields, and create a special bacterial filter that prevents the penetration of hydrocarbons into the atmosphere. Actinomycetes are active producers of practically valuable compounds: vitamins, fatty acids, antibiotics.

Rice. 8. Representative actinomycete Nocardia.

Fungi in microbiology

The object of microbiology is only lower mold fungi (rhizopus, mucor, in particular). Like all mushrooms, they are not able to synthesize substances themselves and require a nutrient medium. The mycelium of the lower representatives of this kingdom is primitive, not divided by partitions. A special niche in microbiological research is occupied by yeast (Fig. 9), characterized by the absence of mycelium.

Rice. 9. Forms of colonies of yeast cultures on a nutrient medium.

Currently, much knowledge has been collected about their beneficial properties. However, yeast continues to be studied for its ability to synthesize practically valuable organic compounds and is actively used as model organisms in genetic experiments. Since ancient times, yeast has been used in fermentation processes. Metabolism differs among different representatives. Therefore, some yeasts are more suitable for a particular process than others.

For example, Saccharomyces beticus, which is more resistant to high alcohol concentrations, is used to create strong wines (up to 24%). While, the yeast S. cerevisiae is able to produce lower concentrations of ethanol. According to the areas of their application, yeasts are classified into feed, bakers, brewers, spirits, and wines.

Pathogenic microorganisms

Disease-causing or pathogenic microorganisms are found everywhere. Along with well-known viruses: influenza, hepatitis, measles, HIV, etc., dangerous microorganisms are rickettsia, as well as streptococci and staphylococci, which cause blood poisoning. Among rod-shaped bacteria there are many pathogens. For example, diphtheria, tuberculosis, typhoid fever (Fig. 10). Many representatives of microorganisms dangerous to humans are found among protozoa, in particular malarial plasmodium, toxoplasma, leishmania, lamblia, trichomonas, and pathogenic amoebas.

Rice. 10. Photo of the bacterium Bacillus anthracis, which causes anthrax.

Many actinomycetes are not dangerous to humans and animals. However, many pathogenic representatives are found among mycobacteria that cause tuberculosis and leprosy. Some actinomycetes initiate a disease such as actinomycosis, accompanied by the formation of granulomas and sometimes an increase in body temperature. Certain types of mold fungi are capable of producing substances toxic to humans - mycotoxins. For example, some representatives of the genus Aspergillus, Fusarium. Pathogenic fungi cause a group of diseases called mycoses. Thus, candidiasis or, simply put, thrush is caused by yeast-like fungi (Fig. 11). They are always present in the human body, but are activated only when the immune system is weakened.

Rice. 11. Candida fungus is the causative agent of thrush.

Fungi can cause a variety of skin lesions, in particular all kinds of lichen, except for herpes zoster, which is caused by a virus. Malassezia yeast, permanent inhabitants of human skin, can cause a decrease in the activity of the immune system. Don't immediately rush to wash your hands. Yeasts and opportunistic bacteria in good health perform an important function, preventing the development of pathogens.

Viruses as an object of microbiology

Viruses are the most primitive organisms on earth. In a free state, no metabolic processes occur in them. Only when they enter a host cell do viruses begin to multiply. In all living organisms, the carrier of genetic material is deoxyribonucleic acid (DNA). Only among viruses are there representatives with a genetic sequence such as ribonucleic acid (RNA).

Viruses are often not classified as truly living organisms.

The morphology of viruses is very diverse (Fig. 12). Typically, their diametrical sizes range from 20-300 nm.

Rice. 12. Diversity of viral particles.

Some representatives reach a length of 1-1.5 microns. The structure of the virus consists of surrounding the genetic material with a special protein frame (capsid), characterized by a variety of shapes (helical, icosahedral, spherical). Some viruses also have an envelope on top formed from the host cell membrane (supercapsid). For example, (Fig. 13) is known as the causative agent of a disease called (AIDS). It contains RNA as genetic material and affects a certain type of immune system cell (helper T-lymphocytes).

Rice. 13. Structure of the human immunodeficiency virus.

Classification of bacteria by shape.

Based on their shape, all bacteria are divided into 3 groups:

Globular or cocci

Rod-shaped or sticks

Twisted shapes of bacteria.

Cocci have a round, spherical, oval, candle-flame, lanceolate shape and are divided into 6 subgroups based on the connection method.

1 micrococci;

2 diplococci;

3 tetracocci;

4 streptococci;

5 staphylococci;

6 sarcinas.

All cocci are immobile and do not form spores.
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Widely distributed in nature. Included in fermented milk starters. May be pathogenic (angina, gonorrhea, meningitis).

Rod-shaped bacteria have an elongated shape. Length is greater than width. They easily change their shape based on living conditions, ᴛ.ᴇ. have polymorphism. Rods are the most common group of all bacteria. They may not be pathogenic, but can cause various diseases (typhoid, dysentery).

Rods can be mobile or immobile, forming or not forming spores. Based on their ability to form spores, rods are divided into three groups:

Bacteria;

bacilli;

Clostridia.

The convoluted forms of bacteria are divided into three groups:

1. vibrios;

2. spirilla;

3. spirochetes.

All convoluted forms are pathogenic.

Structure and functions of the cell membrane of bacteria.

Cell membrane covers the outside of the cell. It is a dense, elastic structure that can withstand differential pressure, consisting of two parts - an outer part called the cell wall and an inner part - the cytoplasmic membrane (CPM). Both the wall and the membrane have pores (holes) through which nutrients pass into the cell and waste products are removed. In this case, nutrients pass through the pores of the cell wall with a molecular weight of no more than 1000, ᴛ.ᴇ. During feeding, the wall acts as a mechanical sieve. Nutrients pass through the pores of the CPM not by mass, but as needed, ᴛ.ᴇ. it is semi-permeable.

The cell membrane performs a number of important functions:

1 – maintains body shape;

2 – protects the cell from external influences;

3 – participates in cell metabolism, ᴛ.ᴇ. allows nutrients to pass through and excretes waste products;

4 – participates in cell movement. Bacteria deprived of a cell membrane lose mobility;

5 – participate in the formation of the capsule.

Classification of bacteria by shape. - concept and types. Classification and features of the category "Classification of bacteria by shape." 2017, 2018.