What is bacteria definition. Biology of bacteria

History of the study

The foundations of general microbiology and the study of the role of bacteria in nature were laid by Beijerinck, Martinus Willem and Vinogradsky, Sergei Nikolaevich.

The study of the structure of bacterial cells began with the invention of the electron microscope in the 1930s. In 1937, E. Chatton proposed dividing all organisms according to the type of cellular structure into prokaryotes and eukaryotes, and in 1961 Steinier and Van Niel finally formalized this division. The development of molecular biology led to the discovery in 1977 of K. Woese of fundamental differences among prokaryotes themselves: between bacteria and archaea.

Structure

The vast majority of bacteria (with the exception of actinomycetes and filamentous cyanobacteria) 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 the abilities of bacteria such as attachment to the surface, mobility, and absorption of nutrients. It has been noted, for example, that oligotrophs, that is, bacteria living with 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 obligatory cellular structures, three are distinguished:

On the outside of the CPM there are several layers (cell wall, capsule, mucous membrane), called cell membrane, and surface structures(flagella, villi). CPM and cytoplasm are combined together into the concept protoplast.

Protoplast structure

The CPM limits the contents of the cell (cytoplasm) from the external environment. The homogeneous fraction of the cytoplasm containing a set of soluble RNA, proteins, products and substrates of metabolic reactions is called cytosol. The other part of the cytoplasm is represented by various structural elements.

All the genetic information necessary for the life of bacteria is contained in one DNA (bacterial chromosome), most often in the form of a covalently closed ring (linear chromosomes are found in Streptomyces And Borrelia). It is attached to the CPM at one point and is placed in a structure isolated, but not separated by a membrane from the cytoplasm, and called nucleoid. Unfolded DNA is more than 1 mm long. The bacterial chromosome is usually presented in a single copy, that is, almost all prokaryotes are haploid, although in certain conditions one cell can contain several copies of its chromosome, and Burkholderia cepacia has three different circular chromosomes (length 3.6, 3.2 and 1.1 million base pairs). The ribosomes of prokaryotes are also different from those of eukaryotes and have a sedimentation constant of 70 S (80 S in eukaryotes).

In addition to these structures, inclusions of reserve substances may also be present in the cytoplasm.

Cell membrane and surface structures

In bacteria, there are two main types of cell wall structure, characteristic of gram-positive and gram-negative species.

The cell wall of Gram-positive bacteria is a homogeneous layer 20-80 nm thick, built mainly of peptidoglycan with a smaller amount of teichoic acids and a small amount of polysaccharides, proteins and lipids (the so-called lipopolysaccharide). The cell wall has pores with a diameter of 1-6 nm, which make it permeable to a number of molecules.

In gram-negative bacteria, the peptidoglycan layer is loosely adjacent to the CPM and has a thickness of only 2-3 nm. It is surrounded by an outer membrane, which, as a rule, has an uneven, curved shape. Between the CPM, the peptidoglycan layer and the outer membrane there is a space called periplasmic and filled with a solution including transport proteins and enzymes.

On the outside of the cell wall there may be a capsule - an amorphous layer that maintains connection with the wall. The mucous layers have no connection with the cell and are easily separated, while the covers are not amorphous, but have a fine structure. However, between these three idealized cases there are many transitional forms.

Dimensions

The average size of bacteria is 0.5-5 microns. Weight - 4⋅10−13 g. Escherichia coli, for example, has dimensions of 0.3-1 by 1-6 microns, Staphylococcus aureus- diameter 0.5-1 microns, Bacillus subtilis- 0.75 by 2-3 microns. The largest known bacteria is Thiomargarita namibiensis, reaching a size of 750 microns (0.75 mm). The second one is Epulopiscium fishelsoni, having a diameter of 80 microns and a length of up to 700 microns and living in the digestive tract of surgical fish Acanthurus nigrofuscus. Achromatium oxaliferum reaches dimensions of 33 by 100 microns, Beggiatoa alba- 10 by 50 microns. Spirochetes can grow up to 250 µm in length with a thickness of 0.7 µm. At the same time, bacteria include the smallest organisms with a cellular structure. Mycoplasma mycoides has a size of 0.1-0.25 microns, which corresponds to the size of large viruses, for example, tobacco mosaic, cowpox or influenza. According to theoretical calculations, a spherical cell with a diameter of less than 0.15-0.20 microns becomes incapable of independent reproduction, since it physically cannot accommodate all the necessary biopolymers and structures in sufficient quantities.

With a linear increase in the radius of a cell, its surface increases in proportion to the square of the radius, and its volume in proportion to the cube, therefore, in small organisms the ratio of surface to volume is higher than in larger ones, which means for the former a more active exchange of substances with the environment. Metabolic activity, measured by various indicators, per unit of biomass is higher in small forms than in large ones. Therefore, small sizes even for microorganisms give bacteria and archaea advantages in the rate of growth and reproduction compared to more complex eukaryotes and determine their important ecological role.

Multicellularity in bacteria

A multicellular organism must meet the following conditions:

• its cells must be aggregated,
• there must be a division of functions between cells,
• stable specific contacts must be established between aggregated cells.

Multicellularity in prokaryotes is known; the most highly organized multicellular organisms belong to the groups of cyanobacteria and actinomycetes. In filamentous cyanobacteria, structures in the cell wall are described that ensure contact between two neighboring cells - microplasmodesmata. The possibility of exchange between cells of substance (dye) and energy (electrical component of the transmembrane potential) has been shown. Some of the filamentous cyanobacteria contain, in addition to the usual vegetative cells, functionally differentiated ones: akinetes and heterocysts. The latter perform nitrogen fixation and intensively exchange metabolites with vegetative cells.

Movement patterns and irritability

Many bacteria are motile. There are several important various types movement of bacteria. The most common movement is with the help of flagella: single bacteria and bacterial associations (swarming). A special case of this is also the movement of spirochetes, which wriggle thanks to axial filaments, similar in structure to flagella, but located in the periplasm. Another type of movement is the sliding of bacteria without flagella on the surface of solid media and the movement in water of flagellated bacteria of the genus Synechococcus. Its mechanism is not yet well understood; it is assumed that it involves the secretion of mucus (pushing the cell) and fibrillar filaments located in the cell wall, causing a “running wave” along the surface of the cell. Finally, bacteria can float and submerge in liquids, changing their density, filling with gases or emptying aerosomes.

Bacteria actively move in the direction determined by certain stimuli. This phenomenon is called taxis. There are chemotaxis, aerotaxis, phototaxis, etc.

Metabolism

Constructive Metabolism

With the exception of some specific points, the biochemical pathways through which the synthesis of proteins, fats, carbohydrates and nucleotides is carried out in bacteria are similar to those in other organisms. However, according to the number possible options These pathways and, accordingly, in the degree of dependence on the supply of organic substances from the outside, they differ.

Some of them can synthesize all the organic molecules they need from inorganic compounds (autotrophs), while others require ready-made organic compounds, which they can only transform (heterotrophs).

Bacteria can satisfy their nitrogen needs both through its organic compounds (like heterotrophic eukaryotes) and through molecular nitrogen (like some archaea). Most bacteria use inorganic nitrogen compounds to synthesize amino acids and other nitrogen-containing organic substances: ammonia (entering cells in the form of ammonium ions), nitrites and nitrates (which are previously reduced to ammonium ions). They are able to absorb phosphorus in the form of phosphate, sulfur in the form of sulfate or, less commonly, sulfide.

Energy metabolism

The ways in which bacteria obtain energy are unique. There are three types of energy production (and all three are known in bacteria): fermentation, respiration and photosynthesis.

Bacteria that carry out only oxygen-free photosynthesis do not have photosystem II. Firstly, these are purple and green filamentous bacteria in which only the cyclic electron transfer pathway functions, aimed at creating a transmembrane proton gradient, due to which ATP is synthesized (photophosphorylation), and NAD(P) + is reduced, which is used for the assimilation of CO 2 . Secondly, these are green sulfur and heliobacteria, which have both cyclic and non-cyclic electron transport, which makes direct reduction of NAD(P) + possible. Reduced sulfur compounds (molecular, hydrogen sulfide, sulfite) or molecular hydrogen are used as an electron donor that fills a “vacancy” in a pigment molecule in oxygen-free photosynthesis.

There are also bacteria with very specific energy metabolism. Thus, in October 2008, a report appeared in the journal Science about the discovery of an ecosystem consisting of representatives of one single previously unknown species of bacterium - Desulforudis audaxviator, which receive energy for their life activity from chemical reactions with the participation of hydrogen formed as a result of the disintegration of water molecules under the influence of radiation from uranium ore bacteria located near the location. Some colonies of bacteria that live on the ocean floor use electric current to transfer energy to their fellows.

Types of life

You can combine the types of constructive and energy metabolism in the following table:

Ways of existence of living organisms (Lvov matrix)
Energy source	Electron donor	Carbon source	Name of way of existence	Representatives
OVR	Inorganic compounds	Carbon dioxide	Chemolithoautotrophy	Nitrifying, thionic, acidophilic iron bacteria
		Organic compounds	Chemolithoheterotrophy	Methane-producing archaebacteria, hydrogen bacteria
	Organic matter	Carbon dioxide	Chemoorganoautotrophy	Facultative methylotrophs, formic acid-oxidizing bacteria
		Organic compounds	Chemoorganoheterotrophy	Most prokaryotes, eukaryotes: animals, fungi, humans
Light	Inorganic compounds	Carbon dioxide	Photolithoautotrophy	Cyanobacteria, purple, green bacteria, from eukaryotes: plants
		Organic compounds	Photolithoheterotrophy	Some cyanobacteria, purple, green bacteria
	Organic matter	Carbon dioxide	Photoorganoautotrophy	Some purple bacteria
		Organic matter	Photoorganoheterotrophy	Halobacteria, some cyanobacteria, purple bacteria, green bacteria

The table shows that the variety of nutritional types of prokaryotes is much greater than that of eukaryotes (the latter are only capable of chemoorganoheterotrophy and photolithoautotrophy).

Reproduction and structure of the genetic apparatus

Bacteria reproduction

Some bacteria do not have a sexual process and reproduce only by equal binary transverse fission or budding. For one group of unicellular cyanobacteria, multiple fission (a series of rapid successive binary fissions leading to the formation of 4 to 1024 new cells) has been described. To ensure the plasticity of the genotype necessary for evolution and adaptation to a changing environment, they have other mechanisms.

Genetic apparatus

Genes necessary for life and determining species specificity are most often located in bacteria in a single covalently closed DNA molecule - the chromosome (sometimes the term genophore is used to designate bacterial chromosomes to emphasize their differences from eukaryotic ones). The region where the chromosome is located is called the nucleoid and is not surrounded by a membrane. In this regard, newly synthesized mRNA is immediately available for binding to ribosomes, and transcription and translation are coupled.

A single cell can contain only 80% of the sum of genes present in all strains of its species (the so-called “collective genome”).

In addition to the chromosome, bacterial cells often contain plasmids - also closed in a DNA ring, capable of independent replication. They can be so large that they become indistinguishable from a chromosome, but contain additional genes needed only under specific conditions. Special mechanisms distribution ensures the preservation of the plasmid in daughter cells so that they are lost with a frequency of less than 10 −7 per cell cycle. The specificity of plasmids can be very diverse: from being present in only one host species to the RP4 plasmid, which is found in almost all Gram-negative bacteria. Plasmids encode mechanisms of antibiotic resistance, destruction of specific substances, etc.; nif genes necessary for nitrogen fixation are also found in plasmids. The plasmid gene can be included in the chromosome with a frequency of about 10−4 - 10−7.

The DNA of bacteria, as well as the DNA of other organisms, contains transposons - mobile segments that can move from one part of the chromosome to another, or to extrachromosomal DNA. Unlike plasmids, they are incapable of autonomous replication and contain IS segments - regions that encode their transport within the cell. The IS segment can act as a separate transposon.

Horizontal gene transfer

In prokaryotes, partial unification of genomes can occur. During conjugation, the donor cell, during direct contact, transfers part of its genome (in some cases, the entire genome) to the recipient cell. Sections of the donor's DNA can be exchanged for homologous sections of the recipient's DNA. The probability of such an exchange is significant only for bacteria of one species.

Similarly, a bacterial cell can absorb DNA freely present in the environment, incorporating it into its genome in the case of a high degree of homology with its own DNA. This process is called transformation. Under natural conditions, genetic information is exchanged with the help of temperate phages (transduction). In addition, the transfer of non-chromosomal genes is possible using plasmids of a certain type that encode this process, the process of exchange of other plasmids and transposon transfer.

With horizontal transfer, new genes are not formed (as is the case with mutations), but different gene combinations are created. This is important for the reason that natural selection acts on the entire set of characteristics of an organism.

Cell differentiation

Cellular differentiation is a change in the set of proteins (usually also manifested in a change in morphology) with an unchanged genotype.

Formation of resting forms

The formation of especially resistant forms with a slow metabolism, serving for preservation in unfavorable conditions and distribution (less often for reproduction) is the most common type of differentiation in bacteria. The most stable of them are endospores, formed by representatives Bacillus, Clostridium, Sporohalobacter, Anaerobacter(forms 7 endospores from one cell and can reproduce with their help) and Heliobacterium. The formation of these structures begins as normal division and in the early stages can be converted into it by certain antibiotics. The endospores of many bacteria can withstand boiling for 10 minutes at 100 °C, drying for 1000 years and, according to some data, remain viable in soils and rocks for millions of years.

Less stable are exospores, cysts ( Azotobacter, gliding bacteria, etc.), akinetes (cyanobacteria) and myxospores (myxobacteria).

Other types of morphologically differentiated cells

Actinomycetes and cyanobacteria form differentiated cells that serve for reproduction (spores, as well as hormogonium and baeocytes, respectively). It is also necessary to note structures similar to bacteroids of nodule bacteria and heterocysts of cyanobacteria, which serve to protect nitrogenase from the effects of molecular oxygen.

Classification

The most famous is the phenotypic classification of bacteria based on the structure of their cell wall, included, in particular, in the IX edition of Bergey’s Key to Bacteria (1984-1987). The largest taxonomic groups in it were 4 divisions: Gracilicutes(gram negative), Firmicutes(gram positive), Tenericutes(mycoplasma) and Mendosicutes(archaea).

Lately everything greater development receives a phylogenetic classification of bacteria (and this is what is used in Wikipedia), based on molecular biology data. One of the first methods for assessing relatedness based on genome similarity was the method of comparing the content of guanine and cytosine in DNA, proposed back in the 1960s. Although identical values ​​for their content cannot provide any information about the evolutionary proximity of organisms, their differences by 10% mean that the bacteria do not belong to the same genus. Another method that revolutionized microbiology in the 1970s was the analysis of gene sequences in 16s rRNA, which made it possible to identify several phylogenetic branches of eubacteria and evaluate the relationships between them. For classification at the species level, the DNA-DNA hybridization method is used. Analysis of a sample of well-studied species suggests that 70% of the level of hybridization characterizes one species, 10-60% - one genus, less than 10% - different genera.

The phylogenetic classification partly repeats the phenotypic one, for example, the group Gracilicutes is present in both. At the same time, the taxonomy of gram-negative bacteria was completely revised, archaebacteria were completely separated into an independent taxon of the highest rank, some taxonomic groups were divided into parts and regrouped, organisms with completely different ecological functions were combined into one group, which caused a number of inconveniences and dissatisfaction of part of the scientific community . The object of criticism is also the fact that the classification of molecules, and not organisms, is actually carried out.

Origin, evolution, place in the development of life on Earth

Bacteria, along with archaea, were among the first living organisms on Earth, appearing about 3.9-3.5 billion years ago. The evolutionary relationships between these groups have not yet been fully studied; there are at least three main hypotheses: N. Pace suggests that they have a common ancestor of protobacteria; Zavarzin considers archaea to be a dead-end branch of the evolution of eubacteria that has mastered extreme habitats; finally, according to the third hypothesis, archaea are the first living organisms from which bacteria originated.

Pathogenic bacteria

Bacteria that parasitize other organisms are called pathogenic. Bacteria cause a large number of human diseases such as plague ( Yersinia pestis), anthrax ( Bacillus anthracis), leprosy (leprosy, pathogen: Mycobacterium leprae), diphtheria ( Corynebacterium diphtheriae), syphilis ( Treponema pallidum), cholera ( Vibrio cholerae), tuberculosis ( Mycobacterium tuberculosis), listeriosis ( Listeria monocytogenes) etc. The discovery of pathogenic properties in bacteria continues: in 1976 Legionnaires' disease, caused by Legionella pneumophila, in the 1980s-1990s it was shown that Helicobacter pylori causes peptic ulcers and even stomach cancer, as well as chronic

Microbiology studies the structure, vital activity, living conditions and development of the smallest organisms called microbes, or microorganisms.

“Invisible, they constantly accompany a person, invading his life either as friends or as enemies,” said academician V. L. Omelyansky. Indeed, microbes are everywhere: in the air, in water and in soil, in the body of humans and animals. They can be useful and are used in the production of many food products. They can be harmful, cause illness in people, spoilage of food, etc.

Microbes were discovered by the Dutchman A. Leeuwenhoek (1632-1723) at the end of the 17th century, when he made the first lenses that provided magnification of 200 times or more. The microcosm he saw amazed him; Leeuwenhoek described and sketched the microorganisms he discovered on various objects. He laid the foundation for the descriptive nature of the new science. The discoveries of Louis Pasteur (1822-1895) proved that microorganisms differ not only in shape and structure, but also in their vital functions. Pasteur established that yeast causes alcoholic fermentation, and some microbes can cause infectious diseases in humans and animals. Pasteur went down in history as the inventor of the vaccination method against rabies and anthrax. The world famous contribution to microbiology is R. Koch (1843-1910) - he discovered the causative agents of tuberculosis and cholera, I. I. Mechnikova (1845-1916) - developed the phagocytic theory of immunity, the founder of virology D. I. Ivanovsky (1864-1920), N F. Gamaleya (1859-1940) and many other scientists.

Classification and morphology of microorganisms

Microbes - These are tiny, mostly single-celled living organisms, visible only through a microscope. The size of microorganisms is measured in micrometers - microns (1/1000 mm) and nanometers - nm (1/1000 microns).

Microbes are characterized by a huge variety of species, differing in structure, properties, and ability to exist in different environmental conditions. They can be unicellular, multicellular And non-cellular.

Microbes are divided into bacteria, viruses and phages, fungi, and yeast. Separately, there are varieties of bacteria - rickettsia, mycoplasma, and a special group consists of protozoa (protozoa).

Bacteria

Bacteria- predominantly unicellular microorganisms ranging in size from tenths of a micrometer, for example mycoplasma, to several micrometers, and in spirochetes - up to 500 microns.

There are three main forms of bacteria - spherical (cocci), rod-shaped (bacillus, etc.), convoluted (vibrios, spirochetes, spirilla) (Fig. 1).

Globular bacteria (cocci) They are usually spherical in shape, but can be slightly oval or bean-shaped. Cocci can be located singly (micrococci); in pairs (diplococci); in the form of chains (streptococci) or grape bunches (staphylococci), in a package (sarcins). Streptococci can cause tonsillitis and erysipelas, while staphylococci can cause various inflammatory and purulent processes.

Rice. 1. Forms of bacteria: 1 - micrococci; 2 - streptococci; 3 - sardines; 4 — sticks without spores; 5 — rods with spores (bacilli); 6 - vibrios; 7- spirochetes; 8 - spirilla (with flagella); staphylococci

Rod-shaped bacteria the most common. The rods can be single, connected in pairs (diplobacteria) or in chains (streptobacteria). The rod-shaped bacteria include Escherichia coli, the causative agents of salmonellosis, dysentery, typhoid fever, tuberculosis, etc. Some rod-shaped bacteria have the ability to form disputes. Spore-forming rods are called bacilli. Spindle-shaped bacilli are called clostridia.

Sporulation is a complex process. Spores are significantly different from an ordinary bacterial cell. They have a dense shell and a very small amount of water, they do not require nutrients, and reproduction completely stops. Spores are able to withstand drying, high and low temperatures for a long time and can remain in a viable state for tens and hundreds of years (spores of anthrax, botulism, tetanus, etc.). Once in a favorable environment, the spores germinate, that is, they turn into the usual vegetative propagating form.

Twisted bacteria can be in the form of a comma - vibrios, with several curls - spirilla, in the form of a thin twisted stick - spirochetes. Vibrios include the causative agent of cholera, and the causative agent of syphilis is a spirochete.

bacterial cell has a cell wall (sheath), often covered with mucus. Often the mucus forms a capsule. The contents of the cell (cytoplasm) are separated from the membrane by the cell membrane. Cytoplasm is a transparent protein mass in a colloidal state. The cytoplasm contains ribosomes, a nuclear apparatus with DNA molecules, and various inclusions of reserve nutrients (glycogen, fat, etc.).

Mycoplasma - bacteria lacking a cell wall and requiring growth factors contained in yeast for their development.

Some bacteria can move. Movement is carried out with the help of flagella - thin threads of different lengths that perform rotational movements. Flagella can be in the form of a single long thread or in the form of a bundle, and can be located over the entire surface of the bacterium. Many rod-shaped bacteria and almost all curved bacteria have flagella. Spherical bacteria, as a rule, do not have flagella and are immobile.

Bacteria reproduce by dividing into two parts. The rate of division can be very high (every 15-20 minutes), and the number of bacteria increases rapidly. This rapid division occurs on foods and other nutrient-rich substrates.

Viruses

Viruses — special group microorganisms that do not have a cellular structure. The sizes of viruses are measured in nanometers (8-150 nm), so they can only be seen using an electron microscope. Some viruses consist of only a protein and one nucleic acid (DNA or RNA).

Viruses cause such common human diseases as influenza, viral hepatitis, measles, as well as animal diseases - foot and mouth disease, animal plague and many others.

Bacterial viruses are called bacteriophages, fungal viruses - mycophages etc. Bacteriophages are found everywhere where there are microorganisms. Phages cause the death of microbial cells and can be used to treat and prevent certain infectious diseases.

Mushrooms are special plant organisms that do not have chlorophyll and do not synthesize organic substances, but require ready-made organic substances. Therefore, fungi develop on various substrates containing nutrients. Some fungi can cause diseases of plants (cancer and late blight of potatoes, etc.), insects, animals and humans.

Fungal cells differ from bacterial cells in the presence of nuclei and vacuoles and are similar to plant cells. Most often they take the form of long and branching or intertwining threads - hyphae. Formed from hyphae mycelium, or mycelium. Mycelium can consist of cells with one or several nuclei or be noncellular, representing one giant multinucleated cell. Fruiting bodies develop on the mycelium. The body of some fungi may consist of single cells, without the formation of mycelium (yeast, etc.).

Fungi can reproduce in different ways, including vegetatively as a result of hyphal division. Most fungi reproduce asexually and sexually through the formation of special reproduction cells - dispute. Spores, as a rule, are able to persist for a long time in the external environment. Mature spores can be transported over considerable distances. Once in the nutrient medium, the spores quickly develop into hyphae.

A large group of fungi are represented by molds (Fig. 2). Widely distributed in nature, they can grow on food products, forming clearly visible plaques of different colors. Food spoilage is often caused by mucor fungi, which form a fluffy white or gray mass. The mucor fungus Rhizopus causes “soft rot” of vegetables and berries, and the botrytis fungus coats and softens apples, pears and berries. The causative agents of molding of products can be fungi of the genus Peniillium.

Certain types of fungi can not only lead to food spoilage, but also produce substances toxic to humans - mycotoxins. These include some types of fungi of the genus Aspergillus, genus Fusarium, etc.

The beneficial properties of certain types of mushrooms are used in the food and pharmaceutical industries and other industries. For example, mushrooms of the genus Peniillium are used to obtain the antibiotic penicillin and in the production of cheeses (Roquefort and Camembert), mushrooms of the genus Aspergillus are used in the production citric acid and many enzyme preparations.

Actinomycetes- microorganisms that have characteristics of both bacteria and fungi. In structure and biochemical properties, actinomycetes are similar to bacteria, and in terms of the nature of reproduction and the ability to form hyphae and mycelium, they are similar to mushrooms.

Rice. 2. Types of mold fungi: 1 - peniillium; 2- aspergillus; 3 - mukor.

Yeast

Yeast- single-celled immobile microorganisms with a size of no more than 10-15 microns. The shape of the yeast cell is often round or oval, less often rod-shaped, sickle-shaped or lemon-shaped. Yeast cells are similar in structure to mushrooms; they also have a nucleus and vacuoles. Yeast reproduces by budding, fission, or spores.

Yeasts are widespread in nature, they can be found in soil and on plants, on food products and various industrial wastes containing sugars. The development of yeast in food products can lead to spoilage, causing fermentation or souring. Some types of yeast have the ability to convert sugar into ethanol and carbon dioxide. This process is called alcoholic fermentation and is widely used in Food Industry and winemaking.

Some types of candida yeast cause a human disease called candidiasis.

In this article we will look at bacteria.

Consider all the bacteria living in the body. And we'll tell you everything about bacteria.

Researchers say that there are about 10 thousand varieties of microbes on earth. However, there is an opinion that their variety reaches 1 million.

Due to their simplicity and unpretentiousness, they exist everywhere. Due to their small size, they penetrate anywhere, even into the smallest crevice. Microbes are adapted to any habitat, they are everywhere, even if it’s a dried-out island, even if it’s frosty, even if it’s 70 degrees hot, they still won’t lose their vitality.

Microbes enter the human body from the environment. And only when they find themselves in conditions favorable to them, they make themselves felt, either helping or causing, ranging from mild skin diseases to serious infectious diseases that lead to death in the body. Bacteria have different names.

These microbes are the most ancient species of creatures living on our planet. Appeared approximately 3.5 billion years ago. They are so tiny that they can only be seen under a microscope.

Since these are the first representatives of life on earth, they are quite primitive. Over time, their structure became more complex, although some retained their primitive structure. A large number of microbes are transparent, but some have a red or greenish tint. Few take on the color of their surroundings.

Microbes are prokaryotes, and therefore have their own separate kingdom - Bacteria. Let's look at which bacteria are harmless and harmful.

Lactobacilli (Lactobacillus plantarum)

Lactobacilli are your body's protectors against viruses. They have lived in the stomach since ancient times, performing very important and useful functions. Lactobacillus plantarum protects the digestive tract from useless microorganisms that can settle in the stomach and worsen the condition.

Lactobacillus helps get rid of heaviness and bloating in the stomach, and fight allergies caused by various foods. Lactobacilli also help remove harmful substances from the intestines. Cleanses the entire body of toxins.

Bifidobacteria (lat. Bifidobacterium)

This is a microorganism that also lives in the stomach. These are beneficial bacteria. Under unfavorable conditions for the existence of Bifidobacterium they die. Bifidobacterium produces acids such as lactic, acetic, succinic and formic.

Bifidobacterium play a leading role in normalizing intestinal function. Also, with a sufficient amount of them, they strengthen the immune system and promote better absorption of nutrients.

They are very useful as they perform a number of important functions, let’s look at the list:

1. Replenish the body with vitamins K, B1, B2, B3, B6, B9, proteins and amino acids.
2. Protects against the appearance of harmful microorganisms.
3. Prevents harmful toxins from entering the intestinal walls.
4. Accelerate the digestion process. - Helps absorb Ca, Fe and vitamin D ions.

Today, there are many medications containing bifidobacteria. But this does not mean that when they are used in medicinal purposes there will be a beneficial effect on the body, since the usefulness of the drugs has not been proven.

Unfavorable microbe Corynebacterium minutissimum

Harmful types of germs can appear in the most unlikely places where you wouldn't expect to find them.

This species, Corynebacterium minutissimum, loves to live and reproduce on phones and tablets. They cause rashes all over the body. There are a lot of anti-virus applications for tablets and phones, but they have never come up with a cure for the harmful Corynebacterium minutissimum.

So you should reduce your contact with phones and tablets so that you do not become allergic to Corynebacterium minutissimum. And remember, after washing your hands, you should not rub your palms together, as the number of bacteria decreases by 37%.

A genus of bacteria that includes more than 550 species. Under favorable conditions, streptomycetes create threads similar to mushroom mycelium. They live mainly in the soil.

In 1940, streptomycins were used in the production of drugs:

• Physostigmine. The painkiller is used in small doses to reduce eye pressure in glaucoma. In large quantities it can become poisonous.
• Tacrolimus. Medicine of natural origin. It is used for treatment and prevention during kidney, bone marrow, heart and liver transplants.
• Allosamidine. A drug to prevent the formation of chitin degradation. Safely used in killing mosquitoes, flies and so on.

But it should be noted that not all bacteria of this kind have a beneficial effect on the human body.

Belly protector Helicobacter pylori

Microbes existing in the stomach. It exists and multiplies in the gastric mucosa. Helicobacter pylori appears in the human body from an early age and lives throughout life. Helps maintain stable weight, controls hormones and is responsible for hunger.

This insidious microbe can also contribute to the development of ulcers and gastritis. Some scientists believe that Helicobacter pylori is useful, but despite a number of existing theories, it has not yet been proven why it is useful. It’s not for nothing that it can be called a belly protector.

The good bad bacterium Escherichia coli

Escherichia coli bacteria are also called E. coli. Escherichia coli, which lives in the lower abdomen. They inhabit the human body at birth and live with him throughout his life. A large number of microbes of this type are harmless, but some of them can cause serious poisoning of the body.

Escherichia coli is a common factor in many abdominal infections. But it reminds us of itself and causes discomfort when it is about to leave our body in an environment more favorable to it. And it is even useful for humans.

Escherichia coli saturates the body with vitamin K, which in turn monitors the health of the arteries. Escherichia coli can also live for a very long time in water, soil, and even in food products, such as milk.

E. coli dies after boiling or disinfection.

Harmful bacteria. Staphylococcus aureus (Staphylococcus aureus)

Staphylococcus aureus is the causative agent of purulent formations on the skin. Often boils and pimples are caused by Staphylococcus aureus, which lives on the skin of a large number of people. Staphylococcus aureus is the causative agent of many infectious diseases.

Pimples are very unpleasant, but just imagine that Staphylococcus aureus penetrating through the skin into the body can have serious consequences, pneumonia or meningitis.

It is found almost throughout the body, but mainly exists in the nasal passages and axillary folds, but it can also appear in the larynx, perineum and abdomen.

Staphylococcus aureus has a golden hue, which is where Staphylococcus aureus gets its name. It is one of the four most common causes of hospital-acquired infections following surgery.

Pseudomonas aeruginosa (Pseudomonas aeruginosa)

This microbe can exist and reproduces in water and soil. Loves warm water and swimming pools. It is one of the causative agents of purulent diseases. They got their name because of their blue-green tint. Pseudomonas aeruginosa living in warm water gets under the skin and develops an infection, accompanied by itching, pain and redness in the affected areas.

This microbe can infect various types of organs and causes a bunch of infectious diseases. Pseudomonas aeruginosa infection affects the intestines, heart, and genitourinary organs. The microorganism is often a factor in the appearance of abscesses and phlegmon. Pseudomonas aeruginosa is very difficult to get rid of because it is resistant to antibiotics.

Microbes are the simplest living microorganisms existing on Earth, which appeared many billions of years ago and are adapted to any environmental conditions. But we must remember that bacteria can be beneficial and harmful.

So, we have dealt with the types of microorganisms, using an example to look at which beneficial bacteria help the body and which are harmful and cause infectious diseases.

Remember that following the rules of personal hygiene will be the best prevention against infection with harmful microorganisms.

BACTERIA
a large group of unicellular microorganisms characterized by the absence of a cell nucleus surrounded by a membrane. At the same time, the genetic material of the bacterium (deoxyribonucleic acid, or DNA) occupies a very specific place in the cell - a zone called the nucleoid. Organisms with such a cell structure are called prokaryotes (“prenuclear”), in contrast to all others - eukaryotes (“true nuclear”), whose DNA is located in the nucleus surrounded by a shell. Bacteria, previously considered microscopic plants, are now classified into the independent kingdom Monera - one of five in the current classification system, along with plants, animals, fungi and protists.

Fossil evidence. Bacteria are probably the oldest known group of organisms. Layered stone structures - stromatolites - dated in some cases to the beginning of the Archeozoic (Archean), i.e. arose 3.5 billion years ago, - the result of the vital activity of bacteria, usually photosynthesizing, the so-called. blue-green algae. Similar structures (bacterial films impregnated with carbonates) are still formed today, mainly off the coast of Australia, the Bahamas, in the California and Persian Gulfs, but they are relatively rare and do not reach large sizes, because herbivorous organisms, such as gastropods, feed on them. Nowadays, stromatolites grow mainly where these animals are absent due to high salinity of water or for other reasons, but before the emergence of herbivorous forms during the evolution, they could reach enormous sizes, constituting an essential element of oceanic shallow water, comparable to modern coral reefs. In some ancient rocks, tiny charred spheres have been found, which are also believed to be the remains of bacteria. The first nuclear ones, i.e. eukaryotic, cells evolved from bacteria approximately 1.4 billion years ago.
Ecology. Bacteria are abundant in the soil, at the bottom of lakes and oceans - wherever organic matter accumulates. They live in the cold, when the thermometer is just above zero, and in hot acidic springs with temperatures above 90 ° C. Some bacteria tolerate very high salinity; in particular, they are the only organisms found in the Dead Sea. In the atmosphere, they are present in water droplets, and their abundance there usually correlates with the dustiness of the air. Thus, in cities, rainwater contains much more bacteria than in rural areas. There are few of them in the cold air of high mountains and polar regions, however, they are found even in the lower layer of the stratosphere at an altitude of 8 km. The digestive tract of animals is densely populated with bacteria (usually harmless). Experiments have shown that they are not necessary for the life of most species, although they can synthesize some vitamins. However, in ruminants (cows, antelopes, sheep) and many termites, they are involved in the digestion of plant food. Additionally, the immune system of an animal raised under sterile conditions does not develop normally due to lack of bacterial stimulation. The normal bacterial "flora" of the intestines is also important for suppressing the ingestion of harmful microorganisms.

STRUCTURE AND LIFE ACTIVITY OF BACTERIA

Bacteria are much smaller than the cells of multicellular plants and animals. Their thickness is usually 0.5-2.0 microns, and their length is 1.0-8.0 microns. Some forms are barely visible at the resolution of standard light microscopes (approximately 0.3 microns), but species are also known with a length of more than 10 microns and a width that also goes beyond the specified limits, and a number of very thin bacteria can exceed 50 microns in length. On the surface corresponding to the point marked with a pencil, a quarter of a million medium-sized representatives of this kingdom will fit.
Structure. Based on their morphological features, the following groups of bacteria are distinguished: cocci (more or less spherical), bacilli (rods or cylinders with rounded ends), spirilla (rigid spirals) and spirochetes (thin and flexible hair-like forms). Some authors tend to combine the last two groups into one - spirilla. Prokaryotes differ from eukaryotes mainly in the absence of a formed nucleus and the typical presence of only one chromosome - a very long circular DNA molecule attached at one point to the cell membrane. Prokaryotes also do not have membrane-enclosed intracellular organelles called mitochondria and chloroplasts. In eukaryotes, mitochondria produce energy during respiration, and photosynthesis occurs in chloroplasts (see also CELL). In prokaryotes, the entire cell (and primarily the cell membrane) takes on the function of a mitochondrion, and in photosynthetic forms, it also takes on the function of a chloroplast. Like eukaryotes, inside bacteria there are small nucleoprotein structures - ribosomes, necessary for protein synthesis, but they are not associated with any membranes. With very few exceptions, bacteria are unable to synthesize sterols, important components of eukaryotic cell membranes. Outside the cell membrane, most bacteria are covered with a cell wall, somewhat reminiscent of the cellulose wall of plant cells, but consisting of other polymers (they include not only carbohydrates, but also amino acids and bacteria-specific substances). This membrane prevents the bacterial cell from bursting when water enters it through osmosis. On top of the cell wall is often a protective mucous capsule. Many bacteria are equipped with flagella, with which they actively swim. Bacterial flagella are structured simpler and somewhat differently than similar structures of eukaryotes.

"TYPICAL" BACTERIAL CELL and its basic structures.

Sensory functions and behavior. Many bacteria have chemical receptors that detect changes in environmental acidity and concentration various substances, such as sugars, amino acids, oxygen and carbon dioxide. Each substance has its own type of such “taste” receptors, and the loss of one of them as a result of mutation leads to partial “taste blindness”. Many motile bacteria also respond to temperature fluctuations, and photosynthetic species respond to changes in light intensity. Some bacteria perceive direction power lines magnetic field, including the Earth’s magnetic field, with the help of particles of magnetite (magnetic iron ore - Fe3O4) present in their cells. In water, bacteria use this ability to swim along lines of force in search of favorable environment. Conditioned reflexes bacteria are unknown, but they have a certain kind of primitive memory. While swimming, they compare the perceived intensity of the stimulus with its previous value, i.e. determine whether it has become larger or smaller, and, based on this, maintain the direction of movement or change it.
Reproduction and genetics. Bacteria reproduce asexually: the DNA in their cell is replicated (doubled), the cell divides in two, and each daughter cell receives one copy of the parent DNA. Bacterial DNA can also be transferred between non-dividing cells. At the same time, their fusion (as in eukaryotes) does not occur, the number of individuals does not increase, and usually only a small part of the genome (the complete set of genes) is transferred to another cell, in contrast to the “real” sexual process, in which the descendant receives a complete set of genes from each parent. This DNA transfer can occur in three ways. During transformation, the bacterium absorbs “naked” DNA from the environment, which got there during the destruction of other bacteria or was deliberately “slipped” by the experimenter. The process is called transformation because in the early stages of its study the main attention was paid to the transformation (transformation) of harmless organisms into virulent ones in this way. DNA fragments can also be transferred from bacteria to bacteria by special viruses - bacteriophages. This is called transduction. A process reminiscent of fertilization and called conjugation is also known: bacteria are connected to each other by temporary tubular projections (copulatory fimbriae), through which DNA passes from a “male” cell to a “female” one. Sometimes bacteria contain very small additional chromosomes - plasmids, which can also be transferred from individual to individual. If the plasmids contain genes that cause resistance to antibiotics, they speak of infectious resistance. It is medically important because it can spread between various types and even genera of bacteria, as a result of which the entire bacterial flora, say, of the intestines, becomes resistant to the action of certain drugs.

METABOLISM

Partly due to the small size of bacteria, their metabolic rate is much higher than that of eukaryotes. Under the most favorable conditions, some bacteria can double their total mass and number approximately every 20 minutes. This is explained by the fact that a number of their most important enzyme systems function at a very high speed. Thus, a rabbit needs a matter of minutes to synthesize a protein molecule, while bacteria take seconds. However, in a natural environment, for example in soil, most bacteria are “on a starvation diet”, so if their cells divide, it is not every 20 minutes, but once every few days.
Nutrition. Bacteria are autotrophs and heterotrophs. Autotrophs (“self-feeding”) do not need substances produced by other organisms. They use carbon dioxide (CO2) as the main or only source of carbon. By incorporating CO2 and other inorganic substances, particularly ammonia (NH3), nitrates (NO-3) and various sulfur compounds, in complex chemical reactions, they synthesize all the biochemical products they need. Heterotrophs (“feeding on others”) use organic (carbon-containing) substances synthesized by other organisms, in particular sugars, as the main source of carbon (some species also need CO2). When oxidized, these compounds supply energy and molecules necessary for cell growth and functioning. In this sense, heterotrophic bacteria, which include the vast majority of prokaryotes, are similar to humans.
Main sources of energy. If mainly light energy (photons) is used for the formation (synthesis) of cellular components, then the process is called photosynthesis, and species capable of it are called phototrophs. Phototrophic bacteria are divided into photoheterotrophs and photoautotrophs depending on which compounds - organic or inorganic - serve as their main source of carbon. Photoautotrophic cyanobacteria (blue-green algae), like green plants, break down water molecules (H2O) using light energy. This releases free oxygen (1/2O2) and produces hydrogen (2H+), which can be said to convert carbon dioxide (CO2) into carbohydrates. Green and purple sulfur bacteria use light energy to break down other inorganic molecules, such as hydrogen sulfide (H2S), rather than water. The result also produces hydrogen, which reduces carbon dioxide, but no oxygen is released. This type of photosynthesis is called anoxygenic. Photoheterotrophic bacteria, such as purple nonsulfur bacteria, use light energy to produce hydrogen from organic substances, in particular isopropanol, but their source can also be H2 gas. If the main source of energy in the cell is oxidation chemical substances, bacteria are called chemoheterotrophs or chemoautotrophs depending on whether the molecules serve as the main source of carbon - organic or inorganic. For the former, organic matter provides both energy and carbon. Chemoautotrophs obtain energy from the oxidation of inorganic substances, such as hydrogen (to water: 2H4 + O2 in 2H2O), iron (Fe2+ in Fe3+) or sulfur (2S + 3O2 + 2H2O in 2SO42- + 4H+), and carbon from CO2. These organisms are also called chemolithotrophs, thereby emphasizing that they “feed” on rocks.
Breath. Cellular respiration is the process of releasing chemical energy stored in “food” molecules for its further use in vital reactions. Respiration can be aerobic and anaerobic. In the first case, it requires oxygen. It is needed for the work of the so-called. electron transport system: electrons move from one molecule to another (energy is released) and ultimately join oxygen along with hydrogen ions - water is formed. Anaerobic organisms do not need oxygen, and for some species of this group it is even poisonous. The electrons released during respiration attach to other inorganic acceptors, such as nitrate, sulfate or carbonate, or (in one form of such respiration - fermentation) to a specific organic molecule, in particular glucose. See also METABOLISM.

CLASSIFICATION

In most organisms, a species is considered to be a reproductively isolated group of individuals. In a broad sense, this means that representatives of a given species can produce fertile offspring by mating only with their own kind, but not with individuals of other species. Thus, the genes of a particular species, as a rule, do not extend beyond its boundaries. However, in bacteria, gene exchange can occur between individuals not only of different species, but also different kinds, therefore, whether it is legitimate to apply here the usual concepts of evolutionary origin and kinship is not entirely clear. Due to this and other difficulties, there is no generally accepted classification of bacteria yet. Below is one of the widely used variants.
KINGDOM OF MONERA

Phylum Gracilicutes (thin-walled gram-negative bacteria)

Class Scotobacteria (non-photosynthetic forms, such as myxobacteria) Class Anoxyphotobacteria (non-oxygen-producing photosynthetic forms, such as purple sulfur bacteria) Class Oxyphotobacteria (oxygen-producing photosynthetic forms, such as cyanobacteria)

Phylum Firmicutes (thick-walled gram-positive bacteria)

Class Firmibacteria (hard-celled forms, such as clostridia)
Class Thallobacteria (branched forms, e.g. actinomycetes)

Phylum Tenericutes (Gram-negative bacteria without a cell wall)

Class Mollicutes (soft-celled forms, such as mycoplasmas)

Phylum Mendosicutes (bacteria with defective cell walls)

Class Archaebacteria (ancient forms, e.g. methane-forming)

Domains. Recent biochemical studies have shown that all prokaryotes are clearly divided into two categories: a small group of archaebacteria (Archaebacteria - "ancient bacteria") and all the rest, called eubacteria (Eubacteria - "true bacteria"). It is believed that archaebacteria, compared to eubacteria, are more primitive and closer to the common ancestor of prokaryotes and eukaryotes. They differ from other bacteria in several significant features, including the composition of ribosomal RNA (rRNA) molecules involved in protein synthesis, the chemical structure of lipids (fat-like substances) and the presence in the cell wall of some other substances instead of the protein-carbohydrate polymer murein. In the above classification system, archaebacteria are considered only one of the types of the same kingdom, which unites all eubacteria. However, according to some biologists, the differences between archaebacteria and eubacteria are so profound that it is more correct to consider archaebacteria within Monera as a special subkingdom. Recently, an even more radical proposal has appeared. Molecular analysis has revealed such significant differences in gene structure between these two groups of prokaryotes that some consider their presence within the same kingdom of organisms to be illogical. In this regard, it is proposed to create a taxonomic category (taxon) of an even higher rank, calling it a domain, and divide all living things into three domains - Eucarya (eukaryotes), Archaea (archaebacteria) and Bacteria (current eubacteria).

ECOLOGY

The two most important ecological functions of bacteria are nitrogen fixation and mineralization of organic residues.
Nitrogen fixation. The binding of molecular nitrogen (N2) to form ammonia (NH3) is called nitrogen fixation, and the oxidation of the latter to nitrite (NO-2) and nitrate (NO-3) is called nitrification. These are vital processes for the biosphere, since plants need nitrogen, but they can only absorb it related forms. Currently, approximately 90% (approx. 90 million tons) of the annual amount of such “fixed” nitrogen is provided by bacteria. The rest is produced by chemical plants or occurs during lightning strikes. Nitrogen in the air, which is approx. 80% of the atmosphere is bound mainly by the gram-negative genus Rhizobium and cyanobacteria. Rhizobium species enter into symbiosis with approximately 14,000 species of leguminous plants (family Leguminosae), which include, for example, clover, alfalfa, soybeans and peas. These bacteria live in the so-called. nodules - swellings formed on the roots in their presence. Bacteria obtain organic substances (nutrition) from the plant, and in return supply the host with fixed nitrogen. Over the course of a year, up to 225 kg of nitrogen per hectare is fixed in this way. Non-legume plants, such as alder, also enter into symbiosis with other nitrogen-fixing bacteria. Cyanobacteria photosynthesize, like green plants, releasing oxygen. Many of them are also capable of fixing atmospheric nitrogen, which is then consumed by plants and ultimately animals. These prokaryotes serve as an important source of fixed nitrogen in the soil in general and rice paddies in the East in particular, as well as its main supplier for ocean ecosystems.
Mineralization. This is the name given to the decomposition of organic residues into carbon dioxide (CO2), water (H2O) and mineral salts. From a chemical point of view, this process is equivalent to combustion, so it requires large amounts of oxygen. The top layer of soil contains from 100,000 to 1 billion bacteria per 1 g, i.e. approximately 2 tons per hectare. Typically, all organic residues, once in the ground, are quickly oxidized by bacteria and fungi. More resistant to decomposition is a brownish organic substance called humic acid, which is formed mainly from lignin contained in wood. It accumulates in the soil and improves its properties.

BACTERIA AND INDUSTRY

Given the variety of chemical reactions bacteria catalyze, it is not surprising that they have been widely used in manufacturing, in some cases since ancient times. Prokaryotes share the glory of such microscopic human assistants with fungi, primarily yeast, which provide most of the processes of alcoholic fermentation, for example, in the production of wine and beer. Now that it has become possible to introduce useful genes into bacteria, causing them to synthesize valuable substances such as insulin, the industrial application of these living laboratories has received a new powerful incentive. See also GENETIC ENGINEERING.
Food industry. Currently, bacteria are used by this industry mainly for the production of cheeses and other fermented milk products and vinegar. The main chemical reactions here are the formation of acids. Thus, when producing vinegar, bacteria of the genus Acetobacter oxidize the ethyl alcohol contained in cider or other liquids to acetic acid. Similar processes occur when cabbage is sauerkraut: anaerobic bacteria ferment the sugars contained in the leaves of this plant into lactic acid, as well as acetic acid and various alcohols.
Ore leaching. Bacteria are used for leaching of low-grade ores, i.e. converting them into a solution of salts of valuable metals, primarily copper (Cu) and uranium (U). An example is the processing of chalcopyrite, or copper pyrite (CuFeS2). Heaps of this ore are periodically watered with water, which contains chemolithotrophic bacteria of the genus Thiobacillus. During their life activity, they oxidize sulfur (S), forming soluble copper and iron sulfates: CuFeS2 + 4O2 in CuSO4 + FeSO4. Such technologies greatly simplify the extraction of valuable metals from ores; in principle, they are equivalent to the processes that occur in nature during the weathering of rocks.
Recycling. Bacteria also serve to transform waste, such as sewage, into less hazardous or even healthy foods. Wastewater is one of the most pressing problems of modern humanity. Their complete mineralization requires huge amounts of oxygen, and in ordinary reservoirs where it is customary to dump this waste, there is no longer enough oxygen to “neutralize” it. The solution lies in additional aeration of the wastewater in special pools (aeration tanks): as a result, the mineralizing bacteria have enough oxygen to completely decompose organic matter, and in the most favorable cases, one of the end products of the process becomes drinking water. The insoluble sediment remaining along the way can be subjected to anaerobic fermentation. To ensure that such water treatment plants take up as little space and money as possible, a good knowledge of bacteriology is necessary.
Other uses. Other important areas of industrial application of bacteria include, for example, flax lobe, i.e. separation of its spinning fibers from other parts of the plant, as well as the production of antibiotics, in particular streptomycin (bacteria of the genus Streptomyces).

COMBATING BACTERIA IN INDUSTRY

Bacteria are not only beneficial; The fight against their mass reproduction, for example in food products or in the water systems of pulp and paper mills, has become a whole area of ​​activity. Food spoils under the influence of bacteria, fungi and its own enzymes that cause autolysis ("self-digestion"), unless they are inactivated by heat or other means. Since the main cause of spoilage is bacteria, the development of systems efficient storage food requires knowledge of the endurance limits of these microorganisms. One of the most common technologies is pasteurization of milk, which kills bacteria that cause, for example, tuberculosis and brucellosis. The milk is kept at 61-63°C for 30 minutes or at 72-73°C for only 15 seconds. This does not impair the taste of the product, but inactivates pathogenic bacteria. Wine, beer and fruit juices can also be pasteurized. The benefits of storing food in the cold have long been known. Low temperatures do not kill bacteria, but they do prevent them from growing and reproducing. True, when frozen, for example, to -25 ° C, the number of bacteria decreases after a few months, but a large number of these microorganisms still survive. At temperatures just below zero, bacteria continue to multiply, but very slowly. Their viable cultures can be stored almost indefinitely after lyophilization (freeze-drying) in a protein-containing medium, such as blood serum. Other known methods of storing food include drying (drying and smoking), adding large amounts of salt or sugar, which is physiologically equivalent to dehydration, and pickling, i.e. placing in a concentrated acid solution. When the acidity of the environment corresponds to pH 4 and below, the vital activity of bacteria is usually greatly inhibited or stopped.

BACTERIA AND DISEASES

STUDYING BACTERIA

Many bacteria are easy to grow in so-called. culture medium, which may include meat broth, partially digested protein, salts, dextrose, whole blood, its serum and other components. The concentration of bacteria in such conditions usually reaches about a billion per cubic centimeter, causing the environment to become cloudy. To study bacteria, it is necessary to be able to obtain their pure cultures, or clones, which are the offspring of a single cell. This is necessary, for example, to determine what type of bacteria infected the patient and what antibiotic this type is sensitive to. Microbiological samples, such as throat or wound swabs, blood, water, or other materials, are highly diluted and applied to the surface of a semi-solid medium, where round colonies develop from individual cells. The hardening agent for the culture medium is usually agar, a polysaccharide obtained from certain seaweeds and indigestible by almost any type of bacteria. Agar media is used in the form of “shoals”, i.e. inclined surfaces, formed in test tubes standing at a large angle when the molten culture medium solidifies, or in the form thin layers in glass Petri dishes - flat round vessels, closed with a lid of the same shape, but slightly larger in diameter. Usually, within a day, the bacterial cell manages to multiply so much that it forms a colony that is easily visible to the naked eye. It can be transferred to another environment for further study. All culture media must be sterile before starting to grow bacteria, and in the future measures should be taken to prevent the settlement of unwanted microorganisms on them. To examine bacteria grown in this way, heat a thin wire loop in a flame, touch it first to a colony or smear, and then to a drop of water applied to a glass slide. Having evenly distributed the taken material in this water, the glass is dried and quickly passed over the burner flame two or three times (the side with the bacteria should be facing up): as a result, the microorganisms, without being damaged, are firmly attached to the substrate. Dye is dripped onto the surface of the preparation, then the glass is washed in water and dried again. Now you can examine the sample under a microscope. Pure cultures of bacteria are identified mainly by their biochemical characteristics, i.e. determine whether they form gas or acids from certain sugars, whether they are able to digest protein (liquefy gelatin), whether they require oxygen for growth, etc. They also check whether they are stained with specific dyes. Sensitivity to certain medications, such as antibiotics, can be determined by placing small disks of filter paper soaked in these substances on a surface infested with bacteria. If any chemical compound kills bacteria, a zone free from them is formed around the corresponding disk.

Collier's Encyclopedia. - Open Society. 2000 .

When we talk about bacteria, we most often imagine something negative. And yet we know very little about them. The structure and activity of bacteria are quite primitive, but, according to some scientists, they are the most ancient inhabitants of the Earth, and for so many years they have not disappeared or become extinct. Many types of such microorganisms are used by humans for their own benefit, while others cause serious diseases and even epidemics. But the harm of some bacteria is sometimes not commensurate with the benefits of others. Let's talk about these amazing microorganisms and get acquainted with their structure, physiology and classification.

Kingdom of bacteria

These are nuclear-free, most often unicellular microorganisms. Their discovery in 1676 is the merit of the Dutch scientist A. Leeuwenhoek, who first saw tiny bacteria under a microscope. But the French chemist and microbiologist Louis Pasteur first began to study their nature, physiology and role in human life in the 1850s. The structure of bacteria began to be actively studied with the advent of electron microscopes. Its cell consists of a cytoplasmic membrane, a ribosome and a nucleotide. The DNA of a bacterium is concentrated in one place (nucleoplasm) and is a ball of thin threads. The cytoplasm is separated from the cell wall by a cytoplasmic membrane; it contains the nucleotide, various membrane systems, and cellular inclusions. The bacterial ribosome consists of 60% RNA, the rest is protein. The photo below shows the structure of Salmonella.

Cell wall and its components

Bacteria have a cellular structure. The cell wall is about 20 nm thick and, unlike higher plants, does not have a fibrillar structure. Its strength is ensured by a special cover called a bag. It consists primarily of a polymeric substance - murein. Its components (subunits) are connected in a certain sequence into special polyglycan strands. Together with short peptides, they form a macromolecule resembling a network. This is the murein sac.

Organs of locomotion

These microorganisms are capable of active movement. It is carried out due to plasmatic flagella, which have a helical structure. Bacteria can move at speeds of up to 200 microns per second and turn around their axis 13 times per second. The ability of flagella to move is ensured by a special contractile protein - flagellin (an analogue of myosin in muscle cells).

Their dimensions are as follows: length - up to 20 microns, diameter - 10-20 nm. Each flagellum extends from a basal body, which is embedded in the bacterial cell wall. The organs of locomotion can be single or arranged in whole bunches, as, for example, in spirilla. The number of flagella may depend on environmental conditions. For example, Proteus vulgaris, with poor nutrition, has only two subpolar flagella, whereas under normal development conditions there can be from 2 to 50 in bundles.

Movement of microorganisms

The structure of the bacterium (diagram below) is such that it can move quite actively. Movement in most cases occurs due to propulsion and occurs mainly in a liquid or moist environment. Depending on the active factor, in other words, a type of external stimulus, it can be:

• chemotaxis is the directed movement of bacteria towards nutrients or, conversely, away from any toxins;
• aerotaxis - movement towards oxygen (in aerobes) or away from it (in anaerobes);
• phototaxis - a reaction to light, manifested in movement, is characteristic primarily of phototrophs;
• magnetotaxis - a reaction to changes in the magnetic field, is explained by the presence of special particles (magnetosomes) in some microorganisms.

In one of the listed ways, bacteria, the structural features of which allow them to move, can create clusters in places with optimal conditions for their livelihoods. In addition to flagella, some species have numerous thinner filaments - they are called “fimbriae” or “pili”, but their function has not yet been sufficiently studied. Bacteria that do not have special flagella are capable of gliding movement, although it is characterized by a very low speed: approximately 250 microns per minute.

The second small group of bacteria is autotrophs. They are capable of synthesizing organic substances from inorganic substances, can partially absorb atmospheric carbon dioxide, and are chemotrophs. These bacteria occupy a very important place in the cycle of chemical elements in nature.

There are also two groups of true phototrophs. The structural features of bacteria in this category are that they contain a substance (pigment) bacteriochlorophyll, which is similar in nature to plant chlorophyll, and since they lack photosystem II, photosynthesis occurs without the release of oxygen.

Reproduction by division

The main method of reproduction is the division of the original mother cell in two (amitosis). For forms that have an elongated shape, this always occurs perpendicular to the longitudinal axis. The structure of the bacterium undergoes short-term changes: a transverse partition is formed from the edge of the cell to the middle, along which the maternal organism is then divided. This explains the old name of the kingdom - Drobyanki. After division, cells can remain connected in unstable, loose chains.

These are the distinctive structural features of certain types of bacteria, for example, streptococci.

Sporulation and sexual reproduction

The second method of reproduction is sporulation. It is directly related to the desire to adapt to unfavorable conditions and is aimed at surviving them. In some rod-shaped bacteria, spores are formed endogenously, that is, inside the cell. They are very resistant to heat and can be preserved even after prolonged boiling. The formation of spores begins with various chemical reactions in the mother cell, during which about 75% of all its proteins are decomposed. Then division occurs. In this case, two daughter cells are formed. One of them (the smaller one) is covered with a thick shell, which can occupy up to 50% by volume - this is the spore. It remains viable and ready to germinate for 200-300 years.

Some species are capable of sexual reproduction. This process was first discovered in 1946, when the structure of the cell of the bacterium Escherichia coli was studied. It turned out that partial transfer of genetic material is possible. That is, DNA fragments are transferred from one cell (donor) to another (recipient) through the process of conjugation. This is done with the help of bacteriophages or by transformation.

The structure of the bacterium and the features of its physiology are such that under ideal conditions the division process occurs constantly and very quickly (every 20-30 minutes). But in the natural environment it is limited by various factors (sunlight, nutrient medium, temperature, etc.).

The classification of these microorganisms is based on the different structure of the bacterial cell wall, which determines the preservation of the aniline dye in the cell or its leaching. This was identified by H. K. Gram, and subsequently, in accordance with his name, two large divisions of microorganisms were identified, which we will discuss below.

Gram-positive bacteria: structural features and vital functions

These microorganisms have a multilayer murein cover (30-70% of the total dry mass of the cell wall), due to which the aniline dye is not washed out of the cells (in the photo above, the structure of a gram-positive bacterium is schematically shown on the left, and the gram-negative one on the right). Their peculiarity is that diaminopimelic acid is often replaced by lysine. The protein content is much lower, and polysaccharides are absent or linked by covalent bonds. All bacteria in this department are divided into several groups:

1. Gram-positive cocci. They are single cells or groups of two, four or more cells (up to 64), held together by cellulose. By type of nutrition, these are, as a rule, obligate or facultative anaerobes, for example, lactic acid bacteria from the Streptococcal family, but there may also be aerobes.
2. Non-spore-forming rods. By the name you can already understand the structure of the bacterial cell. This group includes anaerobic or facultatively aerobic lactic acid species from the Lactobacillus family.
3. Spore-forming rods. They are represented by only one family - Clostridia. These are obligate anaerobes capable of forming spores. Many of them form characteristic chains or threads of individual cells.
4. Corynemorphic microorganisms. The external structure of the bacterial cell of this group can change significantly. Thus, the rods can become club-shaped, short, cocci or weakly branched forms. They do not form endospores. These include propionic acid, streptomycete bacteria, etc.
5. Mycoplasmas. If you pay attention to the structure of the bacterium (the diagram in the figure below - the arrow points to the DNA chain), you can note that it does not have a cell wall (instead there is a cytoplasmic membrane) and, therefore, is not stained with aniline dye, so it cannot be classified as this section based on Gram staining. But according to recent research, mycoplasmas originated from gram-positive microorganisms.

Gram-negative bacteria: functions, structure

In such microorganisms, the murein network is very thin, its share of the dry mass of the entire cell wall is only 10%, the rest is lipoproteins, lipopolysaccharides, etc. Substances obtained during Gram staining are easily washed out. By type of nutrition, gram-negative bacteria are phototrophs or chemotrophs; some species are capable of photosynthesis. The classification within the department is in the process of formation; various families are combined into 12 groups, based on the characteristics of morphology, metabolism and other factors.

The importance of bacteria for humans

Despite their seemingly invisibility, bacteria are of great importance for humans, both positive and negative. The production of many food products is impossible without the participation of individual representatives of this kingdom. The structure and activity of bacteria allow us to obtain many dairy products (cheeses, yoghurts, kefir and much more). These microorganisms are involved in the processes of pickling and fermentation.

Numerous types of bacteria are causative agents of diseases in animals and humans, such as anthrax, tetanus, diphtheria, tuberculosis, plague, etc. But at the same time, microorganisms are involved in various industrial production: this is genetic engineering, production of antibiotics, enzymes and other proteins, artificial decomposition of waste (for example, methane digestion of wastewater), metal enrichment. Some bacteria grow on substrates rich in petroleum products, and this serves as an indicator when searching for and developing new deposits.

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