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Optional anaerobes are what? Examples and classification

Representatives of the kingdom Drobyanka, as well as some algae and parasitic worms and fungi are characterized by a special form of oxidation of organic substances, occurring in the absence of molecular oxygen or at a low concentration. Organisms living in an oxygen-free environment are anaerobes. Optional and obligate species, as well as examples of their livelihoods and classification will be considered by us in this article.

Why Breath Needs

Let's clarify that we will talk about the so-called internal, or cellular, breathing. Its main task is to obtain energy from substances, primarily glucose, entering the cell. If oxygen participates in oxidation processes, organisms are called aerobes. If the individual receives a portion of energy by substrate phosphorylation without an influx of O 2 molecules, these are anaerobic organisms.

This term, introduced by Louis Pasteur in 1861, initially concerned only some types of prokaryotes that carry out oleic acid fermentation. In modern microbiology, this name combines all organisms that use oxygen, not nitrates, hydrogen or organic compounds in the form of a final acceptor. The respiratory chains of aerobes, facultative and obligate anaerobes, which we will consider below, carry out energy metabolism processes , through which glucose, amino acids and fats are oxidized to CO 2 , H 2 O and NH 3. Note also that anaerobic metabolism is less effective than oxygen. This is due to the fact that for growth in the absence of oxygen requires more substrate, for example, glucose. Energy as a result of anoxic cleavage is also released less. For example, glycolysis - 2 moles of ATP from each molecule of glucose, whereas in the case of oxygen cleavage, 36 molecules of adenosine triphosphate are synthesized.

Variety of anaerobes

The modern classification includes various types of organisms, primarily bacteria. For example, facultative anaerobes are single- or multicellular species of prokaryotes, plants or fungi whose catabolism does not require the presence of O 2 . But its presence in the cytosol of the cell or in the external environment is not fatal for the individual. For example, they include bacteria-causative agents of human diseases: anginal streptococcus, hemolytic staphylococcus. Optional anaerobes are also some kinds of bacteria, whose vital activity is useful to humans. So, thermophilic streptococcus, splitting lactose to C 3 H 6 O 3, is used in the production of fermented milk products: sour cream, ryazhenka, soft cheese varieties. In medicine, it is indispensable in the production of probiotics, used to prevent enterocolitis and diarrhea of various etiologies. Continuing to consider the classification of anaerobes, let us pay attention to macro-aerophiles living in an environment where the O 2 concentration does not exceed 0.5-1%.

Among them, many species pathogenic to humans, for example, streptococci, causing pharyngitis and Lyme disease. Other types of facultative aerobes inhabit the human gastrointestinal tract, provoking various types of gastritis, as well as gastric ulcer. The causative agent of the above diseases is the well-known Helicobacter. A large number of macro-aerophiles belonging to facultative anaerobes require an increased content of carbon dioxide for their metabolism. Such prokaryotes are called capnophiles.

Respiratory chain of facultative anaerobes

We will continue to study the features of the metabolism of this group of bacteria. In laboratory conditions it was established that they can be determined in a solution of organic substances containing a different mass fraction of oxygen. These anaerobes will accumulate closer to the bottom of the tube, where the O 2 concentration is low. This is due to the fact that facultative anaerobes are bacteria, to which small doses of oxygen do not have a serious damaging effect. Earlier, we mentioned that in bacteria of some groups, for example, denitrifying, the final acceptor is nitrates, nitrogen compounds that have been oxidized.

In the respiratory chain of facultative anaerobes, a nitrate reductase enzyme participates in catalytic reactions, providing the transport of an electron to the NO 3 - ion. Such bacteria include prokaryotes from the genera Micrococcus, Pseudomonas. They live both in water bodies and in moist soil. These bacteria use the oxygen of nitrate acid salts as an electron acceptor, carrying out the so-called "nitrate respiration".

The role of enzymes in the catabolism of bacteria

In the metabolism of microorganisms, an important function is performed by a catalytic system represented by cytochromes, catalase, flavin enzymes, peroxidase. Thus, flavoproteins play the role of an element that connects the substrate and oxygen molecules, which are then reduced to hydrogen peroxide. Given the fact that facultative anaerobes are microorganisms whose metabolism occurs both in the presence of O 2 and in an oxygen-free environment, two types of these prokaryotes can be distinguished. Let us consider them in more detail.

Types of optional bacteria

Aerobes, anaerobes, facultative anaerobes, microaerophiles are a fairly complete list of prokaryotes whose respiratory chains depend in part or in whole on the presence of oxygen molecules in the nutrient solution. For example, allertolerant bacteria that oxidize milk sugar develop in the presence of O 2 , but do not use it in the respiratory chain. They synthesize energy through fermentation reactions. Other facultative anaerobes, for example, yeast cells, depending on the chemical composition of the substrate, are able to pass from the fermentation process to oxygen breathing.

Cytochromes and their importance in metabolism

Complex proteins - proteins, including heme (iron-containing prosthetic group) - are cytochromes. Participating in cellular respiration in bacteria and yeast, they are both donors and electron acceptors. The iron atom of the prosthetic group reversibly changes its oxidation state from +2 to +3. This allows cytochromes to transport electrons from dehydrogenases to acetaldehyde or pyruvic acid. Optional aerobes, anaerobes and microaerophiles may have electron acceptors represented by carbon dioxide molecules, hydrogen ions, amino acids.

The importance of prokaryotic anaerobes in the cycle of substances in nature

It is impossible to imagine the cycles of the main organogenic elements, for example, nitrogen, occurring in the Earth's biosphere, without the participation of microorganisms. Since facultative anaerobes are primarily denitrifying bacteria, they are able to reduce soil soluble nitric acid salts to N 2 O or to free nitrogen. Denitrification is most active in soils containing an excessive amount of water and nitrogen fertilizers. As a result of chemical reactions, the molecules of free nitrogen again return to the atmosphere, closing the cycle of its transformations in nature.

Probiotics and their significance for humans

Of the more than 500 species of bacteria inhabiting the human gastrointestinal tract, an important place is occupied by facultative anaerobes. This is primarily representatives of the genera Lactobacillus, Streptococcus, Candida. The largest number is located in the large intestine. In it, bacteria regulate peristalsis (movement of food masses) and synthesize vitamins of group B and K. They also participate in the production of protective proteins - immunoglobulins, and they, in turn, ensure bactericidal intestinal contents. Medical researches have established that the content of bacteria in the human large intestine is sharply reduced after the infectious diseases, due to inflammatory processes, and also after antibiotic therapy.

To restore the microflora of the gastrointestinal tract, drugs are used - probiotics. They include useful facultative anaerobes - bifido- and lactobacilli. Getting into the large intestine of a person, they ensure its normal functioning and reduce the abovementioned negative consequences. The most commonly used probiotics, which have proved themselves in gastroenterology, are Hilak Forte, Linex, Lactovit.

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