Anaerobiosis

ANAEROBIOSIS (from Greek a- negative part, aer- air and bios-life), life without air, more precisely without one part of it - without O. This concept is therefore more precisely defined by the word anoxibiosis (oxygenium-oxygen). Under an-oxibiosis is understood the aggregate of exchange processes in the whole organism or its part, proceeding without the participation of oxygen. Organisms capable of developing normally without access to oxygen are called anaerobes, anaerobionts, anoxibionts. The first example of A. was established in 1861 by Pasteur, who showed that microorganisms causing butyric acid fermentation not only can develop without oxygen but also die when exposed to it. The possibility of the existence of complete A. for a long time seemed unlikely. The hypothesis of so-called microaerophilia was put forward, according to which anaerobes differ only in that they can limit themselves to extremely small amounts of free O. However, as early as the end of the last century, Netsky, Beijerinck and others proved that some microorganisms can develop in media where no finest reagents can detect the presence of free O. Those organisms that can develop exclusively without access to O or at its negligible partial pressure are designated as obligate anaerobes. According to Khudyakov, bacteria of butyric acid fermentation die when exposed to air after 4-15 hours. According to Bachmann, vegetative forms of anaerobic bacteria die after 10-60 min., spores - after 8 days on air. The harmful effect of free O on anaerobes was attempted to be explained by peculiarities of their enzymatic system. It is characterized by the absence of catalase, capable of destroying the harmful hydrogen peroxide formed by anaerobes when in contact with atmospheric air. The fungus Actinomyces necrophorus in 4-6 hours when cultivated on air accumulates hydrogen peroxide to a concentration of 1:10,000. The growth of tetanus bacilli completely ceases when hydrogen peroxide is added to the nutrient solution to a concentration of 3:1,000,000. For a considerable part of anaerobes, however, the absence of O is not the optimal condition. Some of them develop better in the presence of small amounts of O. Khudyakov showed that anaerobic bacteria of tetanus and malignant edema not only multiply in an atmosphere containing 0.5% oxygen but actually bind it. In these microbes, therefore, oxibiotic processes can also proceed, although to a very weak degree. Obligate anaerobes can be gradually accustomed to life in an atmosphere containing significant amounts of O. They can then be returned to pure A., gradually decreasing the amounts of free O provided to them. On the other hand, some microbes that usually live aerobically, e.g., Bacillus lactis aerogenes, can switch to anaerobic existence if provided with sufficient amounts of substances capable of fermentation, e.g., sugar. The ability for A. to some extent also depends on temperature. Thus, some thermophilic bacteria at +40°C develop better under anaerobic conditions than aerobic ones. Among bacteria, anaerobes include, among others, the tetanus bacillus and putrefaction microbes. To facultative anaerobes, capable of developing both in the presence and absence of free oxygen, belong the anthrax bacillus, the bacillus of typhoid fever, pyogenic cocci, proteus, prodigiosus and others. Obligate aerobes are the causative agents of plague, influenza, many aquatic and pigment-forming bacteria. Among protozoa, A. has been established in parasitic intestinal infusorians (Opalina, Entodinium, Isotricha). Trypanosoma Lewisi and Leishmania tropica in cultures are obligate aerobes. Spirochetes occupy an intermediate position, designated as "aerotropic anaerobes". Among multicellular invertebrates developing without the participation of free O are parasitic intestinal worms, ascarids, tapeworms. Bunge showed that ascarids can exist for several days with complete lack of access to O. To some extent, medical leeches living in mud and vinegar eels (threadworm - Anguillula aceti) are also anaerobes. Complete A. is a phenomenon little spread among multicellular animals and plants. However, deepening the question of the participation of O in the life processes of organisms showed that between aerophilic and aerophobic organisms (it would be more precise - oxigenophilic and oxigenophobic) there are all transitions, and anoxibiotic processes are not alien to any cell. The need of different organisms for O depends on their organization, on that complex of enzymes which their cells possess, on the conditions of the environment to which they are adapted, on the amount of energy developed by the cell or organism. The exchange processes in the cell, accompanied by the release of free energy due to the breakdown of complex food substances, proceed in two phases: anaerobic (anoxibiotic) and aerobic (oxibiotic). The first phase proceeds without the participation of free O (fermentation phase), the second phase consists in the "burning" of the products formed during the first phase of breakdown, forming mainly carbon dioxide and water. The presence of anoxibiotic "respiration" in higher plants was established as early as 1869 by Lechartier and Bellami, who showed that fresh apples in the absence of access to O form alcohol and acetic acid from disappearing sugar. It is also known that lupine seeds in anoxibiotic conditions can release a sprout, but only if sugar is present in the nutrient solution. The two phases of the respiration process in plants were very clearly characterized by Pfeffer in 1878. The term "intramolecular respiration" introduced by him corresponds to the fermentation phase, and this phase was considered by him as a preliminary preparation for the second, oxygen phase. For muscle cells, these processes were studied by Fletcher, Hopkins and others. Both in a state of rest and during work, the muscle cell in the anoxibiotic phase breaks down glycogen and accumulates lactic acid; in the following oxibiotic phase, a considerable part of the lactic acid is resynthesized into glycogen, while a smaller part "burns", decomposes with the participation of O into carbonic acid and water. In rapidly growing embryonic cells, the first, oxygen-free phase of fermentation is more strongly expressed than in normal cells of the adult organism. Through the work of Warburg, it was established that the intensification of the anaerobic phase at the expense of oxibiotic processes is also characteristic of other cells with uncontrollable growth - of cells of malignant tumors. Corresponding to the intensification of the first phase, these cells accumulate significantly more lactic acid than normal ones. Fischer succeeded by the action of small amounts of arsenic on normal cells (under tissue culture conditions) to turn them into sarcomatous cells. The action of arsenic in this case is explained by its paralyzing effect on the oxibiotic phase of respiration. Cells of warm-blooded animals belong to facultative aerobes: the necessary O they receive inside tissues from the unstable compound of O with Hb. However, some cells, e.g., cells of the central parts of the liver lobule, apparently can do without O almost completely, because, according to the conditions of blood circulation, the central parts of the lobule receive only venous blood (see Liver). Some warm-blooded animals, however, during the period of winter hibernation, at low ambient temperature, when their vital activity is greatly reduced, can cover a considerable part of their necessary energy by anoxibiotic processes, but with an increase in ambient temperature the metabolic processes in them intensify and the need for O increases. Poikilothermic animals (e.g., frogs) also tolerate the absence of O less well at high temperature than at low temperature. Generally, animals tolerate the anoxibiotic state the better the slower their metabolic processes proceed (experiments of Claude Bernard on birds). An intermediate position is occupied by so-called facultative anaerobes, as e.g., some yeast fungi; under anaerobiosis, products of incomplete breakdown (e.g., alcohol) are formed almost exclusively. The same fungi, when oxygen is available, do not form alcohol but carry the breakdown of complex carbohydrates and other substances to the simplest compounds. For a certain amount of disappeared complex substance in this process, a considerably larger amount of released energy corresponds. It is calculated that in the breakdown of glucose into alcohol and carbonic acid only 3-5% of the energy that glucose gives on complete combustion is released. In nature, anaerobic organisms are found where access to O is difficult - in the depths of the soil, at the bottom of bodies of water. They are often found in symbiosis with aerobic organisms that absorb all available O. Anaerobes play an important role in the phenomena of putrefaction and other processes of decomposition and transformation of organic substances, as well as in the processing of some mineral compounds (sulfur, nitrogen). Pathogenic anaerobes develop in the depths of tissues, where all O is bound by surrounding cells, e.g., the tetanus bacillus in the depths of punctured wounds. In the closed cavities of many animals, parasitic worms develop anaerobically.

All the energy they need is drawn from anoxibiotic processes. The reserve substance in many of them is glycogen. Valeric acid was found as a product of anoxibiotic processes in ascarids. In certain special cases, anaerobiosis is achieved chemically (Warburg): oxybiotic processes are paralyzed by adding potassium cyanide to the liquid medium in which the organism or tissue under study is placed. Artificial conditions of A. are created in a number of production processes based on fermentation.