Anaerobes

Anaerobes

 

(also known as anaerobic organisms, an-aerobionts, and anoxybionts), organisms capable of living and developing in the absence of free oxygen and obtaining energy for vital activities by the breakdown of organic and inorganic substances. The term “anaerobes” was introduced by L. Pasteur, who in 1861 discovered the microbes of butyric acid fermentation.

Anaerobes are classified as obligate or facultative. The obligate anaerobes develop well in the complete absence of oxygen. The vegetative forms of these anaerobes die quickly upon coming into contact with the air, while the spores are resistant to oxygen. They are devoid of enzyme systems which are capable of transferring hydrogen to free oxygen. The obligate anaerobes include the vectors of tetanus, gas gangrene, certain streptococci, and other pathogenic microbes. There are also the bifid bacteria, which live in human and animal intestines and play an antagonistic role in relation to harmful microbe flora, and bacteria (including butyric acid bacteria), which develop in media devoid of oxygen (deep portions of a wound, maturing cheese, the mud of benthic deposits, and so forth). Obligate anaerobes are not encountered among multicelled organisms.

Facultative anaerobes are capable of developing both with and without oxygen. Among the facultative anaerobes are microorganisms (yeasts, pyogenic cocci, typhoid bacillus, anthrax bacteria, and others), certain protozoans and multicelled organisms which dwell in rotting mud (ciliata, oligochaeta, mollusks, and others), and parasites in the intestines of large animals (infusoria, nematodes, and platyhelminths). In the facultative anaerobes, the relationship to oxygen varies: in some, development is better in its absence, and in others, development is better in its presence. This is because in many facultative anaerobes, in addition to the enzymes which are capable of transferring hydrogen to various easily reducible compounds (as occurs in the obligate anaerobes), there are also enzymes which transfer the hydrogen to the free oxygen. For this reason, the difference between the anaerobes and the aerobes is to a large extent hypothetical. Anaerobes are found widely in nature (in the soil, in sea water at great depths, in benthic deposits, and so forth), and they play an important role in the conversion of organic and inorganic matter.

REFERENCES

Brand, T. Anaerobioz u bespozvonochnykh. Moscow, 1951. (Translated from English.)
Ierusalimskii, N. D. Osnovy fiziologii mikrobov. Moscow, 1963.
Metabolizm bakterii. Moscow, 1963. (Translated from English.)