Methanogen
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Methanogens are Archaea that produce methane as a metabolic by-product. They are common in wetland, where they are responsible for marsh gas, and in the guts of animals such as ruminants and human, where they are responsible for flatulence. They are also common in soils in which the oxygen has been depleted. Others are extremophiles, found in environments such as hot springs and submarine hydrothermal vents.
Methanogens are anaerobic. All methanogens are rapidly killed in the presence of oxygen. Some, called hydrotrophic, use carbon dioxide as a source of carbon and hydrogen as a source of energy (hydrogen functions as a reducing agent). Some of the carbon dioxide is reacted with the hydrogen to produce methane, which produces a proton motive force across a membrane, which is used to generate ATP. In contrast, plants and algae use water as their reducing agent. Other methanogens use acetate (CH3COO-) as a source of carbon and a source of energy. This type of matabolism is referred to as "acetotrophic" or "aceticlastic," breaking down acetate to produce carbon dioxide and methane. Other methanogens are able to utilize methylated compunds such as methyalmines, methanol, and methy thiols, as well.
Ecologically, methanogens play the vital role in anaerobic environments of removing excess hydrogen and fermentation products that have been produced by other forms of anaerobic respiration. Methanogens typically thrive in environments in which all other electron acceptors (such as oxygen, nitrate, sulfate, and trivalent iron) have been depleted.
There are over 50 species of methanogens, divided into three classes - the Methanobacteria, Methanococci, and Methanopyri. All are included among the Euryarchaeota. They are paraphyletic, and there is some reason to suppose the Methanococci are paraphyletic as well.ja:メタン菌