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Concept
Methanogen
Summary
Methanogens are microorganisms that produce methane as a metabolic byproduct in hypoxic conditions. They are prokaryotic and belong to the domain Archaea. All known methanogens are members of the archaeal phylum Euryarchaeota. Methanogens are common in wetlands, where they are responsible for marsh gas, and in the digestive tracts of animals such as ruminants and many humans, where they are responsible for the methane content of belching in ruminants and flatulence in humans. In marine sediments, the biological production of methane, also termed methanogenesis, is generally confined to where sulfates are depleted, below the top layers. Moreover, methanogenic archaea populations play an indispensable role in anaerobic wastewater treatments. Others are extremophiles, found in environments such as hot springs and submarine hydrothermal vents as well as in the "solid" rock of Earth's crust, kilometers below the surface.
Methanogens are coccoid (spherical shaped) or bacilli (rod shaped). There are over 50 described species of methanogens, which do not form a monophyletic group (since haloarchaea emerged from within them), although all known methanogens belong to Euryarchaeota. They are mostly anaerobic organisms that cannot function under aerobic conditions, but recently a species (Candidatus Methanothrix paradoxum) has been identified that can function in anoxic microsites within aerobic environments. They are very sensitive to the presence of oxygen even at trace level. Usually, they cannot sustain oxygen stress for a prolonged time. However, Methanosarcina barkeri is exceptional in possessing a superoxide dismutase (SOD) enzyme, and may survive longer than the others in the presence of O2. Some methanogens, called hydrogenotrophic, use carbon dioxide (CO2) as a source of carbon, and hydrogen as a reducing agent.
The reduction of carbon dioxide into methane in the presence of hydrogen can be expressed as follows:
CO2 + 4 H2 → CH4 + 2H2O
Some of the CO2 reacts with the hydrogen to produce methane, which creates an electrochemical gradient across the cell membrane, used to generate ATP through chemiosmosis.
Official source
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