Methanogen

Methanogens are microorganisms that produce methane as a metabolic byproduct in hypoxic conditions. They belong to the domain Archaea and are members of the phylum Euryarchaeota. Methanogens are common in wetlands, where they are responsible for marsh gas, and can occur in the digestive tracts of animals including ruminants and humans, where they are responsible for the methane content of belching and flatulence.^[1] In marine sediments, the biological production of methane, termed methanogenesis, is generally confined to where sulfates are depleted below the top layers.^[2] Methanogens play an indispensable role in anaerobic wastewater treatments.^[3] Other methanogens 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 in the deep biosphere.