Methanogens are organisms that make methane via a unique metabolic pathway with unique enzymes and cofactors. All of the methanogens are lithotrophs that can make their own energy only by methanogenesis.
Most methanogens can make methane from carbon dioxide and hydrogen gas.
Some methanogens can use other 1-carbon compounds, such as carbon monoxide or formic acid, and a few others can use acetate and methylamines. Enzymes in the metabolic pathway are very oxygen sensitive. Bacteria in the Methanosarcina family are slow developers and are sensitive to sudden change in physical and chemical conditions, but they are capable of growth in a variety of substrates. This metabolic diversity makes them an especially attractive target for genetic analysis. It has also been reported that Methanosarcina barkeri fusaro lives in the rumen of cattle.