Methanobacterium

A genus of strictly anaerobic bacteria that reduce CO using molecular hydrogen, H2, to give methane. They show a number of features that distinguish them from other bacteria, and are now classified as a separate group, the Archaebacteria. Methanobacteria are found in the anaerobic sediment at the bottom of ponds and marshes (hence marsh gas is the common name for methane) and as part of the microflora of the rumen in cattle and other herbivorous mammals.