Elongated rods (0.4-0.8 micron wide) can form long chains, non-motile, Gram-positive or variable. Produce methane from H2 + CO2 and formate for some species ( Methanobacterium formicicum ) and sometimes secondary alcohols. Mesophilic or thermophilic organisms, some species are acidophilic and alkaliphilic. The wall contains a pseudomurein. These organisms are common in all anaerobic habitats. DNA contains 33 to 50 mol% G+ C The genus includes 13 species, including the type species Methanobacterium formicicum .
