Enzymology of the fermentation of acetate to methane by Methanosarcina thermophila

Biologically-produced CH4 derives from either the reduction Of CO2 or the methyl group of acetate by two separate pathways present in anaerobic microbes from the Archaea domain. Elucidation of the pathway for CO2 reduction to CH4, the first to be investigated, has yielded several novel enzymes and cofactors. Most of the CH4 produced in nature derives from the methyl group of acetate. Methanosarcina thermophila is a moderate thermophile which ferments acetate by reducing the methyl group to CH4 with electrons derived from oxidation of the carbonyl group to CO2. The pathway in M. thermophila is now understood on a biochemical and genetic level comparable to understanding of the CO2-reducing pathway. Enzymes have been purified and characterized. The genes encoding these enzymes have been cloned, sequenced, transcriptionally mapped, and their regulation defined on a molecular level. This review emphasizes recent developments concerning the. enzymes which are unique to the acetate fermentation pathway in M. thermophila.