Enzymology of the fermentation of acetate to methane by Methanosarcina thermophila

Biologically‐produced CH 4 derives from either the reduction of CO 2 or the methyl group of acetate by two separate pathways present in anaerobic microbes from the Archaea domain. Elucidation of the pathway for CO 2 reduction to CH 4 , the first to be investigated, has yielded several novel enzymes and cofactors. Most of the CH 4 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 CH 4 with electrons derived from oxidation of the carbonyl group to CO 2 . The pathway in M. thermophila is now understood on a biochemical and genetic level comparable to understanding of the CO 2 ‐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 .