Catabolic Pathways and Enzymes Involved in Anaerobic Methane Oxidation

Microbes use two distinct catabolic pathways for life with the fuel methane: aerobic methane oxidation carried out by bacteria and anaerobic methane oxidation carried out by archaea. The archaea capable of anaerobic oxidation of methane, anaerobic methanotrophs (ANME), are phylogenetically related to methanogens. While the carbon metabolism in ANME follows the pathway of reverse methanogenesis, the mode of electron transfer from methane oxidation to the terminal oxidant is remarkably versatile. This chapter discusses the catabolic pathways of methane oxidation coupled to the reduction of nitrate, sulfate, and metal oxides. Methane oxidation with sulfate and metal oxides are hypothesized to involve direct interspecies electron transfer and extracellular electron transfer. Cultivation of ANME, their mechanisms of energy conservation, and details about the electron transfer pathways to the ultimate oxidants are rather new and quickly developing research fields, which may reveal novel metabolisms and redox reactions. The second section focuses on the carbon catabolism from methane to CO2 and the biochemistry in ANME with its unique enzymes containing Fe, Ni, Co, Mo, and W that are compared with their homologues found in methanogens