Methanogenesis

Recent genomic sequencing, proteomic analyses, and development of genetic systems continue to expand one's understanding of methanogenesis and the Archaea. The conversion of the methyl group of acetate to methane (acetate fermentation pathway) produces about two-thirds of the annual production, whereas one-third derives from the reduction of carbon dioxide with electrons supplied from the oxidation of formate or hydrogen (carbon dioxide reduction pathway). Thus, the methanogens rely on the first two groups to supply substrates for growth and methanogenesis. Methanogens are the main constituency of the Euryarchaeota and are subdivided into five orders, including such as Methanobacteriales, Methanococcales and Methanomicrobiales; each with distinctive characteristics. Methanofuran (MF) and tetrahydromethanopterin (THMPT) function as one-carbon carriers, the latter coenzyme also functioning in methylotrophic microbes from the Bacteria domain. A proteomic and transcriptional analysis of cold adaptation has revealed the thermal regulation of several genes essential for methanogenesis by dismutation of the methyl group of trimethylamine. The extent of regulation of genes essential for methanogenesis and other fundamental processes in response to temperature is consistent with a role in providing the cell with an ecological advantage in cold environments. The genome sequences of M. acetivorans, M. mazei, and M. thermophila harbor two homologs of mtaA, three homologs of mtaB, and three homologs of mtaC encoding enzymes specific for methanogenesis from methanol.