Methanogen Genes and the Molecular Biology of Methane Biosynthesis

Methanogenic bacteria (methanogens) produce methane (natural gas; sometimes called biogas) as the end product of their energy-generating metabolism. This biochemical process, termed methanogenesis, is the rate-limiting and final step in the anaerobic biodegradation of organic compounds. It occurs naturally in freshwater and marine sediments, marshes, paddy fields, geothermal springs, and in the digestive tracts of invertebrates and vertebrates. Termites and ruminants are major sources of biologically produced methane. Approximately 65% of the methane released to the atmosphere, equal to approximately 1% of the atmospheric carbon cycle, is of biological origin; the remainder is produced geologically from wells, mines, and natural vents (Ehhalt, 1974; Daniels, 1984).