Methanogenic

Methanogenic organisms, commonly called methanogens, are a group of strictly anaerobic archaea that produce methane as a metabolic end product. They thrive in anoxic environments where other organisms cannot survive, including wetlands, lake and marine sediments, the guts of ruminant animals and termites, anaerobic digesters, and certain hydrothermal and tectonically active habitats.

Methanogenesis converts simple carbon substrates into methane through several pathways. Hydrogenotrophic methanogenesis reduces CO2 with H2 to CH4; acetoclastic methanogenesis splits acetate into CH4 and CO2; and methylotrophic methanogenesis oxidizes methylated compounds such as methanol or methylamines. Energy conservation occurs via electron transport chains across the archaeal cell membrane.

The final step in most pathways is catalyzed by methyl-coenzyme M reductase (MCR), producing methane from a methyl group bound to coenzyme M. Methanogens employ unique coenzymes, such as coenzyme M and coenzyme B, and possess distinctive archaeal lipids and enzyme systems. They are generally oxygen-sensitive and strictly anaerobic.

Taxonomically, methanogens form a diverse group within the domain Archaea, primarily in the phylum Euryarchaeota. Major orders include Methanobacteriales, Methanomicrobiales, Methanococcales, Methanopyrales, and Methanosarcinales, which contain species with hydrogenotrophic, acetoclastic, and methylotrophic lifestyles.

They play a central role in the global carbon cycle by producing methane in anaerobic environments and contribute to greenhouse gas emissions when released to the atmosphere. In engineered systems such as anaerobic digesters, methanogens convert organic matter into biogas (methane and carbon dioxide) for renewable energy and waste treatment.