methanogene

Methanogens are a group of strictly anaerobic archaea that produce methane as a metabolic end product. They are commonly referred to as methanogens, though some older or non-English sources use the term methanogene. These organisms occupy oxygen-free environments and play a key role in the global carbon cycle by converting reduced compounds into methane.

Metabolism in methanogens occurs through methanogenesis, a set of biochemical pathways that reduce carbon substrates to methane. The main routes include hydrogenotrophic methanogenesis (CO2 reduced with hydrogen to CH4), acetoclastic methanogenesis (acetate split into methane and CO2), and methylotrophic methanogenesis (utilizing methylated compounds such as methanol or methylamines). The final step typically involves the enzyme methyl-coenzyme M reductase, and many methanogens rely on nickel-containing cofactors and the coenzymes coenzyme M and coenzyme B.

Ecology and distribution: Methanogens are obligate anaerobes found in wetlands and other anaerobic sediments, rice paddies, the guts of ruminant animals and termites, anaerobic digesters, and certain geothermal or marine environments. In these habitats, they often occupy the terminal step of organic matter decomposition, consuming substrates produced by syntrophic partners.

Taxonomy and diversity: Methanogens form a deep lineage within the Archaea, primarily associated with the phylum Euryarchaeota, and include genera such as Methanobacterium, Methanococcus, Methanosarcina, and Methanospirillum. They are biochemically distinct from bacterial methane producers.

Importance and applications: Methanogens contribute to natural methane emissions and are central to anaerobic digestion processes used in waste treatment and biogas production. They are studied for bioenergy, greenhouse gas dynamics, and potential biotechnological applications, as well as ecological interactions with other microbes and responses to environmental change.