methanogenesis

Methanogenesis is a biological process by which certain archaea produce methane as a metabolic end product. Occurring in strictly anaerobic environments, including wetlands, sediments, the guts of ruminants and some invertebrates, and anaerobic digesters, methanogenesis completes the terminal step of anaerobic respiration for methanogenic archaea.

Most methane is produced by three principal pathways: hydrogenotrophic methanogenesis, reducing CO2 with molecular hydrogen to methane and water (CO2 + 4 H2 -> CH4 + 2 H2O); acetoclastic methanogenesis, splitting acetate into methane and carbon dioxide (CH3COO− -> CH4 + CO2); and methylotrophic methanogenesis, converting one-carbon compounds such as methanol or methylamines into methane. The key enzyme complex is methyl-coenzyme M reductase, which catalyzes the final step of methane formation and uses cofactor F430. Methanogenesis is energetically marginal under many conditions, yielding only a small amount of energy per mole of substrate, which constrains growth and requires specialized adapted organisms.

Methanogens belong primarily to the archaeal phylum Euryarchaeota, with other lineages reported. They play a central role in global carbon cycling and contribute substantially to atmospheric methane, a potent greenhouse gas. In anthropogenic contexts, methanogenesis underpins anaerobic digestion and biogas production; it is also a target of strategies to mitigate methane emissions. Inhibition or stimulation of methanogenesis can influence wastewater treatment, cattle farming, and climate-related impacts.