Metanogeneesi

Metanogeneesi, or methanogenesis, is a biochemical process by which methane (CH4) is produced as a metabolic end product. It is carried out primarily by a specialized group of archaea known as methanogens, which thrive under anaerobic conditions and utilize CO2, formate, acetate, or methylated compounds as substrates. The process plays a central role in the global carbon cycle and in anaerobic ecosystems.

Most methanogens generate methane through three main pathways: hydrogenotrophic methanogenesis, in which CO2 is reduced with hydrogen to methane; acetoclastic methanogenesis, where acetate is split into methane and CO2; and methylotrophic methanogenesis, using methylated substrates such as methanol or methylamines. A common feature is the enzyme methyl-coenzyme M reductase (MCR), which catalyzes the final step of methane formation and depends on the cofactor F430. Energy yields are modest, and methanogens conserve energy by establishing ion gradients across their membranes.

Methanogenesis occurs in wetlands, the guts of ruminants, sediments, landfills, and in anaerobic digesters used for wastewater treatment and biogas production. Because methane is a potent greenhouse gas, methanogenesis contributes to natural methane emissions and is a key consideration in climate studies. Oxygen exposure or high ammonia can inhibit methanogens, while temperature, pH, and substrate availability influence activity and community composition.

Methanogens are strictly anaerobic archaea, distributed across diverse environments from marine sediments to geothermal systems. In biotechnology, controlled methanogenesis is exploited to convert organic waste into biogas (mostly methane and carbon dioxide) in anaerobic digestion facilities. Understanding methanogenesis informs strategies to manage methane emissions in agriculture and waste management.