Metanogena

Metanogena, commonly referred to as methanogens, are a group of archaea that produce methane as a metabolic byproduct in strictly anaerobic environments. They obtain energy through methanogenesis, a process that reduces carbon dioxide to methane or converts substrates such as acetate or methylated compounds into methane. The main metabolic routes are hydrogenotrophic methanogenesis (CO2 with H2), acetoclastic methanogenesis (acetate), and methylotrophic methanogenesis (methylated compounds such as methanol or methylamines).

Habitat and ecological role: Methanogens are found in a wide range of anaerobic settings, including wetlands, rice paddies, sediments, the guts of ruminants and termites, marine and freshwater sediments, landfills, and anaerobic digesters. They are obligately anaerobic and generally tolerate only limited oxygen exposure. They span temperature and pH optima from mesophilic to thermophilic and hyperthermophilic conditions, reflecting diverse ecological niches. In ecosystems, methanogens form syntrophic relationships with other microbes that provide substrates like H2 or acetate, and they are key players in the global carbon cycle by producing methane.

Taxonomy and examples: Methanogens belong to the domain Archaea, primarily within the phylum Euryarchaeota. Notable genera include Methanobacterium, Methanobrevibacter, Methanococcus, Methanosarcina, and Methanosaeta (Methanothrix). They possess distinctive cofactors such as coenzyme M and coenzyme B and use archaeal membrane lipids that differ from those of bacteria and eukaryotes.

Significance: Methanogenesis is an ancient energy-yielding metabolism and a major source of methane in the atmosphere. Engineered anaerobic digestion processes exploit methanogens to convert organic waste into biogas for energy.