Methanococcales

Methanococcales is an order of methanogenic archaea within the class Methanococci, phylum Euryarchaeota. Members are strictly anaerobic and produce methane as a metabolic end product through methanogenesis. Most members are hydrogenotrophic, reducing CO2 with molecular hydrogen, although some can utilize formate as an electron donor. They are typically coccoid or irregular in shape and possess cell envelopes composed of archaeal lipids rather than peptidoglycan.

Taxonomy and diversity: The order comprises two families, Methanococcaceae and Methanocaldococcaceae, which include several genera such as Methanococcus and Methanocaldococcus. The exact composition of genera can vary with taxonomic updates, but Methanococcus and Methanocaldococcus are representative members.

Habitat and ecology: Methanococcales inhabit oxygen-depleted environments, including marine and freshwater sediments, hydrothermal vent systems, and anaerobic digesters. They contribute to the production of methane in these environments and play a role in global carbon cycling.

Notable species: Methanococcus maripaludis is a mesophilic representative within the group. Methanocaldococcus jannaschii is a hyperthermophile isolated from a hydrothermal vent; its genome was among the first archaeal genomes to be sequenced, providing foundational insights into archaeal biology.

Significance: As methanogens, Methanococcales contribute to the methane cycle and serve as model organisms for studying archaeal metabolism, genetics, and unique lipid and enzyme systems involved in methanogenesis, such as methyl-coenzyme M reductase. Their biology helps illuminate differences between archaeal and bacterial/eukaryotic biochemistry.