Methanogens are anaerobic archaea that produce methane as a byproduct of their energy metabolism, i.e., catabolism. Methane production, or methanogenesis, is the only biochemical pathway for ATP generation in methanogens. All known methanogens belong exclusively to the domain Archaea, although some bacteria, plants, and animal cells are also known to produce methane. However, the biochemical pathway for methane production in these organisms differs from that in methanogens and does not contribute to ATP formation. Methanogens belong to various phyla within the domain Archaea. Previous studies placed all known methanogens into the superphylum Euryarchaeota. However, recent phylogenomic data have led to their reclassification into several different phyla. Methanogens are common in various anoxic environments, such as marine and freshwater sediments, wetlands, the digestive tracts of animals, wastewater treatment plants, rice paddy soil, and landfills. While some methanogens are extremophiles, such as Methanopyrus kandleri, which grows between 84 and 110°C, or Methanonatronarchaeum thermophilum, which grows at a pH range of 8.2 to 10.2 and a Na+ concentration of 3 to 4.8 M, most of the isolates are mesophilic and grow around neutral pH.
Chrysiogenaceae is a family of bacteria.
The Thermoprotei is a class of the Thermoproteota.
Archaeoglobus is a genus of the phylum Euryarchaeota. Archaeoglobus can be found in high-temperature oil fields where they may contribute to oil field souring.
In taxonomy, the Thermoplasmataceae are a family of the Thermoplasmatales. It contains only one genus, Thermoplasma. All species within Thermoplasmataceae are thermoacidophiles, and they grow at a temperature of 60 °C and pH 2. They were isolated from hydrothermal vents, fumaroles and similar environments.
Methanosarcina is a genus of euryarchaeote archaea that produce methane. These single-celled organisms are known as anaerobic methanogens that produce methane using all three metabolic pathways for methanogenesis. They live in diverse environments where they can remain safe from the effects of oxygen, whether on the earth's surface, in groundwater, in deep sea vents, and in animal digestive tracts. Methanosarcina grow in colonies.
Methanococcus is a genus of coccoid methanogens of the family Methanococcaceae. They are all mesophiles, except the thermophilic M. thermolithotrophicus and the hyperthermophilic M. jannaschii. The latter was discovered at the base of a “white smoker” chimney at 21°N on the East Pacific Rise and it was the first archaeal genome to be completely sequenced, revealing many novel and eukaryote-like elements.
Methanobacteria is a class of archaeans in the kingdom Euryarchaeota. Several of the classes of the Euryarchaeota are methanogens and the Methanobacteria are one of these classes.
In the taxonomy of microorganisms, the Methanomicrobia are a class of the Euryarchaeota.
The Desulfurococcales is an order of the Thermoprotei, part of the kingdom Archaea. The order encompasses some genera which are all thermophilic, autotrophs which utilise chemical energy, typically by reducing sulfur compounds using hydrogen. Desulfurococcales cells are either regular or irregular coccus in shape, with forms of either discs or dishes. These cells can be single, in pairs, in short chains, or in aciniform formation.
Methanobacteriales is an order of archaeans in the class Methanobacteria. Species within this order differ from other methanogens in that they can use fewer catabolic substrates and have distinct morphological characteristics, lipid compositions, and RNA sequences. Their cell walls are composed of pseudomurein. Most species are Gram-positive with rod-shaped bodies and some can form long filaments. Most of them use formate to reduce carbon dioxide, but those of the genus Methanosphaera use hydrogen to reduce methanol to methane.
In taxonomy, the Ferroplasmaceae are a family of the Thermoplasmatales.
In taxonomy, the Methanosarcinaceae are a family of the Methanosarcinales.
The Pyrodictiaceae are a family of disc-shaped anaerobic microorganisms belonging to the order Desulfurococcales, in the domain Archaea. Members of this family are distinguished from the other family (Desulfurococcaceae) in the order Desulfurococcales by having an optimal growth temperature above 100 °C, rather than below 100 °C.
In taxonomy, Methanosaeta is a genus of microbes within Methanosaetaceae. Like other species in this family, those of Methanosaeta metabolize acetate as their sole source of energy. The genus contains two species, Methanosaeta concilii, which is the type species and Methanosaeta thermophila. For a time, some scientists believed there to be a third species, Methanosaeta soehngenii, but because it has not been described from a pure culture, it is now called Methanothrix soehngenii.
The genus Methanimicrococcus was described based on the strain PA, isolated from the hindgut of a cockroach, Periplaneta americana. The species was initially named Methanomicrococcus blatticola; however, the name was later corrected to Methanimicrococcus blatticola, making it the only genus of methanogens that has -i as a connecting vowel rather than -o in the name.
In taxonomy, Methanocorpusculum is a genus of microbes within the family Methanocorpusculaceae. The species within Methanocorpusculum were first isolated from biodisgester wastewater and activated sludge from anaerobic digestors. In nature, they live in freshwater environments. Unlike most other methanogenic archaea, they do not require high temperatures or extreme salt concentrations to live and grow.
In taxonomy, Methanospirillum is a genus of microbes within the family Methanospirillaceae. All its species are methanogenic archaea. The cells are bar-shaped and form filaments. Most produce energy via the reduction of carbon dioxide with hydrogen, but some species can also use formate as a substrate. They are Gram-negative and move using archaella on the sides of the cells. They are strictly anaerobic, and they are found in wetland soil and anaerobic water treatment systems.
Methanocalculus is a genus of the Methanomicrobiales, and is known to include methanogens.
In the taxonomy of microorganisms, the Methanothrix is a genus of methanogenic archaea within the Euryarchaeota. Methanothrix cells were first isolated from a mesophilic sewage digester but have since been found in many anaerobic and aerobic environments. Methanothrix were originally understood to be obligate anaerobes that can survive exposure to high concentrations of oxygen, but recent studies have shown at least one Candidatus operational taxonomic unit proposed to be in the Methanothrix genus not only survives but remains active in oxic soils. This proposed species, Ca. Methanothrix paradoxum, is frequently found in methane-releasing ecosystems and is the dominant methanogen in oxic soils.
