Methanothrix is a
genus
Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...
of
methanogenic archaea within the phylum
Methanobacteriota
Methanobacteriota is a phylum in the domain Archaea.
Taxonomy
The phylum ''Methanobacteriota'' was introduced to prokaryotic nomenclature in 2023. It contains following classes:
*Archaeoglobi Garrity & Holt (2002)
*Halobacteria Grant ''et al ...
. ''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
In prokaryote nomenclature, ''Candidatus'' (abbreviated ''Ca.''; Latin for "candidate of Roman office") is used to name prokaryotic taxa that are well characterized but yet- uncultured. Contemporary sequencing approaches, such as 16S ribosomal R ...
''
operational taxonomic unit
An operational taxonomic unit (OTU) is an operational definition used to classify groups of closely related individuals. The term was originally introduced in 1963 by Robert R. Sokal and Peter H. A. Sneath in the context of numerical taxonomy, wh ...
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.
''Methanothrix'' are non-motile rod-shaped cells which connect together to form long filaments.
These filaments are enclosed in a proteinaceous sheath.
''Methanothrix'' species, like their close relative
Methanosarcina barkeri
''Methanosarcina barkeri'' is the type species of the genus ''Methanosarcina'', characterized by its wide range of substrates used in methanogenesis. While most known methanogens produce methane from H2 and CO2, ''M. barkeri'' can also dismutate ...
, have membranes entirely composed of diphytanylglycerol diethers.
Phylogeny
Metabolism
''Methanothrix'' species use acetate
and carbon dioxide
as carbon substrates.
When using acetate, ''Methanothrix'' species use an incomplete
citric acid cycle
The citric acid cycle—also known as the Krebs cycle, Szent–Györgyi–Krebs cycle, or TCA cycle (tricarboxylic acid cycle)—is a series of chemical reaction, biochemical reactions that release the energy stored in nutrients through acetyl-Co ...
in the oxidative direction.
After formation of
acetyl-CoA
Acetyl-CoA (acetyl coenzyme A) is a molecule that participates in many biochemical reactions in protein, carbohydrate and lipid metabolism. Its main function is to deliver the acetyl group to the citric acid cycle (Krebs cycle) to be oxidation, o ...
, the carbon-carbon bond of acetate is cleaved by a carbon monoxide dehydrogenase/acetyl-CoA synthase enzyme. The methyl moiety is transferred through multiple complexes until it is finally reduced to methane by a
methyl-CoM reductase
In enzymology, coenzyme-B sulfoethylthiotransferase, also known as methyl-coenzyme M reductase (MCR) or most systematically as 2-(methylthio)ethanesulfonate:N-(7-thioheptanoyl)-3-O-phosphothreonine S-(2-sulfoethyl)thiotransferase is an enzyme that ...
.
''Methanothrix'' species have been observed receiving electrons to reduce carbon dioxide to methane through direct interspecies electron transfer (DIET) with ''
Geobacter
''Geobacter'' is a genus of bacteria. ''Geobacter'' species use anaerobic respiration to alter the redox state of minerals and many pollutants, a trait that makes them useful in bioremediation. ''Geobacter'' was the first organism described wit ...
'' species.
Geobacter sulfurreducens
''Geobacter sulfurreducens'' is a gram-negative metal- and sulphur-reducing proteobacterium. It is rod-shaped, aerotolerant anaerobe, non-fermentative, has flagellum and type four pili, and is closely related to '' Geobacter metallireducens''. ...
transfers electrons into ''Methanothrix'' cells using electrically conductive pili.
Microbial Ecology
Compared to the acetotrophic ''
Methanosarcina
''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 e ...
'' species, ''Methanothrix'' species have lower
Monod Equation
The Monod equation is a mathematical model for the growth of microorganisms. It is named for Jacques Monod (1910–1976, a French biochemist, Nobel Prize in Physiology or Medicine in 1965), who proposed using an equation of this form to relate micr ...
parameters. ''Methanothrix'' have slower maximum growth rates and smaller half-saturation coefficients due to differences in the genera's aceticlastic pathways.
Consequently, when acetate concentrations are high, ''Methanothrix'' species are likely to be outcompeted by ''Methanosarcina'', which can utilize the available substrate faster. However, in low acetate environments, ''Methanothrix'' species will dominate due to their lower minimum threshold for acetate. This expectation is consistent with observations of abundant ''Methanothrix'' in low-acetate ecosystems across the world.
Because ''Methanothrix'' species are well adapted to survive exposure to oxygen and thrive using either acetate or carbon dioxide as a carbon substrate, they are thought to be one of the largest microbial contributors to methanogenesis on Earth.
See also
*
List of Archaea genera
This article lists the genera of the Archaea. The currently accepted taxonomy is based on the List of Prokaryotic names with Standing in Nomenclature (LPSN) and National Center for Biotechnology Information (NCBI). However, in the List provided bel ...
References
External links
{{Taxonbar, from=Q6823605
Archaea genera