Methanobacteriati (formerly"Euryarchaeota", fromAncient Greekεὐρύς eurús, "broad, wide") is akingdom ofarchaea.[4] Methanobacteriati are highly diverse and includemethanogens, which produce methane and are often found in intestines;halobacteria, which surviveextreme concentrations of salt; and some extremelythermophilic aerobes and anaerobes, which generally live at temperatures between 41 and 122 °C. They are separated from the other archaeans based mainly onrRNA sequences and their unique DNA polymerase.[5] The onlyvalidly published name for this group under theProkaryotic Code isMethanobacteriati.[6]
The Methanobacteriati are diverse in appearance and metabolic properties. The kingdom contains organisms of a variety of shapes, including bothrods andcocci. Methanobacteriati may appear eithergram-positive or gram-negative depending on whetherpseudomurein is present in the cell wall.[7] Methanobacteriati also demonstrate diverse lifestyles, including methanogens, halophiles, sulfate-reducers, and extreme thermophiles in each.[7] Others live in the ocean, suspended with plankton and bacteria. Although these marine Methanobacteriati are difficult to culture and study in a lab, genomic sequencing suggests that they are motileheterotrophs.[8]
Though it was previously thought that Methanobacteriati only lived in extreme environments (in terms of temperature, salt content and/or pH), a paper by Korzhenkov et al. published in January 2019 showed that Methanobacteriati also live in moderate environments, such as low-temperature acidic environments. In some cases, Methanobacteriati outnumbered the bacteria present.[9] Methanobacteriati have also been found in other moderate environments such as water springs, marshlands, soil andrhizospheres.[10] Some Methanobacteriati are highly adaptable; an order calledHalobacteriales are usually found in extremely salty and sulfur-rich environments but can also grow in salt concentrations as low as that of seawater 2.5%.[10] In rhizospheres, the presence of Methanobacteriati seems to be dependent on that ofmycorrhizalfungi; a higher fungal population was correlated with higher Methanobacteriatil frequency and diversity, while absence of mycorrihizal fungi was correlated with absence of Methanobacteriati.[10]
Under theInternational Code of Nomenclature of Prokaryotes, there has been no (and cannot be any) valid name for this group, as it exceeds the level of aphylum. In 2024, theCode was amended to included the levels of kingdom and domain. In the same year, the nameMethanobacteriati wasvalidly published for this group, making it the first and only "valid name" under theCode.[6] TheLPSN, which aligns itself with theCode, adopts this view and[11] lists the earlier Methanobacteriati as an invalidly published phylum.[12]
The competingSeqCode for uncultivated taxa also has no level above phylum, hence "Methanobacteriati" also has no standing there. The Methanobacteriati name has no standing either: SeqCode only automatically accepts a name made under the Prokaryotic Code if it's older than 2023.[13]
Methanobacteriati was listed inNational Center for Biotechnology Information (NCBI) taxonomy browser[14] as a current name for phylum (MethanobacteriatiGarrity and Holt 2002) till September 2024, considering Methanobacteriota as heterotypic synonym.[15] From October 2024 the names Methanobacteriati for kingdom and Halobacteriota, Methanobacteriota and Thermoplasmatota for included phyla are listed.[16]
The taxon Methanobacteriati is also listed in the Bergey's Manual of Systematics of Archaea and Bacteria, but this is because the latest version of the chapter was published in 2017.[17]
Methanobacteriati / "Euryarchaeota" is not listed as a taxon in the Genome Taxonomy Database (GTDB), as the algorithm does not generate kingdoms.
Other phylogenetic analyzes have suggested that the archaea of the kingdomNanobdellati may also belong to Methanobacteriati and that they may even be apolyphyletic group occupying different phylogenetic positions within Methanobacteriati. It is also debated whether the phylumAltiarchaeota should be classified in Nanobdellati or Methanobacteriati.[21] A cladogram summarizing this proposal is graphed below.[22][23] The groups marked in quotes are lineages assigned to Nanobdellati, but phylogenetically separated from the rest.
Dombrowski et al. 2019,[21] Jordan et al. 2017[22] and Cavalier-Smith 2020.[23]
^Hogan CM (2010). E. Monosson, C. Cleveland (eds.)."Archaea".Encyclopedia of Earth. National Council for Science and the Environment. Retrieved18 August 2017.
^Bergey's Manual of Systematics of Archaea and Bacteria:A-Z Listing. Last updated: 27 March 2017. Wiley Online Library, John Wiley & Sons, Inc. Retrieved 25 September 2024.
