Euryarchaeota (from Ancient Greekεὐρύς eurús, "broad, wide") is a kingdom of archaea.[3] Euryarchaeota are highly diverse and include methanogens, which produce methane and are often found in intestines; halobacteria, which survive extreme concentrations of salt; and some extremely thermophilic aerobes and anaerobes, which generally live at temperatures between 41 and 122 °C. They are separated from the other archaeans based mainly on rRNA sequences and their unique DNA polymerase.[4]
The Euryarchaeota are diverse in appearance and metabolic properties. The phylum contains organisms of a variety of shapes, including both rods and cocci. Euryarchaeota may appear either gram-positive or gram-negative depending on whether pseudomurein is present in the cell wall.[5]Euryarchaeota also demonstrate diverse lifestyles, including methanogens, halophiles, sulfate-reducers, and extreme thermophiles in each.[5] Others live in the ocean, suspended with plankton and bacteria. Although these marine euryarchaeota are difficult to culture and study in a lab, genomic sequencing suggests that they are motile heterotrophs.[6]
Though it was previously thought that euryarchaeota 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 euryarchaeota also live in moderate environments, such as low-temperature acidic environments. In some cases, euryarchaeota outnumbered the bacteria present.[7] Euryarchaeota have also been found in other moderate environments such as water springs, marshlands, soil and rhizospheres.[8] Some euryarchaeota are highly adaptable; an order called Halobacteriales 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%.[8] In rhizospheres, the presence of euryarchaeota seems to be dependent on that of mycorrhizalfungi; a higher fungal population was correlated with higher euryarchaeotal frequency and diversity, while absence of mycorrihizal fungi was correlated with absence of euryarchaeota.[8]
In 2022, the proposed kingdom Methanobacteriati was introduced as a valid name for Euryarchaeota, which was claimed to be taxonomically invalid according to International Code of Nomenclature of Prokaryotes,[9] which gives priority to the first description of euryarchaeal cultivated species/genus (using the systematic suffix -ati for kingdom). This proposal is preferred by LPSN,[10] listing the Euryarchaeota as a not validly published phylum.[11]
The name Euryarchaeota is also currently considered as having no standing or validity according to the competitive SeqCode, which accepts descriptions of not cultivated taxa identified from sequence data.[12]
Euryarchaeota was listed in National Center for Biotechnology Information (NCBI) taxonomy browser[13] as a current name for phylum (Euryarchaeota Garrity and Holt 2002) till September 2024, considering Methanobacteriota as heterotypic synonym.[14] From October 2024 the names Methanobacteriati for kingdom and Halobacteriota, Methanobacteriota and Thermoplasmatota for included phyla are listed.[15]
The taxon Euryarchaeota is also listed in the Bergey's Manual of Systematics of Archaea and Bacteria.[16]
Euryarchaeota/Methanobacteriati is not listed as a taxon in the Genome Taxonomy Database (GTDB) applying not the level kingdom, even if it could be identified as a clade (Euryarchaeota s.s.).
Other phylogenetic analyzes have suggested that the archaea of the clade DPANN may also belong to Euryarchaeota and that they may even be a polyphyletic group occupying different phylogenetic positions within Euryarchaeota. It is also debated whether the phylum Altiarchaeota should be classified in DPANN or Euryarchaeota.[20] A cladogram summarizing this proposal is graphed below.[21][22] The groups marked in quotes are lineages assigned to DPANN, but phylogenetically separated from the rest.
Dombrowski et al. 2019,[20] Jordan et al. 2017[21] and Cavalier-Smith 2020.[22]
^Hogan CM (2010). E. Monosson, C. Cleveland (eds.). "Archaea". Encyclopedia of Earth. National Council for Science and the Environment. Retrieved 18 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.