Korarchaeia

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"Candidatus Korarchaeia" is a class of Archaea under the phylum Thermoproteota. The name is derived from the Greek noun koros or kore, meaning "young man" or "young woman", and the Greek adjective archaios which means "ancient".<ref>Template:Cite journal</ref> It was previously designated as phylum Korarchaeota and as kingdom with various names like Crenarchaeida or Proteoarchaeota.<ref name=":0">Template:Cite journal</ref>

Taxonomy

"Candidatus Korarchaeia" had been designated as Korarchaeota in the domain, Archaea. They are thought to have diverged relatively early in the genesis of Archaea and are among the deep-branching lineages.<ref name="Elkins_2008">Template:Cite journal</ref> They have been classified as phylum (and sometimes as kingdom<ref name=":1">Template:Cite journal</ref>) Korarchaeota, along with Thaumarchaeota, Aigarchaeota, Crenarchaeota, under the kingdom Thermoproteati. The evolutionary link between Promethearchaeati and Thermoproteati.<ref name="Liu 218–222">Template:Cite journal</ref>

The first member of "Candidatus Korarchaeia" to have its genome reconstructed was Korarchaeum cryptofilum, which was found in a hot spring, Obsidian Pool, in Yellowstone National Park and described in 2008.<ref name="Elkins_2008"/><ref>Template:Cite journal</ref> Since then only a few Korarchaeal genomes have been described.<ref>Template:Cite journal</ref> To check for "Candidatus Korarchaeia", samples from a variety of hot springs in Iceland and Kamchatka were gathered. According to the samples and analysis, the Icelandic samples contained about 87 distinct 16S ribosomal nucleic acid sequences, whereas the Kamchatkan samples contained about 33.<ref name=":1" />

Based on protein sequences and phylogenetic analysis of conserved single genes, the "Candidatus Korarchaeia" was identified as a "deep archaeal lineage" with a possible relationship to the Crenarchaeota. Furthermore, given the known genetic makeup of archaea, the "Candidatus Korarchaeia" may have preserved a set of biological traits that correspond to the earliest known archaeal form.<ref name="Elkins_2008"/>

Analysis of their 16S rRNA gene sequences suggests that they are a deeply branching lineage that does not belong to the main archaeal groups, Thermoproteota and Euryarchaeota.<ref>Template:Cite journal</ref> Analysis of the genome of one "Candidatus Korarchaeia" that was enriched from a mixed culture revealed a number of both Crenarchaeota- and Euryarchaeota-like features and supports the hypothesis of a deep-branching ancestry.<ref name="Elkins_2008"/>

Revision

In 2001, George M. Garrity and John G. Holt described the phylum Crenarchaeota to include a single class Thermoprotei.<ref>Template:Citation</ref> With the growing number of prokaryotic taxa and the inconsistent nomenclature and classification, there was a need to revise the overall classification of archaea. In 2014, French taxonomists led by David Moreira designated "TACK", generally considered as a superphylum, into a single kingdom named Proteoarchaeota.<ref>Template:Cite journal</ref> However, such revision was not valid under the rules of the International Committee on Systematics of Prokaryotes (ICSP).<ref>Template:Cite journal</ref> In 2021, a team of Australian scientists led by Christian Rinke and Philip Hugenholtz published a new classification on archaea in which their genetic evidence indicated Thermoproteati archaea belong to a unified phylum Thermoproteota, which could be divided into the classes "Candidatus Korarchaeia", Thermoprotei, Methanomethylicia (former phylum Ca. Verstraetearchaeota), Bathyarchaeia and Nitrososphaeria (former phylum Ca. Thaumachaeota).<ref name="rinke 2021">Template:Cite journal</ref> The List of Prokaryotic names with Standing in Nomenclature (LPSN), an authority on maintenance and cataloguing prokaryotic taxons, upheld this classification of "Candidatus Korarchaeia" as a "preferred name" as a class.<ref>Template:Cite web</ref>

In 2022, the ICSP revised its International Code of Nomenclature of Prokaryotes (ICNP, Prokaryotic Code).<ref>Template:Cite journal</ref> Following the revised code, Markus Göker and Aharon Oren (leaders of the ICSP), revised the domain and kingdom classifications 2024 in which the traditionally named "TACK" group was renamed to kingdom Thermoproteati.<ref name=":0" /> In this way, previous designations such as phylum Korarchaeota or kingdom Proteoarchaeota are invalidated.<ref>Template:Cite web</ref>

Species

The currently accepted taxonomy is based on the List of Prokaryotic names with Standing in Nomenclature (LPSN) and National Center for Biotechnology Information (NCBI).

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Listed below are the known species of "Candidatus Korarchaeia":<ref name="Schoch-2020"/>

  • Order Panguiarchaeales Qu et al. 2023
    • Family Panguiarchaeaceae Qu et al. 2023
      • Genus Panguiarchaeum Qu et al. 2023
        • Species Panguiarchaeum symbiosum Qu et al. 2023
  • Order Korarchaeales Petitjean et al. 2015<ref>Rooting the Domain Archaea by Phylogenomic Analysis Supports the Foundation of the New Kingdom Proteoarchaeota</ref>
    • Family Korarchaeaceae Rinke et al. 2020
      • Genus "Candidatus Korarchaeum" Elkins et al. 2008
        • Species "Ca. Korarchaeum cryptofilum" Elkins et al. 2008<ref name="Elkins_2008"/>
          • "Ca. Korarchaeum cryptofilum" OPF8<ref name="Elkins_2008"/>
      • Genus "Ca. Methanodesulfokores" corrig. McKay et al. 2019<ref name="McKay-2019">Template:Cite journal</ref>
        • Species "Ca. Methanodesulfokores washburnensis" corrig. McKay et al. 2019<ref name="McKay-2019" />
      • Genus "Ca. Korarchaeota"<ref name="Schoch-2020">Template:Cite journal</ref>
      • Genus "Ca. Korarchaeota archaeon" NZ13-K<ref name="Schoch-2020" />
      • Genus Korarchaeote SRI-306<ref name="Schoch-2020" />
      • Genus environmental samples<ref name="Schoch-2020" />
        • uncultured korarchaeote pBA5<ref name="Schoch-2020" />
        • uncultured korarchaeote pJP27<ref name="Schoch-2020" />
        • uncultured korarchaeote pJP78<ref name="Schoch-2020" />

Reference species

A strain of Korarchaeum cryptofilum was cultivated from an enrichment culture from a hot spring in Yellowstone National Park, USA and described in 2008.<ref name="Elkins_2008" /> The cells are long and needle-shaped, which gave the species its name, alluding to its "cryptical filaments". This organism lacks the genes for purine nucleotide biosynthesis and thus relies on environmental sources to meet its purine requirements.<ref>Template:Cite journal</ref>

Characteristics

"Candidatus Korarchaeia" exhibit characteristics such as having a cell wall without peptidoglycan, as well as lipid membranes that are ether-linked.<ref name="Miller-2008">Template:Cite journal</ref> They have a surface layer of paracrystalline protein.<ref name="Rodrigues-Oliveira-2017">Template:Cite journal</ref> This surface layer, known as the S-layer, is densely packed and consists of 1-2 proteins form various lattice structures and are most likely what maintains the cells' structural integrity.<ref name="Miller-2008"/><ref name="Rodrigues-Oliveira-2017" /> They are typically rod-shaped, however, it has been found that this morphology can change to be thicker-shaped in the presence of higher sodium dodecyl sulfate (SDS) concentrations.<ref name="Elkins-2007">Template:Cite report</ref> The cells have an ultrathin filamentous morphology that may vary in length.<ref name="Elkins_2008"/> They typically average 15 μm in length and 0.16 μm in diameter but can be seen up to 100 μm long.<ref name="Elkins-2007" /> Some Archaea can fix carbon dioxide through the 3-hydroxypropionate/4-hydroxybutyrate pathway into organic compounds<ref>Template:Cite journal</ref>

Ecology

"Candidatus Korarchaeia" have only been found in hydrothermal environments ranging from terrestrial, including hot springs <ref name="Elkins_2008"/><ref>Template:Cite journal</ref> to marine, including shallow hydrothermal vents and deep-sea hydrothermal vents. Previous research has shown greater diversity of "Candidatus Korarchaeia" found in terrestrial hot springs compared to marine environments.<ref name=":1" /> "Candidatus Korarchaeia" have been found in nature in only low abundances.<ref name="KamKors">Template:Cite journal</ref><ref>Template:Cite thesis</ref> Korarcheota likely originated in marine environments and then adapted to terrestrial ones.<ref>Template:Cite journal</ref>

Geographically, "Candidatus Korarchaeia" have been found in a variety of locations around the world including Japan, Yellowstone National Park, the Gulf of California, Iceland and Russia.<ref name=":1" /><ref name="Miller-2008"/>

"Candidatus Korarchaeia" are thermophiles, having been found living in conditions of up to 128 degrees Celsius.<ref name=":1" /> The lowest temperature they have been found in is 52 degrees Celsius.<ref name="Miller-2008" /> While they have frequently been observed living in acidic conditions, they have also been found living in conditions up to a pH of 10.<ref>Template:Cite journal</ref>

Researchers have identified a virus that can potentially infect "Candidatus Korarchaeia".<ref>Template:Cite journal</ref>

Each of these six hot springs (from top left, clockwise: Uzon4, Uzon7, Uzon8, Uzon9, Mut11, Mut13) in Kamchatka were found to contain Korarchaeota.
Each of these six hot springs (clockwise from top left: Uzon4, Uzon7, Uzon8, Uzon9, Mut11, Mut13) in Kamchatka was found to contain "Candidatus Korarchaeia".<ref name="KamKors" />

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See also

References

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Further reading

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