TheKorarchaeota is a proposedphylum within theArchaea.[2] The name is derived from the Greek noun koros or kore, meaningyoung man oryoung woman, and the Greek adjective archaios which meansancient.[3] They are also known asXenarchaeota. The name is equivalent toCandidatus Korarchaeota, and they go by the name Xenarchaeota or Xenarchaea as well.[4]
The Korarchaeota are a proposed phylum in the domain,Archaea.[5] They are thought to have diverged relatively early in the genesis of Archaea and are among the deep-branching lineages.[5] Korarchaeota are also known as Xenarchaeota. Korarchaeaota, along with Thaumarchaeota, Aigarchaeota, Crenarchaeota, belong to the superphylum called TACK.[6] The evolutionary link between Asgard archaea and Korarchaeota of TACK (Thaumarchaeota, Aigarchaeota, Crenarchaeota, Korarchaeota) is yet unknown.[6]
The first member of Korarchaeota to have its genome reconstructed wasKorarchaeum crypotfilum, which was found in a hot spring in Yellowstone National Park and described in 2008.[7] Since then only a few Korarchaeal genomes have been described.[8] To check for Korarchaeota, 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 distinct16S ribosomal nucleic acid sequences, whereas the Kamchatkan samples contained about 33.[9]
Based on protein sequences and phylogenetic analysis of conserved single genes, the Korarchaeote was identified as a “deep archaeal lineage” with a possible relationship to the Crenarchaeota.[10] Furthermore, given the known genetic makeup of archaea, the Korarchaeota may have preserved a set of biological traits that correspond to the earliest known archaeal form.[10]
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 andEuryarchaeota.[11] Analysis of the genome of one korarchaeote 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.[12]
A strain ofKorarchaeum cryptofilum was cultivated from an enrichment culture from a hot spring in Yellowstone National Park, USA and described in 2008.[12] The cells are long and needle-shaped, which gave the species its name, alluding to its "cryptical filaments". This organism lacks the genes forpurinenucleotide biosynthesis and thus relies on environmental sources to meet its purine requirements.[20]
Korarchaeota are a proposed phylum within the domain,Archaea, and therefore exhibit characteristics such as having a cell wall without peptidoglycan, as well as lipid membranes that are ether-linked.[21] They have a surface layer of paracrystalline protein.[22] 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.[21][22] 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.[23] Korarchaeota cells have an ultrathin filamentous morphology that may vary in length.[5] They typically average 15 μm in length and 0.16 μm in diameter but can be seen up to 100 μm long.[23] Some Archaea can fix carbon dioxide through the3-hydroxypropionate/4-hydroxybutyrate pathway into organic compounds[24]
Korarcheota have only been found in hydrothermal environments ranging from terrestrial, including hot springs[5][25] to marine, including shallow hydrothermal vents and deep-sea hydrothermal vents.[26] Previous research has shown greater diversity of Korarchaea found in terrestrial hot springs compared to marine environments.[26] Korarchaeota have been found in nature in only low abundances.[27][28][29] Korarcheota likely originated in marine environments and then adapted to terrestrial ones.[30]
Geographically, Korarcheota have been found in a variety of locations around the world including Japan, Yellowstone National Park, the Gulf of California, Iceland and Russia.[21][26]
Korarchaeota arethermophiles, having been found living in conditions of up to 128 degrees Celsius.[26] The lowest temperature they have been found in is 52 degrees Celsius.[21] While they have frequently been observed living in acidic conditions, they have also been found living in conditions up to a pH of 10.[31][26]
Researchers have identified a virus that can potentially infect Korarcheota.[32]
Each of these six hot springs (clockwise from top left: Uzon4, Uzon7, Uzon8, Uzon9, Mut11, Mut13) in Kamchatka was found to contain Korarchaeota.[27]
^Rooting the Domain Archaea by Phylogenomic Analysis Supports the Foundation of the New Kingdom Proteoarchaeota
^abMcKay LJ, Dlakić M, Fields MW, Delmont TO, Eren AM, Jay ZJ, et al. (April 2019). "Co-occurring genomic capacity for anaerobic methane and dissimilatory sulfur metabolisms discovered in the Korarchaeota".Nature Microbiology.4 (4):614–622.doi:10.1038/s41564-019-0362-4.OSTI1779059.PMID30833730.S2CID256705892.
^abAuchtung TA, Shyndriayeva G, Cavanaugh CM (January 2011). "16S rRNA phylogenetic analysis and quantification of Korarchaeota indigenous to the hot springs of Kamchatka, Russia".Extremophiles.15 (1):105–116.doi:10.1007/s00792-010-0340-5.PMID21153671.S2CID12091232.
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