Domain (biology)

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Australian green tree frog (Litoria caerulea)
Scanning electron micrograph of S. aureus; false color added
Electron micrograph of Sulfolobus infected with Sulfolobus virus STSV1.
The three-domain system includes Eukarya (represented by the Australian green tree frog, left), Bacteria (represented by S. aureus, middle) and Archaea (represented by Sulfolobus, right).

In biological taxonomy, a domain (also superregnum, superkingdom, empire, or regio) is the highest taxonomic rank of organisms in the three-domain system of taxonomy designed by Carl Woese, an American microbiologist and biophysicist. According to the Woese system, introduced in 1990, the Tree of Life consists of three domains: Archaea (a term which Woese created), Bacteria, and Eukarya.[1] The first two are all prokaryotic microorganisms, or single-celled organisms whose cells have no nucleus. All life that has a nucleus and membrane-bound organelles, and most multi-cellular life is included in the Eukarya.

Alternative classifications[edit]

Bacteria Archaea Eucaryota Aquifex Thermotoga Cytophaga Bacteroides Bacteroides-Cytophaga Planctomyces Cyanobacteria Proteobacteria Spirochetes Gram-positive bacteria Green filantous bacteria Pyrodicticum Thermoproteus Thermococcus celer Methanococcus Methanobacterium Methanosarcina Halophiles Entamoebae Slime mold Animal Fungus Plant Ciliate Flagellate Trichomonad Microsporidia Diplomonad
A speculatively rooted tree for rRNA genes, showing major branches Bacteria, Archaea, and Eukaryota

Alternative classifications of life so far proposed include:

Exclusion of viruses[edit]

None of the three systems currently include non-cellular life. As of 2011 there is talk about Nucleocytoplasmic large DNA viruses possibly being a fourth branch domain of life, a view supported by researchers in 2012 who explain in their abstract, "The discovery of giant viruses with genome and physical size comparable to cellular organisms, remnants of protein translation machinery and virus-specific parasites (virophages) have raised intriguing questions about their origin. Evidence advocates for their inclusion into global phylogenomic studies and their consideration as a distinct and ancient form of life." They continue, "Results call for a change in the way viruses are perceived. They likely represent a distinct form of life that either predated or coexisted with the last universal common ancestor (LUCA) and constitute a very crucial part of our planet’s biosphere."[7]

See also[edit]

References[edit]

  1. ^ Woese C, Kandler O, Wheelis M (1990). "Towards a natural system of organisms: proposal for the domains Archaea, Bacteria, and Eucarya.". Proc Natl Acad Sci USA 87 (12): 4576–9. Bibcode:1990PNAS...87.4576W. doi:10.1073/pnas.87.12.4576. PMC 54159. PMID 2112744. Retrieved 11 February 2010. 
  2. ^ Mayr, Ernst (1998). "Two empires or three?". Proc Natl Acad Sci USA 95 (17): 9720–9723. Bibcode:1998PNAS...95.9720. doi:10.1073/pnas.95.17.9720. PMC 33883. PMID 9707542. Retrieved 5 September 2011. 
  3. ^ Cavalier-Smith, T. (2004). "Only six kingdoms of life". Proc. R. Soc. Lond. B 271 (1545): 1251–62. doi:10.1098/rspb.2004.2705. PMC 1691724. PMID 15306349. Retrieved 2010-04-29 
  4. ^ Archibald, John M. (23 December 2008). "The eocyte hypothesis and the origin of eukaryotic cells". PNAS 105 (51): 20049–20050. 
  5. ^ Lake, James A.; Henderson, Eric; Oakes, Melanie; Clark, Michael W. (June 1984). "Eocytes: A new ribosome structure indicates a kingdom with a close relationship to eukaryotes". PNAS 81: 3786–3790. 
  6. ^ Williams, Tom A.; Foster, Peter G.; Cox, Cymon J.; Embley, T. Martin (December 2013). "An archaeal origin of eukaryotes supports only two primary domains of life". Nature 504 (7479): 231–236. doi:10.1038/nature12779. PMID 24336283. 
  7. ^ Nasir, Arshan; Kim, Kyung Mo; and Caetano-Anolles, Gustavo, "Giant viruses coexisted with the cellular ancestors and represent a distinct supergroup along with superkingdoms Archaea, Bacteria and Eukarya." BMC Evol Biol. 2012; 12: 156. Published online 2012 August 24. doi:10.1186/1471-2148-12-156