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Archaea (Archaebacteria)
Temporal range: 3.5-0Ga
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Paleoarchean or perhaps Eoarchean – recent

Halobacterium sp. strain NRC-1,
each cell about 5 μm long
Scientific classification
Domain: Archaea
Woese, Kandler & Wheelis, 1990
Kingdoms and phyla
  • "Euryarchaeota" Woese et al. 1990
    • "Methanopyri" Garrity and Holt 2002
    • "Methanococci" Boone 2002
    • "Eurythermea" Cavalier-Smith 2002
    • "Neobacteria" Cavalier-Smith 2002
  • "DPANN"
    • "ARMAN"
      • "Micrarchaeota" Baker et al. 2010
      • "Parvarchaeota" Rinke et al. 2013
    • "Aenigmarchaeota" Rinke et al. 2013
    • "Diapherotrites" Rinke et al. 2013
    • "Nanoarchaeota" Huber et al. 2002
    • "Nanohaloarchaeota" Rinke et al. 2013
    • "Pacearchaeota" Castelle et al. 2015
    • "Woesearchaeota" Castelle et al. 2015
  • "Proteoarchaeota" Petitjean et al. 2015
    • (TACK)"Filarchaeota" Cavalier-Smith, T. 2014
      • "Aigarchaeota" Nunoura et al. 2011
      • "Bathyarchaeota" Meng et al. 2014
      • Crenarchaeota Garrity & Holt 2002
      • "Geoarchaeota" Kozubal et al. 2013
      • "Korarchaeota" Barns et al. 1996
      • Thaumarchaeota Brochier-Armanet et al. 2008
    • "Asgardarchaeota" Violette Da Cunha et al., 2017
      • "Lokiarchaeota" Spang et al. 2015
      • "Thorarchaeota" Seitz et al. 2016
      • "Odinarchaeota" Katarzyna Zaremba-Niedzwiedzka et al. 2017
      • "Heimdallarchaeota" Katarzyna Zaremba-Niedzwiedzka et al. 2017
Synonyms
  • Archaebacteria Woese & Fox, 1977
  • Mendosicutes Gibbons & Murray, 1978
  • Metabacteria Hori and Osawa 1979
Colourful Thermophilic Archaebacteria Stain in Midway Geyser Basin
Colourful archaea at Midway geyser

The Archaea (or Archea) are a group of single-celled organisms. The name comes from Greek αρχαία, "old ones". They are a major division of living organisms.

Archaea are tiny, simple organisms. They were originally discovered in extreme environments (extremophiles), but are now thought to be common to more average conditions. Many can survive at very high (over 80 °C) or very low temperatures, or highly salty, acidic or alkaline water. Some have been found in geysers, black smokers, oil wells, and hot vents in the deep ocean. Recent research has found ammonia-eating archaea in soil and seawater.

In the past they had been classed with bacteria as prokaryotes (or Kingdom Monera) and named archaebacteria, but this is a mistake. The Archaea have an independent evolutionary history and show many differences in their biochemistry from other forms of life. They are now classified as a separate domain in the three-domain system. In this system, the three distinct branches of evolutionary descent are the Archaea, Bacteria and Eukaryota.

Archaea are, like bacteria, prokaryotes: single-celled organisms that do not have nuclei and cell organelles of the eukaryote type.

Comparison to other domains

The following table compares some major characteristics of the three domains, to illustrate their similarities and differences. Many of these characteristics are also discussed below.

Property Archaea Bacteria Eukarya
Cell membrane Ether-linked lipids, pseudopeptidoglycan Ester-linked lipids, peptidoglycan Ester-linked lipids, various structures
Gene structure Circular chromosomes, similar translation and transcription to Eukarya Circular chromosomes, unique translation and transcription Multiple, linear chromosomes, similar translation and transcription to Archaea
Internal cell structure No membrane-bound organelles (but questioned:) or nucleus No membrane-bound organelles or nucleus Membrane-bound organelles and nucleus
Metabolism Various, with methanogenesis unique to Archaea Various, including photosynthesis, aerobic and anaerobic respiration, fermentation, and autotrophy Photosynthesis, cellular respiration and fermentation
Reproduction Asexual reproduction, horizontal gene transfer Asexual reproduction, horizontal gene transfer Sexual and asexual reproduction

= Interesting facts about archaea:

Related pages

  • Barry E.R. & Bell S.D. 2006. DNA replication in the Archaea. Microbiology and molecular biology reviews (MMBR) '70, 876-887.
  • Kelman L.M. & Kelman Z. 2003. Archaea: An archetype for replication initiation studies? Molecular microbiology, 48, 605-615.
  • Archaea -Citizendium

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