Global InformationArchaea information
| Archaea Temporal range:
Paleoarchean – present
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Scientific classification 
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| Domain: | Archaea Woese, Kandler & Wheelis, 1990[1] |
| Kingdoms[2][3] | |
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| Synonyms | |
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Archaea (/ɑːrˈkiːə/ ⓘ ar-KEE-ə; sg.: archaeon /ɑːrˈkiːən/ ar-KEE-ən) is a domain of single-celled organisms. These microorganisms lack cell nuclei and are therefore prokaryotic. Archaea were initially classified as bacteria, receiving the name archaebacteria (in the Archaebacteria kingdom), but this term has fallen out of use.[4]
Archaeal cells have unique properties separating them from the other two domains, Bacteria and Eukaryota. Archaea are further divided into multiple recognized phyla. Classification is difficult because most have not been isolated in a laboratory and have been detected only by their gene sequences in environmental samples. It is unknown if these are able to produce endospores.
Archaea and bacteria are generally similar in size and shape, although a few archaea have very different shapes, such as the flat, square cells of Haloquadratum walsbyi.[5] Despite this morphological similarity to bacteria, archaea possess genes and several metabolic pathways that are more closely related to those of eukaryotes, notably for the enzymes involved in transcription and translation. Other aspects of archaeal biochemistry are unique, such as their reliance on ether lipids in their cell membranes,[6] including archaeols. Archaea use more diverse energy sources than eukaryotes, ranging from organic compounds such as sugars, to ammonia, metal ions or even hydrogen gas. The salt-tolerant Haloarchaea use sunlight as an energy source, and other species of archaea fix carbon (autotrophy), but unlike plants and cyanobacteria, no known species of archaea does both. Archaea reproduce asexually by binary fission, fragmentation, or budding; unlike bacteria, no known species of Archaea form endospores. The first observed archaea were extremophiles, living in extreme environments such as hot springs and salt lakes with no other organisms. Improved molecular detection tools led to the discovery of archaea in almost every habitat, including soil,[7] oceans, and marshlands. Archaea are particularly numerous in the oceans, and the archaea in plankton may be one of the most abundant groups of organisms on the planet.
Archaea are a major part of Earth's life. They are part of the microbiota of all organisms. In the human microbiome, they are important in the gut, mouth, and on the skin.[8] Their morphological, metabolic, and geographical diversity permits them to play multiple ecological roles: carbon fixation; nitrogen cycling; organic compound turnover; and maintaining microbial symbiotic and syntrophic communities, for example.[7][9]
No clear examples of archaeal pathogens or parasites are known. Instead they are often mutualists or commensals, such as the methanogens (methane-producing strains) that inhabit the gastrointestinal tract in humans and ruminants, where their vast numbers facilitate digestion. Methanogens are also used in biogas production and sewage treatment, and biotechnology exploits enzymes from extremophile archaea that can endure high temperatures and organic solvents.
- ^ Cite error: The named reference
Woesewas invoked but never defined (see the help page). - ^ Petitjean C, Deschamps P, López-García P, Moreira D (December 2014). "Rooting the domain archaea by phylogenomic analysis supports the foundation of the new kingdom Proteoarchaeota". Genome Biology and Evolution. 7 (1): 191–204. doi:10.1093/gbe/evu274. PMC 4316627. PMID 25527841.
- ^ "NCBI taxonomy page on Archaea".
- ^ Pace NR (May 2006). "Time for a change". Nature. 441 (7091): 289. Bibcode:2006Natur.441..289P. doi:10.1038/441289a. PMID 16710401. S2CID 4431143.
- ^ Stoeckenius W (October 1981). "Walsby's square bacterium: fine structure of an orthogonal procaryote". Journal of Bacteriology. 148 (1): 352–60. doi:10.1128/JB.148.1.352-360.1981. PMC 216199. PMID 7287626.
- ^ "Archaea Basic Biology". March 2018.
- ^ a b Chow C, Padda KP, Puri A, Chanway CP (September 2022). "An Archaic Approach to a Modern Issue: Endophytic Archaea for Sustainable Agriculture". Current Microbiology. 79 (11): 322. doi:10.1007/s00284-022-03016-y. PMID 36125558. S2CID 252376815.
- ^ Bang C, Schmitz RA (September 2015). "Archaea associated with human surfaces: not to be underestimated". FEMS Microbiology Reviews. 39 (5): 631–48. doi:10.1093/femsre/fuv010. PMID 25907112.
- ^ Moissl-Eichinger C, Pausan M, Taffner J, Berg G, Bang C, Schmitz RA (January 2018). "Archaea Are Interactive Components of Complex Microbiomes". Trends in Microbiology. 26 (1): 70–85. doi:10.1016/j.tim.2017.07.004. PMID 28826642.