Editing Microorganism (section)

===Archaea===
{{main|Archaea}}
{{further|Prokaryote}}

Archaea are [[prokaryote|prokaryotic]] unicellular organisms, and form the first domain of life in [[Carl Woese]]'s [[three-domain system]]. A prokaryote is defined as having no [[cell nucleus]] or other [[lipid bilayer|membrane bound]]-[[organelle]]. Archaea share this defining feature with the bacteria with which they were once grouped. In 1990 the microbiologist Woese proposed the three-domain system that divided living things into bacteria, archaea and eukaryotes,<ref>{{Cite journal |author1=Woese, C. |author1-link=Carl Woese | author2=Kandler, O. | author3=Wheelis, M. | title=Towards a natural system of organisms: proposal for the domains Archaea, Bacteria, and Eucarya | doi= 10.1073/pnas.87.12.4576 | journal=Proc Natl Acad Sci USA | volume=87 | issue=12 | pages=4576–4579 | year=1990 | pmid=2112744 | pmc=54159 | bibcode=1990PNAS...87.4576W|doi-access=free }}</ref> and thereby split the prokaryote domain.

Archaea differ from bacteria in both their genetics and biochemistry. For example, while bacterial [[cell membrane]]s are made from [[phospholipid|phosphoglycerides]] with [[ester]] bonds, Achaean membranes are made of [[ether lipid]]s.<ref>{{Cite journal |author1=De Rosa, M. |author2=Gambacorta, A. | author3=Gliozzi, A. |title=Structure, biosynthesis, and physicochemical properties of archaebacterial lipids |journal=Microbiol. Rev. |volume=50 |issue=1 |pages=70–80 |date=1 March 1986|pmid=3083222 |pmc=373054 |doi=10.1128/mmbr.50.1.70-80.1986}}</ref> Archaea were originally described as [[extremophile]]s living in [[extreme environment]]s, such as [[hot spring]]s, but have since been found in all types of [[habitat]]s.<ref>{{Cite journal |author1=Robertson, C. |author2=Harris, J. |author3=Spear, J. |author4=Pace, N. | title=Phylogenetic diversity and ecology of environmental Archaea | journal=Curr Opin Microbiol | volume=8 | issue=6 | pages=638–642 | year=2005 | pmid=16236543 | doi=10.1016/j.mib.2005.10.003}}</ref> Only now are scientists beginning to realize how common archaea are in the environment, with [[Thermoproteota]] (formerly Crenarchaeota) being the most common form of life in the ocean, dominating ecosystems below {{convert|150|m}} in depth.<ref>{{Cite journal |author=Karner, M. B. |author2=DeLong, E. F. |author3=Karl, D. M. |title=Archaeal dominance in the mesopelagic zone of the Pacific Ocean |journal=Nature |volume=409 |issue=6819 |pages=507–510 |year=2001 |pmid=11206545 | doi=10.1038/35054051|bibcode=2001Natur.409..507K |s2cid=6789859 }}</ref><ref>{{Cite journal |author=Sinninghe Damsté, J. S. |author2=Rijpstra, W. I. |author3=Hopmans, E. C. |author4=Prahl, F. G. |author5=Wakeham, S. G. |author6=Schouten, S. |title=Distribution of Membrane Lipids of Planktonic Crenarchaeota in the Arabian Sea |journal=Appl. Environ. Microbiol. |volume=68 |issue=6 |pages=2997–3002 |date=June 2002 |pmid=12039760 |pmc=123986 | doi=10.1128/AEM.68.6.2997-3002.2002|bibcode=2002ApEnM..68.2997S }}</ref> These organisms are also common in soil and play a vital role in [[ammonia]] oxidation.<ref name=LeiningerUrich2006>{{cite journal |last1=Leininger |first1=S. |last2=Urich |first2=T. |last3=Schloter |first3=M. |last4=Schwark |first4=L.|last5=Qi|first5=J. |last6=Nicol |first6=G. W. |last7=Prosser |first7=J. I. |author-link7=James I. Prosser |last8=Schuster |first8=S. C. |last9=Schleper |first9=C.|title=Archaea predominate among ammonia-oxidizing prokaryotes in soils |journal=[[Nature (journal)|Nature]] |volume=442 |issue=7104 |year=2006|pages=806–809|pmid= 16915287 |doi=10.1038/nature04983|bibcode=2006Natur.442..806L|s2cid=4380804 }}</ref>

The combined domains of archaea and bacteria make up the most diverse and abundant group of [[organism]]s on Earth and inhabit practically all environments where the temperature is below +{{convert|140|°C}}. They are found in [[water]], [[soil]], [[Earth's atmosphere|air]], as the [[microbiome]] of an organism, [[hot spring]]s and even deep beneath the Earth's crust in [[Rock (geology)|rocks]].<ref name=Gold>{{Cite journal|author=Gold, T. |title=The deep, hot biosphere |journal=Proc. Natl. Acad. Sci. USA |volume=89 |issue=13 |pages=6045–6049 |year=1992 |pmid=1631089 |doi= 10.1073/pnas.89.13.6045 |pmc=49434 |bibcode=1992PNAS...89.6045G|doi-access=free }}</ref> The number of prokaryotes is estimated to be around five nonillion, or 5 × 10<sup>30</sup>, accounting for at least half the [[Biomass (ecology)|biomass]] on Earth.<ref>{{Cite journal|author=Whitman, W. |author2=Coleman, D. |author3=Wiebe, W. | title=Prokaryotes: The unseen majority | doi= 10.1073/pnas.95.12.6578 | journal=PNAS | volume=95 | issue=12 | pages=6578–6583 | year=1998 | pmid=9618454 | pmc=33863|bibcode=1998PNAS...95.6578W |doi-access=free }}</ref>

The biodiversity of the prokaryotes is unknown, but may be very large. A May 2016 estimate, based on laws of scaling from known numbers of species against the size of organism, gives an estimate of perhaps 1&nbsp;trillion species on the planet, of which most would be microorganisms. Currently, only one-thousandth of one percent of that total have been described.<ref name="NSF-2016002">{{cite news |title=Researchers find that Earth may be home to 1 trillion species |url=https://www.nsf.gov/news/news_summ.jsp?cntn_id=138446 |date=2 May 2016 |work=[[National Science Foundation]] |access-date=6 May 2016 }}</ref> [[Archaea|Archael cells]] of some species aggregate and transfer [[DNA]] from one cell to another through direct contact, particularly under stressful environmental conditions that cause [[DNA damage (naturally occurring)|DNA damage]].<ref>{{cite journal |last1=van Wolferen |first1=M.|last2=Wagner |first2=A|last3=van der Does |first3=C.|last4=Albers |first4=S. V. | year = 2016 | title = The archaeal Ced system imports DNA | journal = Proc Natl Acad Sci USA | volume = 113 | issue = 9| pages = 2496–501 | doi = 10.1073/pnas.1513740113 | pmid = 26884154 | pmc = 4780597 | bibcode = 2016PNAS..113.2496V | doi-access = free }}</ref><ref>Bernstein H, Bernstein C. Sexual communication in archaea, the precursor to meiosis. pp. 103–117 in Biocommunication of Archaea (Guenther Witzany, ed.) 2017. Springer International Publishing {{ISBN|978-3-319-65535-2}} DOI 10.1007/978-3-319-65536-9</ref>