Editing Extremophile (section)

==Classification==
===Definitions===
[[File:Microorganisms from the hypersaline Lake Tyrrell.jpg|thumb|upright=1.5| Microscopic image from the hypersaline [[Lake Tyrrell]] (salinity> 20% w/v), in which the eukaryotic [[chlorophyte]], ''[[Dunaliella salina]]'', can be tentatively identified. ''Dunaliella salina'' is grown commercially for the carotenoid, [[β-carotene]], which is widely used as a natural food colorant as well as a precursor to vitamin A. Alongside is the haloarchaeon, ''[[Haloquadratum walsbyi]]'', which has flat square-shaped cells with gas vesicles that allow flotation to the surface, most likely to acquire oxygen.]]

*[[Acidophile (organisms)|Acidophile]]: an organism with optimal growth at [[pH]] levels of 3.0 or below.

*[[Alkaliphile]]: an organism with optimal growth at [[pH]] levels of 9.0 or above.

*[[Capnophile]]: an organism with optimal growth conditions in high concentrations of carbon dioxide. An example would be ''[[Mannheimia succiniciproducens]],'' a bacterium that inhabits a ruminant animal's digestive system.<ref>{{Cite journal |last1=Hong |first1=Soon Ho |last2=Kim |first2=Jin Sik |last3=Lee |first3=Sang Yup |last4=In |first4=Yong Ho |last5=Choi |first5=Sun Shim |last6=Rih |first6=Jeong-Keun |last7=Kim |first7=Chang Hoon |last8=Jeong |first8=Haeyoung |last9=Hur |first9=Cheol Goo |last10=Kim |first10=Jae Jong |date=2004-09-19 |title=The genome sequence of the capnophilic rumen bacterium Mannheimia succiniciproducens |journal=Nature Biotechnology |volume=22 |issue=10 |pages=1275–81 |doi=10.1038/nbt1010 |issn=1087-0156 |pmid=15378067 |doi-access=free |s2cid=35247112}}</ref>

*[[Halophile]]: an organism with optimal growth at a concentration of dissolved salts of 50&nbsp;g/L (= 5% m/v) or above (for comparison, the [[ocean salinity]] is about 35&nbsp;g/L (= 3.5% m/v)).

*[[Piezophile|Hyperpiezophile]]: an organism with optimal growth at [[hydrostatic pressure]]s above 50&nbsp;MPa (= 493&nbsp;atm = 7,252&nbsp;psi).

*[[Hyperthermophile]]: an organism with optimal growth at temperatures above {{Convert|80|C||abbr=on}}.

*[[Metallotolerant]]: an organism capable of tolerating high levels of dissolved heavy metals in solution, such as [[copper]], [[cadmium]], [[arsenic]], and [[zinc]]. Examples include ''[[Ferroplasma]] sp.'', ''[[Cupriavidus metallidurans]]'' and [[GFAJ-1]].<ref name="refute">{{Cite news |date=9 July 2012 |title=Studies refute arsenic bug claim |work=BBC News |url=https://www.bbc.co.uk/news/science-environment-18770964 |access-date=10 July 2012}}</ref><ref>{{Cite journal |author-link5=Julia Vorholt |vauthors=Erb TJ, Kiefer P, Hattendorf B, Günther D, Vorholt JA |date=July 2012 |title=GFAJ-1 is an arsenate-resistant, phosphate-dependent organism |journal=Science |volume=337 |issue=6093 |pages=467–70 |bibcode=2012Sci...337..467E |doi=10.1126/science.1218455 |pmid=22773139 |s2cid=20229329|doi-access=free }}</ref><ref>{{Cite journal |vauthors=Reaves ML, Sinha S, Rabinowitz JD, Kruglyak L, Redfield RJ |date=July 2012 |title=Absence of detectable arsenate in DNA from arsenate-grown GFAJ-1 cells |journal=Science |volume=337 |issue=6093 |pages=470–73 |arxiv=1201.6643 |bibcode=2012Sci...337..470R |doi=10.1126/science.1219861 |pmc=3845625 |pmid=22773140}}</ref>

*[[Oligotroph]]: an organism with optimal growth in nutritionally limited environments.

*[[Osmophile]]: an organism with optimal growth in environments with a high sugar concentration.

*[[Piezophile]] or barophile: an organism with optimal growth in [[hydrostatic pressure]]s above 10&nbsp;MPa (= 99&nbsp;atm = 1,450&nbsp;psi).

*Polyextremophile (mixed Latin/Greek compound for ''affection for many extremes''): not a well-defined category itself – an organism that qualifies as an extremophile under more than one category.

*[[Psychrophile]] or cryophile: an organism with optimal growth at temperatures of {{Convert|15|C||abbr=}} or lower.

*[[Radioresistant]]: organisms resistant to high levels of [[ionizing radiation]], most commonly [[ultraviolet radiation]]. This category also includes organisms capable of resisting [[nuclear radiation]], notably [[gamma ray]]s.

*Sulphophile: an organism with optimal growth conditions in high concentrations of [[sulfur]]. An example would be ''[[Sulfurovum epsilonproteobacteria]]'', a sulfur-oxidizing bacteria that inhabits deep-water sulfur vents.<ref>{{Cite journal |last1=Meier |first1=Dimitri V |last2=Pjevac |first2=Petra |last3=Bach |first3=Wolfgang |last4=Hourdez |first4=Stephane |author5-link=Peter Girguis|last5=Girguis |first5=Peter R |last6=Vidoudez |first6=Charles |last7=Amann |first7=Rudolf |last8=Meyerdierks |first8=Anke |date=2017-04-04 |title=Niche partitioning of diverse sulfur-oxidizing bacteria at hydrothermal vents |journal=The ISME Journal |volume=11 |issue=7 |pages=1545–58 |doi=10.1038/ismej.2017.37 |issn=1751-7362 |pmc=5520155 |pmid=28375213|bibcode=2017ISMEJ..11.1545M }}</ref>

*[[Thermophile]]: an organism with optimal growth at temperatures above {{Convert|45|C||abbr=on}}.

*[[Xerophile]]: an organism with optimal growth at [[water activity]] below 0.8.

===Overview===
{| class="wikitable" style="border: none;"
! colspan="4"| Limits of known life on Earth<ref name="Marion2004">{{Cite journal |last1=Marion |first1=Giles M. |last2=Fritsen |first2=Christian H. |last3=Eicken |first3=Hajo |last4=Payne |first4=Meredith C. |date=December 2003 |title=The Search for Life on Europa: Limiting Environmental Factors, Potential Habitats, and Earth Analogues |journal=Astrobiology |volume=3 |issue=4 |pages=785–811 |bibcode=2003AsBio...3..785M |doi=10.1089/153110703322736105 |pmid=14987483}}</ref>
|-
! Factor !! Environment / source !! Limits !! Examples
|-
| High temperature || [[Hydrothermal vent|Submarine hydrothermal vents]], [[oceanic crust]]|| {{convert|110|°C}} to {{convert|122|°C}}<ref name=":0" /><ref name="Marion2004" /> || ''[[Pyrolobus fumarii]]'', ''[[Pyrococcus furiosus]]'', [[Thermophile|other species]]
|-
| Low temperature || Ice || {{convert|-20|°C}} to {{convert|-25|°C}}<ref name="NeufeldClarke20132">{{Cite journal |last1=Neufeld |first1=Josh |last2=Clarke |first2=Andrew |last3=Morris |first3=G. John |last4=Fonseca |first4=Fernanda |last5=Murray |first5=Benjamin J. |last6=Acton |first6=Elizabeth |last7=Price |first7=Hannah C. |year=2013 |title=A Low Temperature Limit for Life on Earth |journal=PLOS ONE |volume=8 |issue=6 |page=e66207 |bibcode=2013PLoSO...866207C |doi=10.1371/journal.pone.0066207 |pmc=3686811 |pmid=23840425 |doi-access=free}}</ref> || ''[[Rhodotorula glutinis]]'', [[Psychrophile|other species]]
|-
| [[Alkalinity|Alkaline]] systems || [[Soda lake]]s || [[pH]] > 11<ref name="Marion2004" /> || ''[[Psychrobacter]]'', ''[[Vibrio]]'', ''[[Arthrobacter]]'', ''[[Natronobacterium]], [[Alkaliphile|other species]]''
|-
| [[Acid]]ic systems || Volcanic springs, [[acid mine drainage]] || pH 0.06 to 1.0<ref name="Marion2004" /> ||  ''[[Picrophilus]]'', [[Acidophile|other species]]
|-
| [[Ionizing radiation]] || [[Cosmic ray]]s, [[X-ray]]s, [[radioactive decay]] || 1,500 to 6,000 [[Gray (unit)|Gy]]<ref name="Marion2004" />
| rowspan="2" | ''[[Deinococcus radiodurans]]'', ''[[Rubrobacter]]'', ''[[Thermococcus gammatolerans]]''
|-
| [[UV radiation]] || Sunlight || 5,000 [[Joule|J]]/m<sup>2</sup><ref name="Marion2004" />

|-
| High pressure || [[Mariana Trench]] || 1,100 [[Bar (unit)|bar]]<ref name="Marion2004" /> || ''[[Pyrococcus]]'' sp., [[Piezophile|other species]]
|-
| Salinity || High salt concentration || [[Water activity|a<sub>w</sub>]] ~ 0.6<ref name="Marion2004" /> ||  ''[[Halobacteriaceae]]'', ''[[Dunaliella salina]]'', [[Halophile|other species]]
|-
| [[Desiccation]] || [[Atacama Desert]] (Chile), [[McMurdo Dry Valleys]] (Antarctica) || ~60% relative humidity<ref name="Marion2004" /> || ''[[Chroococcidiopsis]], [[Xerophile|other species]]''
|-
| Deep crust || Accessed in some gold mines ||  ||  ''[[Desulforudis audaxviator]]'', ''[[Halicephalobus mephisto]]'', ''[[Mylonchulus brachyurus]]'', unidentified arthropods
|}

===Polyextremophiles===
There are many classes of extremophiles that range all around the globe; each corresponding to the way its environmental niche differs from mesophilic conditions.  These classifications are not exclusive. Many extremophiles fall under multiple categories and are classified as '''polyextremophiles'''. For example, organisms living inside hot rocks deep under Earth's surface are thermophilic and piezophilic such as ''Thermococcus barophilus''.<ref>{{Cite journal |vauthors=Marteinsson VT, Birrien JL, Reysenbach AL, Vernet M, Marie D, Gambacorta A, Messner P, Sleytr UB, Prieur D |date=April 1999 |title=Thermococcus barophilus sp. nov., a new barophilic and hyperthermophilic archaeon isolated under high hydrostatic pressure from a deep-sea hydrothermal vent |journal=International Journal of Systematic Bacteriology |volume=49 Pt 2 |issue=2 |pages=351–59 |doi=10.1099/00207713-49-2-351 |pmid=10319455 |doi-access=free}}</ref> A polyextremophile living at the summit of a mountain in the [[Atacama Desert]] might be a [[radioresistant]] [[xerophile]], a [[psychrophile]], and an [[oligotroph]]. Polyextremophiles are well known for their ability to tolerate both high and low [[pH]] levels.<ref>{{Cite journal |display-authors=6 |vauthors=Yadav AN, Verma P, Kumar M, Pal KK, Dey R, Gupta A, Padaria JC, Gujar GT, Kumar S, Suman A, Prasanna R |date=2014-05-31 |title=Diversity and phylogenetic profiling of niche-specific Bacilli from extreme environments of India |journal=Annals of Microbiology |volume=65 |issue=2 |pages=611–29 |doi=10.1007/s13213-014-0897-9 |s2cid=2369215|doi-access=free }}</ref> Note that "tolerant" or "resistant" organisms are not necessarily extremophiles: tolerant or resistant organisms may ''survive despite harsh conditions'' instead of ''thriving in harsh conditions''. For example, the [[tardigrade]] (''Tardigrada'' spp.), despite being highly resistant to many stresses, is not an extremophile properly speaking.<ref name="LauraRobertson">{{cite web |url=https://frontlinegenomics.com/everything-you-need-and-want-to-know-about-tardigrades/|title=Everything you need (and want) to know about tardigrades|publisher=Front Line Genomics|access-date=17 May 2025|vauthors = Robertson L |date=October 2022}}</ref>