psychrophile

File:Chlamydomonas nivalis.jpg Chlamydomonas nivalis.]]

The cold environments that psychrophiles inhabit are ubiquitous on Earth, as a large fraction of the planetary surface experiences temperatures lower than 10 °C. They are present in permafrost, polar ice, glaciers, snowfields and deep ocean waters. These organisms can also be found in pockets of sea ice with high salinity content. Microbial activity has been measured in soils frozen below −39 °C.{{cite journal |doi=10.1016/j.soilbio.2005.07.004 |title=Microbial activity in soils frozen to below −39°C |journal=Soil Biology and Biochemistry |volume=38 |issue=4 |pages=785–794 |year=2006 |last1=Panikov |first1=N.S. |last2=Flanagan |first2=P.W. |last3=Oechel |first3=W.C. |last4=Mastepanov |first4=M.A. |last5=Christensen |first5=T.R. }} In addition to their temperature limit, psychrophiles must also adapt to other extreme environmental constraints that may arise as a result of their habitat. These constraints include high pressure in the deep sea, and high salt concentration on some sea ice.{{cite journal |last1=Feller |first1=Georges |last2=Gerday |first2=Charles |date=December 2003 |title=Psychrophilic enzymes: hot topics in cold adaptation |journal=Nature Reviews Microbiology |volume=1 |issue=3 |pages=200–208 |doi=10.1038/nrmicro773|pmid=15035024 |s2cid=6441046 }}{{cite journal |author1=D'Amico, Salvino |author2=Tony Collins |author3=Jean-Claude Marx |author4=Georges Feller |author5=Charles Gerday |year=2006 |title=Psychrophilic Microorganisms: Challenges for Life |journal=EMBO Reports |volume=7 |issue=4 |pages=385–9 |doi=10.1038/sj.embor.7400662 |pmc=1456908 |pmid=16585939 }}

Psychrophiles are protected from freezing and the expansion of ice by ice-induced desiccation and vitrification (glass transition), as long as they cool slowly. Free living cells desiccate and vitrify between −10 °C and −26 °C. Cells of multicellular organisms may vitrify at temperatures below −50 °C. The cells may continue to have some metabolic activity in the extracellular fluid down to these temperatures, and they remain viable once restored to normal temperatures.

They must also overcome the stiffening of their lipid cell membrane, as this is important for the survival and functionality of these organisms. To accomplish this, psychrophiles adapt lipid membrane structures that have a high content of short, unsaturated fatty acids. Compared to longer saturated fatty acids, incorporating this type of fatty acid allows for the lipid cell membrane to have a lower melting point, which increases the fluidity of the membranes.{{cite journal |doi=10.1007/bf02705110 |title=A branched chain fatty acid promotes cold adaptation in bacteria |journal=Journal of Biosciences |volume=28 |issue=4 |pages=363–364 |year=2003 |last1=Chattopadhyay |first1=M. K. |last2=Jagannadham |first2=M. V. |pmid=12799482 |s2cid=44268024 }}{{cite journal |doi=10.1021/acs.jpclett.0c01675 |title=Cryostabilization of the Cell Membrane of a Psychrotolerant Bacteria via Homeoviscous Adaptation |journal= J. Phys. Chem. Lett. |volume=11|pages=7709–7716 |year=2020 |last1=Erimban |first1=S. |last2=Daschakraborty |first2=S. |issue=18 |pmid=32840376 |s2cid=221305712 }} In addition, carotenoids are present in the membrane, which help modulate the fluidity of it.{{cite journal |doi=10.1007/bf02705244 |title=Mechanism of bacterial adaptation to low temperature |journal=Journal of Biosciences |volume=31 |pages=157–165 |year=2006 |last1=Chattopadhyay |first1=M. K. |issue=1 |pmid=16595884 |s2cid=27521166 }}

Antifreeze proteins are also synthesized to keep psychrophiles' internal space liquid, and to protect their DNA when temperatures drop below water's freezing point. By doing so, the protein prevents any ice formation or recrystallization process from occurring.

The enzymes of these organisms have been hypothesized to engage in an activity-stability-flexibility relationship as a method for adapting to the cold; the flexibility of their enzyme structure will increase as a way to compensate for the freezing effect of their environment.

Certain cryophiles, such as Gram-negative bacteria Vibrio and Aeromonas spp., can transition into a viable but nonculturable (VBNC) state.{{Cite journal|last1=Maayer|first1=Pieter De|last2=Anderson|first2=Dominique|last3=Cary|first3=Craig|last4=Cowan|first4=Don A.|date=May 15, 2015|title=Some like it cold: understanding the survival strategies of psychrophiles|journal=EMBO Reports|volume=15|issue=5|pages=508–517|doi=10.1002/embr.201338170|pmc=4210084|pmid=24671034}} During VBNC, a micro-organism can respire and use substrates for metabolism – however, it cannot replicate. An advantage of this state is that it is highly reversible. It has been debated whether VBNC is an active survival strategy or if eventually the organism's cells will no longer be able to be revived.{{cite journal |doi=10.3389/fmicb.2014.00258 |pmid=24917854 |pmc=4040921 |title=The importance of the viable but non-culturable state in human bacterial pathogens |journal=Frontiers in Microbiology |volume=5 |pages=258 |year=2014 |last1=Li |first1=Laam |last2=Mendis |first2=Nilmini |last3=Trigui |first3=Hana |last4=Oliver |first4=James D. |last5=Faucher |first5=Sebastien P. |doi-access=free }} There is proof however it may be very effective – Gram positive bacteria Actinobacteria have been shown to have lived about 500,000 years in the permafrost conditions of Antarctica, Canada, and Siberia.{{cite journal |doi=10.1073/pnas.0706787104 |pmid=17728401 |pmc=1958816 |bibcode=2007PNAS..10414401J |title=Ancient bacteria show evidence of DNA repair |journal=Proceedings of the National Academy of Sciences |volume=104 |issue=36 |pages=14401–5 |last1=Johnson |first1=Sarah Stewart |last2=Hebsgaard |first2=Martin B. |last3=Christensen |first3=Torben R. |last4=Mastepanov |first4=Mikhail |last5=Nielsen |first5=Rasmus |last6=Munch |first6=Kasper |last7=Brand |first7=Tina |last8=Gilbert |first8=M. Thomas P. |last9=Zuber |first9=Maria T. |last10=Bunce |first10=Michael |last11=Rønn |first11=Regin |last12=Gilichinsky |first12=David |last13=Froese |first13=Duane |last14=Willerslev |first14=Eske |year=2007 |doi-access=free }}

Psychrophiles include bacteria, lichens, snow algae, phytoplankton, fungi, and insects.

Among the bacteria that can tolerate extreme cold are Arthrobacter sp., Psychrobacter sp. and members of the genera Halomonas, Pseudomonas, Hyphomonas, and Sphingomonas.{{cite journal |doi=10.1146/annurev-earth-040610-133514 |bibcode=2013AREPS..41...87S |title=Psychrophiles |journal=Annual Review of Earth and Planetary Sciences |volume=41 |pages=87–115 |last1=Siddiqui |first1=Khawar S. |last2=Williams |first2=Timothy J. |last3=Wilkins |first3=David |last4=Yau |first4=Sheree |last5=Allen |first5=Michelle A. |last6=Brown |first6=Mark V. |last7=Lauro |first7=Federico M. |last8=Cavicchioli |first8=Ricardo |year=2013 }} Another example is Chryseobacterium greenlandensis, a psychrophile that was found in 120,000-year-old ice.

Umbilicaria antarctica and Xanthoria elegans are lichens that have been recorded photosynthesizing at temperatures ranging down to −24 °C, and they can grow down to around −10 °C.{{cite journal |doi=10.1017/S1473550413000438 |bibcode=2014IJAsB..13..141C |title=The thermal limits to life on Earth |journal=International Journal of Astrobiology |volume=13 |issue=2 |pages=141–154 |last1=Clarke |first1=Andrew |year=2014 |url=http://nora.nerc.ac.uk/id/eprint/507274/1/Clarke.pdf |doi-access=free }}{{cite journal |last1=Barták |first1=Miloš |last2=Váczi |first2=Peter |last3=Hájek |first3=Josef |last4=Smykla |first4=Jerzy |title=Low-temperature limitation of primary photosynthetic processes in Antarctic lichens Umbilicaria antarctica and Xanthoria elegans |journal=Polar Biology |volume=31 |issue=1 |year=2007 |pages=47–51 |doi=10.1007/s00300-007-0331-x|bibcode=2007PoBio..31...47B |s2cid=46496194 }} Some multicellular eukaryotes can also be metabolically active at sub-zero temperatures, such as some conifers;{{cite book |title=Les résineux - Tome 1 : connaissance et reconnaissance |author=Riou-Nivert, Philippe |publisher=Institut pour le développement forestier |year=2001 |page=79}} those in the Chironomidae family are still active at −16 °C.{{cite journal |doi=10.1038/310225a0 |bibcode=1984Natur.310..225K |title=A novel cold-tolerant insect found in a Himalayan glacier |journal=Nature |volume=310 |issue=5974 |pages=225–227 |last1=Kohshima |first1=Shiro |year=1984 |s2cid=35899097 }}

File:Chlamydomonas3 (Antarctique).jpg can tolerate cold temperatures, like this Chlamydomonas green algae growing on snow in Antarctica.]]

Microalgae that live in snow and ice include green, brown, and red algae. Snow algae species such as Chloromonas sp., Chlamydomonas sp., and Chlorella sp. are found in polar environments.{{cite journal | last1=Davey | first1=Matthew P. | last2=Norman | first2=Louisa | last3=Sterk | first3=Peter | last4=Huete-Ortega | first4=Maria | last5=Bunbury | first5=Freddy | last6=Loh | first6=Bradford Kin Wai | last7=Stockton | first7=Sian | last8=Peck | first8=Lloyd S. | last9=Convey | first9=Peter | last10=Newsham | first10=Kevin K. | last11=Smith | first11=Alison G. | title=Snow algae communities in Antarctica: metabolic and taxonomic composition | journal=New Phytologist | publisher=Wiley | volume=222 | issue=3 | date=27 February 2019 | issn=0028-646X | doi=10.1111/nph.15701 | pages=1242–1255| pmid=30667072 | pmc=6492300 }}{{cite journal | last1=Khan | first1=Alia L. | last2=Dierssen | first2=Heidi M. | last3=Scambos | first3=Ted A. | last4=Höfer | first4=Juan | last5=Cordero | first5=Raul R. | title=Spectral characterization, radiative forcing and pigment content of coastal Antarctic snow algae: approaches to spectrally discriminate red and green communities and their impact on snowmelt | journal=The Cryosphere | publisher=Copernicus GmbH | volume=15 | issue=1 | date=13 January 2021 | issn=1994-0424 | doi=10.5194/tc-15-133-2021 | pages=133–148| bibcode=2021TCry...15..133K | s2cid=234356880 | doi-access=free }}

Some phytoplankton can tolerate extremely cold temperatures and high salinities that occur in brine channels when sea ice forms in polar oceans. Some examples are diatoms like Fragilariopsis cylindrus, Nitzchia lecointeii, Entomoneis kjellmanii, Nitzchia stellata, Thalassiosira australis, Berkelaya adeliense, and Navicula glaciei.{{cite journal | last1=Lauritano | first1=Chiara | last2=Rizzo | first2=Carmen | last3=Lo Giudice | first3=Angelina | last4=Saggiomo | first4=Maria | title=Physiological and Molecular Responses to Main Environmental Stressors of Microalgae and Bacteria in Polar Marine Environments | journal=Microorganisms | publisher=MDPI AG | volume=8 | issue=12 | date=9 December 2020 | issn=2076-2607 | doi=10.3390/microorganisms8121957 | page=1957| pmid=33317109 | pmc=7764121 | doi-access=free }}{{cite journal | last1=Young | first1=Jodi N. | last2=Goldman | first2=Johanna A. L. | last3=Kranz | first3=Sven A. | last4=Tortell | first4=Philippe D. | last5=Morel | first5=Francois M. M. | title=Slow carboxylation of R ubisco constrains the rate of carbon fixation during A ntarctic phytoplankton blooms | journal=New Phytologist | publisher=Wiley | volume=205 | issue=1 | date=3 October 2014 | issn=0028-646X | doi=10.1111/nph.13021 | pages=172–181| pmid=25283055 | doi-access=free }}{{cite journal | last1=Young | first1=JN | last2=Kranz | first2=SA | last3=Goldman | first3=JAL | last4=Tortell | first4=PD | last5=Morel | first5=FMM | title=Antarctic phytoplankton down-regulate their carbon-concentrating mechanisms under high CO2 with no change in growth rates | journal=Marine Ecology Progress Series | publisher=Inter-Research Science Center | volume=532 | date=21 July 2015 | issn=0171-8630 | doi=10.3354/meps11336 | pages=13–28| bibcode=2015MEPS..532...13Y | s2cid=87147116 | doi-access=free }}

Penicillium is a genus of fungi found in a wide range of environments including extreme cold.{{cite journal |doi=10.5958/2230-732x.2014.00258.7 |title=Extremophiles: An Overview of Microorganism from Extreme Environment |journal=International Journal of Agriculture, Environment and Biotechnology |volume=7 |issue=2 |pages=371 |year=2014 |last1=Gupta |first1=G.N. |last2=Srivastava |first2=S. |last3=Khare |first3=S.K. |last4=Prakash |first4=V. }}

Among the psychrophile insects, the Grylloblattidae or ice crawlers, found on mountaintops, have optimal temperatures between 1–4 °C.{{cite book|title=Evolution of the Insects|author1=Grimaldi, David |author2=Engel, Michael S. |date=2005 |chapter=Polyneoptera: Grylloblattodea: The Ice Crawlers |pages=222–224 |publisher=Cambridge University Press| location=New York City |isbn=9780521821490}} The wingless midge (Chironomidae) Belgica antarctica can tolerate salt, being frozen and strong ultraviolet, and has the smallest known genome of any insect. The small genome, of 99 million base pairs, is thought to be adaptive to extreme environments.{{cite web|last1=Gough|first1=Zoe|title=Antarctic midge has smallest insect genome|url=https://www.bbc.co.uk/nature/28525963|publisher=BBC|access-date=14 January 2018|date=12 August 2014}}

Psychrotrophic microbes are able to grow at temperatures below {{convert |7 |C |sigfig=3}}, but have better growth rates at higher temperatures. Psychrotrophic bacteria and fungi are able to grow at refrigeration temperatures, and can be responsible for food spoilage and as foodborne pathogens such as Yersinia. They provide an estimation of the product's shelf life, but also they can be found in soils,{{cite journal |doi=10.1111/j.1365-2672.1970.tb02215.x |title=An Ecological Study of the Psychrotrophic Bacteria of Soil, Water, Grass and Hay |journal=Journal of Applied Bacteriology |volume=33 |issue=2 |pages=420–435 |year=1970 |last1=Druce |first1=R. G. |last2=Thomas |first2=S. B. |pmid=5448255 }} in surface and deep sea waters,{{cite journal |doi=10.1007/s10126-001-0050-1 |pmid=14961338 |title=Characterization of Psychrotrophic Bacteria in the Surface and Deep-Sea Waters from the Northwestern Pacific Ocean Based on 16S Ribosomal DNA Analysis |journal=Marine Biotechnology |volume=3 |issue=5 |pages=454–462 |year=2001 |last1=Radjasa |first1=Ocky Karna |last2=Urakawa |first2=Hidetoshi |last3=Kita-Tsukamoto |first3=Kumiko |last4=Ohwada |first4=Kouichi |bibcode=2001MarBt...3..454R |s2cid=23054036 |url=http://eprints.undip.ac.id/355/1/Abstract_of_01OckyMarBiotech-2001.PDF }} in Antarctic ecosystems,{{cite web |url=http://es.scribd.com/doc/33323896/Psychrotrophic-Bacteria |title=Psychrotrophic bacteria isolated from Antarctic ecosystems |date=2007 |first1=A. |last1=Correa-Guimaraes |first2=J. |last2=Martín-Gil |first3=M. C. |last3=Ramos-Sánchez |first4=L. |last4=Vallejo-Pérez |publisher=Department of Forestry, Agricultural and Environmental Engineering, ETSIA, Avenida de Madrid, 57, Palencia, Spain}} and in foods.{{cite web |url=http://www.encyclopedia.com/doc/1G1-14605181.html |title=Psychrotrophic Bacteria in Foods: Disease and Spoilage. – Food Trade Review |publisher=Encyclopedia.com |date=1993-09-01 |access-date=2010-09-01}}

Psychrotrophic bacteria are of particular concern to the dairy industry.{{cite web |url=http://www.leonthemilkman.com/2006/03/18/the-case-of-psychrotrophic-bacteria/ |title=The case of Psychrotrophic bacteria |publisher=Leon the Milkman's Blog |date=2006-03-18 |access-date=2010-09-01 |archive-url=https://web.archive.org/web/20110713201215/http://www.leonthemilkman.com/2006/03/18/the-case-of-psychrotrophic-bacteria/ |archive-date=2011-07-13 |url-status=dead }}{{self-published inline|date=November 2018}} Most are killed by pasteurization; however, they can be present in milk as post-pasteurization contaminants due to less than adequate sanitation practices. According to the Food Science Department at Cornell University, psychrotrophs are bacteria capable of growth at temperatures at or less than {{convert |7 |C |sigfig=3}}. At freezing temperatures, growth of psychrotrophic bacteria becomes negligible or virtually stops.[https://web.archive.org/web/20100623132829/http://foodscience.cornell.edu/cals/foodsci/extension/upload/Bact-Milk-Shelf-Life-Doc.doc Steven C. Murphy, "Shelf Life of Fluid Milk Products – Microbial Spoilage", Food Science Department, Cornell University.]. Retrieved 22 November 2009.

All three subunits of the RecBCD enzyme are essential for physiological activities of the enzyme in the Antarctic Pseudomonas syringae, namely, repairing of DNA damage and supporting the growth at low temperature. The RecBCD enzymes are exchangeable between the psychrophilic P. syringae and the mesophilic E. coli when provided with the entire protein complex from same species. However, the RecBC proteins (RecBCPs and RecBCEc) of the two bacteria are not equivalent; the RecBCEc is proficient in DNA recombination and repair, and supports the growth of P. syringae at low temperature, while RecBCPs is insufficient for these functions. Finally, both helicase and nuclease activity of the RecBCDPs are although important for DNA repair and growth of P. syringae at low temperature, the RecB-nuclease activity is not essential in vivo.{{cite journal |doi=10.1371/journal.pone.0009412 |pmid=20195537 |pmc=2828478 |bibcode=2010PLoSO...5.9412P |title=All Three Subunits of RecBCD Enzyme Are Essential for DNA Repair and Low-Temperature Growth in the Antarctic Pseudomonas syringae Lz4W |journal=PLOS ONE |volume=5 |issue=2 |pages=e9412 |last1=Pavankumar |first1=Theetha L. |last2=Sinha |first2=Anurag K. |last3=Ray |first3=Malay K. |year=2010 |doi-access=free }}

File:Broken pack ice with cryopelagic antarctic diatoms.jpg algae covering the underwater surface of broken sea ice in the Ross Sea.]]

Microscopic algae that can tolerate extremely cold temperatures can survive in snow, ice, and very cold seawater. On snow, cold-tolerant algae can bloom on the snow surface covering land, glaciers, or sea ice when there is sufficient light. These snow algae darken the surface of the snow and can contribute to snow melt. In seawater, phytoplankton that can tolerate both very high salinities and very cold temperatures are able to live in sea ice. One example of a psychrophilic phytoplankton species is the ice-associated diatom Fragilariopsis cylindrus. Phytoplankton living in the cold ocean waters near Antarctica often have very high protein content, containing some of the highest concentrations ever measured of enzymes like Rubisco.

File:Belgica antarctica mating.jpg) Belgica antarctica.]]

Insects that are psychrotrophic can survive cold temperatures through several general mechanisms (unlike opportunistic and chill susceptible insects): (1) chill tolerance, (2) freeze avoidance, and (3) freeze tolerance.{{Cite journal|last=Sinclair|first=B.|date=1999|title=Insect cold tolerance: How many kinds of frozen?|url=https://www.eje.cz/artkey/eje-199902-0009_Insect_cold_tolerance_How_many_kinds_of_frozen.php|journal=Eur. J. Entomol.|volume=96|pages=157–164}} Chill tolerant insects succumb to freezing temperatures after prolonged exposure to mild or moderate freezing temperatures.{{Cite journal|last=Bale|first=J.|date=1996|title=Insect cold hardiness: A matter of life and death|url=https://www.eje.cz/artkey/eje-199603-0009_Insect_cold_hardiness_A_matter_of_life_and_death.php|journal=Eur. J. Entomol.|volume=93|pages=369–382}} Freeze avoiding insects can survive extended periods of time at sub-freezing temperatures in a supercooled state, but die at their supercooling point. Freeze tolerant insects can survive ice crystal formation within their body at sub-freezing temperatures. Freeze tolerance within insects is argued to be on a continuum, with some insect species exhibiting partial (e.g., Tipula paludosa,{{Cite journal|last1=Todd|first1=C.|last2=Block|first2=W.|date=1995|title=A comparison of the cold hardiness attributes in larvae of four species of Diptera|journal=CryoLetters|volume=16|pages=137–146}} Hemideina thoracica{{cite journal|last1=Sinclair|first1=Brent J.|last2=Worland|first2=M. Roger|last3=Wharton|first3=David A.|title=Ice nucleation and freezing tolerance in New Zealand alpine and lowland weta, Hemideina spp. (Orthoptera: Stenopelmatidae) |journal=Physiological Entomology|volume=24|issue=1|date=March 1999|pages=56–63|issn=0307-6962|doi=10.1046/j.1365-3032.1999.00112.x|s2cid=85725823}}

), moderate (e.g., Cryptocercus punctulatus{{cite journal|last1=Hamilton|first1=R. L.|last2=Mullins|first2=D. E.|last3=Orcutt|first3=D. M.|title=Freezing-tolerance in the woodroachCryptocercus punctulatus (Scudder)|journal=Experientia|volume=41|issue=12|year=1985|pages=1535–1537|issn=0014-4754|doi=10.1007/BF01964793|s2cid=40606283}}), and strong freezing tolerance (e.g., Eurosta solidaginis{{cite book|last1=Baust|first1=John G.|last2=Nishino|first2=Misako|title=Insects at Low Temperature|chapter=Freezing Tolerance in the Goldenrod Gall Fly (Eurosta solidaginis)|year=1991|pages=260–275|doi=10.1007/978-1-4757-0190-6_11|isbn=978-1-4757-0192-0}} and Syrphus ribesii{{cite journal|last1=Hart|first1=Andrew|last2=Bale|first2=Jeffrey|title=Evidence for the first strongly freeze-tolerant insect found in the U.K.|journal=Ecological Entomology|volume=22|issue=2|year=1997|pages=242–245|issn=0307-6946|doi=10.1046/j.1365-2311.1997.t01-1-00048.x|bibcode=1997EcoEn..22..242H |s2cid=85423418}}), and other insect species exhibiting freezing tolerance with low supercooling point (e.g., Pytho deplanatus{{cite journal|last1=Ring|first1=Richard A|title=Freezing-tolerant insects with low supercooling points|journal=Comparative Biochemistry and Physiology Part A: Physiology|volume=73|issue=4|year=1982|pages=605–612|issn=0300-9629|doi=10.1016/0300-9629(82)90267-5}}).

In 1940, ZoBell and Conn stated that they had never encountered "true psychrophiles" or organisms that grow best at relatively low temperatures.{{cite journal |author=Ingraham, J. L. |title=Growth of psychrophilic bacteria |journal=Journal of Bacteriology |volume=76 |issue=1 |pages=75–80 |year=1958 |doi=10.1128/jb.76.1.75-80.1958 |pmc=290156 |pmid=13563393}} In 1958, J. L. Ingraham supported this by concluding that there are very few or possibly no bacteria that fit the textbook definitions of psychrophiles. Richard Y. Morita emphasizes this by using the term psychrotroph to describe organisms that do not meet the definition of psychrophiles. The confusion between the terms psychrotrophs and psychrophiles was started because investigators were unaware of the thermolability of psychrophilic organisms at the laboratory temperatures. Due to this, early investigators did not determine the cardinal temperatures for their isolates.{{cite journal |author=Morita, Richard Y. |title=Psychrophilic bacteria |journal=Bacteriological Reviews |volume=39 |issue=2 |pages=144–67 |year=1975 |doi=10.1128/br.39.2.144-167.1975 |pmc=413900 |pmid=1095004}}

The similarity between these two is that they are both capable of growing at zero, but optimum and upper temperature limits for the growth are lower for psychrophiles compared to psychrotrophs.{{cite journal |vauthors=Russell NJ, Harrisson P, Johnston IA, Jaenicke R, Zuber M, Franks F, Wynn-Williams D|title=Cold Adaptation of Microorganisms [and Discussion] |journal= Philosophical Transactions of the Royal Society of London |series=Series B Biological Sciences |volume=326 |pages=595–611 |number=1237, Life at Low Temperatures |year=1990 |jstor=2398707 |doi=10.1098/rstb.1990.0034|pmid=1969649 |bibcode=1990RSPTB.326..595R |doi-access= }} Psychrophiles are also more often isolated from permanently cold habitats compared to psychrotrophs. Although psychrophilic enzymes remain under-used because the cost of production and processing at low temperatures is higher than for the commercial enzymes that are presently in use, the attention and resurgence of research interest in psychrophiles and psychrotrophs will be a contributor to the betterment of the environment and the desire to conserve energy.

• Chionophile
• Extremophile
• Halophile
• Ice algae
• Mesophile
• Osmophile
• Pathogenic microorganisms in frozen environments
• Thermophile
• Xerophile

{{Reflist}}

• {{cite book | author=Bej, Asim K. | author2=Jackie Aislabie | author3=Ronald M. Atlas | title=Polar Microbiology: The Ecology, Biodiversity and Bioremediation Potential of Microorganisms in Extremely Cold Environments | publisher=Crc Pr Inc | date=15 December 2009 | isbn=978-1420083842}}
• {{Cite journal |author=Murata, Yoshinori |display-authors=etal |title=Genome-wide expression analysis of yeast response during exposure to 4C |journal=Extremophiles |date=2006 |volume=10 |pages=117–128 |doi=10.1007/s00792-005-0480-1 |pmid=16254683 |issue=2 |arxiv=1109.6589 |s2cid=11658804 }}
• {{Cite journal |author=Mikucki, J. A. |display-authors=etal |title=A contemporary microbially maintained subglacial ferrous 'ocean' |journal=Science |volume=324 |pages=397–400 |date=2009 |doi=10.1126/science.1167350 |pmid=19372431 |issue=5925|bibcode=2009Sci...324..397M |s2cid=44802632 }}
• {{cite journal |author=Sandle, T. |author2=Skinner, K. |year=2013 |title=Study of psychrophilic and psychrotolerant microorganisms isolated in cold rooms used for pharmaceutical processing |journal=Journal of Applied Microbiology |volume=114 |issue=4 |pages=1166–1174 | doi=10.1111/jam.12101|pmid=23216715 |s2cid=26032521 }}

{{Extremophile}}

Category:Microbial growth and nutrition

Category:Cryobiology