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Psychrophile

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ThelichenXanthoria eleganscan continue tophotosynthesizeat −24 °C.[1]

Psychrophilesorcryophiles(adj.psychrophilicorcryophilic) areextremophilicorganismsthat are capable ofgrowthandreproductionin low temperatures, ranging from −20 °C (−4 °F)[2]to 20 °C (68 °F).[3]They are found in places that are permanently cold, such as the polar regions and the deep sea. They can be contrasted withthermophiles,which are organisms that thrive at unusually high temperatures, andmesophilesat intermediate temperatures. Psychrophile is Greek for 'cold-loving', fromAncient Greekψυχρός(psukhrós)'cold, frozen'.

Many such organisms arebacteriaorarchaea,but someeukaryotessuch aslichens,snow algae,phytoplankton,fungi, andwingless midges,are also classified as psychrophiles.

Biology

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Snow surface withsnow algaeChlamydomonas nivalis.

Habitat

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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 inpermafrost,polar ice,glaciers,snowfieldsanddeep oceanwaters. These organisms can also be found in pockets of sea ice with high salinity content.[4]Microbial activity has been measured insoilsfrozen below −39 °C.[5]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.[6][4]

Adaptations

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Psychrophiles are protected from freezing and the expansion of ice by ice-induceddesiccationandvitrification(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.[2]

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.[7][8]In addition,carotenoidsare present in the membrane, which help modulate the fluidity of it.[9]

Antifreeze proteinsare also synthesized to keep psychrophiles' internal space liquid, and to protect theirDNAwhen temperatures drop below water's freezing point. By doing so, the protein prevents any ice formation or recrystallization process from occurring.[9]

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.[4]

Certain cryophiles, such as Gram-negative bacteriaVibrioandAeromonasspp., can transition into aviable but nonculturable (VBNC)state.[10]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.[11]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.[12]

Taxonomic range

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

Among the bacteria that can tolerate extreme cold areArthrobactersp.,Psychrobactersp. and members of the generaHalomonas,Pseudomonas,Hyphomonas,andSphingomonas.[13]Another example isChryseobacterium greenlandensis,a psychrophile that was found in 120,000-year-old ice.

Umbilicaria antarcticaandXanthoria elegansare lichens that have been recorded photosynthesizing at temperatures ranging down to −24 °C, and they can grow down to around −10 °C.[14][1]Some multicellular eukaryotes can also be metabolically active at sub-zero temperatures, such as some conifers;[15]those in theChironomidaefamily are still active at −16 °C.[16]

Psychrophilicalgaecan tolerate cold temperatures, like thisChlamydomonasgreen algae growing on snow inAntarctica.

Microalgaethat live in snow and ice include green, brown, and red algae.Snow algaespecies such asChloromonassp.,Chlamydomonassp.,andChlorellasp.are found in polar environments.[17][18]

Somephytoplanktoncan tolerate extremely cold temperatures and high salinities that occur in brine channels whensea iceforms in polar oceans. Some examples arediatomslikeFragilariopsis cylindrus,Nitzchia lecointeii,Entomoneis kjellmanii,Nitzchia stellata,Thalassiosira australis,Berkelaya adeliense,andNavicula glaciei.[19][20][21]

Penicilliumis a genus of fungi found in a wide range of environments including extreme cold.[22]

Among the psychrophile insects, theGrylloblattidaeor ice crawlers, found on mountaintops, have optimal temperatures between 1–4 °C.[23]The wingless midge (Chironomidae)Belgica antarcticacan tolerate salt, being frozen and strong ultraviolet, and has the smallest known genome of any insect. The smallgenome,of 99 millionbase pairs,is thought to be adaptive to extreme environments.[24]

Psychrotrophic bacteria

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Psychrotrophic microbes are able to grow at temperatures below 7 °C (44.6 °F), 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 asfoodborne pathogenssuch asYersinia.They provide an estimation of the product's shelf life, but also they can be found in soils,[25]in surface and deep sea waters,[26]in Antarctic ecosystems,[27]and in foods.[28]

Psychrotrophic bacteria are of particular concern to thedairy industry.[29][self-published source?]Most are killed bypasteurization;however, they can be present in milk as post-pasteurization contaminants due to less than adequate sanitation practices. According to the Food Science Department atCornell University,psychrotrophs are bacteria capable of growth at temperatures at or less than 7 °C (44.6 °F). At freezing temperatures, growth of psychrotrophic bacteria becomes negligible or virtually stops.[30]

All three subunits of the RecBCD enzyme are essential for physiological activities of the enzyme in the AntarcticPseudomonas syringae,namely, repairing of DNA damage and supporting the growth at low temperature. The RecBCD enzymes are exchangeable between the psychrophilicP. syringaeand the mesophilicE. coliwhen 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 ofP. syringaeat 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 ofP. syringaeat low temperature, the RecB-nuclease activity is not essential in vivo.[31]

Psychrophilic microalgae

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Antarcticdiatomalgae covering the underwater surface of brokensea icein theRoss 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.[18]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 diatomFragilariopsis cylindrus.[19]Phytoplankton living in the cold ocean waters nearAntarcticaoften have very high protein content, containing some of the highest concentrations ever measured of enzymes likeRubisco.[20]

Psychrotrophic insects

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The wingless midge (Chironomidae)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.[32]Chill tolerant insects succumb to freezing temperatures after prolonged exposure to mild or moderate freezing temperatures.[33]Freeze avoiding insects can survive extended periods of time at sub-freezing temperatures in a supercooled state, but die at theirsupercoolingpoint.[33]Freeze tolerant insects can survive ice crystal formation within their body at sub-freezing temperatures.[33]Freeze tolerance within insects is argued to be on a continuum, with some insect species exhibiting partial (e.g.,Tipula paludosa,[34]Hemideina thoracica[35] ), moderate (e.g.,Cryptocercus punctulatus[36]), and strong freezing tolerance (e.g.,Eurosta solidaginis[37]andSyrphus ribesii[38]),and other insect species exhibiting freezing tolerance with low supercooling point (e.g.,Pytho deplanatus[39]).[32]

Psychrophile versus psychrotroph

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In 1940, ZoBell and Conn stated that they had never encountered "true psychrophiles" or organisms that grow best at relatively low temperatures.[40]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 termpsychrotrophto describe organisms that do not meet the definition of psychrophiles. The confusion between the termspsychrotrophsandpsychrophileswas 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.[41]

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.[42]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.[42]

See also

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References

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  1. ^abBarták, Miloš; Váczi, Peter; Hájek, Josef; Smykla, Jerzy (2007). "Low-temperature limitation of primary photosynthetic processes in Antarctic lichens Umbilicaria antarctica and Xanthoria elegans".Polar Biology.31(1): 47–51.doi:10.1007/s00300-007-0331-x.S2CID46496194.
  2. ^abNeufeld, Josh; Clarke, Andrew; Morris, G. John; Fonseca, Fernanda; Murray, Benjamin J.; Acton, Elizabeth; Price, Hannah C. (2013)."A Low Temperature Limit for Life on Earth".PLOS One.8(6): e66207.Bibcode:2013PLoSO...866207C.doi:10.1371/journal.pone.0066207.PMC3686811.PMID23840425.
  3. ^Moyer, Craig L.; Collins, Eric R.; Morita, Richard Y. (2017-01-01)."Psychrophiles and Psychrotrophs".Reference Module in Life Sciences.Elsevier.doi:10.1016/b978-0-12-809633-8.02282-2.ISBN978-0-12-809633-8.Retrieved2022-05-22.
  4. ^abcD'Amico, Salvino; Tony Collins; Jean-Claude Marx; Georges Feller; Charles Gerday (2006)."Psychrophilic Microorganisms: Challenges for Life".EMBO Reports.7(4): 385–9.doi:10.1038/sj.embor.7400662.PMC1456908.PMID16585939.
  5. ^Panikov, N.S.; Flanagan, P.W.; Oechel, W.C.; Mastepanov, M.A.; Christensen, T.R. (2006). "Microbial activity in soils frozen to below −39°C".Soil Biology and Biochemistry.38(4): 785–794.doi:10.1016/j.soilbio.2005.07.004.
  6. ^Feller, Georges; Gerday, Charles (December 2003). "Psychrophilic enzymes: hot topics in cold adaptation".Nature Reviews Microbiology.1(3): 200–208.doi:10.1038/nrmicro773.PMID15035024.S2CID6441046.
  7. ^Chattopadhyay, M. K.; Jagannadham, M. V. (2003). "A branched chain fatty acid promotes cold adaptation in bacteria".Journal of Biosciences.28(4): 363–364.doi:10.1007/bf02705110.PMID12799482.S2CID44268024.
  8. ^Erimban, S.; Daschakraborty, S. (2020). "Cryostabilization of the Cell Membrane of a Psychrotolerant Bacteria via Homeoviscous Adaptation".J. Phys. Chem. Lett.11(18): 7709–7716.doi:10.1021/acs.jpclett.0c01675.PMID32840376.S2CID221305712.
  9. ^abChattopadhyay, M. K. (2006). "Mechanism of bacterial adaptation to low temperature".Journal of Biosciences.31(1): 157–165.doi:10.1007/bf02705244.PMID16595884.S2CID27521166.
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  11. ^Li, Laam; Mendis, Nilmini; Trigui, Hana; Oliver, James D.; Faucher, Sebastien P. (2014)."The importance of the viable but non-culturable state in human bacterial pathogens".Frontiers in Microbiology.5:258.doi:10.3389/fmicb.2014.00258.PMC4040921.PMID24917854.
  12. ^Johnson, Sarah Stewart; Hebsgaard, Martin B.; Christensen, Torben R.; Mastepanov, Mikhail; Nielsen, Rasmus; Munch, Kasper; Brand, Tina; Gilbert, M. Thomas P.; Zuber, Maria T.; Bunce, Michael; Rønn, Regin; Gilichinsky, David; Froese, Duane; Willerslev, Eske (2007)."Ancient bacteria show evidence of DNA repair".Proceedings of the National Academy of Sciences.104(36): 14401–5.Bibcode:2007PNAS..10414401J.doi:10.1073/pnas.0706787104.PMC1958816.PMID17728401.
  13. ^Siddiqui, Khawar S.; Williams, Timothy J.; Wilkins, David; Yau, Sheree; Allen, Michelle A.; Brown, Mark V.; Lauro, Federico M.; Cavicchioli, Ricardo (2013). "Psychrophiles".Annual Review of Earth and Planetary Sciences.41:87–115.Bibcode:2013AREPS..41...87S.doi:10.1146/annurev-earth-040610-133514.
  14. ^Clarke, Andrew (2014)."The thermal limits to life on Earth"(PDF).International Journal of Astrobiology.13(2): 141–154.Bibcode:2014IJAsB..13..141C.doi:10.1017/S1473550413000438.
  15. ^Riou-Nivert, Philippe (2001).Les résineux - Tome 1: connaissance et reconnaissance.Institut pour le développement forestier. p. 79.
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  17. ^Davey, Matthew P.; Norman, Louisa; Sterk, Peter; Huete‐Ortega, Maria; Bunbury, Freddy; Loh, Bradford Kin Wai; Stockton, Sian; Peck, Lloyd S.; Convey, Peter; Newsham, Kevin K.; Smith, Alison G. (27 February 2019)."Snow algae communities in Antarctica: metabolic and taxonomic composition".New Phytologist.222(3). Wiley: 1242–1255.doi:10.1111/nph.15701.ISSN0028-646X.PMC6492300.PMID30667072.
  18. ^abKhan, Alia L.; Dierssen, Heidi M.; Scambos, Ted A.; Höfer, Juan; Cordero, Raul R. (13 January 2021)."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".The Cryosphere.15(1). Copernicus GmbH: 133–148.Bibcode:2021TCry...15..133K.doi:10.5194/tc-15-133-2021.ISSN1994-0424.S2CID234356880.
  19. ^abLauritano, Chiara; Rizzo, Carmen; Lo Giudice, Angelina; Saggiomo, Maria (9 December 2020)."Physiological and Molecular Responses to Main Environmental Stressors of Microalgae and Bacteria in Polar Marine Environments".Microorganisms.8(12). MDPI AG: 1957.doi:10.3390/microorganisms8121957.ISSN2076-2607.PMC7764121.PMID33317109.
  20. ^abYoung, Jodi N.; Goldman, Johanna A. L.; Kranz, Sven A.; Tortell, Philippe D.; Morel, Francois M. M. (3 October 2014)."Slow carboxylation of R ubisco constrains the rate of carbon fixation during A ntarctic phytoplankton blooms".New Phytologist.205(1). Wiley: 172–181.doi:10.1111/nph.13021.ISSN0028-646X.PMID25283055.
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  23. ^Grimaldi, David; Engel, Michael S. (2005). "Polyneoptera: Grylloblattodea: The Ice Crawlers".Evolution of the Insects.New York City:Cambridge University Press.pp. 222–224.ISBN9780521821490.
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Further reading

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Retrieved from "https://en.wikipedia.org/w/index.php?title=Psychrophile&oldid=1198624106#Psychrotrophic_bacteria"