Psychrophiles or cryophiles (adj. cryophilic) are extremophilic organisms that are capable of growth and reproduction in cold temperatures, ranging from −15°C to +10°C. Temperatures as low as −15°C are found in pockets of very salty water (brine) surrounded by sea ice. They can be contrasted with thermophiles, which thrive at unusually hot temperatures. The environments they inhabit are ubiquitous on Earth, as a large fraction of our planetary surface experiences temperatures lower than 15°C. They are present in alpine and arctic soils, high-latitude and deep ocean waters, polar ice, glaciers, and snowfields. They are of particular interest to astrobiology, the field dedicated to the formulation of theory about the possibility of extraterrestrial life, and to geomicrobiology, the study of microbes active in geochemical processes. In experimental work at University of Alaska Fairbanks, a 1000 litre biogas digester using psychrophiles harvested from "mud from a frozen lake in Alaska" has produced 200–300 litres of methane per day, about 20–30% of the output from digesters in warmer climates.
Psychrophiles use a wide variety of metabolic pathways, including photosynthesis, chemoautotrophy (also sometimes known as lithotrophy), and heterotrophy, and form robust, diverse communities. Most psychrophiles are bacteria or archaea, and psychrophily is present in widely diverse microbial lineages within those broad groups. Additionally, recent[when?] research has discovered novel groups of psychrophilic fungi living in oxygen-poor areas under alpine snowfields. A further group of eukaryotic cold-adapted organisms are snow algae, which can cause watermelon snow. Psychrophiles are characterized by lipid cell membranes chemically resistant to the stiffening caused by extreme cold, and often create protein 'antifreezes' to keep their internal space liquid and protect their DNA even in temperatures below water's freezing point.
- Gupta, Sujata (2010-11-06). "Biogas comes in from the cold". New Scientist (London: Sunita Harrington). p. 14. Retrieved 2011-02-04.
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- Yoshinori Murata, et al. (2006). "Genome-wide expression analysis of yeast response during exposure to 4C". Extremophiles 10 (2): 117–112. doi:10.1007/s00792-005-0480-1.
- Mikucki JA, et al. (2009). "A contemporary microbially maintained subglacial ferrous 'ocean'". Science 324 (5925): 397–400. doi:10.1126/science.1167350. PMID 19372431.
- Sandle, T. and Skinner, K. (2013). Study of psychrophilic and psychrotolerant microorganisms isolated in cold rooms used for pharmaceutical processing, Journal of Applied Microbiology, 114 (4), 1166—1174 DOI: 10.1111/jam.12101