Harley, John P. Department of Biological Sciences, Eastern Kentucky University, Richmond, Kentucky.
Last reviewed:May 2021
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An organism that tolerates and grows optimally under extreme environmental conditions. Extremophiles are organisms, predominantly microorganisms, that thrive in environmental conditions hostile to most life, including extremes of temperature (both high and low), acidity or alkalinity, salt concentration, and pressure. Most extremophile organisms are prokaryotes belonging to the domains Bacteria and Archaea that have adapted to survive in ecological niches that would be deadly to most other life forms (see illustration). One well-known extremophile is Thermus aquaticus, which grows in geothermal springs at 70°C (158°F) and uses the process called chemosynthesis to convert the springs' heat and mineral compounds into metabolic energy. Another interesting extremophile is Desulforudis audaxviator, which lives 3.2 km (2 miles) beneath the Earth's surface and utilizes radioactive decay from uranium to generate energy. The unique metabolic and enzymatic strategies that these microorganisms employ to withstand extreme conditions have made them objects of intense interest to basic research and innovative biotechnology. Nevertheless, because the harsh conditions under which extremophiles live make their discovery difficult, it is estimated that only 1% of them have been isolated from nature. See also: Archaea; Bacteria; Bacterial physiology and metabolism; Bacteriology; Biochemistry; Ecology; Ecosystem; Microbial ecology; Microbiology; Population ecology
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