Extremophile
An extremophile is an organism that thrives in extreme conditions that are detrimental to most life on Earth. In contrast, organisms from moderate temperature or neutral pH environments may be termed mesophiles or neutrophiles.
In the 1980s and 1990s, biologists found that microbial life has a capacity for surviving in extreme environments. These are niches that are extraordinarily hot, or cold, or dry, or under immense pressures. They are completely inhospitable to complex organisms. Some scientists even concluded that life may have begun on Earth in hydrothermal vents far under the ocean's surface.[1]
Most known extremophiles are microbes. The domain Archaea contains renowned examples, but extremophiles are present in numerous and diverse genetic lineages of both bacteria and archaeans. Furthermore, it is erroneous to use the term extremophile to encompass all archaeans, as some are mesophilic. Neither are all extremophiles unicellular; protostome animals found in similar environments.
Types of extremophiles
Many extremophiles fall under multiple categories. For example, organisms living inside hot rocks deep under Earth's surface are both thermophilic and barophilic.
- Acidophiles
- An organism with optimal growth at pH levels of 3 or below
- Alkaliphiles
- An organism with optimal growth at pH levels of 9 or above
- Endoliths
- An organism that lives in microscopic spaces within rocks, fissures, aquifers, and faults filled with groundwater in the deep subsurface
- Halophiles
- An organism requiring at least 0.2molar concentrations of salt (NaCl) for growth[2]
- Hyperthermophile
- An organism that can thrive at temperatures between 80–122 °C, such as those found in hydrothermal systems
- Hypoliths
- An organism that lives inside rocks in cold deserts
- Lithoautotrophs
- An organism (usually bacteria) whose sole source of carbon is carbon dioxide and exergonic inorganic oxidation (chemolithotrophs) such as Nitrosomonas europaea; these organisms are capable of deriving energy from reduced mineral compounds like pyrites, and are active in geochemical cycling and the weathering of parent bedrock to form soil
- Metalotolerant
- capable of tolerating high levels of dissolved heavy metals in solution, such as copper, cadmium, arsenic, and zinc; examples include Ferroplasma sp. and Ralstonia metallidurans
- Oligotroph
- An organism capable of growth in nutritionally limited environments
- Osmophile
- An organism capable of growth in environments with a high sugar concentration
- Piezophile
- An organism that lives optimally at high hydrostatic pressure; common in the deep terrestrial subsurface, as well as in oceanic trenches
- Polyextremophile
- An organism that qualifies as an extremophile under more than one category
- Psychrophile/Cryophile
- An organism that grows better at temperatures of 15 °C or lower; common in cold soils, permafrost, polar ice, cold ocean water, and in or under alpine snowpack
- Radioresistant
- Organisms resistant to high levels of ionizing radiation, most commonly ultraviolet radiation, but also including organisms capable of resisting nuclear radiation
- Thermophile
- An organism that can thrive at temperatures between 60–80 °C
- Thermoacidophile
- Combination of thermophile and acidophile that prefer temperatures of 70–80 °C and pH between 2 and 3
- Xerophile
- An organism that can grow in extremely dry, desiccating conditions; this type is exemplified by the soil microbes of the Atacama Desert
References
- ↑ "Mars Exploration - Press kit" (PDF). NASA. June 2003. Retrieved 2009-07-14.
- ↑ Cavicchioli R. & Thomas T. 2000. Extremophiles. In: J. Lederberg (ed) Encyclopedia of Microbiology, 2nd ed, Vol 2, pp317–337. Academic Press, San Diego.