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Thermophiles, a type of extremophile, produce some of the bright colors of Grand Prismatic Spring, Yellowstone National Park

An extremophile (from Latin extremus meaning "extreme" and Greek philiā (φιλία) meaning "love") is an organism that thrives in and even may require physically or geochemically extreme conditions that are detrimental to the majority of 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 an amazing flexibility for surviving in extreme environments - niches that are extraordinarily hot, or cold, or dry, or under immense pressures - that would be 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 include the Pompeii worm, the psychrophilic Grylloblattodea (insects), Antarctic krill (a crustacean), and the "water bear".

Contents

Types of extremophiles

There are many different classes of extremophiles, each corresponding to the way its environmental niche differs from mesophilic conditions. These classifications are not exclusive. Many extremophiles fall under multiple categories. For example, organisms living inside hot rocks deep under Earth's surface are both thermophilic and barophilic.

Acidophile
An organism with optimal growth at pH levels of 3 or below
Alkaliphile
An organism with optimal growth at pH levels of 9 or above
Endolith
An organism that lives in microscopic spaces within rocks, such as pores between aggregate grains; these may also be called cryptoendoliths, a term that also includes organisms populating fissures, aquifers, and faults filled with groundwater in the deep subsurface
Halophile
An organism requiring at least 0.2M 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
Hypolith
An organism that lives inside rocks in cold deserts
Lithoautotroph
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

Extremophiles and astrobiology

Astrobiology is the field concerned with forming theories, such as panspermia, about the distribution, nature, and future of life in the universe. In it, microbial ecologists, astronomers, planetary scientists, geochemists, philosophers, and explorers cooperate constructively to guide the search for life on other planets. Astrobiologists are particularly interested in studying extremophiles, as many organisms of this type are capable of surviving in environments similar to those known to exist on other planets. For example, Mars may have regions in its deep subsurface permafrost that could harbor endolith communities. The subsurface water ocean of Jupiter's moon Europa may harbor life, especially at hypothesized hydrothermal vents at the ocean floor.

References

  1. ^ "Mars Exploration - Press kit" (PDF). NASA. June 2003. http://marsrovers.jpl.nasa.gov/newsroom/merlaunch.pdf. Retrieved 2009-07-14.  
  2. ^ Cavicchioli, R. & Thomas, T. 2000. Extremophiles. In: J. Lederberg. (ed.) Encyclopedia of Microbiology, Second Edition, Vol. 2, pp. 317–337. Academic Press, San Diego.

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