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