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An extremophile is an organism that thrives in extreme conditions that are harmful 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 extreme in some way. They may be extraordinarily hot, or cold, or dry, or under immense pressures, or very salty or acidic. Such conditions are inhospitable to complex organisms. Some scientists suggest that life may have begun on Earth in hydrothermal vents far below the ocean surface.[1] High temperature habitats such as hot oceans, hot springs and deep ocean thermal vents would have occurred widely in the early Archaean eon (from 3.9 billion years ago). Adaptation to these conditions may have been crucial to the development of early forms of life.[2]

Types of extremophiles[change | change source]

Most known extremophiles are microbes. The domain Archaea contains well-known examples, but extremophiles occur in bacteria as well. It is a mistake to use the term extremophile for all archaeans, as some are mesophilic. Nor are all extremophiles unicellular; protostome animals found in similar environments.

Some extremophiles fall under several categories. For example, organisms living inside hot rocks deep under Earth's surface are both thermophilic and barophilic.

An organism with optimal growth at pH levels of 3 or below
An organism with optimal growth at pH levels of 9 or above
An organism that lives in microscopic spaces within rocks, fissures, aquifers, and faults filled with groundwater in the deep subsurface
An organism requiring at least 0.2molar concentrations of salt (NaCl) for growth[3]
An organism that can thrive at temperatures between 80–122 °C, such as those found in hydrothermal systems
An organism that lives inside rocks in cold deserts
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
An organism capable of growth in nutritionally limited environments
An organism capable of growth in environments with a high sugar concentration
An organism that lives optimally at high hydrostatic pressure; common in the deep terrestrial subsurface, as well as in oceanic trenches
An organism that qualifies as an extremophile under more than one category
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
An organism that can thrive at temperatures between 60–80 °C

References[change | change source]

  1. "Mars Exploration - Press kit" (PDF). NASA. June 2003. http://marsrovers.jpl.nasa.gov/newsroom/merlaunch.pdf. Retrieved 2009-07-14.
  2. Gouy M. & Chaussidon M. 2008. Ancient bacteria liked it hot. Nature 451: p635.
  3. Cavicchioli R. & Thomas T. 2000. Extremophiles. In: J. Lederberg (ed) Encyclopedia of Microbiology, 2nd ed, Vol 2, pp317–337. Academic Press, San Diego.