Extremophile
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An extremophile is an organism, usually unicellular, which thrives in or requires "extreme" conditions. The definition of "extreme" is anthropocentric; to the organism itself its environment is completely normal. Thus, strictly, "extremophilic" labels should be used to describe the environment that an organism thrives in, regardless of how "normal" or "extreme" they may seem to human beings. For example, human beings are classified as a mesophilic aerobe.
When used in the context of describing organisms that thrive in environments that are extreme from human perspectives, most extremophiles are members of the Archaea family, although the terms are occasionally used interchangeably to describe the many extremophilic bacteria and eukarya. Not all extremophiles are unicellular. Examples of extremophilic metazoa are the psychrophilic Grylloblattodea (insects) and antarctic krill (crustaceans).
Types of extremophiles
There are many different classes of extremophiles, each corresponding to the way its chosen environment differs from what is considered "normal" by other organisms. 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 an optimum pH level at or below pH 3.
- Aerobe: requires O2 to survive.
- Alkaliphile: An organism with optimal growth at pH levels of 9 or above.
- Anaerobic: does not need O2 to survive.
- Endolith: An organism that lives inside rocks.
- Halophile: An organism requiring at least 0.2M of NaCl for growth.
- Hypolith: An organism that lives inside rocks in cold deserts.
- Mesophile: An organism that thrives in temperatures between 15-60 °C.
- Metalotolerant: capable of tolerating high levels of heavy metals, such as copper, cadmium, arsenic, and zinc.
- Microaerophilic: requires levels of O2 that are lower than atmospheric levels.
- Oligotroph: An organism capable of growth in nutritionally limited environments.
- Piezophile: An organism that lives optimally at high hydrostatic pressure. See also Barophile
- Psychrophile: An organism that can thrive at temperatures of 15 °C or lower.
- Radioresistant: resistant to high levels of ionizing radiation.
- Thermophile: An organism that can thrive at temperatures between 60-80 °C.
- Xerotolerant: requires very little water to survive.
Bacteria on the Moon
Apollo 12 astronauts retrieved parts from the lunar probe Surveyor 3 for analysis. A common bacteria, Streptococcus mitis, was unintentionally present inside the spacecraft's camera at launch. Around 50 to 100 of these bacteria survived dormant in this harsh environment for three years, to be detected when Apollo 12 brought the camera back to Earth. Many bacteria have dormant forms which can survive in harsh environments, and merely being dormant is not sufficient to make an organism be considered an extremophile.
External links
- http://www.nhm.ac.uk/zoology/extreme.html
- Extremophiles 2002 (http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=12813059&itool=iconpmc)
- DaveDarling's Encyclopedia of Astrobiology, Astronomy, and Spaceflight (http://www.daviddarling.info/encyclopedia/E/extremophile.html|)fr:Extrémophile