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. Non-extremophilic organisms are called mesophiles.

Many extremophiles are members of the Archaea family, and indeed the terms are occasionally used interchangeably even though there are many mesophilic archaea as well as 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 a the way its environments differs from what is considered normal. 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.

• Alkaliphile: An organism with optimal growth at pH values of 9 and above.
• Barophile: An organism that lives optimally at high hydrostatic pressure.
• Endolith: An organism that lives inside rocks.
• Hypolith: An organism that lives inside rocks in cold deserts.
• Acidophile: An organism with a pH optimum for growth at, or below, pH 3.
• Halophile: An organism requiring at least 0.2M salt for growth.
• Thermophile or Hyperthermophile: An organism having a growth temperature optimum of 80 �C or higher.
• Oligotroph: An organism with optimal growth in nutrient limited conditions.
• Psychrophile: An organism having a growth temperature optimum of 15 �C or lower, and a maximum temperature of 20 �C.
• Toxitolerant: An organism able to withstand high levels of damaging agents. For example, living in water saturated with benzene, or in the water-core of a nuclear reactor (see Deinococcus radiodurans).
• Xerotolerant: An organism capable of growth at low water activity. For example, extreme halophile or endolith.

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)

ja:極限環境微生物