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A thermophile is an organism — a type of extremophile — that thrives at relatively high temperatures, between 45 and 80 °C[1] (113 and 176 °F). Many thermophiles are archaea. It has been suggested that thermophilic eubacteria are among the earliest bacteria.[2]

Thermophiles are found in various geothermally heated regions of the Earth such as hot springs like those in Yellowstone National Park (see image) and deep sea hydrothermal vents, as well as decaying plant matter such as peat bogs and compost.

As a prerequisite for their survival, thermophiles contain enzymes that can function at high temperature. Some of these enzymes are used in molecular biology (for example, heat-stable DNA polymerases for PCR), and in washing agents.

"Thermophile" is derived from the Greek: θερμότητα (thermotita), meaning heat, and Greek: φίλια (philia), love.



Thermophiles are classified into obligate and facultative thermophiles: Obligate thermophiles (also called extreme thermophiles) require such high temperatures for growth, whereas facultative thermophiles (also called moderate thermophiles) can thrive at high temperatures but also at lower temperatures (below 50 °C). Hyperthermophiles are particularly extreme thermophiles for which the optimal temperatures are above 80 °C.

Extreme thermophiles

Thermophiles, meaning heat-loving organisms, are organisms with an optimum growth temperature of 50 °C or more, a maximum of up to 70 °C or more, and a minimum of about 40 degrees C, but these are only approximate. Some extreme thermophiles (hyperthermophiles) require a very high temperature (80 °C to 105 °C) for growth. Their membranes and proteins are unusually stable at these extremely high temperatures. Thus many important biotechnological processes utilize thermophilic enzymes because of their ability to withstand intense heat.

Many of the hyperthermophiles Archea require elemental sulfur for growth. Some are anaerobes that use the sulfur instead of oxygen as an electron acceptor during cellular respiration. Some are lithotrophs that oxidize sulfur to sulfuric acid as an energy source, thus requiring the microorganism to be adapted to very low pH (i.e., it is an acidophile as well as thermophile). These organisms are inhabitants of hot, sulfur-rich environments usually associated with volcanism, such as hot springs, geysers, and fumaroles. In these places, especially in Yellowstone National Park, we find a zonation of microorganisms according to their temperature optima. Often these organisms are coloured, due to the presence of photosynthetic pigments.

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