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A thermophile is an organism – a type of extremophile – which thrives at relatively high temperatures, above 45 °C. Many thermophiles are archaea.
Thermophiles have been 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 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 polymerase chain reaction), and in washing agents.
Thermophiles are classified into obligate and facultative thermophiles: obligate thermophiles (also called extreme thermophiles) require such high temperatures for growth, while facultative thermophiles (also called moderate thermophiles) can thrive at high temperatures but also at lower temperatures (below 50 °C). Hyperthermophiles are particular extreme thermophiles of which optimal temperatures are above 80 °C].
Importance of enzymes from thermophiles
The enzymes isolated from some extremophiles have proven to be of great use in the biotechnology industry, able to function under conditions that would denature enzymes taken from most "normal" organisms.
The most commonly used DNA polymerase for the polymerase chain reaction technique is Taq DNA polymerase, originally isolated from Thermus aquaticus, a bacterial species found in surface aquatic locations such as Yellowstone National Park hot springs. For a few PCR applications, the lack of proofreading by Taq DNA polymerase is a problem.
The DNA polymerase from Thermococcus litoralis was shown to have a proofreading exonuclease activity. (Mattila et al, 1991)Thermococcus litoralis was isolated from a deep sea hydrothermal vent. This DNA polymerase is marketed as "Vent" polymerase.
Another heat stable polymerase comes from the organism Pyrococcus furiosus, (Pfu). This organism grows optimally at temperatures between 105-113 degrees celsius, making it a hyperthermophile.
Taq DNA polymerase is adequate for most PCR, but one study (Hamilton et al, 2001). reported that higher fidelity thermostable DNA polymerases such as Vent account for as much as 30% of DNA polymerase sales.
In addition, the study of proteins from thermophilic organisms has provided important insight into the mechanism of protein folding because these proteins must be stable at temperatures that would denature typical proteins. Therefore, understanding how thermophilic proteins have evolved to be stable can yield information about the modulation of folding landscapes.
Some thermophilic organisms
- Thermus aquaticus
- Thermus thermophilus
- Chloroflexus aurantiacus (photosynthetic bacterium)
- Thermococcus litoralis (see extremophiles)
- Pyrodictium abyssi (archaea)
- Bacillus stearothermophilus
The Pompeii worm survives the scalding temperatures surrounding deep-sea hydrothermal vents thanks to a symbiotic relationship with thermophilic bacteria.
Extreme Thermophiles
Thermophiles are heat-loving (hence the name), with an optimum growth temperature of 50 °C or more, a maximum of up to 70 °C or more, and a minimum of about 20 °C, but these are only approximate. Some extreme thermophiles require a very high temperature (80 °C to 105 °C) for growth. Their membranes and enzymes are unusually stable at high temperatures, which is necessary for the PCR process which involves cycles of heating to break the hydrogen bonds in DNA and leave single strands that can be copied repeatedly. Most of these Archea require elemental sulfur for growth. Some are anaerobes that use the sulfur as an electron acceptor that they use for respiration instead of oxygen. Some are lithotrophs that oxydize sulfur as an energy source. These live in environments with a very low pH (less than pH 2) level because they acidify their own environment by oxidizing sulfur to sulfuric acid. These hyperthermophiles are inhabitants of hot, sulfur-rich environments usually associated with volcanism, such as hot springs, geysers and fumaroles. When thermophilic prokaryotes are present in hot springs and geothermic vents and are specially adapted to grow in these environments. In these places, especially in Yellowstone National Park, we find a zonation of microorganisms according to their temperature optima. Often these organisma are coloured, due to the presence of photosynthetic pigments.
See also
References
- Mattila P, Korpela J, Tenkanen T, Pitkanen K. (1991) "Fidelity of DNA synthesis by the Thermococcus litoralis DNA polymerase--an extremely heat stable enzyme with proofreading activity" in Nucleic Acids Res. Sep 25;19(18):4967-73
- Hamilton SC, Farchaus JW, Davis MC (2001) "DNA polymerases as engines for biotechnology" by . in Biotechniques, 31:370-6, 378-80, 382-3
- Zierenberg Robert A., Adams Michael W. W., and Arp Alissa J. (2000) "Life in extreme environments: Hydrothermal vents" in Proc Natl Acad Sci U S A. 2000 November; 97(24): 1296112962.
- Thermophilic Microorganisms and Life at High Temperatures by Brock, Thomas D. New York: Springer-Verlag, 1978.
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Thermophil | Organisme thermophile | 好熱菌 | Thermofiel | 嗜熱生物
"Thermophile"