A thermophile is an organism — a type of extremophile — which at relatively high temperatures, between 45 and 80 °C [cite book |title=Brock Biology of Microorganisms | year=2006| author=Madigan MT, Martino JM | edition=11th ed. |pages=136 |publisher=Pearson |isbn=0-13-196893-9] (113 and 176 °F). Many thermophiles are archaea.

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.

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 particularly extreme thermophiles for which the 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 PCR 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.cite journal|last=Mattila|first=P.|coauthors=Korpela J, Tenkanen T, Pitkanen K.|url=|title=Fidelity of DNA synthesis by the "Thermococcus litoralis" DNA polymerase--an extremely heat stable enzyme with proofreading activity|journal=Nucleic Acids Res.|date=September 25, 1991|volume=19|issue=18|pages=4967–73|pmid=1923765|doi=10.1093/nar/19.18.4967] "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 100°C, making it a hyperthermophile.

Taq DNA polymerase is adequate for most PCR, but one study reported that higher fidelity thermostable DNA polymerases such as Vent account for as much as 30% of DNA polymerase sales. [cite journal|last=Hamilton|first=SC|coauthors=Farchaus JW, Davis MC|year=2001|title=DNA polymerases as engines for biotechnology|journal=Biotechniques|volume=31|pages=370–6, 378–80, 382–3|pmid=11515374]

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 functional modulation of folding landscapes. It has been shown, in studies comparing homologous proteins from thermophilic and mesophilic organisms, that proteins from thermophilic organisms have a lower change in heat capacity upon unfolding. It is thought that this is due to residual structure in the unfolded state of the protein from the thermophilic organism.

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 20 °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 as an electron acceptor during respiration instead of oxygen. 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 organisma are coloured, due to the presence of photosynthetic pigments.

Genomic and Proteomic Features of Thermophiles

The genome and proteome composition of thermophiles are characterized by overrepresentation of purine bases in protein coding sequences, higher GC-content of the structural RNAs, distinct synonymous codon usage, enhanced usage of positively charged residues and aromatic residues, decrease in polar uncharged residues in the encoded protein. [cite journal|last=Das|first=S|coauthors=Paul S, Bag S, Dutta C.|year=2006|url=|title=Analysis of Nanoarchaeum equitans genome and proteome composition: indications for hyperthermophilic and parasitic adaptation|journal=BMC Genomics|volume=7|pages=186|doi=10.1186/1471-2164-7-186|pmid=16869956]

ee also

*Anaerobic digestion


*cite book|url=|title=The Microbes of Yellowstone|last=Sheehan|first=Kathy B|coauthors=Patterson David J, Dicks Brett Leigh, and Henson Joan M.|publisher=The Globe Pequot Press|year=2006
*cite book|url=|title=Microorganisms and Life at High Temperatures|last=Brock|first=Thomas D.|publisher=Springer-Verlag|year=1978|location=New York

External links

* [ Extreme Thermophile] Dead link|date=June 2008
* [ Major Groups Of Prokaryotes] Dead link|date=June 2008

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