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 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 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 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.
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 functional modulation of folding landscapes.
Some thermophilic organisms
- Pyrococcus furiosus
- Thermus aquaticus
- Thermus thermophilus
- Chloroflexus aurantiacus (photosynthetic bacterium)
- Thermococcus litoralis (see extremophiles)
- Pyrodictium abyssi (archaea)
- Bacillus stearothermophilus
- Thermobifida fusca (bacterium often found in decaying plant matter)
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 (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 process 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.
Books Examining Thermophiles
"The Microbes of Yellowstone" by Sheehan Kathy B, Patterson David J, Dicks Brett Leigh, and Henson Joan M. The Globe Pequot Press (2006)
Microorganisms and Life at High Temperatures by Brock Thomas D. Springer-Verlag (1978).
- 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.