Thermus aquaticus
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| Thermus aquaticus Brock & Freeze, 1969 |
Thermus aquaticus is a species of bacterium that can tolerate high temperatures, one of several thermophilic bacteria that belong to the Deinococcus-Thermus group. It is the source of the heat-resistant enzyme Taq DNA Polymerase, one of the most important enzymes in molecular biology because of its use in the polymerase chain reaction (PCR) DNA amplification technique.
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[edit] History
When studies of biological organisms in hot springs began in the 1960s, scientists thought that the life of thermophilic bacteria could not be sustained in temperatures above about 55° Celsius (131° Fahrenheit)[1]. Soon, however, it was discovered that many bacteria in different springs not only survived but also thrived in higher temperatures. In 1969, Thomas Brock and Hudson Freeze of Indiana University reported a new species of thermophilic bacterium which they named Thermus aquaticus[2]. The bacterium was first discovered in the Great Fountain region of Yellowstone National Park, and has since been found in similar thermal habitats around the world.
[edit] Biology
It thrives at 70°C (160°F), but can survive at temperatures of 50°C to 80°C (120°F to 175°F). This bacterium is a chemotroph - it performs chemosynthesis in order to obtain food. However, since its range of temperature overlaps somewhat with that of the photosynthetic cyanobacteria that share its ideal environment, it is sometimes found living in conjuncture with its neighbors, obtaining energy for growth from their photosynthesis.
[edit] Enzymes from T. aquaticus
T. aquaticus has become famous as a source of thermostable enzymes, particularly the "Taq" DNA Polymerase, as described below.
- Aldolase
- Studies of this extreme thermophilic bacterium that could be grown in cell culture was initially centered on attempts to understand how protein enzymes (which normally inactivate at high temperature) can function at high temperature in thermophiles. In 1970 Freeze and Brock published an article describing a thermostable aldolase enzyme from Thermus aquaticus.[3]
- RNA polymerase
- The first polymerase enzyme isolated from Thermus aquaticus in 1974, was a DNA-dependent RNA polymerase[4], used in the process of Transcription.
- Taq I restriction enzyme
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For more details on this topic, see TaqI.
- Most molecular biologists probably became aware of Thermus aquaticus in the late 1970s or early 1980s because of the isolation of useful restriction endonucleases from this organism[5]. Use of the term "Taq" to refer to Thermus aquaticus arose at this time from the convention of giving restriction enzymes short names such as Sal and Hin, names derived from the genus and species of the source organisms.
- DNA polymerase ("Taq pol")
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For more details on this topic, see Taq polymerase.
- DNA polymerase was first isolated from Thermus aquaticus in 1976[6]. The first advantage that was found for this thermostable (temperature optimum 80°C) DNA polymerase was that it could be isolated in a purer form (free of other enzyme contaminants) than could the DNA polymerase from other sources. Later, Kary Mullis and other investigators at Cetus Corporation discovered that this enzyme could be used in the polymerase chain reaction (PCR) process for amplifying short segments of DNA[7], eliminating the need to add enzyme after every cycle of thermal denaturation of the DNA. The enzyme was also cloned, sequenced, modified (to produce the shorter 'Stoffel Fragment'), and produced in large quantities for commercial sale[8]. In 1989 Science magazine named Taq polymerase as its first "Molecule of the Year"[9]. In 1993, Dr. Mullis was awarded the Nobel Prize for his work with PCR.
- Other enzymes
- The high optimum temperature for Thermus aquaticus allows researchers to study reactions under conditions for which other enzymes lose activity. Other enzymes isolated from this organism include DNA ligase, Alkaline Phosphatase, NADH Oxidase, Isocitrate Dehydrogenase, Amylomaltase, and the ever-popular Fructose 1,6-Bisphosphate-Dependent L-Lactate Dehydrogenase.
[edit] Controversy
The commercial use of enzymes from T. aquaticus has not been without controversy. After Dr. Brock's studies, samples of the organism were deposited in the American Type Culture Collection, a public repository. Other scientists, including those at Cetus, obtained it from there. As the commercial potential of Taq Polymerase became apparent in the 1990s[10], the National Park Service labeled its use as the "Great Taq Rip-off."[11] Researchers working in National Parks are now required to sign "benefits sharing" agreements that would send a portion of later profits back to the Park Service.
[edit] See also
[edit] References
- ^ Thomas Brock's essay "Life at High Temperatures", available at [1]
- ^ Brock TD and Freeze H "Thermus aquaticus, a Nonsporulating Extreme Thermophile" J. Bact. vol. 98(1) pp.289-297 (Apr-1969).
- ^ Freeze H and Brock TD "Thermostable Aldolase from Thermus aquaticus" J. Bact. vol. 101(2) pp. 541-550 (Feb-1970).
- ^ Air GM and Harris JI "DNA-Dependent RNA Polymerase From the Thermophilic Bacterium Thermus aquaticus" FEBS Letters vol. 38(3) pp. 277-281 (1974).
- ^ Sato, S (Feb 1978). "A single cleavage of Simian virus 40 (SV40) DNA by a site specific endonuclease from Thermus aquaticus, Taq I". J. Biochem (Tokyo) 83 (2): 633–5.
- ^ Chien, A; Edgar DB, and Trela JM. "Deoxyribonucleic acid polymerase from the extreme thermophile Thermus aquaticus". J. Bact. 127 (3): 1550–1557.
- ^ Saiki, RK; et al. (1988). "Primer-directed enzymatic amplification of DNA with a thermostable DNA polymerase". Science 239: 487–91.
- ^ Lawyer FC et al. (1993). "High-level expression, purification, and enzymatic characterization of full-length Thermus aquaticus DNA polymerase ...". PCR Methods Appl. 2: 275-287. PMID 8324500.
- ^ Science Magazine, Dec. 22, 1989, p. 1543.
- ^ Detailed history of Cetus and the commercial aspects of PCR. available at [2]
- ^ Robbins J The Search for Private Profit in the Nation's Public Parks, The New York Times, Nov. 28, 2006.
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