Hyperthermophile

A hyperthermophile is an organism that thrives in extremely hot environments— from 60 °C (140 °F) upwards. An optimal temperature for the existence of hyperthermophiles is above 80 °C (176 °F). Hyperthermophiles are a subset of extremophiles, which are often micro-organisms within the domain Archaea, although some bacteria are able to tolerate temperatures of around 100 °C (212 °F), as well. Some bacteria can live at temperatures higher than 100 °C at large depths in sea where water does not boil because of high pressure. Many hyperthermophiles are also able to withstand other environmental extremes such as high acidity or radiation levels.

History

Hyperthermophiles were first discovered by Thomas D. Brock in 1965, in hot springs in Yellowstone National Park, Wyoming.^[1][2] Since then, more than 70 species have been discovered.^[3] The most hardy hyperthermophiles yet discovered live on the superheated walls of deep-sea hydrothermal vents, requiring temperatures of at least 90 °C for survival. An extraordinary heat-tolerant hyperthermophile is the recently discovered Strain 121^[4] which has been able to double its population during 24 hours in an autoclave at 121 °C (hence its name); the current record growth temperature is 122 °C, for Methanopyrus kandleri.

Although no hyperthermophile has yet been discovered living at temperatures above 122 °C, their existence is very possible (Strain 121 survived being heated to 130 °C for two hours, but was not able to reproduce until it had been transferred into a fresh growth medium, at a relatively cooler 103 °C). However, it is thought unlikely that microbes could survive at temperatures above 150 °C, as the cohesion of DNA and other vital molecules begins to break down at this point.

Research

Early research into hyperthermophiles speculated that their genome could be characterized by high guanine-cytosine content; however, recent studies show that "there is no obvious correlation between the GC content of the genome and the optimal environmental growth temperature of the organism."^[5][6]

The protein molecules in the hyperthermophiles exhibit hyperthermostability—that is, they can maintain structural stability (and therefore function) at high temperatures. Such proteins are homologous to their functional analogues in organisms which thrive at lower temperatures, but have evolved to exhibit optimal function at much greater temperatures. Most of the low-temperature homologues of the hyperthermostable proteins would be denatured above 60 °C. Such hyperthermostable proteins are often commercially important, as chemical reactions proceed faster at high temperatures.^[7][8]

Cell structure

The cell membrane contains high levels of saturated fatty acids to retain its shape at high temperatures.

Specific hyperthermophiles

Archaea

• Strain 121, an archaeon living at 121 °C in the Pacific Ocean.
• Pyrolobus fumarii, an archaeon living at 113 °C in Atlantic hydrothermal vents.
• Pyrococcus furiosus, an archaeon which thrives at 100 °C, first discovered in Italy near a volcanic vent.
• Archaeoglobus fulgidus
• Methanococcus jannaschii
• Aeropyrum pernix
• Sulfolobus
• Methanopyrus kandleri strain 116, an archaeon in 80–122 °C in a Central Indian Ridge.

Gram-negative Bacteria

• Geothermobacterium ferrireducens, which thrives in 65–100 °C in Obsidian Pool, Yellowstone National Park.
• Aquifex aeolicus
• Thermotoga, especially Thermotoga maritima

See also

• Mesophile
• Psychrophile
• Thermophile
• Unique properties of hyperthermophilic archaea

References

1. Joseph Seckbach, et al.: Polyextremophiles - life under multiple forms of stress. Springer, Dordrecht 2013, ISBN 978-94-007-6487-3,preface; @google books
2. The Value of Basic Research: Discovery of Thermus aquaticus and Other Extreme Thermophiles
3. Hyperthermophilic Microorganisms
4. Microbe from depths takes life to hottest known limit
5. High guanine-cytosine content is not an adaptation to high temperature: a comparative analysis amongst prokaryotes
6. Zheng H, Wu H; Wu (December 2010). "Gene-centric association analysis for the correlation between the guanine-cytosine content levels and temperature range conditions of prokaryotic species". BMC Bioinformatics 11: S7. doi:10.1186/1471-2105-11-S11-S7. PMC: 3024870. PMID 21172057.
7. "Analysis of Nanoarchaeum equitans genome and proteome composition: indications for hyperthermophilic and parasitic adaptation."
8. Saiki, R. K.; Gelfand, D. H.; Stoffel, S; Scharf, S. J.; Higuchi, R; Horn, G. T.; Mullis, K. B.; Erlich, H. A. (1988). "Primer-directed enzymatic amplification of DNA with a thermostable DNA polymerase". Science 239 (4839): 487–91. doi:10.1126/science.2448875. PMID 2448875.

Further reading

Stetter, Karl (Feb 2013). "A brief history of the discovery of hyperthermophilic life". Biochemical Society Transactions 41 (1): 416–420. doi:10.1042/BST20120284. PMID 23356321.