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 often above 80 °C (176 °F).[1] Hyperthermophiles are often within the domain Archaea, although some bacteria are also able to tolerate extreme temperatures. Some of these bacteria are able to live at temperatures greater than 100 °C, deep in the ocean where high pressures increase the boiling point of water. Many hyperthermophiles are also able to withstand other environmental extremes, such as high acidity or high radiation levels. Hyperthermophiles are a subset of extremophiles. Their existence may support the possibility of extraterrestrial life, showing that life can thrive in environmental extremes.

History

Hyperthermophiles isolated from hot springs in Yellowstone National Park were first reported by Thomas D. Brock in 1965.[2][3] Since then, more than 70 species have been established.[4] The most extreme hyperthermophiles 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 Strain 121,[5] 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 shown to thrive at temperatures >122 °C, their existence is possible. Strain 121 survives 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.

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."[6][7]

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 analogs in organisms that thrive at lower temperatures but have evolved to exhibit optimal function at much greater temperatures. Most of the low-temperature homologs 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.[8][9]

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

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

References

Stetter, K. (2006). "History of discovery of the first hyperthermophiles". Extremophiles. 10 (5): 357–362. doi:10.1007/s00792-006-0012-7. S2CID 36345694.
Joseph Seckbach, et al.: Polyextremophiles - life under multiple forms of stress. Springer, Dordrecht 2013, ISBN 978-94-007-6487-3,preface; @google books
The Value of Basic Research: Discovery of Thermus aquaticus and Other Extreme Thermophiles
Hyperthermophilic Microorganisms
Microbe from depths takes life to hottest known limit
High guanine-cytosine content is not an adaptation to high temperature: a comparative analysis amongst prokaryotes
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.
"Analysis of Nanoarchaeum equitans genome and proteome composition: indications for hyperthermophilic and parasitic adaptation."
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. Bibcode:1988Sci...239..487S. doi:10.1126/science.239.4839.487. PMID 2448875.