Hyperthermophile

A hyperthermophile is an organism that thrives in extremely hot environments— from 60 degrees Celsius (140 degrees Fahrenheit) upwards. An optimal temperature for the existence of Hypothermophiles are above 80°C (176°F). Hyperthermophiles are a subset of extremophiles, micro-organisms within the domain Archaea, although some bacteria are able to tolerate temperatures of around 100°C (212°F), too. Many hyperthermophiles are also able to withstand other environmental extremes such as high acidity or radiation levels.

History

Hyperthermophiles were first discovered in the 1960s, in hot springs in Yellowstone National Park, Wyoming. Since then, more than fifty species have been discovered. 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. The most heat-tolerant hyperthermophile is the recently-discovered "Strain 121" [http://www.astrobiology.com/news/viewpr.html?pid=12337 Microbe from depths takes life to hottest known limit] ] which has been able to double its population during 24 hours in an autoclave at 121°C (hence its name).

Although no hyperthermophile has yet been discovered living at temperatures above 121°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 genomes 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." [http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1088632 High guanine-cytosine content is not an adaptation to high temperature: a comparative analysis amongst prokaryotes ] ]

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. The genomic signature of hyperthermophilic adaptation is characterized by the overrepresentation of purine bases in protein coding sequences and higher GC-content in tRNA/rRNA sequences. [ [http://www.biomedcentral.com/1471-2164/7/186 "Analysis of Nanoarchaeum equitans genome and proteome composition: indications for hyperthermophilic and parasitic adaptation."] ]

pecific hyperthermophiles

* "Methanopyrus kandleri" Strain 116, an Archaea in 80–122°C in a Central Indian Ridge.
* Strain 121, an Archaea living at 121°C in the Pacific.
* "Pyrolobus fumarii", an Archaea living at 113°C in Atlantic hydrothermal vents.
* "Pyrococcus furiosus", an Archaea which thrives at 100°C, first discovered in Italy near a volcanic vent.
* "Geothermobacterium ferrireducens", Bacteria which thrive in 65–100°C in Obsidian Pool, Yellowstone National Park.
* "Aquifex aeolicus", Bacteria living at 85–95°C in Yellowstone National Park.

References

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ee also

* Mesophile
* Thermophile