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Hyperthermophiles

Dateline: 07/17/00

By Alan Bruzel

What Are Hyperthermophiles?

They are microscopic organisms that thrive at temperatures ranging from 85 to 105^oC (185 to 221^oF). By comparison, mesophiles such as humans thrive best in the temperature range of 25 to 40°C (77 to 104^oF). Hyperthermophiles have been placed in the domain Archaea (named from the Archaean age, 3.8 to 2.5 billion years ago, when life first appeared on Earth) and are as different from bacteria as they are from eukaryotes (plants and animals). It is likely that today's hyperthermophiles descended from life forms of a younger Earth with its intense volcanic activity and oxygen-free atmosphere. Future investigations of hot planets and their satellites will benefit from studies of these organisms from Earth's past.

Where Are They Found?

As would be expected, hyperthermophiles can be found near volcanoes both on land and in the ocean. Good sources are deep-sea hydrothermal vents that yield methane, hydrogen, hydrogen sulfide, iron, manganese, and sulfur when magma of about 380^oC (716^oF) violently mixes with cold deep-sea water at about 2^oC (36^oF). Hyperthermophiles partake of these inorganic molecules for their energy needs using, for example, sulfur as an electron acceptor. (We, and a host of equally prosaic beings, use oxygen as an electron acceptor.) Hyperthermophiles are also quite different from most other organisms in that their ultimate energy source is strictly chemical, not solar.

How Hyperthermophiles Maintain Their Integrity

Creatures living at the temperature of boiling water must be constructed using slightly different blueprints than those used for organisms residing in more tepid surroundings. Hyperthermophiles need to maintain the integrity of their cellular components, in spite of their toasty surroundings, and have elaborated several ways of doing this. For example, lipids in their cell membranes use thermally stable ether linkages, and are not the ester-based lipids found in bacteria and eukaryotes. Short, thermodynamically stable histones along with other DNA-binding proteins provide protection against high-temperature DNA breakage. In addition to structural changes that confer added stability, hyperthermophile proteins can be protected from thermal damage by high levels of cellular diglycerol phosphate and large multimers of heat shock proteins.

What the Web Has to Say about:
Hyperthermophiles

Adenylosuccinate Synthetase from Hyperthermophilic Archaeon Pyrococcus Species
Amino acid comparisons show this enzyme differs remarkably from the enzyme of mesophilic organisms. From Ahmed Bouyoub et al., Journal of Molecular Biology Online.

Antifreeze Proteins
An article from this Web site describing how some molecular adaptations allow organisms to survive at the freezing point of water.

Extremophiles
Journal that features research papers about organisms existing at low or high temperatures, pressures, and pH levels.

Great Bugs of Fire
Growing crystals of thermophilic enzymes aboard the Space Shuttle. From David Noever, Space Science News, NASA.

Hot-Vent Microbes
Background of these archaeons and potential commercial uses. From Myrna E. Watanabe, The Scientist.

Hyperthermophiles and Their Thermoresistance
Research involving role of chaperonins in thermal stability. From the University of Bergen.

Hyperthermophilic Enzymes
Structure/function relationship of enzymes from the hyperthermophilic archaeon Pyrococcus horikoshii. From the Centre National de la Recherche Scientifique.

Life at the Boiling Point
Where thermophiles are found and how to grow them in the laboratory. From Judy Purdy, University of Georgia.

Major Groups of Prokaryotes
Phylogeny, structure, and metabolism of these microorganisms. From Kenneth Todar, University of Wisconsin at Madison.

Microbiology of Vent Ecosystems
Characterization of mid-ocean ridge hydrothermal vent systems including geochemistry and biochemistry. From the Natural Environment Research Council.

Missing Links in the Deep
Deep-sea communities located near and supported by hot vents. From About.com's Geology Guide.

Pyrococcus abyssi
DNA sequence analysis of this hyperthermophile. From the Centre National de Séquençage.

Size Limits of Very Small Microorganisms
US National Academy of Sciences study from Karl O. Stetter, Universität Regensburg, describes variable sizes of some hyperthermophilic Archaea.

Vent Fluid Chemistry and the Microbial Habitat
Swirling metals and reduced gases that encourage thermophile activity. From the Pacific Marine Environmental Laboratory.

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