Hyperthermophile

Hyperthermophile

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A hyperthermophile is an organism that thrives in extremely hot environments— from 60 degrees C (140 degrees F) upwards. An optimal temperature for the existence of hyperthermophiles is above 80°C (176°F). Hyperthermophiles are a subset of extremophile
Extremophile
An extremophile is an organism that thrives in physically or geochemically extreme conditions that are detrimental to most life on Earth. In contrast, organisms that live in more moderate environments may be termed mesophiles or neutrophiles...

s, micro-organisms within the domain Archaea
Archaea
The Archaea are a group of single-celled microorganisms. A single individual or species from this domain is called an archaeon...

, although some bacteria
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...

 are able to tolerate temperatures of around 100°C (212°F), as well. 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
Thomas D. Brock
Thomas Dale Brock is an American microbiologist known for his discovery of hyperthermophiles living in hot springs at Yellowstone National Park....

 in 1969
1969 in science
The year 1969 in science and technology involved some significant events, listed below.-Astronomy and space exploration:* January 15 - The Soviet Union launches Soyuz 5.* March 3 - Apollo program: NASA launches Apollo 9 to test the lunar module....

, in hot springs in Yellowstone National Park
Yellowstone National Park
Yellowstone National Park, established by the U.S. Congress and signed into law by President Ulysses S. Grant on March 1, 1872, is a national park located primarily in the U.S. state of Wyoming, although it also extends into Montana and Idaho...

, Wyoming
Wyoming
Wyoming is a state in the mountain region of the Western United States. The western two thirds of the state is covered mostly with the mountain ranges and rangelands in the foothills of the Eastern Rocky Mountains, while the eastern third of the state is high elevation prairie known as the High...

. Since then, more than 70 species have been discovered. The most hardy hyperthermophiles yet discovered live on the superheated
Superheating
In physics, superheating is the phenomenon in which a liquid is heated to a temperature higher than its boiling point, without boiling...

 walls of deep-sea hydrothermal vent
Hydrothermal vent
A hydrothermal vent is a fissure in a planet's surface from which geothermally heated water issues. Hydrothermal vents are commonly found near volcanically active places, areas where tectonic plates are moving apart, ocean basins, and hotspots. Hydrothermal vents exist because the earth is both...

s, requiring temperatures of at least 90°C for survival.
An extraordinary heat-tolerant hyperthermophile is the recently discovered Strain 121
Strain 121
Strain 121 is a single-celled microbe, of the domain Archaea. First discovered off Puget Sound in a hydrothermal vent, it is a hyperthermophile, able to survive and reproduce at . It was the only known form of life that can tolerate such high temperatures...

which has been able to double its population during 24 hours in an autoclave
Autoclave
An autoclave is an instrument used to sterilize equipment and supplies by subjecting them to high pressure saturated steam at 121 °C for around 15–20 minutes depending on the size of the load and the contents. It was invented by Charles Chamberland in 1879, although a precursor known as the...

 at 121°C (hence its name); the current record growth temperature is 122°C, for Methanopyrus kandleri
Methanopyrus
In taxonomy, Methanopyrus is a genus of the Methanopyraceae.Methanopyrus is a genus of methanogen, with a single described species, M. kandleri. It is a hyperthermophile, discovered on the wall of a black smoker from the Gulf of California at a depth of 2000 m, at temperatures of 84-110 °C...

.

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
Bacteriostatic agent
A bacteriostatic agent or bacteriostat, abbreviated Bstatic, is a biological or chemical agent that stops bacteria from reproducing, while not necessarily harming them otherwise. Depending on their application, bacteriostatic antibiotics, disinfectants, antiseptics and preservatives can be...

 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
DNA
Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...

 and other vital molecules begins to break down at this point.

Research


Early research into hyperthermophiles speculated that their genome
Genome
In modern molecular biology and genetics, the genome is the entirety of an organism's hereditary information. It is encoded either in DNA or, for many types of virus, in RNA. The genome includes both the genes and the non-coding sequences of the DNA/RNA....

 could be characterized by high guanine-cytosine content
GC-content
In molecular biology and genetics, GC-content is the percentage of nitrogenous bases on a DNA molecule that are either guanine or cytosine . This may refer to a specific fragment of DNA or RNA, or that of the whole genome...

; 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."

The protein
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...

 molecules in the hyperthermophiles exhibit hyperthermostability—that is, they can maintain structural stability (and therefore function) at high temperatures. Such proteins are homologous
Homology (biology)
Homology forms the basis of organization for comparative biology. In 1843, Richard Owen defined homology as "the same organ in different animals under every variety of form and function". Organs as different as a bat's wing, a seal's flipper, a cat's paw and a human hand have a common underlying...

 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
Denaturation (biochemistry)
Denaturation is a process in which proteins or nucleic acids lose their tertiary structure and secondary structure by application of some external stress or compound, such as a strong acid or base, a concentrated inorganic salt, an organic solvent , or heat...

 above 60°C. Such hyperthermostable proteins are often commercially important, as chemical reactions proceed faster at high temperatures.

Cell structure


The cell membrane
Cell membrane
The cell membrane or plasma membrane is a biological membrane that separates the interior of all cells from the outside environment. The cell membrane is selectively permeable to ions and organic molecules and controls the movement of substances in and out of cells. It basically protects the cell...

 contains high levels of saturated fatty acids which are usually arranged in a C40 monolayer
Monolayer
- Chemistry :A Langmuir monolayer or insoluble monolayer is a one-molecule thick layer of an insoluble organic material spread onto an aqueous subphase. Traditional compounds used to prepare Langmuir monolayers are amphiphilic materials that possess a hydrophilic headgroup and a hydrophobic tail...

 to retain its shape at high temperatures.

Specific hyperthermophiles

  • Methanopyrus
    Methanopyrus
    In taxonomy, Methanopyrus is a genus of the Methanopyraceae.Methanopyrus is a genus of methanogen, with a single described species, M. kandleri. It is a hyperthermophile, discovered on the wall of a black smoker from the Gulf of California at a depth of 2000 m, at temperatures of 84-110 °C...

     kandleri
    strain 116, an archaeon in 80–122°C in a Central Indian Ridge
    Central Indian Ridge
    The Central Indian Ridge is a divergent tectonic plate boundary between the African Plate and the Indo-Australian Plate, traversing the western regions of the Indian Ocean...

    .
  • Strain 121
    Strain 121
    Strain 121 is a single-celled microbe, of the domain Archaea. First discovered off Puget Sound in a hydrothermal vent, it is a hyperthermophile, able to survive and reproduce at . It was the only known form of life that can tolerate such high temperatures...

    , an archaeon living at 121°C in the Pacific Ocean.
  • Pyrolobus fumarii, an archaeon living at 113°C in Atlantic hydrothermal vents.
  • Pyrococcus furiosus
    Pyrococcus furiosus
    Pyrococcus furiosus is an extremophilic species of Archaea. It can be classified as a hyperthermophile because it thrives best under extremely high temperatures—higher than those preferred of a thermophile...

    , an archaeon which thrives at 100°C, first discovered in Italy near a volcanic vent.
  • Geothermobacterium ferrireducens, Bacteria
    Bacteria
    Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...

     which thrive in 65–100°C in Obsidian Pool, Yellowstone National Park.
  • Aquifex
    Aquifex
    Aquifex is a genus of bacteria, one of the few in the phylum Aquificae. The two species generally classified in Aquifex are A. pyrophilus and A. aeolicus. Both are highly thermophilic, growing best in water temperature of 85 °C to 95 °C...

     aeolicus
    , Bacteria
    Bacteria
    Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...

    living at 85–95°C in Yellowstone National Park.