A thermophile is an organism—a type of extremophile—that thrives at relatively high temperatures, between 41 and 122 °C. Many thermophiles are archaea, though some of them are bacteria and fungi. Thermophilic eubacteria are suggested to have been among the earliest bacteria.
Nanoarchaeum equitans is a species of marine archaea that was discovered in 2002 in a hydrothermal vent off the coast of Iceland on the Kolbeinsey Ridge by Karl Stetter. It has been proposed as the first species in a new phylum. Strains of this microbe were also found on the Sub-polar Mid Oceanic Ridge, and in the Obsidian Pool in Yellowstone National Park. Since it grows in temperatures approaching boiling, at about 80 degrees Celsius, it is considered to be a thermophile. It grows best in environments with a pH of 6, and a salinity concentration of 2%. Nanoarchaeum appears to be an obligate symbiont on the archaeon Ignicoccus; it must be in contact with the host organism to survive. Nanoarchaeum equitans cannot synthesize lipids but obtains them from its host. Its cells are only 400 nm in diameter, making it the smallest known living organism, and the smallest known archaeon.
The Thermoproteota are archaea that have been classified as a phylum of the Archaea domain. Initially, the Thermoproteota were thought to be sulfur-dependent extremophiles but recent studies have identified characteristic Thermoproteota environmental rRNA indicating the organisms may be the most abundant archaea in the marine environment. Originally, they were separated from the other archaea based on rRNA sequences; other physiological features, such as lack of histones, have supported this division, although some crenarchaea were found to have histones. Until recently all cultured Thermoproteota had been thermophilic or hyperthermophilic organisms, some of which have the ability to grow at up to 113 °C. These organisms stain Gram negative and are morphologically diverse, having rod, cocci, filamentous and oddly-shaped cells.
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). 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.
Ferroglobus is a genus of the Archaeoglobaceae.
Methanopyrus is a genus of the Methanopyraceae.
Methanococcus is a genus of coccoid methanogens of the family Methanococcaceae. They are all mesophiles, except the thermophilic M. thermolithotrophicus and the hyperthermophilic M. jannaschii. The latter was discovered at the base of a “white smoker” chimney at 21°N on the East Pacific Rise and it was the first archaeal genome to be completely sequenced, revealing many novel and eukaryote-like elements.
Pyrobaculum is a genus of the Thermoproteaceae.
In taxonomy, Vulcanisaeta is a genus of the Thermoproteaceae.
In taxonomy, Thermococcus is a genus of thermophilic Archaea in the family the Thermococcaceae.
Pyrolobus is a genus of the Pyrodictiaceae.
In taxonomy, Ignisphaera is a genus of the Desulfurococcales. Ignisphaera aggregans is a coccoid- shaped, fourth type strain that is strictly anaerobes with anaerobic respiration. This archaea species are hyperthermophiles that were found in New Zealand's hot springs in Kuirau Park, Rotorua.
Aeropyrum pernix is a species of extremophile archaea in the archaeal phylum Thermoproteota. It is an obligatorily thermophilic species. The first specimens were isolated from sediments in the sea off the coast of Japan.
Thermococcus celer is a Gram-negative, spherical-shaped archaeon of the genus Thermococcus. The discovery of T. celer played an important role in rerooting the tree of life when T. celer was found to be more closely related to methanogenic Archaea than to other phenotypically similar thermophilic species. T. celer was the first archaeon discovered to house a circularized genome. Several type strains of T. celer have been identified: Vu13, ATCC 35543, and DSM 2476.
Thermococcus kodakarensis is a species of thermophilic archaea. The type strain T. kodakarensis KOD1 is one of the best-studied members of the genus.
Pyrobaculum aerophilum is a single-celled microorganism in the genus Pyrobaculum. The first Pyrobaculum species to be sequenced was P. aerophilum. It is a rod-shaped hyperthermophilic archaeum first isolated from a boiling marine water hole at Maronti Beach, Ischia. It forms characteristic terminal spherical bodies like Thermoproteus and Pyrobaculum. Its type strain is IM2; DSM 7523). Its optimum temperature for growth is around boiling point for water. Its optimum pH for growth is 7.0. Sulfur was found to inhibit its growth.
Pyrococcus abyssi is a hyperthermophilic archaeon isolated from a deep-sea hydrothermal vent in the North Fiji Basin at 2,000 metres (6,600 ft). It is anaerobic, sulfur-metabolizing, gram-negative, coccus-shaped and highly motile. Its optimum growth temperature is 96 °C (205 °F). Its type strain is GE5. Pyrococcus abyssi has been used as a model organism in studies of DNA polymerase. This species can also grow at high cell densities in bioreactors.
Methanothermus sociabilis is a species of methanogen. It grows in large clusters 1 to 3 mm in diameter and in temperatures of up to 97 °C (207 °F). It is found solely in the solfataric fields in Iceland. The cells are bar-shaped and grow strictly through the reduction of carbon dioxide with hydrogen, producing methane.
Saccharolobus solfataricus is a species of thermophilic archaeon. It was transferred from the genus Sulfolobus to the new genus Saccharolobus with the description of Saccharolobus caldissimus in 2018.
