8.15D: Thermoplasmatales, Thermocaccales, and Methanopyrus

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There are many classes in the phylum Euryarchaeota, many of which are extremophiles.

Learning Objectives

Recognize the characteristics associated with the Euryarchaeota classes of thermophiles: Thermoplasmatales, Thermococcales and Methanopyri

Key Points

Thermoplasmatales are an order of the class Thermoplasmata. All are acidophiles, growing optimally at pH below 2.
Another anaerobic Euryarchaeota, often hyperthermophiles, are the Thermococcales of the class Thermocococci.
Methanopyrus is a genus of methanogen, with a single described species, M. kandleri.

Key Terms

acidophiles: an organism that thrives under highly acidic conditions (usually at pH 2.0 or below)
hyperthermophile: An organism that lives and thrives in an extremely hot environment like a deep sea smoker vent; often a member of the Archaea.

There are many classes in the phylum Euryarchaeota, many of which are extremophiles, surviving in extreme conditions that are uninhabitable for most other organisms. Thermoplasmatales, Thermococcales, and Methanopyri are all Euryarchaeota Classes of thermophiles.

Thermoplasmatales are an order of the class Thermoplasmata. All are acidophiles, growing optimally at pH below 2. Picrophilus is currently the most acidophilic of all known organisms growing at a minimum pH of 0.06. Many of these organisms do not contain a cell wall, although this is not true in the case of Picrophilus. Most members of the Thermotoplasmata are thermophilic. A thermophile is an extremophile that thrives at relatively high temperatures, between 45 and 122 °C. Many of them are archaea. Thermophilic eubacteria are suggested to have been among the earliest bacteria. Thermophiles contain enzymes that can function at high temperatures, and can even survive at much higher temperatures, whereas other bacteria would be damaged and sometimes killed if exposed to the same temperatures.

Another anaerobic Euryarchaeota, often hyperthermophiles, are the Thermococcales of the class Thermocococci.

Methanopyrus is a genus of methanogen, with a single described species, Methanopyrus 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. Strain 116 was discovered in black smoker fluid of the Kairei hydrothermal field; it can survive and reproduce at 122 °C. It lives in a hydrogen-carbon dioxide rich environment, and like other methanogens reduces the latter to methane. It is placed among the Euryarchaeota, in its own class, Methanopyri.