Thermococcus
In taxonomy, Thermococcus is a genus of extreme thermophiles in the family the Thermococcaceae.
Members of the genus Thermococcus are all Archaea, having thermophillic-hyperthermophillic characteristics. These microorganisms are typically irregularly shaped coccoid species, ranging in size from 0.6-2.0 μm in diameter. Some species of Thermococcus are immobile, and some species have motility, using flagella as their main source of movement. These flagella typically exist at a specific pole of the organism. This movement has been seen at room temperature or at high temperature, depending on the specific organism. In some species, these microorganisms can aggregate and form white-gray plaques, while all of these organisms dwell in temperatures from 70-<100oC, either in the presence of black smokers (hydrothermal vents), or freshwater springs, amongst salt (NaCl) concentrations of 1%-3%. Species in this genus are strictly anaerobes, and most are barophiles as well as thermophiles, living in depths between 200-<1000 ft. These organisms thrive at pH levels of 5.6-7.9. Members of this genus have been found in many hydrothermal vent systems in the world, including from the seas of Japan, to off the coasts of California. Surprisingly salt (NaCl) is not a required substrate for these organisms, as one study showed Thermococcus members living in fresh hot water systems in New Zealand, however they do require a low concentration of lithium ion for growth.Thermococcus members are described as heterotrophic, chemotrophic and organotrophic sulfanogens; utilizing elemental sulfur (So) and carbon sources including amino acids, carbohydrates, and organic acids such as pyruvate.
Metabolically, Thermococcus have developed a different form of glycolysis than eukaryotes and prokaryotes. One example of a metabolic pathway for these organisms is the metabolism of peptides, which occurs in three steps: first, there is hydrolysis of the peptides to amino acids catalyzed by peptidases, then there is conversion of the amino acids to keto acids catalyzed by aminotransferases, and finally CO2 is released from the oxidative decarboxylation or the keto acids by four different enzymes, which produces coenzyme A derivatives that are used in other important metabolic pathways.Thermococcus species also have the enzyme Rubisco (ribulose-1,5-bisphosphate carboxylase/oxygenase), which is made from enzymes involved in the metabolism of nucleic acids in Thermococcus kodakarensis, showing how integrated these metabolic systems truly are for these hyperthermophilic microorganisms. Some nutrients are limiting when it comes to Thermococcus cell growth. Nutrients that affect cell growth the most in thermococci species are carbon and nitrogen sources. Since thermococci species do not metabolically generate all necessary amino acids, some have to be provided by the environment in which these organisms thrive. Some of these needed amino acids are leucine, isoleucine, and valine (the branched chain amino acids). When Thermococcus species are supplemented with these amino acids, they can metabolize them and produce acetyl-CoA or succinyl-CoA, which are important precursors used in other metabolic pathways essential for cellular growth and respiration. With today's technology, Thermococcus members are relatively easy to grow in labs, and are therefore considered model organisms for studying the physiological and molecular pathways of extremophiles.Thermococcus kodakarensis is one example of a model Thermococcus species, a microorganism in which has had its entire genome examined and replicated.
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