Thermococcus gammatolerans
A Microbial Biorealm page on the genus Thermococcus gammatolerans
Classification
Archaea; Euryarchaeota; Thermococci; Thermococcales; Thermococcaceae; Thermococcus; gammatolerans NCBI
Description and significance
Thermococcus gammatolerans are not human or animal pathogens, but are strictly anaerobic hyperthermophiles, naturally found in highly extreme environmental conditions of temperature, salinity, pressure and acidity. This species was discovered in 2003 on a hydrothermal vent in the Guaymas Basin off of the coast of California at a depth of 2616 m, and thrives at 88 °C and a pH of 6.0, while withstanding temperature ranges of 55 to 95 °C (1). It's prime salinity concentration of NaCl is 20 g/L (1). It is the most radiation-resistant organism discovered to date, surviving in gamma radiation of 30 KGy (1). Elucidating the mechanisms of this resistance has initiated further research of this organism in the hopes that more information on DNA repair and maintenance can be learned (4).
Genome structure
The genome of the Thermococcus gammatolerans strain EJ3 has been sequenced. It contains one main circular chromosome of 2,045,438 nucleotides which code for 2,157 proteins(2,3). There are not commonly and extra-chromosomal elements (3). The radioresistant nature of this species has made the study of its genome and proteome an up and coming area of study in order to determine the mechanism of its resistance (4).
Cell structure, metabolism & life cycle
Cells of Thermococcus gammatolerans form regular cocci with polar flagella allowing for motility (1). Cell diameter ranges from 0.6 to 1.4 µm and are found both singly and in pairs. The strictly anaerobic heterotroph requires elemental sulfur and cystine to grow properly and were reduced to hydrogen sulfide (1). It differs from other species in the genus Thermococcus in its 51.3 % G+C content, sensitivity to rifampicin, salinity preference of 20 g/L, optimal pH of 6.0, and its in ability to metabolize starch and maltose (1). Thermococcus gammatolerans grows preferentially on substrates with proteolysis products like yeast extract, peptone and tryptone, while unable to grow on Casamino acids, acetate, succinate, proionate, pyruvate, gelatin, glucose, maltose or starch (1). While sulfur or cystine are necessary for growth, thiosulfate, sulfate and sulfite cannot be used as termianl electron acceptors (1). Cell division occurs by constriction (1).
Ecology
Found almost exclusively in hydrothermal vents, this anaerobic species can exist only in the extreme ranges of temperature, pressure and pH of the deep sea chimney community (4). Thermococcus gammatolerans grows heterotrophically, reducing elemental sulfur or cystine to hydrogen sulfide. Chemosynthetic bacteria, like Thermococcus gammatolerans, form the basis of the hydrothermal vent biological community as opposed to most ecological communities which depend on the energy from sunlight to provide chemical energy for other organisms (3).
Interesting feature
The most interesting feature of Thermococcus gammatolerans is their incredible resistance to gamma radiation, the level of which could kill a human 6,000 times over (1). A human can be killed from exposure to 5 Gy, while Thermococcus gammatolerans can withstand 30,000 Gy (1). The mechanism of this resistance is not fully understood as of yet, but it appears to be the result of proteins yet to be characterized rather than a large number of known DNA repair enzymes (4). A number of reactive oxygen species (ROS) coping mechanisms are present in Thermococcus gammatolerans to manage the large amounts of ROS produced by gamma rays, but the massive amount of DNA repair has not been attributed to a specific mechanism yet (4).
References
(1) [http://ijs.sgmjournals.org/content/53/3/847.long Jolivet, E., L'Haridon, S., Corre, E., Forte, P., and Prieur, D. "Thermococcus gammatolerans sp. nov., a hyperthermophillic archaeon from a deep-sea hydrothermal vent that resists ionizing radiation". International Journal of Systematic and Evolutionary Microbiology. 2003. Volume 53. p. 847-851.
(2) NCBI Taxonomic page for Thermococcus gammatolerans
(3) Tunnicliffe, Verena (1991). "The Biology of Hydrothermal Vents: Ecology and Evolution". Oceanography and Marine Biology an Annual Review 29: 319–408
(4) [http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2718504/?tool=pubmed Zivanovic, Y. et al. "Genome analysis and genome-wide prtoeomics ofThermococcus gammatolerans, the most radioresistant organism known among the Archaea". Genome Biology. 2009. Volume 10. published online.
