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Sulfolobus tokodaii: A genome from Japan
By Birgit Reinert

Japanese researchers have determined the complete genome sequence of Sulfolobus tokodaii strain7, an organism that was isolated from Beppu hot springs in Kyusyu, Japan in 1983. The microorganism is able to convert hydrogen sulfide to sulfate, and the identification of genes involved in this intracellular process may have applications in industry, such as the treatment of industrial wastewater.

Beppu hot springs in Japan.

Yutaka Kawarabayasi, of the Biotechnology Center at the National Institute of Technology and Evaluation in Tokyo, Japan, and colleagues determined the S. tokodaii genome sequence using the whole-genome shotgun method. The genome is about 2.69 million base pairs long, and the analysis of the genome revealed 2,826 genes, or protein-coding regions.

The researchers identified many genes related to energy metabolism and a total of eight genes related to sulfide metabolism. "Confirmation of their activities would provide valuable information for sulfide metabolism in this microorganism and facilitate the improvement of this system for industrial applications," the researchers write in DNA Research.

Sulfolobus tokodaii grows optimally at 80 degrees Celsius in an acidic, sulfur-rich environment.

Beppu hot springs in Japan.

The researchers could distinguish between genes of known and unknown function by comparing the S. tokodaii sequence to two closely related species—Aeropyrum pernix and Pyrococcus horikoshii—whose genome sequences they had previously determined. About one third of the genes had no known function and did not show any significant similarity to the registered sequences of the other two organisms.

Sequence comparison also identified remnants of a plasmid from an ancestral species, which is integrated in the S. tokodaii genome. The vast majority of genes associated with the plasmid is scattered across the genome and their function is yet unknown. The researchers suggest that they "may be indispensable for S. tokodaii strain7, as these genes have been maintained in the genome until now."

Sulfolobus tokodaii is a member of the archaea, a third branch of life next to eukaryotes (animals, plants, and fungi) and bacteria. The researchers detected fourteen genes that resemble those in eukaryotes, which have not been found in other archaea before. This led the researchers to conclude that of all the sequenced archaea to date, S. tokodaii is the one most closest related to eukaryotes.

Archaea thrive in the most extreme environments on earth, and laboratories worldwide are exploring the thermostability of proteins and the biological catalysts, or enzymes.

A physical map of the S. tokodaii genome can be viewed at the Biotechnology Center's website.

See related GNN article
»Life at very high temperatures: The genome of Sulfolobus solfataricus is sequenced

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Kawarabayasi, Y. et al. Complete genome sequence of an aerobic thermoacidophilic crenarchaeon, Sulfolobus tokodaii strain7. DNA Res 8, 123-140 (August 2001).
Kawarabayasi, Y. et al. Complete genome sequence of an aerobic hyper-thermophilic crenarchaeon, Aeropyrum pernix K1. DNA Res 6, 83-101, 145-152 (April 1999).
Kawarabayasi, Y. et al. Complete sequence and gene organization of the genome of a hyper-thermophilic archaebacterium, Pyrococcus horikoshii OT3. DNA Res 5, 55-76 (April 1998).

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