Sulfolobus hakonensis sp. nov., a novel species of acidothermophilic archaeon.

We characterized a microbial strain that was isolated from a hot spring at a geothermal area in Hakone, Japan. This isolate, whose lobed-shaped cells were about 1.0 micron in diameter, was a facultative chemolitho-autotroph that required aerobic conditions for growth. The optimum pH was 3.0 (pH range, 1.0 to 4.0), and the optimum temperature was 70 degrees C (temperature range, 50 to 80 degrees C). Lithotrophically, this strain grew on elemental sulfur and reduced sulfur compounds. The G+C content of the genomic DNA was 38.4 mol%. This organism contained calditoglycerocaldarchaeol, which is characteristic of members of the Sulfolobaceae. The levels of 16S rRNA sequence similarity between the new isolate and Sulfolobus acidocaldarius, Sulfolobus solfataricus, and Sulfolobus shibatae were less than 89.8%. Unlike S. acidocaldarius, S. solfataricus, and S. shibatae, the new isolate utilized sugars and amino acids poorly as sole carbon sources, and the levels of DNA-DNA hybridization between the new isolate and these Sulfolobus species were very low. Phenotypically, the new isolate was also distinct from the obligately lithotrophic organism Sulfolobus metallicus. We concluded that the new organism belongs to a new Sulfolobus species, for which we propose the name Sulfolobus hakonensis.