SULFOLOBUS HAKONENSIS SP-NOV, A NOVEL SPECIES OF ACIDOTHERMOPHILIC ARCHAEON

We characterized a microbial strain that was isolated from a hot sprin g at a geothermal area in Hakone, Japan, This isolate, whose lobed-sha ped cells were about 1.0 mu m in diameter, was a facultative chemolith oautotroph 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 de grees C (temperature range, 50 to 80 degrees C). Lithotrophically, thi s strain grew on elemental sulfur and reduced sulfur compounds. The GC content of the genomic DNA was 38.4 mol%. This organism contained ca lditoglycerocaldarchaeol, which is characteristic of members of the Su lfolobaceae. The levels of 16S rRNA sequence similarity between the ne w 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 am ino acids poorly as sole carbon sources, and the levels of DNA-DNA hyb ridization between the new isolate and these Sulfolobus species were v ery low. Phenotypically, the new isolate was also distinct from the ob ligately lithotrophic organism Sulfolobus metallicus. We concluded tha t the new organism belongs to a new Sulfolobus species, for which we p ropose the name Sulfolobus hakonensis.