ISOLATION AND CHARACTERIZATION OF THERMOCOCCUS-BAROSSII, SP. NOV., A HYPERTHERMOPHILIC ARCHAEON ISOLATED FROM A HYDROTHERMAL VENT FLANGE FORMATION

A new hyperthermophilic microorganism, Thermococcus barossii, was isol ated from rock fragments of a hydrothermal vent flange formation, loca ted along the East Pacific Rise of the Juan cie Fuca Ridge. This organ ism is obligately anaerobic and grows over a temperature range of at l east 60-92 degrees C in artificial seawater-based media, containing el emental sulfur, tryptone and yeast extract. The addition of a maltooli gosaccharide mixture and tungsten to this medium improved growth to so me extent. At the T-opt for growth (82.5 degrees C), cell densities as high as 4x10(8) cells/ml could be obtained in IS-liter batch fermenta tions, with a doubling time of approximately 40 minutes, if culture ac cess to elemental sulfur was sufficient. In continuous culture at the same temperature, comparable cell densities could be obtained but only at slower growth rates. Morphologically T. barossii is coccoid-shaped , forming irregularly-shaped spheres; under optimal conditions, these coccoids become more regular and smaller, a characteristic of other hy perthermophilic archaea. Negatively-stained preparations showed no pil l or flagella associated with the cell surface. 16S rRNA sequencing re veals that T. barossii is most similar to Thermococcus celer (99.7%). Yet, further comparisons with T celer showed that T. barossii is a new Thermococcus species: different growth temperature optimum (82.5 degr ees C vs. 88 degrees C), ol>ligatr requirement for suifur, higher G+C content (60% vs. 56.7%) and 47.7% DNA-DNA hybridization. The nucleotid e and translated amino acid sequence for the gene encoding a DNA polym erase from T. barossii was compared to sequences of related genes from other Thermococcales. The polymerase phylogenies were congruent with those obtained from the 16S rRNA phylogenetic analyses. Based on the h igh degree of similarity among members of the genus Termococcus for th e criteria used thus far, aspects of enzymology may be an important me chanism of differentiating one species from another.