PHENOTYPIC CHARACTERIZATION, DNA SIMILARITIES, AND PROTEIN PROFILES OF 20 SULFUR-METABOLIZING HYPERTHERMOPHILIC ANAEROBIC ARCHAEA ISOLATED FROM HYDROTHERMAL VENTS IN THE SOUTHWESTERN PACIFIC-OCEAN

We performed phenotypic and physiological studies with 20 hyperthermop hilic microorganisms isolated from hydrothermal vents located in the N orth Fiji Basin (southwestern Pacific Ocean) at a depth of 2,000 m. Th ese isolates were strict anaerobes that were regular to irregular cocc oids and used elemental sulfur in their metabolism. Growth was observe d at temperatures ranging from 50 to 101 degrees C. The DNA base compo sitions varied from 43 to 60 mol%. All of these organisms were heterot rophs and fermented peptides to acetate, isovalerate, isobutyrate, and propionate, They contained both diether and tetraether lipids in thei r membranes, which indicates that they belong to the domain Archaea. D NA-DNA hybridization experiments revealed that there were two distinct homology groups, which correlated well with results obtained from sod ium dodecyl sulfate-polyacrylamide gel electrophoresis of soluble whol e-cell proteins, and these groups corresponded to the genera Pyrococcu s and Thermococcus. Five isolates exhibited levels of DNA-DNA relatedn ess with Pyrococcus abyssi ranging from 71 to 100% and produced almost identical protein patterns. The remaining isolates formed a weakly ho mogeneous group based on DNA-DNA similarity data and protein patterns; the results of unweighted pair group duster analyses suggested that t hese isolates were members of five new species of the genus Thermococc us.