CHARACTERIZATION OF A NEW THERMOPHILIC SULFATE-REDUCING BACTERIUM - THERMODESULFOVIBRIO YELLOWSTONII, GEN-NOV AND SP-NOV - ITS PHYLOGENETICRELATIONSHIP TO THERMODESULFOBACTERIUM COMMUNE AND THEIR ORIGINS DEEPWITHIN THE BACTERIAL DOMAIN

A thermophilic sulfate-reducing vibrio isolated from thermal vent wate r in Yellowstone Lake, Wyoming, USA is described. The gram-negative, c urved rod-shaped cells averaged 0.3 mu m wide and 1.5 mu m long. They were motile by means of a single polar flagellum. Growth was observed between 40 degrees and 70 degrees C with optimal growth at 65 degrees C. Cultures remained viable for one year at 27 degrees C although spor e-formation was not observed. Sulfate, thiosulfate and sulfite were us ed as electron accepters. Sulfur, fumarate and nitrate were not reduce d. In the presence of sulfate, growth was observed only with lactate, pyruvate, hydrogen plus acetate, or formate plus acetate. Pyruvate was the only compound observed to support fermentative growth. Pyruvate a nd lactate were oxidized to acetate. Desulfofuscidin and c-type cytoch romes were present. The G + C content was 29.5 mol%. The divergence in the 16S ribosomal RNA sequences between the new isolate and Thermodes ulfobacterium commune suggests that these two thermophilic sulfate-red ucing bacteria represent different genera. These two bacteria depict a lineage that branches deeply within the Bacteria domain and which is clearly distinct from previously defined phylogenetic lines of sulfate -reducing bacteria. Strain YP87 is described as the type strain of the new genus and species Thermodesulfovibrio yellowstonii.