Sulfur-oxidizing bacteria (n = 161) were enriched and isolated from samples of vent water, invertebrates, and chimney rocks collected at two deep-sea hydrothermal vents (2000 m) in back-arc basins from the southwestern Pacific: the North Fiji Basin and the Lau Basin. Several types of heterotrophic sulfur-oxidizing bacteria were repeatedly isolated. They oxidized thiosulfate either to sulfate (acid producing) or to polythionate (base producing). In most of the acid-producing cultures, thiosulfate was transitorily oxidized to polythionate. All of the bacteria were Gram negative, 37% were fermentative, and 88% were denitrifiers or nitrate reducers. Numerical taxonomy and analysis of the G+C content showed that they belong to several genera including Pseudomonas, Acinetobacter, and Vibrio.Key words: hydrothermal vent, culturable thiosulfate-oxidizing bacteria, numerical taxonomy.
