CHEMOAUTOTROPHIC SULFUR-OXIDIZING BACTERIA FROM THE BLACK-SEA

In contrast to earlier attempts, we were able to isolate nine strains of obligately chemoautolithotropic, sulfur-oxidizing bacteria from three offshore stations in the western basin of the Black Sea (R.V. Knorr Cruise 134-9, Black Sea leg 2). The isolates grew with doubling times averaging 1.3 h over a pH range of 6.5-9.0 in artificial sea water containing thiosulfate. They also oxidized hydrogen sulfide, elemental sulfur and tetrathionate. Although acid producing, growth of the isolates was neutrophilic (optimum pH 7.5). Nitrate or manganese and iron oxides were not utilized as alternate electron acceptors. If acetate was present, not more than 10% of the incorporated carbon was mixotrophically obtained from the organic source. With a DNA base composition range of 37-40 mol % G+C, the new isolates appear to belong to the genus Thiomicrospira (36-44 mol % G+C) rather than Thiobacillus (55-68 mol % G+C). Experimental studies on the potential sulfide oxidation by the new isolates under in situ conditions suggest that, above a certain density of active cells (ca 10(4) ml-1), biological sulfide oxidation appears to be able to compete successfully with its spontaneous chemical oxidation.