BACTERIAL SULFUR REDUCTION IN SHALLOW-WATER HOT VENTS OF THE SOUTHWESTERN PART OF THE PACIFIC-OCEAN

Bacterial sulfur reduction was investigated in shallow-water hot vents of the southwestern part of the Pacific Ocean (New Zealand, New Guine a) and of the Kraternaya Bight (Kurile Islands). Sulfur reduction rate s in sediments with temperatures of 50 - 90 degrees C were determined by the radioisotopic method. The method of serial dilutions was used t o determine the quantity of thermophilic sulfur-reducing bacteria util izing different energy sources. In high-temperature vents (> 80 degree s C) the sulfur-reducing population is represented by extremely thermo philic peptide-fermenting archaebacteria which number up to 10(7) cell s/ml. Being obligately dependent on elemental sulfur in laboratory cul tures, in natural habitats these organisms seem to develop at the expe nse of fermentation. The in situ rates of bacterial sulfur reduction i n these systems are 0.51 - 2.7 mg S/(liter day). In littoral hot vents with temperatures around 50 degrees C the redox conditions change per iodically, providing renewal of the elemental sulfur pool. Bacterial s ulfur reduction rates in the littoral hot vents can be as high as 5736 .8 mg S/(liter day) with a turnover time of 0.25 day (Matupy Harbor, N ew Guinea). In such biotopes a multicomponent bacterial population was found to be capable of reducing elemental sulfur both via fermentatio n and via sulfur respiration through oxidation of non-fermentable subs trates.