OXIDATION OF POLYMETAL SULFIDES BY CHEMOLITHOAUTOTROPHIC BACTERIA FROM DEEP-SEA HYDROTHERMAL VENTS

Aerobic mesophilic sulfur-oxidizing bacteria were tested for their abi lity to utilize a variety of natural and commercial polymetal sulfides as energy sources at near neutral pH. Substantial fixation of (CO2)-C -14 by natural microbial populations covering polymetal sulfide deposi ts was observed in in situ experiments conducted from DSV ALVIN at the Mid-Atlantic Ridge hydrothermal vent sites at a depth of 3600 m. In s hipboard experiments, similar rates were measured with natural populat ions on intact or pulverized sulfide minerals. In laboratory experimen ts with four vent isolates, the rate of (CO2)-C-14 incorporation depen ded on the particular strain and the type of polymetal sulfide substra te used. Vent sample material rich in chalcopyrite (CuFeS2) resulted i n higher activities than on sphalerite (ZnS), galena (PbS), or chalcoc ite (CuS2) alone. Growth on polymetal sulfides, determined as protein, and (CO2)-C-14 fixation by strain MA-3 (the most active of four isola tes) were in the range of 5-10% of the corresponding values obtained o n thiosulfate as the substrate. While the hydrothermal vent isolates l owered the pH to approximately 4.8 in thiosulfate medium cultures grow n on polymetal sulfides plateaued at higher pH values. Growth of isola tes on polymetal sulfides was not enhanced by an addition of thiosulfa te. Optimal growth occurred at near neutral pH on both the soluble and insoluble fractions of polymetal sulfides. The massive polymetal sulf ide deposits at tectonic ocean spreading centers must be considered lo ng-term sources of electrons for the chemosynthetic production of biom ass in the deep sea.