FACTORS AFFECTING MICROBIAL SULFATE REDUCTION BY DESULFOVIBRIO-DESULFURICANS IN CONTINUOUS CULTURE - LIMITING NUTRIENTS AND SULFIDE CONCENTRATION

The effects of sulfate and nitrogen concentrations on the rate and stoichiometry of microbial sulfate reduction were investigated for Desulfovibrio desulfuricans grown on lactate and sulfate in a chemostat at pH 7.0. Maximum specific growth rates (mu(max)), half-saturation coefficients (K(sul)), and cell yields (Y(c/Lac)) Of 0.344 +/- 0.007 and 0.352 +/- 0.003 h-1, 1.8 +/- 0.3 and 1.0 +/- 0.2 mg/L, and 0.020 +/- 0.003 and 0.017 +/- 0.003 g cell/g lactate, respectively, were obtained under sulfate-limiting conditions at 35-degrees-C and 43-degrees-C. Maintenance energy requirements for D. desulfuricans were significant under sulfate-limiting conditions. The extent of extracellular polymeric substance (EPS) produced was related to the carbon:nitrogen ratio in the medium. EPS production rate increased with decreased nitrogen loading rate. Nitrogen starvation also resulted in decreased cell size of D. desulfuricans. The limiting C:N ratio (w/w) for D. desulfuricans was in the range of 45:1 to 120:1. Effects of sulfide on microbial sulfate reduction, cell size, and biomass production were also investigated at pH 7.0. Fifty percent inhibition of lactate utilization occurred at a total sulfide concentration of approximately 500 mg/L. The cell size of D. desulfuricans decreased with increasing total sulfide concentration. Sulfide inhibition of D. desulfuricans was observed to be a reversible process.