Effects of temperature and phosphorous concentration on microbial sulfate reduction by Desulfovibrio desulfuricans

The effects of temperature and phosphorous concentration on the rate and the extent of microbial sulfate reduction with lactate as carbon and energy source were investigated for Desulfovibrio desulfuricans. The continuous culture experiments (chemostat) were conducted at pH 7.0 from 12 to 48 degrees C. The maximum specific growth rate (micro(max)) was relatively constant in the range 25 degrees C-43 degrees C and dramatically decreased outside this temperature range. The half-saturation coefficient was minimum at 25 degrees C. Cell yield was highest in the optimum temperature range (35 degrees C-43 degrees C) for growth. Maintenance energy requirements for D. desulfuricans were not significant. Two moles of lactate is consumed for every mole of sulfate reduced, and this stoichiometric ratio is not temperature dependent. Steady state rate and stoichiometric coefficients accurately predicted transient behavior during temperature shifts. The extent of extracellular polymeric substance (EPS) is related to the concentration of phosphorous in the medium. EPS production rate increased with decreased phosphorous loading rate. Failure to discriminate between cell and EPS formation by D. desulfuricans leads to significant overestimates of the cell yield. The limiting C:P ratio for D. desulfuricans was in the range of 400:1 to 800:1.