Kinetic Description of the Competitive Interaction between Lactate Oxidizers and Fermenters in a Biosulfidogenic System

In order to describe the relative predominance of lactate oxidation and fermentation under conditions of biological sulfate reduction, kinetic constants ( max and Ks) were determined. Chemostat cultures under various conditions were employed. The kinetics of sulfate reduction and lactate utilization were investigated at residence times 1 to 5 d and feed sulfate concentrations of 1.0 to 10.0 g l. At low lactate concentration, lower max and Ks characterized the lactate oxidizers (sulfate reducing bacteria) relative to the lactate fermenters. The kinetic properties of the lactate oxidizers (LO) were max of 0.2 h -1 and Ks of 0.6 g l -1 compared with a max of 0.3 h -1 and Ks of 3.3 g l -1 for the lactate fermenters (LF). The interaction between lactate oxidizers and lactate fermenters was demonstrated with the use of mathematical models. The LO outcompeted the LF under conditions of low lactate concentration (≤5 g l) and high sulfide concentration (0.3-0.6 g l). Lactate fermenters outcompeted the oxidizers under conditions of excess lactate concentration (>5 g l). The predictions by the mathematical models employed were in good agreement with the experimental results obtained for bacterial growth rates. The importance of an understanding of the impact of physicochemical conditions on the metabolic dominance in optimizing biological sulfate reduction (BSR) system, was highlighted in this study.