Competition for ethanol between sulfate-reducing and fermenting bacteria

Competition for ethanol between the sulfate-reducing bacteria Desulfobulbus propionicus, Desulfotomaculum orientis, Desulfovibrio vulgaris Marburg, Desulfovibrio gigas, Desulfovibrio desulfuricans Essex and the fermenting bacteria Pelobacter propionicus and Acetobacterium carbinolicum were studied in batch culture. A number of these bacteria was also chosen for competition experiments under ethanol limitation in chemostat culture. The maximum growth rates determined by washout experiments were higher for the fermenting bacteria (_max=0.096 resp. 0.335h^–1) than for the sulfate-reducing bacteria (_max0.03h^–1). In contrast, the saturation concentrations for half maximum growth rates (K_s values) for ethanol were lower for the sulfate-reducing bacteria (K_s5 M) than for the fermenting bacteria (K_s50 M). In batch culture competition experiments the fermenting bacteria turned out to be the better competitors, degrading 51–80% of the ethanol added. In competition experiments with ethanollimited chemostat cultures the sulfate-reducing bacteria Desulfobulbus propionicus and Desulfovibrio vulgaris outcompeted Pelobacter propionicus at dilution rates below their maximum specific growth rates. At a high dilution rate, a fast growing population of Desulfobulbus propionicus originated and was enriched in the chemostat during the competition experiment.