Competition for ethanol between sulfate-reducing and fermenting bacteria

Abstract

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 (μ_max=0.096 resp. 0.335h⁻¹) than for the sulfate-reducing bacteria (μ_max≈0.03h⁻¹). In contrast, the saturation concentrations for half maximum growth rates (K_s values) for ethanol were lower for the sulfate-reducing bacteria (K_s≈5 μM) than for the fermenting bacteria (K_s≥50 μM). 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.