Ecological significance of acetate assimilation by Chlorobium phaeobacteroides

The effect of different concentrations of sulfide and sulfur on the assimilation of acetate by Chlorobium phaeobacteroides was investigated in batch and continuous cultures. In batch cultures the assimilation of acetate strictly depends on the initial concentration of sulfide. In continuous cultures the uptake of acetate depends not only on the reservoir concentration of sulfide but also on the dilution rate. The more severe the limitation of sulfide the higher the incorporation of acetate. The very efficient uptake of acetate was also observed in batch cultures, but only immediately prior to sulfide depletion. After sulfide depletion, with sulfur still available, the uptake of acetate per mmol reducing power increased even further. This phenomenon, which has been overlooked since growth decreases drastically after sulfide depletion due to incapacity for assimilatory sulfate reduction is of ecological importance in the formation of blooms of brown Chlorobium species.