The kinetics of sulfate and acetate uptake was studied in the sulfate-reducing bacterium Desulfobacter postgatei (DSM 2034). Kinetic parameters (Km and Vmax) were estimated from substrate consumption curves by resting cell suspensions with [35S]sulfate and [14C]acetate. Both sulfate and acetate consumption followed Michaelis-Menten saturation kinetics. The half-saturation constant (Kin) for acetate uptake was 70 ,uM with cells from either long-term sulfateor long-term acetate-limited chemostat

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... ultures. The average Km value for sulfate uptake by D. postgatei was about 200 ,uM. Km values for sulfate uptake did not differ significantly when determined with cells derived either from batch cultures or sulfateor acetate-limited chemostat cultures. Acetate consumption was observed at acetate concentrations of c1 ,uM, whereas sulfate uptake usually ceased at 5 to 20 puM. The results show that D. postgatei is not freely permeable to sulfate ions and further indicate that sulfate uptake is an energy-requiring process.