Na+-dependent accumulation of sulfate and thiosulfate in marine sulfate-reducing bacteria

Uptake of 35S-labelled sulfate and thiosulfate was studied in twenty sulfate-reducing bacteria. Micromolar additions of these substrates were highly accumulated by washed cells of freshwater and marine strains. In marine strains accumulation required Na+. Generally, the uptake capacity was increased after sulfate limitation during growth. With two marine species, Desulfovibrio salexigens and Desulfobacterium autotrophicum, the effects of various ionophores and inhibitors affecting the transmembrane pH or Na+ gradient or the membrane potential were studied. In both strains transport was reversible. There was no discrimination between sulfate and thiosulfate. With increasing additions the amount taken up increased, while the accumulation factor (Cin/Cout) decreased. Uptake was not directly correlated with the ATP level inside the cells. From these results and the action patterns of the inhibitors tested it is concluded that marine sulfate-reducing bacteria accumulate sulfate and thiosulfate electrogenically in symport with Na+ ions, while in freshwater strains protons are symported. The high-accumulating systems are induced only at low sulfate concentration, while low-accumulating systems are active at sulfate-sufficient conditions.