Characterization of sulfate transport in Desulfovibrio desulfuricans

Abstract

Uptake of 35S-labelled sulfate was studied with a new isolate of Desulfovibrio desulfuricans, strain CSN. Micromolar additions of sulfate (1-10 microM or nmol/mg protein) to cell suspensions incubated in 150 mM KCl at -1 degrees C were almost completely taken up and accumulated about 5,000-fold. Accumulation was not influenced by incubation in NaCl instead of KCl, by acidic pH (5.5) or by incubation under air for 10 min. In alkaline milieu (pH 8.5), after prolonged contact with air (2 h), or after growth with excess sulfate or thiosulfate as electron acceptor, the amount taken up was diminished approximately by half. Pasteurization inhibited sulfate uptake completely. With increasing concentrations of added sulfate (0.1 to 2.5 mM) the intracellular concentration increased only slowly up to 25 mM, and the accumulation factor decreased down to 8. Sulfate transport was reversible. Accumulated sulfate was rapidly lost from the cells after addition of excess non-labelled sulfate or after addition of the uncoupler carbonyl cyanide m-chlorophenylhydrazone (CCCP). The ATPase inhibitor dicyclohexylcarbodiimide (DCCD) specifically inhibited sulfate reduction but had no immediate influence on sulfate accumulation. Addition of the phosphate analogue arsenate (5 mM) was without effect. These results were not in favour of an ATP-dependent transport system. The K+-H+-antiporter nigericin (in 150 mM KCl) and the Na+-H+-antiporter monensin (in 150 mM NaCl) caused partial inhibition of sulfate accumulation, whereas the K+-transporter valinomycin (in 150 mM KCl) and the Na+-H+ exchange inhibitor amiloride (2 mM) were without effect.(ABSTRACT TRUNCATED AT 250 WORDS)