EFFECT OF CD2+ ON PHOSPHATE-UPTAKE BY CADMIUM-RESISTANT AND CADMIUM-SENSITIVE STAPHYLOCOCCUS-AUREUS

The effect of Cd2+ on phosphate (Pi) uptake was investigated in the growing cells of Cd2+-resistant Staphylococcus aureus 17810R and Cd2+-sensitive S. aureus 17810S. Inhibitor and ionophore studies showed that 32Pi uptake in the two strains occurred via the Pi porter down pH gradient (DELTA-pH) generated by the respiratory chain. Cd2+ inhibited 32Pi uptake in the cadmium-sensitive strain 17810S at all concentrations used (10-mu-M-1 mM). In strain 17810R, possessing the plasmid-coded Cd2+ efflux system, 10-100 mu-M Cd2+ did not inhibit 32Pi uptake. Even at 1 mM Cd2+, inhibition of 32pi uptake in strain 1 781 OR was reversed when the external Cd2+ was chelated with cysteine and activity of Cd2+ efflux system was restored. Cd2+ efflux induced by cysteine was energized either by membrane potential (DELTA-PSI) or by DELTA-pH, which indicated that electrochemical gradient of protons (DELTA-mu-approximately-H+) was required for this efflux.