TRANSPORT AND TOXICITY OF CADMIUM - ITS REGULATION IN THE CYANOBACTERIUM SYNECHOCYSTIS-AQUATILIS

Cadmium entrance into cells of the cyanobacterium Synechocystis aquatilis was energy-dependent requiring light. Cells exposed to cadmium in the dark took up considerably less Cd2+ than in the light. The metal taken up under different light conditions caused changes in cellular adenylate metabolism; the ATP/ADP ratio increased significantly in cells exposed to cadmium. The ATP/ADP ratio increased with duration of Cd exposure in light much more than in dark. Cd2+ transport was affected by the uncouplers CCCP, DNP and DCMU at concentrations that inhibited phosphorylation and decreased membrane electropotential; DCCD, an inhibitor of the FoFl-reverse ATP-ase, had no effect. Cadmium transport increased with temperature in the range 10-30-degrees-C. Cadmium toxicity was modified by temperature as well. The Cd inhibition of CO2 fixation in S. aquatilis was by 50% at 30-degrees-C, and only by 5% at 10-degrees-C. The cadmium transport process displayed saturation Michaelis-Menten kinetics; the apparent K(m) and V(max) were estimated at 286 muM and 1.43 mumol min-1 x g dry wt, respectively. Calcium, magnesium and zinc cations were inhibitory to Cd2+ transport at equimolar concentration (8.9 muM); manganese and potassium were not.