Potentiation by salicylate and salicyl alcohol of cadmium toxicity and accumulation in Escherichia coli

Abstract

The toxicity of Cd2+ in Escherichia coli K-12 was potentiated by salicylate and several related compounds. The efficiency of plating on Luria broth plates was reduced by more than 10(5)-fold when 10 mM salicylate and 200 microM CdCl2 were present simultaneously but was unaffected when either compound was present by itself. Synergistic effects were found at pH 7.4 with certain other weak acids (acetyl salicylate [aspirin], benzoate, and cinnamate) and with a nonacidic salicylate analog, salicyl alcohol, but not with acetate or p-hydroxy benzoate. Thus, the synergism with Cd2+ is determined by the structure of the compounds and not merely by their acidity. The kinetics of 109Cd2+ uptake by cells grown and assayed in broth indicated the presence of two uptake systems with Kms of 1 and 52 microM Cd2+ and Vmaxs of 0.059 and 1.5 mumol of Cd2+ per min per g of cells, respectively. The kinetics of uptake for cells grown and assayed with 20 mM salicyl alcohol showed 2.5-fold increases in the Vmaxs of both systems but no change in the Kms. Salicylate-grown cells also exhibited increased rates of 109Cd2+ uptake by both systems. Thus, enhanced uptake of Cd2+ may be responsible for the potentiation of Cd2+ toxicity by salicylate and salicyl alcohol.