The effect of zinc and cadmium ions on Escherichia coli B

The effect of the two metal ions Zn+2 and Cd+2 on the viability and activity of Escherichia coli B bacteria was studied in experimental conditions. Addition of Cd+2 (0.05 ppm) to the incubation medium caused an inhibition of 16 h in the culture's growth. In similar conditions and concentrations, Zn+2 did not affect the bacterial growth. Only concentrations of 0.5 ppm Zn+2 and more caused growth inhibition of 6 h. Accumulation of the metal ions in the E. coli cells has shown that there is a linear relation between the concentrations of Zn+2 and Cd+2 in the cells and their concentrations in the culture media. On the other hand, a decrease in the Cd+2 accumulation was noticed when the concomitant Zn+2 concentrations were higher in the incubation media. Exposure of E. coli to various concentrations of these ions resulted in an increase of the total protein and the metal binding proteins amount in the cells. The activity of alkaline phosphatase was increased 4-fold in the presence of these ions. Separation of protein fractions revealed three protein fractions which contain Zn+2 with MWs of 80, 40, and 10 kD. Three Cd+2 binding proteins have been separated and their molecular weights were 75, 50, and 25 kD. The two high molecular weight proteins were able to bind Zn+2. Conclusions from these results may contribute to the understanding of events and processes in the natural environment.