Fig. 4

Comparison of the growth curves of the chassis cells with the selection plasmid in response to lead and zinc in the presence of ampicillin. The optical density at 600 nm of the E. coli (pZE21-PBS) strain was measured with metal ions at a 20 µM and b 50 µM. Ampicillin was used at 100 µg mL⁻¹. Squares: lead ions; Circles: zinc ions. Experiments were performed in triplicate, and data represent the averages and standard deviations of the means