Growth curves of the transformed BL21 strains with empty pGEX-4T-1(negative control) and recombinant pGEX-4T-1-EpGSTN-31 plasmids.

A total of 200 mg L^-1 IPTG was added to each culture to induce the expression of the recombinant protein. (a) 50 mg L^-1 Cd²⁺ (b) 100 mg L^-1 Pb²⁺ (c) 70 mg L^-1 Cu²⁺ and (d) 100mg L^-1 Zn ²⁺. Each treatment was conducted independently four times. Asterisks indicate significant differences (p < 0.05*, p < 0.01**, p < 0.001***) compared to the control according to Independent-Samples T test.