A unique metallothionein-engineered in Escherichia coli for biosorption of lead, zinc, and cadmium; absorption or adsorption?

The present study introduced and evaluated modification of E. coli BL21 (DE3) to improve its biosorption capacity by the transfer of the Corynebacterium glutamicum metallothionein gene (C.gMT). The C.gMT sequence was extracted and cloned in pET28a vector and the ligation product was transferred into E. coli BL21 (DE3). It has been also submitted to the GenBank database (accession number KJ638906.1). The performance of the recombinant bacterium was evaluated at different metal ions concentrations, contact times, pH values, and co-ions. The results show that recombinant BL21 (DE3) was able to uptake Pb+2, and Zn+2 at greater percentages than could BL21 (DE3). The optimum pH for the removal of each heavy metal was different. As contact time increased, Pb+2 and Zn+2 biosorption by the recombinant bacterium increased, while the biosorption of Cd+2 remained at a nearly steady rate for contact times of more than 1 h. Increasing the concentrations of Pb+2 and Zn+2 in solution increased biosorption of these metals by the recombinant BL21 (DE3) over that of Cd+2. It could be hypothesized that Pb+2 and Zn+2 removal by C.gMT-engineered BL21 (DE3) occurred mainly via intracellular biosorption (absorption) and that Cd+2 was mainly taken up through cell surface biosorption (adsorption).