Surface expression of metallothionein enhances bioremediation in Escherichia coli

Cadmium contamination is prevalent, and microorganisms are commonly employed for bioremediation to treat cadmium contamination in water. Bacteria accumulated Cd primarily through the cell wall or by secreting polysaccharides and proteins. Metallothionein (MT) is a protein with high affinity for Cd found in a variety of organisms. In this study, the EGR_09832 gene from Echinococcus granulosus was fused with Lpp-OmpA in the outer membrane of Escherichia coli by constructing a recombinant plasmid pBSD-LEF encoding LPP-OmpA- EGR_09832-Flag fusion protein. Then we displayed the metallothionein EGR_09832 from Echinococcus granulosus on the surface of E. coli DH5 alpha cells, as verified by flow cytometry. The result indicated that displaying MT on the cell membrane indeed enhanced the cadmium tolerance of E. coli from 60 mg/L to 160 mg/L. Furthermore, Cd adsorption ability was more than double compared to the wild E. coli. Fourier-transform infrared spectroscopy indicated the amide II band at 1533 cm(-1) may be associated with the MT displayed on the cell membrane. This study suggested that the expressing Cd-binding short peptides such as MT onto the surface of bacterial cells can improve microbial bioremediation. It proposed a novel solution of Cd bioremediation.