Influence of sulfhydryl sites on palladium (II) adsorption by displaying EC20 on the surface of Escherichia coli

BACKGROUND Sulfhydryl binding dominates metal adsorption onto bacteria, however, their role in palladium adsorption under high metal loading conditions remains unclear. We investigated their influence on palladium adsorption by increasing (expression of EC20 protein) and decreasing (selective blocking of -SH) the number of sulfhydryl sites on the surface of Escherichia coli (E. coli). RESULTS Kinetic and equilibrium studies confirmed that the sulfhydryl sites in the EC20 protein played an important role in Pd (II) adsorption, while blocking the sulfhydryl sites resulted in the decrease of adsorption capacity. The accumulation of palladium in the surface of E. coli BL21 cells was enhanced by displaying EC20 protein, and morphology properties of Pd-loaded cells changed considerably. SEM and TEM analyses showed that palladium ions were absorbed both in the exterior and interior of cells. Pd-S bond was detected by XPS in Pd-loaded cells, and it was demonstrated that the unbound sulfhydryl site was a contributor in Pd (II) adsorption. CONCLUSION Sulfhydryl sites on the surface of E. coli are significant functional groups in Pd (II) adsorption, increasing their number by EC20 protein expression leads to the increase of Pd (II) adsorption capacity, and vice versa. (c) 2018 Society of Chemical Industry