Biochemical and genetic basis of cadmium biosorption by Enterobacter ludwigii LY6, isolated from industrial contaminated soil.

In this study, a cadmium-tolerant bacterium, Enterobacter ludwigii LY6, was isolated from cadmium-contaminated soil in Shifang, Sichuan province, China. The cadmium chloride removal rate of the strain LY6 with a treatment of 100 mg/L cadmium chloride reached 56.0%. Scanning electron microscopy showed that exopolysaccharides (EPS) might be the main means of cadmium adsorption by the strain. X-ray powder diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDS) analyses indicated that cadmium sulfide nanoparticles formed on the surface of bacteria cultured in a medium containing 100 mg/L cadmium chloride. In addition, the expression of several genes increased with the increase of the cadmium concentration in the medium, including the multiple antibiotic resistance proteins marA and marR, and the cold shock protein CspA. GO functions, such as the redox activity, respiratory chain and transport functions, and KEGG pathways involved in "bacterial chemotaxis" and "terpenoid backbone biosynthesis" were found to be closely related to bacterial cadmium tolerance and biosorption. This is the first report that E. ludwigii can reduce sulfate to form cadmium sulfide nanoparticles under high concentration cadmium exposure. The genes related to cadmium tolerance identified in this study lay a foundation for the genetic breeding of cadmium-tolerant strains.