Bioadsorption and biostabilization of cadmium by Enterobacter cloacae TU

- The mutant E.cloacae TU grows well in high concentration of Cd as much as 250 mg/L.
- The maximum adsorption capacity by E. cloacae TU were 67.0 mg/g.
- The absorbed Cd distributes mainly at the surface of cells.
- The groups of OH, NH, SH and CO on the surface of E.clocacae TU are the major binding sites.
- E. cloacae TU can stabilize Cd in the soil to reduce the plant uptake for remediation purpose.

Biostabilization of cadmium, a hazardous chemical found widely in China, was attempted using Enterobacter cloacae TU (E.cloacae TU). A cadmium (Cd)-tolerant E.cloacae TU was obtained by mutagenesis using an atmosphere pressure glow discharge plasma system, and it displayed regular growth behavior in the presence of 250 mg/L Cd in solution. The maximum stabilization capacity of E.cloacae TU toward Cd reached 67.0 ± 3.5 mg/g dry cell weight at an initial Cd concentration of 200 mg/L. The percentage of Cd removal by E.cloacae TU reached 97.4± 0.3% at an initial Cd concentration of 20 mg/L. A desorption experiment confirmed both extracellular adsorption and intracellular uptake contribute to biostabilization, although Cd was mainly distributed on the surface of E.cloacae TU cells due to over-secretion of extracellular polysaccharides under Cd stimulus. The changes in morphology and functional groups of the E.cloacae TU cell surface in the presence of Cd were analyzed using X-ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM) and Fourier Transform Infrared Spectoscopy (FT-IR). The feasibility of using E.cloacae TU for this purpose was further confirmed by on site remediation, in which the application of E.cloacae TU reduced the bioavailability and moreover the accumulation of Cd in tobacco plants without affecting the quality of flue-cured tobacco.