Immobilization of Cd Using Mixed <i>Enterobacter</i> and <i>Comamonas</i> Bacterial Reagents in Pot Experiments with <i>Brassica rapa</i> L.

Abstract

<i>Enterobacter</i> sp. A11 and <i>Comamonas</i> sp. A23 were isolated and identified. Coculturing these two strains with Cd(II) led to the production of biofilm, H₂S, and succinic acid (SA), and Cd(II) was adsorbed by cells and formed CdS precipitates. After centrifugation, 97% Cd(II) was removed from the coculture. Proteomic and metabolomic analyses of the cocultured bacteria revealed that H₂S and SA production pathways, metal transportation, and TCA cycle were active under Cd(II) stress. In vitro addition of SA enhanced the production of H₂S and biofilm formation and Cd(II) adsorption. Two-season greenhouse pot experiments with <i>Brassica rapa</i> L. were performed with and without the coculture bacteria. Compared with the control, the average Cd amounts of the two-season pot experiments of the aboveground plants were decreased by 71.3%, 62.8%, and 38.6%, and the nonbioavailable and immobilized Cd in the soils were increased by 211.8%, 213.4%, and 116.7%, for low-, medium-, and high- Cd-spiked soils, respectively. The two strains survived well in soil during plant growth using plate counting, quantitative real-time PCR, and metagenomics analysis. Our results indicate that the combination of <i>Enterobacter</i> and <i>Comamonas</i> strains with the production of H₂S and biofilm are important effectors for the highly efficient immobilization of Cd.