Effects of Bacteria on Cadmium Bioaccumulation in the Cadmium Hyperaccumulator Plant Beta Vulgaris Var. Cicla L.

To investigate the effects of two cadmium-tolerant bacteria, Staphylococcus pasteuri (S. pasteuri X1) and Agrobacterium tumefaciens (A. tumefaciens X2), on cadmium uptake by the cadmium hyperaccumulator plant Beta vulgaris var. cicla L., a pot experiment with artificially contaminated soil was conducted. The results demonstrated that both cadmium-tolerant bacteria enhanced the dry weight of Beta vulgaris var. cicla L. The total dry weights of plants in the control CK20, S. pasteuri X1 and A. tumefaciens X2 treatments were 0.85, 1.13, and 1.38 g/pot, respectively. Compared with the control CK20 findings, the total dry weight of plants was increased by 32.8 and 61.1% after inoculation with S. pasteuri X1 and A. tumefaciens X2, respectively, indicating that A. tumefaciens X2 more strongly promoted the growth of Beta vulgaris var. cicla L. than S. pasteuri X1. In addition, inoculation with S. pasteuri X1 and A. tumefaciens X2 significantly (p < 0.05) promoted cadmium uptake by plants and improved the bioaccumulation of cadmium by the plants from the soil. Moreover, the inoculation of S. pasteuri X1 and A. tumefaciens X2 effectively facilitated the transfer of cadmium in the soil from the Fe-Mn oxide and residual fractions to the soluble plus exchangeable and weakly specially adsorbed fractions in the rhizosphere soils of plants. The bacterial enhancement of cadmium phytoavailability might provide a potential and promising method to increase the efficiency of phytoextraction.