Reduction of cadmium uptake in rice endophytically colonized with the cadmium-tolerant bacterium Cupriavidus taiwanensis KKU2500-3.

The effects of the cadmium (Cd)-tolerant bacterium Cupriavidus taiwanensis KKU2500-3 on the growth, yield, and Cd concentration in rice grains were investigated in the rice variety Phitsanulok 2 (PL2), which was cultivated in a hydroponic greenhouse. The numbers of Cd-tolerant bacteria isolated from the roots and shoots of plants under the RB (rice with bacteria) and RBC (rice with bacteria and Cd) treatments ranged from 2.60 to 9.03 and from 3.99 to 9.60 log cfu·g-1 of PL2, respectively. This KKU2500-3 strain was successfully colonized in rice, indicating that it was not only nontoxic to the plants but also became distributed and reproduced throughout the plants. Scanning electron microscopy analysis revealed attachment of the bacterium to the root surface, whereas the internally colonized bacteria were located in the vascular tissue, cell wall, and intercellular space. Although the Cd contents found in PL2 were very high (189.10 and 79.49 mg·kg-1 in the RC (rice with Cd) and RBC roots, respectively), the Cd accumulated inside the rice seeds at densities of only 3.10 and 1.31 mg·kg-1 , respectively; thus, the bacteria reduced the Cd content to 57.74% of the control content. Therefore, the colonizing bacteria likely acted as an inhibitor of Cd translocation in PL2.