A cadmium-tolerant bacterium (Cupriavidus taiwanensis KKU2500-3) reduces cadmium accumulation in grains of KDML105 rice cultivated in a contaminated paddy field

Abstract

Cadmium (Cd)-contaminated soil is an important environmental issue affecting the global production of economically important plants, such as rice. This study assessed the effects of Cd-tolerant Cupriavidus taiwanensis KKU2500-3 on the growth and yield of and Cd accumulation in KDML105 rice grown in a Cd-contaminated paddy field. The plots were divided into a no-Cd plot and plots with 2.44 and 2.73 (LOW), 7.43 and 9.60 (M1), and 10.69 and 14.17 (M2) of available and total Cd (in ppm), respectively. The physicochemical properties of paddy soils varied among the plots. No significant differences in yield and related parameters were found between noninoculated and KKU2500-3-inoculated rice, but the panicle number, 1000-grain weight, and filled-grain percentage were higher in the KKU2500-3-inoculated rice. An analysis of the total Cd-tolerant bacteria that colonized KKU2500-3-inoculated rice revealed 99% similarity to KKU2500-3. The Cd content in inoculated rice roots at 30, 60 and 120 DAT was 7.9–8.7%, 0.4–82.9%, and 13.0–81.8% higher than that in noninoculated rice, respectively, but was significantly lower than those in shoots and leaves. In addition, the root-to-shoot translocation of Cd in inoculated rice was lower than that in noninoculated rice, and the Cd content in KKU2500-3-inoculated rice grains was 41.14% (0.162 ppm), 24.76% (0.255 ppm) and 83.20% (0.316 ppm) lower in the LOW, M1, and M2 plots, respectively. In summary, C . taiwanensis KKU2500-3 effectively colonized and reduced Cd accumulation in KDML105 rice grains, and KKU2500-3 inoculation into rice at the early growth stage successfully produced low-Cd KDML105 rice grains in Cd-contaminated paddy fields. • Bacterium was highly competitive and successfully colonized rice tissues. • Colonized bacteria restricted Cd in roots and reduced translocation of Cd to shoots. • Cd contents in rice grains were below the CODEX standard of 0.4 ppm Cd.