Rhizobacterial consortia reduce grain arsenic in rice to below regulatory limits under field conditions

Arsenic (As) contamination in rice grains poses a significant global food safety challenge. This study evaluated the potential of As(III)-oxidizing and plant growth-promoting rhizobacterial consortia to mitigate As accumulation in rice grains under field conditions in Thailand's Loei and Khon Kaen (KK) regions. The experiments were conducted on paddy soils with varying levels of native As concentrations and physicochemical properties. The results revealed no significant interactions between the paddy soil and bacterial treatments across most growth parameters during the various stage of rice growth. However, inoculation consistently increased plant growth, photosynthetic pigment levels, and grain yield across all the sites, demonstrating that the robust performance of the inoculants occurred irrespective of soil variation. Notably, the bacterial treatments significantly reduced As accumulation in rice, with the mixtures KKU2500-3 and 4.25 (RB-3/4.25) and KKU2500-3 and 4.44 (RB-3/4.44) decreasing As content by 20.5% and 6.8% in Loei-1 and Loei-2, respectively. In the most contaminated field (Loei-2, soil As concentration of 4.70 mg/kg), the top-performing consortium (KKU2500-3/4.25) lowered grain As levels to less than the stringent 0.1 mg/kg in polished rice safety limits for infant food. At the KK site, the As content decreased by 11.8-12.8%. Mechanistic investigations revealed that the inoculants stimulated the production of glutathione (GSH), phytochelatins (PCs), and root sulfides, indicating a dual action of immobilizing As in the rhizosphere and enhancing the internal detoxification pathways of plants. These findings demonstrate the potential of rhizobacterial consortia as biotechnological tools to produce safe rice in As-contaminated regions, addressing substantial public health issue.