PGPR-mediated alleviation of arsenic and cadmium toxicity in rice (Oryza sativa L.) through regulation of rhizosphere Microbiome and oxidative stress biomarkers

Abstract Heavy metal contamination, particularly by arsenic (As) and cadmium (Cd), severely impairs rice ( Oryza sativa L.) growth, physiological performance, and food safety. This study evaluated the effectiveness of plant growth-promoting rhizobacteria (PGPR), including Rhizobium leguminosarum , Bacillus subtilis , and Serratia marcescens , in mitigating As and Cd toxicity in O. sativa under a controlled pot experiment. Plants exposed to individual As and Cd stress at 0, 100, and 200 mg kg⁻¹ exhibited marked reductions in plant growth, photosynthetic pigments, gas exchange parameters, antioxidant balance, nutrient uptake, and rhizosphere microbial diversity, along with pronounced increases in oxidative stress indicators. Conversely, R. leguminosarum , B. subtilis , and S. marcescens inoculation significantly improved plant growth and biomass, enhanced photosynthetic efficiency and gas exchange traits, strengthened antioxidant defense systems, and improved mineral nutrition. PGPR application reduced malondialdehyde and hydrogen peroxide levels, enhanced the ascorbate–glutathione cycle and proline metabolism, and limited As and Cd accumulation in plant tissues, resulting in reduced health risk indices. In addition, rhizosphere microbial diversity increased substantially, indicating improved soil microbial stability under metal stress. RT-qPCR-based gene expression analysis further supported PGPR-mediated enhancement of stress-responsive antioxidant and detoxification pathways. Overall, PGPR particularly B. subtilis proved effective in restoring physiological balance, reducing metal toxicity, and improving rhizosphere health. These findings highlight PGPR as a sustainable and eco-friendly strategy for improving rice performance and food safety in heavy metal-contaminated soils.