Metalloid-resistant Serratia marcescens RB11 mitigate arsenic-selenium co-toxicity and regulate mineral nutrient...

Contamination of irrigation water with nonpoint-sources pollutant has remain a critical concern in food and environmental safety. Intensive water demand for rice cultivation coupled with heavy metals (HM) accumulation present a major challenge to remediation. Although HM-resistant microorganisms have shown promises in bioremediation, their ability to detoxify co-occurring contaminants while balancing mineral nutrients under co-toxicity remain unreported. This trial explored potential of Serratia marcescens RB11 to detoxify combined arsenic and selenium (As+Se) dose of 5.58 mM to enhance resistance of Ethyl methanesulfonate (EMS) rice lines. Quantification of metalloid and mineral nutrient accumulation under co-toxicity and co-treatment revealed high tolerance of strain RB11 to As+Se in vitro, producing siderophore, exopolysaccharide (EPS), and phosphate solubilization. Co-treatment enhanced germination, growth and regulated As/Se uptake, phosphorus (P), sulfur (S), and iron (Fe) mobility, while elevating magnesium (Mg) and calcium (Ca) assimilation. We noticed increase in biomass, photosynthetic efficiency and activity of catalase, superoxide dismutase, as well as content of glutathione (GSH) salicylic and jasmonic acid activating cross-signaling pathways. Further, co-toxicity elevated As/Se root to shoot bioconcentration factor (BCF) by 17.72% and 10.81% respectively, while co-treatment reduced As BCF (15.38%) stabilizing redox conditions and resilience. These results suggest that RB11-driven secretion of EPS, organic acids, organic Se, and GSH promoted P-As/S-Se sequestration, Fe-As^3 + and Fe²⁺-As⁵⁺ complexation, enhanced As³⁺ methylation, and supported Se^4+/6+ reduction. Interestingly, this uptake regulation and nutrient cycling immobilized As/Se limiting co-toxicity and stabilized paddy redox status pitching RB11 as an additive for reclamation of As+Se contaminants within agro-ecosystem.