Sundarbans-derived halotolerant Bacillus inaquosorum SWA3TU mitigates arsenic and lead stress in Oryza sativa L.

The production of Oryza sativa L. (rice) in polluted agroecosystems is severely affected by arsenic (As) and lead (Pb) toxicity. This study evaluates the efficacy of a novel halotolerant Bacillus inaquosorum SWA3TU (NCBI GenBank Accession No.: PQ097957), isolated from Sundarbans mangrove soil, as a plant growth-promoting bacterium (PGPR) for alleviating individual As and Pb stress in the IR-64 rice cultivar. SWA3TU demonstrated tolerance to NaCl (up to 10%) and heavy metals (As and Pb up to 150 µg/mL), along with plant growth-promoting traits including IAA production, phosphate and zinc solubilization, siderophore secretion, nitrogen fixation, exopolysaccharide synthesis, and antifungal activity. Under hydroponic conditions at 12 µg/mL (selected concentration) of As and Pb, SWA3TU inoculation significantly reduced toxicity. Compared to stressed controls, it increased biomass by 45%–62%, root and shoot length by 42%-57%, and chlorophyll content by 72%-78%. Antioxidant enzyme activities were elevated under stress and reduced by 31%-43% following bacterial inoculation, indicating mitigation of oxidative stress. Additionally, H 2 O 2 levels and electrolyte leakage decreased by 36%-40% and 35%-38%, respectively. A 42%-46% reduction in As and Pb accumulation was observed, along with increased expression of Aux/IAA gene. Although the isolate is halotolerant, salinity stress was not included in plant experiments and is considered only as an environmental background factor relevant to the Sundarbans ecosystem. These findings highlight B. inaquosorum SWA3TU as a promising bioinoculant for mitigating arsenic and lead stress in rice.