Bacillus subtilis enhances maize yield by restricting cadmium translocation and modulating ion homeostasis

Cadmium (Cd) pollution in soils severely impacts maize growth. This study investigates the potential application of Bacillus subtilis to soil (BSS) as a bioremediator to mitigate Cd-induced stress during the V8 and VT growth stages of maize. The effects of B. subtilis on maize growth, photosynthesis, antioxidant defense, cellular ultrastructure, osmo-regulatory substances, ion homeostasis, and yield under Cd stress were evaluated. Cd exposure (Cd25 and Cd50 mg/kg) significantly reduced plant height, shoot biomass, leaf area, chlorophyll content, and photosynthetic efficiency by 8 %-47 % while increasing oxidative stress markers (superoxide anion (O₂^•-), hydrogen peroxide (H₂O₂), malondialdehyde (MDA)) up to 3-fold. Co-exposure of B. subtilis with Cd stress (Cd25BSS and Cd50BSS) improved these parameters, enhancing plant growth and photosynthetic performance by 7 %-40 % and reduced stress biomarkers by 8 %-38 %. Cd25BSS also enhanced superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX), and glutathione reductase (GR) by 12 %-34 % and upregulated antioxidant genes (ZmSOD1, ZmPOD4, ZmCAT1, ZmAPX1, and ZmGR1) compared to Cd25. Additionally, Cd25BSS increased osmotic regulation through higher soluble sugars and proteins, contributing to cellular stability under stress. Ion homeostasis was improved by increasing essential nutrients from 6 %-70 % while reducing Cd accumulation by 25 %-85 % in different maize tissues at both growth stages. Moreover, yield exhibited a strong positive correlation with growth parameters and essential ions (nitrogen, phosphorous, potassium, iron, and zinc), while showing negative correlation with MDA and Cd accumulation. This study highlights B. subtilis as an effective strategy for mitigating Cd stress, improving maize productivity in contaminated soils, and supporting sustainable agricultural practices.