Bacillus-derived selenium nanoparticles modulate chromium(VI) toxicity through regulation of metal uptake and oxidative stress in chickpea (Cicer arietinum L.).

This study explores the bioinorganic potential of selenium nanoparticles (SeNPs) biosynthesized by Bacillus sp. (AKS_bp1, PQ824612) in mitigating hexavalent chromium [Cr(VI)] toxicity in chickpea (Cicer arietinum L.). SeNPs were produced via microbial reduction of sodium selenite and characterized by nanoscale size (~ 100-150 nm), negative surface charge (- 20 mV), and biomolecular capping. Under controlled hydroponic Cr(VI) exposure (0-100 ppm), SeNP treatment significantly reduced Cr accumulation in plant tissues, with decreases of 24% in roots and 45% in shoots, indicating restricted translocation and improved metal homeostasis. This suggests a Se-mediated modulation of Cr mobility within the plant system. At the physiological and biochemical levels, SeNPs alleviated Cr-induced oxidative stress, as evidenced by reductions in superoxide (65%) and hydrogen peroxide (52%) levels, along with enhanced antioxidant defense and photosystem II efficiency (a 21% increase in photochemical performance). Improved chlorophyll fluorescence and stomatal regulation further indicated restoration of cellular functionality under metal stress. Importantly, SeNPs exhibited intrinsic redox activity with catecholase-like catalytic behavior (kcat = 3.11 × 106 s- 1), suggesting a potential role in electron-transfer processes relevant to oxidative stress modulation. Overall, bacteriogenic SeNPs mitigate Cr(VI) toxicity through a combination of reduced metal uptake, altered intracellular metal dynamics, and attenuation of reactive oxygen species. These findings highlight the bioinorganic functionality of SeNPs as redox-active nanomaterials influencing metal-plant interactions and oxidative stress pathways.