Aggregated Biogenic Selenium Nanoparticles by Bacillus thuringiensis MSF10 and Their Antibacterial Activity

Selenium nanomaterials synthesized via biological routes have attracted significant attention due to their notable antimicrobial properties, lower toxicity compared to inorganic selenium, and environmental compatibility. In this study, a newly isolated strain, Bacillus thuringiensis MSF10, was evaluated for its ability to reduce sodium selenite (Na 2 SeO 3 ) and biosynthesize selenium nanostructures. The isolate demonstrated high sodium selenite reduction efficiency (SSRE), reaching 94.29% at pH 10 and 99.52% at 42 °C under optimized conditions. Morphological analysis by SEM revealed predominantly spherical aggregated structures ranging from 50 to 750 nm, while dynamic light scattering (DLS) indicated hydrodynamic diameters of 2345 nm (untreated) and 571 nm after ultrasonication, reflecting aggregation behavior. X-ray diffraction (XRD) analysis confirmed the presence of crystalline selenium with an average crystallite size of approximately 15.19 nm, indicating nanoscale crystalline domains within larger biogenic aggregates. FT-IR analysis suggested the involvement of proteinaceous biomolecules as stabilizing agents. The biosynthesized selenium nanostructures exhibited antibacterial activity against Escherichia coli and Staphylococcus aureus , highlighting their potential as eco-friendly selenium-based antimicrobial materials.