Bacillus atrophaeus as a high-performance microbial nanofactory for monodisperse selenium nanoparticles with exceptional antifungal potency, antioxidant capacity, anticancer activity, and validated molecular docking interactions

Biogenic selenium nanoparticles are a promising new branch of functional nanomaterials with attractive antimicrobial activity, antioxidant properties, and anticancer properties but their complete integrated characterization between synthesis, structure, molecular pathway, and safety has not fully been investigated. A rhizosphere Bacillus atrophaeus isolate was used in this research as an effective microbial nanofactory to produce highly uniform extracellular selenium nanoparticles. The resulting particles had a Z-average diameter of 126.4 ± 0.5 nm, a small polydispersity index of 0.145 and a stable negative surface charge of -32.5 mV. Biomolecular capping, amorphous structure, and spherical morphology were confirmed by physicochemical methods including UV-vis spectroscopy, TEM, SEM, XRD, and FTIR. The nanoparticles exhibited effective broad-spectrum antimicrobial effects with 16.5–24.2 mm bacterial and 22.0–39.3 mm fungal inhibition areas, and Aspergillus ochraceus was the most susceptible to the nanoparticles (39.3 mm). Assessment of antioxidants demonstrated a high radical scavenging ability with the IC50 equals 41.92 µg/mL, anticancer evaluation against HepG2 cells displayed dose-dependent cytotoxicity with the IC50 equals 94.71 µg/mL and also up to 77% cell viability reduction at a 200 µg/mL concentration. Molecular docking revealed that it interacts well with catalytic regions of bacterial DNA gyrase and fungal RNA polymerase in view of the antimicrobial mechanism observed. A positive forecast of safety margin, with no organ-level, mutagenic, carcinogenic, immunotoxic, and metabolic toxicity was predicted by in silico toxicity profiling. Taken altogether, the analysis of these results confirms that B. atrophaeus is a promising microbial system to be used in sustainable manufacturing of versatile selenium nanoparticles with an enormous therapeutic and biotechnological potential.