Green synthesis of silver nanoparticles by isolated Bacillus velezensis BS1 and their applications

This study aimed to isolate a local silver-resistant bacterial strain capable of efficiently synthesizing silver nanoparticles (AgNPs) and to optimize the parameters affecting bacterial growth and the bioreduction process. The biosynthesized AgNPs were characterized using UV-Vis spectroscopy, TEM, FTIR, and zeta potential analyses, and their biological activities were assessed through antibacterial, cytotoxicity, and seed germination assays. Bacillus velezensis BS1 was identified as the most promising isolate for AgNPs biosynthesis. Optimal bioreduction conditions were achieved at 70 °C and pH 9 after 3 h with 5 mM AgNO₃. The UV-Vis spectra exhibited surface plasmon resonance peaks at 410-450 nm, confirming the formation of AgNPs. The resulting AgNPs were spherical, negatively charged, and capped with the microbial proteins. They exhibited strong antibacterial activity against Staphylococcus aureus and Escherichia coli, with bactericidal effects verified through growth kinetics and inhibition zone assay. The AgNPs also demonstrated significant cytotoxicity against human epidermoid carcinoma (A431) cells and enhanced the germination and growth of pea and chickpea seeds, except at 100 µg mL⁻¹ in chickpeas, where clear toxicity effects were observed on the roots. These findings suggest that B. velezensis BS1, a silver-resistant isolate, represents a promising, safe, and sustainable route for the biosynthesis of AgNPs, thereby supporting green nanotechnology applications and guiding future studies on their biological effects and their potential toxicity. KEY POINTS: • Bacillus velezensis BS1 efficiently achieved green synthesis of silver nanoparticles. • AgNPs showed strong antibacterial and cytotoxic activities against cancer cells. • AgNPs improved seed germination, highlighting potential in sustainable agriculture.