IIntroduction:

Biosynthesized nanoparticles have attracted significant attention in biomedical research due to their biocompatibility, natural origin, and potent antibacterial properties. Silver nanoparticles (AgNPs), in particular, are valued for their cost-effectiveness, eco-friendliness, and strong antimicrobial activity. This study aimed to establish a sustainable and scalable extracellular green synthesis platform for AgNPs using Bacillus strains isolated from spring water.

Methods:

Eighteen Bacillus isolates were screened for their ability to reduce silver ions. The most efficient strain-mediated synthesis was optimized under 3 mM AgNO₃, pH 10, 37 °C, for 72 h. The synthesized AgNPs were characterized using UV–visible spectroscopy, scanning electron microscopy (SEM), dynamic light scattering (DLS), X-ray diffraction (XRD), and Fourier-transform infrared (FTIR) analyses to assess morphology, size, crystallinity, surface charge, and biomolecular capping.

Results:

UV–Vis spectroscopy revealed a distinct surface plasmon resonance peak at 430 nm. SEM and DLS analyses confirmed well-dispersed, nearly spherical nanoparticles with diameters of 30–50 nm and high colloidal stability (zeta potential −34/9 mV). XRD patterns indicated a crystalline face-centered cubic structure, while FTIR spectra suggested biomolecular capping via amide and hydroxyl functional groups. The AgNPs demonstrated 98 % antibacterial inhibition at 10 mg/mL and MIC values of 0.5–1 mg/mL against Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa, comparable to gentamicin.

Conclusion:

This study presents a rapid, reproducible, and eco-friendly extracellular biosynthesis of AgNPs using a novel Bacillus strain, highlighting its potential as a sustainable nanoplatform for combating multidrug-resistant pathogens in biomedical applications.

Keywords: Silver nanoparticles; Bacillus; green synthesis; antibacterial activity; antibiotic resistance; nanobiotechnology