Isolation, Characterization And Antibacterial Activity Of Bioinspired Silver Nanoparticles From Bacillus Licheniformis

Abstract

The present study describes a green, cost-effective, and eco-friendly approach for the synthesis of silver nanoparticles (AgNPs) using Bacillus licheniformis isolated from rhizospheric soil. Molecular identification of the isolate via 16S rRNA gene sequencing confirmed its identity with 99.8% similarity to Bacillus licheniformis (GenBank Accession No. LC814576). The biosynthesis of AgNPs was evidenced by a rapid color change from pale yellow to dark brown and further confirmed by a strong surface plasmon resonance (SPR) peak observed at approximately 430 nm using UV–Visible spectroscopy. Fourier-transform infrared (FTIR) spectroscopy revealed the presence of functional groups such as hydroxyl, amide, and carboxyl, indicating the involvement of bacterial metabolites in the reduction and stabilization of AgNPs. Transmission electron microscopy (TEM) demonstrated that the synthesized nanoparticles were predominantly spherical, with a uniform size distribution ranging between 20–30 nm. X-ray diffraction (XRD) analysis confirmed their crystalline nature, showing characteristic peaks corresponding to the face-centered cubic (FCC) structure of silver. Differential scanning calorimetry (DSC) exhibited an exothermic peak at ~102.25 °C, supporting the presence of a stable organic capping layer. The biosynthesized AgNPs exhibited potent antimicrobial activity against multidrug-resistant bacterial pathogens including Staphylococcus aureus, Escherichia coli, Klebsiella pneumoniae, and Pseudomonas aeruginosa. These findings highlight the potential of B. licheniformis as a promising biogenic source for sustainable nanoparticle production with applications in antimicrobial therapeutics and environmental biotechnology.