Novel bio-fabrication of silver nanoparticles using the cell-free extract of Lysinibacillus fusiformis sp. and their potent activity against pathogenic fungi

Green synthesis of nanoparticles is considered an efficient method when compared with chemical and physical methods. Herein, an extracellular green method was adopted to synthesize silver nanoparticles (AgNPs) by using the cell-free extract of a new silver-resistant bacterium, Lysinibacillus fusiformis sp., which was isolated from the sewage treatment plant and identified by 16 S rRNA gene sequencing. Without using any toxic organic solvents and reducing agents, the cell-free extract effectively reduced Ag⁺ to AgNPs with a conversion rate of 72.21% under the optimal condition of pH 9.0, 50 °C, and 5 mM of silver nitrate solution. The newly-developed AgNPs were characterized by the methods of ultraviolet-visible spectroscopy (UV–vis), Fourier transform infrared spectroscopy (FTIR), x-ray diffraction (XRD), transmission electron microscopy (TEM), zeta potential/size distribution analysis and energy-dispersive x-ray spectroscopy (EDS). Characterization results showed that the as-prepared AgNPs were spherical in shape and well-dispersed with an average size of ∼50 nm. The results of the Oxford cup plate assay used for measuring the antifungal activity indicated a pronounced antifungal activity of the biosynthesized nanoparticles against pathogenic fungi of tinea pedis, i.e., Candida albicans, Trichophyton rubrum, Trichophyton mentagrophytes. In conclusion, the biosynthesized AgNPs might display a high potential as novel antifungal agents in medicine. However, it is indispensable to conduct in vivo studies to explore the biocompatibility of AgNPs for their future therapeutic applications. (paper)