Green Extracellular Synthesis of the Silver Nanoparticles Using Thermophilic Bacillus Sp. AZ1 and its Antimicrobial Activity Against Several Human Pathogenetic Bacteria

Background: Silver nanoparticles (AgNPs) are among the most effective antimicrobial agents that are used in the medicine and pharmaceutics. During the past decades, metal nanoparticles synthesis through application of the biological methods has increasingly been used, as the biologically synthesized particles are mostly non-toxic as well as effective. Objectives: The main goal for undertaking the present investigation was to evaluate the extracellular synthesis of the AgNPs by a native thermophilic Bacillus Sp. AZ1 that was isolated from a hot spring in Ardebil province. Subsequently the antimicrobial potentials of the nanoparticle was evaluated against several human pathogenic organisms. Materials and Methods: The biosynthesized AgNPs were confirmed visually by appearance of a dark brown color formation in the mixture as well as silver surface plasmon resonance band by using UV-Visible spectroscopy. The AgNPs were further characterized by SEM, EDX and TEM. The antimicrobial activity of the AgNPs was investigated using Salmonella typhi, Escherichia coli, Staphylococcus epidermis, and Staphylococcus aureus, by applying disk diffusion method. Results: Identification of the strain AZ1 by the 16S rRNA sequence analysis showed 99% sequence homology between this strain and B. licheniformis. The obtained UV-Visible spectrum of the aqueous medium containing silver ion, showed a peak at 425 nm which indicates a correspondence to the plasmon absorbance of the silver nanoparticles. The biosynthesized AgNPs were found to be in the size range of ~7-31 nm with spherical the shape.  Studies  regarding the antibacterial effect of the particles showed the highest inhibitory effect against the two strains; E. coli, and S. typhi, respectively. Conclusions: Our study presents a simple green synthesis process for the production of an extracellular nanoparticles which is environmental friendly. Biosynthesis of the AgNPs by a thermophilic bacillus from the hot spring (Qeynarjeh, Ardebil) in Iran with the highest similarity to Bacillus licheniformis is reported for the first time.