Extracellular synthesis of silver nanoparticles by Isoptericola variabilis using rice bran

Green methods are environmentally friendly methods for the synthesis of nanoparticles. These methods use a wide range of biological and reducing agents produced by bacteria, fungi, yeasts, algae, and plants for making metal nanoparticles. The object of this study was the extracellular synthesis of silver nanoparticles using rice bran by Isoptericola variabilis and the subsequent comparison of the antibacterial activity of the synthesized optimized and non- optimized silver nanoparticles. Optimal conditions for producing silver nanoparticles were obtained using an experimental response surface methodology (RSM) design. Nanoparticles were characterized by SEM, FT-IR, and UV-visible spectroscopy. Antibacterial activity of the silver nanoparticles (AgNPs) was investigated using the disk diffusion method against E.coli on Mueller Hinton agar medium. The SEM images of the optimized AgNPs showed an increase in uniform generated spherical nanoparticles. In addition, optimizing the production conditions of nanoparticles not only developed their antibacterial activity but reduced their sensitivity threshold compared with synthetic nanoparticles in the initial conditions. The effective concentration of nanoparticles against E. coli decreased from 500 μg/mL to 100 μg/mL (a 5-fold reduction). In conclusion, silver nanoparticles can be produced by Isoptericola variabilis, and its optimization process not only led to increased productivity but also improved the antibacterial efficiency against E. coli.