Investigation of silver nanoparticles biosynthesis by Bacillus strains isolated from various sources

Keywords: Bacillus, nanoparticle, biosynthesis, silver In this study, the abilities of 28 bacteria, isolated from some soil and food samples, to synthesize silver nanoparticles (AgNP) were investigated, and the best producer isolate was selected and nanoparticle (NP) production conditions of this isolate were optimized. The produced AgNPs were characterized and their antioxidant and antimicrobial properties were investigated. Within the scope of the study, it was determined that the ZGT9 strain, which was isolated from a soil sample and determined to belong to the Bacillus genus according to 16S rDNA sequence analysis, produced AgNPs. For this reason, the study was continued with the bacterium coded as ZGT9. The effects of pH (6-10), temperature (30-40℃), and AgNO3 concentration (1-10 mM) on NP production were determined. Depending on the parameters applied, it was observed that the color of the Nutrient Broth medium changed from light yellow to brown during the formation of AgNP, and the absorbance values were measured by UV-VIS spectrophotometer at a wavelength of 414 nm. As a result of spectrophotometric measurements, it was determined that the best production was at 40°C and 48 hours in the medium with 8 mM AgNO3 concentration, pH 8-9. Field emission scanning electron microscopy (FESEM) analyzes were performed and NPs were found to be spherical in size having diameters between 1 and 50 nm. Due to agglomeration at 40°C, analyzes were continued at 33°C. It was determined that AgNP biosynthesis did not occur at pH 6 and 7, 1 mM and 2 mM AgNO3 concentrations and 24 hours. Although the color change and surface plasmon resonance were best observed at pH 10, difficulties were encountered in the final stage of purification. The produced nanoparticles exhibited antioxidant and antimicrobial activity. DPPH radical reducing activity was in the range of 39,4%-70%. In the antimicrobial analysis in liquid culture, it reached 100% inhibition at the 6th hours.