Investigation of the productions of copper, zinc, and selenium nanoparticles by some Bacillus strains

Keywords: Bacillus, nanoparticle, biosynthesis, selenium In this study, the abilities of Bacillus strains isolated from some soil and food samples to produce copper, zinc, and selenium nanoparticles were investigated. Nanoparticle (NP) production was performed using cell-free extract obtained after centrifugation of the bacteria that were grown on nutrient broth medium. A total of 34 isolates were used in the study and none of them were able to produce copper and zinc NPs. Besides, a novel strain that was isolated from a soil sample collected from Kocaeli province has produced selenium nanoparticles (SeNPs). For that reason, the study was continued by using this bacterium for SeNPs production. The effects of pH (3-11), temperature (30-45°C), SeO2 concentration (3.5-9.0 mM) and reaction time (0-96 hours) on the synthesis of NPs were determined. The formation of SeNPs was inspected by observing the color change from light yellow to brick-red and by measuring the absorbance at 568 nm using a UV-VIS spectrophotometer. SeNPs production was realized only at pH 7 and 9 in the pH range studied. According to spectrophotometric measurements, the best production was achieved in the medium contained 6.5 mM SeO2 concentration at pH 9.0 and 33°C in 96 hours. Furthermore, the effects of the production conditions on the size of NPs were determined by performing the field emission scanning electron microscopy (FESEM) analysis of NPs. According to the results of the analysis, it was determined that the average sizes of NPs synthesized were between 50 and 150 nm. The smallest sizes of NPs were obtained in the medium having 5.6 mM SeO2, on the other hand increased SeO2 concentrations led to an increase in the size of NPs. In addition, the size of NPs also increased at pH 9, and this pH caused the aggregation of NPs. The smallest NPs were synthesized at 33°C and the sizes increased at temperatures below and over 33°C. NPs were analyzed by Fourier-transform infrared (FTIR) spectroscopy and it was revealed that the biological molecules served as the capping agents for the NPs. X-ray diffractometer (XRD) analysis indicated that the NPs were amorphous. SeNPs did not have antimicrobial and antifungal properties; however antioxidant activity was detected.