Biosynthesis of Bt-Ag₂O nanoparticles using Bacillus thuringiensis and their pesticidal and antimicrobial activities

Nanosilver oxide exhibits strong antibacterial and photocatalytic properties and has shown great application potential in food packaging, biochemical fields, and other fields involving diseases and pest control. In this study, Ag₂O nanoparticles were synthesized using Bacillus thuringiensis (Bt-Ag₂O NPs). The physicochemical characteristics of the Bt-Ag₂O NPs were analyzed by UV‒vis spectroscopy, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscope (SEM), inductively coupled plasma emission spectrometry (ICP), high-resolution transmission electron microscopy (HR-TEM), and zeta potential. The phis-chemical characterization revealed that the Bt-Ag₂O NPs are in spherical shape with the small particle size (18.24 nm), high crystallinity, well dispersity, and stability. The biopesticidal and antifungal effects of Bt-Ag₂O NPs were tested against Tribolium castaneum, Aspergillus flavus, and Penicillium chrysogenum. The survival, growth, and reproduction of tested pests and molds were significantly inhibited by Bt-Ag₂O NPs in a dose-dependent manner. Bt-Ag₂O NPs showed higher pesticidal activities against T. castaneum than Bt and commercial Ag₂O NPs. The LC₅₀ values of Bt, Ag₂O NPs, and Bt-Ag₂O NPs were 0.139%, 0.072%, and 0.06% on day 14, respectively. The Bt-Ag₂O NPs also showed well antifungal activities against A. flavus and P. chrysogenum, while it resulted a small inhibition zone than commercial Ag₂O NPs did. In addition, A. flavus showed much more sensitive to Bt-Ag₂O NP treatments, compared to P. chrysogenum. Our results revealed that Bt-Ag₂O NPs synthesized using B. thuringiensis could act as pesticides and antifungal agents in stored-product fields. KEY POINTS: • Bt-Ag₂O NPs could be synthesized using Bacillus thuringiensis (Bt). • The NPs showed a high degree of crystallinity, spherical shape, and small particle size. • The NPs also showed excellent insecticidal and antifungal activity.