A novel method for biosynthesis of different polymorphs of TiO₂ nanoparticles as a protector for Bacillus...

Bacillus thuringiensis (Bt) were used for biosynthesis of amorphous TiO₂ converted to distinct polymorphs (anatase, rutile, mix) under different temperature conditions. Characterizations of TiO₂ nanoparticles were performed by using X-ray diffraction spectroscopy (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and, energy-dispersive X-ray spectroscopy (EDX) analysis. Stability of five formulations under ultraviolet (UV) radiation with spore viability and mortality test on Ephestia kuehniella Zeller larvae were investigated. TiO₂(mix) showed the highest viabilities of 79.76% after exposure to ultraviolet (UVA385 nm), while viabilities of non-protected spores under these conditions were 41.32%. The mortality of TiO₂(mix), TiO₂(anatase), TiO₂(rutile), TiO₂(amorphous) and free spore formulations on second-instar larvae of Ephestia kuehniella were 73.76%, 71.24%, 57.12%, 51.32%, and 50.32%, respectively on the 10th day of the experiment. The obtained results suggest that TiO₂(amorphous) does not increase Bt resistance, but both phases of TiO₂ nanoparticles synthesized (anatase and rutile) through the Bacillus thuringiensis and phase mixture can increase the persistence of Bt to the UV light. Furthermore, the combination of both crystalline phases of TiO₂(mix) has the highest performance in improving the Bt resistance.