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[Biosynthesis of spherical selenium nanoparticles with halophilic Bacillus subtilis subspecies stercoris strain XP for inhibition of strawberry pathogens].

Biosynthesis of nanomaterials has attracted much attention for its excellent characteristics such as low energy consumption, high safety, and environmental friendliness. As we all know, the toxic selenite can be transformed into higher-value nanomaterials by using bacteria. In this study, nano-selenium was synthesized by halophilic Bacillus subtilis subspecies stercoris strain XP in LB medium supplemented with selenite (electron acceptor). The physicochemical characteristics of nano-selenium were analyzed by scanning electron microscope (SEM), X-ray energy dispersive spectral analysis (EDAX), X-ray diffraction (XRD), and fourier transform infrared spectroscopy (FTIR). Meanwhile, the antifungal activity of nano-selenium to strawberry pathogens (fusarium wilt, erythema, and purple spot fungi) was determined. The products from reduction of selenite by strain XP was amorphous spherical selenium nanoparticles (SeNPs) with a diameter range of 135-165 nm. The production of SeNPs was positively correlated with time (0-48 h) and no changes were observed on cell morphology. Selenium was dominant in the surface of SeNPs where the organic elements (C, O, N, and S) existed at the same time. SeNPs were coated with biomolecules containing functional groups (such as -OH, C=O, N-H, and C-H) which were associated with the stability and bioactivity of particles. Although the highest concentration of SeNPs had significant (P<0.05) inhibitory effects on three strains of strawberry pathogens, antifungal activity to erythema and fusarium wilt pathogenic fungi was higher than that to purple spot pathogenic fungi from strawberry. In conclusion, strain XP not only has strong tolerance to high salt stress, but can be also used to synthesize biological SeNPs with good stability and biological activity. Thus, the strain XP has bright perspectives and great potential advantage in pathogens control and green selenium-rich strawberry planting as well as other fields.