Antifungal screening of silver nanoparticles biosynthesized by Aliinostoc oryzae against plant pathogenic fungi

Abstract

Metallic nanoparticles exhibit exceptional antifungal characteristics and are regarded as a feasible substitute for the control of diverse fungus species. Cyanobacteria have received significant recognition as nanobiofactories across all identified taxa owing to their remarkable ability to assimilate toxins from their environment. Consequently, cyanobacteria-mediated metal nanoparticle synthesis represents an innovative strategy for biological regulation. The present investigation assessed the effectiveness of silver nanoparticles (AgNPs) manufactured using Iranian cyanobacteria, Aliinostoc oryzae, as fungus inhibitors against plant pathogens. For this purpose, the cyanobacterial strain was cultured in BG-110, medium and AgNPs were synthesized by the wet biomass method. The AgNPs were then characterized by UV–visible spectroscopy, DLS, zeta potential, field emission scanning electron microscope (FESEM), transmission electron microscopy (TEM), fourier transform infrared spectroscopy (FT-IR), and X-ray diffraction tests. Afterwards, the antifungal activities of fabricated nanoparticles were tested against fungal strains of Botrytis cinerea, Alternaria alternate, Colletotrichum gloeosporioides, Fusarium oxysporum, Phytophthora capsici, Pythium ultimum, and Rhizopus stolonifera. The results of UV–vis spectrophotometry confirmed the AgNP formation with a color change to dark brown at a wavelength range of 430–432 nm. Morphological examination through the Field Emission Scanning Electron Microscope (FESEM) indicated irregular and spherical shapes. X-ray diffraction (XRD) results showed a cubic crystalline structure with a crystallite size of approximately 20 nm. The zeta potential and electrophoretic mobility of the nanoparticles were −33.67 mV and 0.35 Vs/cm2, respectively. Fourier-transform infrared spectroscopy (FTIR) analysis identified a sharp and intense peak at 538 cm−1, corresponding to the stretching vibration of silver nanoparticle bonds. Based on the antifungal activity results, Pythium ultimum had the largest growth inhibition zone. On the other hand, Colletotrichum gloeosporioides and Alternaria alternate had the smallest inhibition zones. These findings demonstrate the ability to characterize and test AgNPs produced by Iranian cyanobacteria for their antifungal activity.