A polyphasic approach to the characterization of potential silver-nanoparticles-producing and non-producing isolates of Alternaria species and antifungal activity against mycotoxigenic fungi

A polyphasic approach consisting of physical, chemical and molecular characterization was applied to three Alternaria species, A. alternata, A. chlamydospora and A. solani, to characterize and identify isolates producing and non-producing silver nanoparticles (AgNPs). Based on physical characters, the synthesized AgNPs were characterized by transmission electron microscopy and formation of spherical AgNPs sized 5 nm to 60 nm. Scanning electron microscopy (SEM) of the AgNPs did not show a uniform surface; the shape was irregular, like a coral reef. Energy Dispersive Spectroscopy (EDS) showed the presence of Ag element. Fourier transform-infrared spectroscopy (FTIR) confirmed the conversion of Ag ions to AgNPs by fungal metabolites. A. alternata PNU75 non-producing AgNPs showed negative results when characterized by physical devices. Chemical characterization involved the screening of three Alternaria species for fatty acids (FAs) with similar FAs composition while different in terms of relative concentration. The principal FAs were palmitic, stearic, oleic acid and linoleic acid, which comprised 90% or more of the total FAs composition of these species. Molecularly, the fungal protein pattern of the three Alternaria species showed changes against the control by finding 6 proteins associated with AgNPs-producing species. Inter simple sequence repeats (ISSR) analysis using ten primers indicated a high level of genetic variability of three Alternaria species producing and non-producing AgNPs. The results also indicated that the AgNPs synthesized by A. alternata at the concentration 100 mg/L gave the highest inhibition zone against Aspegillus flavus and Aaltenaria alternata, where the percentages of reduction were 77.1% and 87.6% respectively.