Eco-Friendly Biosynthesis of Silver Nanoparticles by Aspergillus Terreus FS4: Optimization, Characterization, and Evaluation of Agricultural Biological Activities

This study aimed to isolate a local silver-resistant fungal strain capable of efficient biosynthesis of AgNPs. It also aimed to optimize the parameters affecting growth and the bioreduction reaction, characterizing AgNPs using UV-Vis spectroscopy, TEM, FTIR, and zeta potential analysis. Furthermore, the antifungal activity of the AgNPs was evaluated against three phytopathogenic fungi, along with their effect on seed germination and growth parameters. Aspergillus terreus FS4 was selected among nine silver-resistant fungal isolates then identified genetically through 18S rRNA gene sequencing and demonstrated the highest efficiency in AgNPs biosynthesis. The optimal conditions for AgNPs biosynthesis were 30 °C and pH 7 during fungal growth for 48 h, followed by a bioreduction reaction conducted at 70 °C and pH 9 for 3 h in the presence of 5 mM AgNO3. The biosynthesized AgNPs were predominantly spherical in shape, with particle sizes varying between 3 and 22 nm. They carried a negative surface charge (–18.4 mV) and were capped with proteins and amino acids. The AgNPs showed strong antifungal activity, with inhibition growth percentages of 84.29% against Aspergillus niger, 79.05% against Fusarium oxysporum, and 46.43% against Rhizoctonia solani at 400 µg/mL. Additionally, they significantly (p < 0.05) enhanced seed germination and early growth of pea and chickpea plants. These results highlight the potential of biosynthesized AgNPs by A. terreus FS4, as effective agents in plant disease management and growth promotion, offering promising applications in sustainable agriculture.