Green synthesized silver nanoparticles and elicitors enhance stevioside glycoside production in the endophyte Acremonium sclerotigenum from Stevia rebaudiana

Green synthesis of nanoparticles offers a sustainable and eco-friendly approach for biomedical and biotechnological applications. In this study, silver nanoparticles (AgNPs) were synthesized using Stevia rebaudiana leaf extract and characterized by UV-Vis spectroscopy, FTIR, FESEM, DLS, XRD, and zeta potential analysis. The AgNPs showed an average particle size of 22.1 nm by FESEM, a hydrodynamic diameter of 46.7 nm by DLS, and a zeta potential of -21.9 mV, indicating good colloidal stability. The AgNPs exhibited strong antibacterial activity in a dose- and condition-dependent manner, with inhibition zones up to 21.8 mm against Staphylococcus aureus and Escherichia coli, and statistically validated MIC values. Antioxidant activity increased with dose and time, showing DPPH scavenging of 63.9 ± 0.008% and FRAP activity of 74.1 ± 0.008%, with an IC50 of 74.1 µg/mL. Cytotoxicity assays on HEK-293 cells revealed a time- and dose-dependent decline in viability, with an IC50 of approximately 200 µg/mL after 24 h. Notably, combined application of AgNPs with elicitors on the fungal endophyte Acremonium sclerotigenum significantly enhanced stevioside production. Salicylic acid at 200 mM yielded 19.8 mg/mL stevioside, compared with 4.24 mg/mL in controls. Enhanced biosynthesis is attributed to AgNPs-induced ROS signaling and elicitor-mediated activation of defense pathways.