Bioinspired green synthesis of silver nanoparticles by using a native Bacillus sp. strain AW1-2: Characterization and antifungal activity against Colletotrichum falcatum Went

Abstract

Zero-valent silver nanoparticles (ZV-AgNPs) are known as potential antimicrobials and here we report antifungal activity of ZV-AgNPs against Colletotrichum falcatum Went for the first time. ZV-AgNPs were synthesized by using a native Bacillus sp. strain AW1-2, which was identified through 16S rRNA gene sequence analysis. Biogenic ZV-AgNPs were confirmed by monitoring a characteristic absorption peak of UV-vis spectroscopy that was measured at 447 nm. Further, it was found through FTIR and XRD analysis that ZV-Ag nanocrystals were capped with proteins of bacterial origin and their size ranged from 22.33-41.95 nm. The ultrastructure imaging through scanning electron microscopy (SEM) and transmission electron microscopy (TEM) confirmed the morphology of ZV-AgNPs as mono-dispersed spheres and energy dispersive X-ray spectroscopy (EDX) revealed the dominance of silver (84.21 %) in the nano-powder. The ZV-AgNPs significantly inhibited the hyphal growth of Colletotrichum falcatum Went as compared to non-treated control and commercial fungicide both in solid and broth media. The ultrastructure SEM and TEM studies revealed the disrupted hyphal structure and damage to the internal cellular organelles of Colletotrichum falcatum Went treated with 20 μg mL^-1 ZV-AgNPs, respectively. It was concluded that green ZV-AgNPs of bacterial origin could be used to formulate a nano-based fungicide to effectively control Colletotrichum falcatum Went, the causal agent of red rot of sugarcane.

Keywords: Fungicides; Green synthesis; Nanoparticles; Red rot; Sugar cane.