N-Acetyl-O-methyl-tyrosine from Bipolaris bicolor: A novel fungicide for postharvest anthracnose and citrus preservation

Abstract

The necessity for safe and effective alternatives to conventional chemical fungicides is underscored by postharvest citrus fruit losses due to anthracnose, caused by Colletotrichum gloeosporioides. In this context, the biocontrol fungus Bipolaris bicolor WZU-HOG4, isolated from Ougan pericarp, was identified as possessing antimicrobial activity. Through bioassay-guided fractionation and subsequent metabolite profiling, N-Acetyl-O-methyl-tyrosine was identified as the active antifungal compound using NMR and HRESIMS. This compound demonstrated significant inhibitory effects against C. gloeosporioides and other pathogens, exhibiting a relatively broad-spectrum antifungal activity. Molecular docking analysis indicated that N-acetyl-O-methyl-tyrosine binds to tyrosinase with greater affinity than Vitamin C, effectively inhibiting its activity. Furthermore, Ougan fruits treated with the compound exhibited increased activities of antioxidant enzymes SOD, POD, and CAT, reduced MDA content, and decreased oxidative stress during storage. Cytotoxicity assays conducted on HEK-293 cells confirmed the compound's safety at the tested concentrations. N-acetyl-O-methyl-tyrosine emerges as a promising natural antifungal and tyrosinase inhibitor for citrus postharvest preservation, providing a safe alternative to chemical preservatives for extending shelf life.