Fusarium foetens AQF6 Isolated from Amentotaxus ynnanensis H.L.Li as a Prolific Source of Antioxidant Compounds

Abstract

Amentotaxus yunnanensis H.L.Li is a threatened conifer distributed only in China, Laos, and Vietnam, whose fungal endophytes have not been exploited yet. The aims of this study were to screen and characterize antioxidant metabolites from endophytic fungi obtained from A. yunnanensis. Using the surface sterilization method, sixteen endophytic fungi were isolated from A. yunnanensis and classified into seven genera including Fusarium, Penicillium, Aspergillus, Diaporthe, Neopestalotiopsis, Purpureocillium, and Simplicillium through the analysis of Internal Transcribed Spacer (ITS) gene sequences. Among the ethyl acetate crude extracts, Fusarium foetens AQF6 contained the highest amount of polyphenol (117.76 ± 0.94 mg gallic acid equivalent/g) and flavonoid (169.01 ± 2.09 mg quercetin equivalent/g). Importantly, 400 µg/mL AQF6 extract exhibited 95.75 ± 1.1% and 85.66 ± 1.91% of 1,1-diphenyl-2-picrylhydrazyl (DPPH) and hydroxyl radical-scavenging activities, respectively. Chemical investigation led to the isolation and identification of a new bisabolane-type sesquiterpene fusafoetriol (FUS) and 14 known compounds, among which six pure compounds showed free-radical scavenging activity against DPPH and hydroxyl radicals. Under H2O2 stress, the yeast model Saccharomyces cerevisiae treated with 4 mM FUS showed 43.31% increase in viability. FUS has the potential to be applied in nutraceutical, pharmaceutical and food technological applications. Thus, this is the first report demonstrating the presence of endophytic fungi inhabiting A. yunnanensis and their potential as a prolific source of antioxidant metabolites.