Antifungal activity of bio-active cell-free metabolites and volatile organic compounds (VOCs) synthesised by endophytic fungal isolates of Garden Nasturtium

Abstract

The increasing resistance of fungal pathogens against available antifungal agents is a serious threat to mankind. The most suitable solutions can only be found from untapped novel natural sources and endophytic metabolites are emerging as one of the dominant contributors in this field. In the present study, Ethyl acetate (EA) extract of cell-free metabolites and volatile metabolites of endophytic fungi Colletotrichum aenigma TML3 and Curvularia lunata TML9, isolated from leaves of Tropaeolum majus, exhibited broad-spectrum antifungal activity against four species of Candida and nine taxa of post-harvest phyto pathogens respectively. EA extract hampered the biofilm formation, minimised haemolytic effect, and blocked the transformation of Candida cells from yeast to hyphal form with an MFC of 200–600 µg mL− 1. Central carbohydrate metabolism, ergosterol synthesis, and membrane permeability were adversely affected and caused the lethal leakage of necessary macromolecules of C. albicans. Volatile metabolites inhibited the growth of phytopathogens up to 89% with an IC50 value of 21.3–69.6 µL 50 mL− 1 and caused leakage of soluble proteins and other intracellular molecules. Citrusy sweet odor volatiles minimised the infections of Penicillium digitatum (green mold), in VOC-exposed sweet oranges (Citrus sinensis). In total twenty-one non-volatile and thirteen volatile metabolites were detected from the TML3, and TML9 endophytic fungi respectively. Citrusy sweet odor volatiles of TML9 cultured in wheat-husk minimised the infections of Penicillium digitatum (green mold), in VOC-exposed sweet oranges (Citrus sinensis). Volatile and non-volatile antifungal metabolites of these two T. majus endophytes hold agricultural and pharmaceutical interests.