Antifungal activity of compounds isolated from Aspergillus niger and their molecular docking studies with tomatinase

Using a dual culture antagonism assay, Aspergillus niger exhibited 51.5 ± 1.1% growth inhibition against Fusarium oxysporum f.sp. lycopersici, the wilt pathogen of tomato. For enhanced production of antifungal metabolites, nutrient optimization was performed and in vitro well-diffusion antifungal assays demonstrated that crude extract obtained from GPYB culture showed a maximum zone of inhibition (8.8 ± 0.4 mm) against the wilt pathogen, which is corroborated by the comparative LCMS profiles of the extracts from all three media i.e. GPYB, YEB and PDB. Two known compounds, Asperazine (m/z 665 [M + H]⁺) and Nigerone (m/z 571 [M + H]⁺), were isolated from A. niger and their antifungal activity is reported here for the first time. In MIC experiments, Asperazine and Nigerone inhibited the pathogen at 60 and 80 µg·mL^-1 respectively. Molecular docking studies of Nigerone and Asperazine with F. oxysporum tomatinase showed five and six binding interactions respectively.