Metabolites of Colletrotricum species, an endophytic fungus isolated from Vernonia amygdalina Del possess antimicrobial and antioxidant activities

The endophytic fungus, colletrotricum species, isolated from the leaves of Vernonia amygdalina was investigated for its chemical constituents and biological activity. The pure fungus was grown using solid fermentation on rice medium and the metabolites were extracted using ethyl acetate. Further purification of the extract was carried out using vacuum liquid chromatography (VLC) and gel chromatography on Sephadex LH-20. The chemical constituents were detected by dereplication using HPLC-DAD. Antimicrobial assay of the Sephadex fractions EC3-1 and EC3-3 were evaluated using agar well diffusion assay against seven pathogenic microorganisms (Staphylococcus aureus, Escherichia coli, Salmonella typhi, Bacillus subtilis, Pseudomonas aeruginosa, Aspergillus niger and Candida albicans). EC3-3 was also subjected to antioxidant assay using DPPH free radical scavenging model. HPLC-DAD analysis of the VLC fractions revealed the presence of compounds like Hydroxybenzaldehyde, Cladosporin, Desmethyldichlorodiaportin and p-Hydroxybenzoic acid. EC3-1 and EC3-3 showed mild antimicrobial activity against S. aureus, S. typhi and A. niger strains, with minimal inhibitory concentrations ranging from 0.19 to 0.46 mg/mL. EC3-3 was found to exhibit very high ability to scavenge DPPH radicals with IC₅₀ of 3.16 µg/mL compared to Ascorbic acid (IC50 of 50.72 µg/mL). HPLC analysis of EC3-3 revealed the presence of Palitantin, which has been shown to possess antimicrobial and antioxidant activity, and two unidentified major peaks. The endophytic fungus, Colletotrichum species isolated from Vernonia amydalina produced bioactive metabolites which exhibited antimicrobial and antioxidant activities thus projecting Vernonia amydalina as a potential source of fungal endophytes that can be further studied for generation of novel bioactive compounds.