Biologically active secondary metabolites of an endophytic fungus of Psidium guajava

Endophytes possess several phytohormones and bioactive metabolites of medicinal importance and thus, continue to generate research interest as candidates in drug discovery programmes. This study was carried out to investigate the secondary metabolites of an endophytic fungus isolated from leaves of Psidium guajava. Endophytic fungal isolation, fungal fermentation; and extraction of secondary metabolites in ethyl acetate were carried out using standard methods. The crude extract was subjected to Vacuum Liquid Chromatography (VLC) using binary combinations of Hexane:Ethyl acetate and Dichloromethane:Methanol to obtain fourteen sub-fractions designated PG55-1 to PG55-14. The fungal crude extracts and VLC sub-fractions were screened for antimicrobial activity and were also subjected to high-performance liquid chromatography-diode-array detection (HPLC-DAD) analysis for the identification of bioactive compounds. An endophytic fungus, PG55 was isolated from the leaf of Psidium guajava. The fungal secondary metabolites showed antibacterial properties, with minimum inhibitory concentrations ranging from 0.0625 – 1 mg/ml. No antifungal activity was observed. HPLC-DAD analysis of the extract suggested the presence p-hydroxybenzoic acid, pentenedioic acid and palitantin in one of the fractions of PG55. Some of these compounds are known antimicrobial agents and may be responsible for the antimicrobial activities recorded for the fungal extracts. The results of this study, suggests the many potentials possessed by Nigerian plants as hosts of endophytes that could be reservoirs for excellent sources of pharmacologically active compounds.