Isolation, characterization, and screening of secondary metabolites from endophytic fungi isolated from Nigerian Piliostigma thonningii for antimicrobial activities

Abstract

Piliostigma thonningii leaves are used in Nigeria folk medicine for the treatment and management of diverse ailments. This study was carried out to investigate the antimicrobial activity of the secondary metabolites produced from endophytic fungi isolated from the leaves of Piliostigma thonningii. The isolation of endophytic fungi was carried out according to the standard procedures. The fungi were subjected to solid-state fermentation on rice medium and the secondary metabolites extracted using ethyl acetate. The fungal crude extracts were screened for antimicrobial activity against selected clinically important microbes using the agar well diffusion method. The fungus with the best antimicrobial activity was molecularly characterized and its secondary metabolites profiled using Gas Chromatography - Mass Spectroscopy to establish the correlation between the observed activity and its phytochemical composition. The fungal extracts showed antimicrobial activity with inhibitory zone diameter ranging from 2.00 to 9.00 mm. The secondary metabolites of Aspergillus fumigatus (the most bioactive endophyte) contain 50 compounds with several of them having established antimicrobial activity. The results of this study suggest that Aspergillus fumigatus an endophytic fungus associated with P. thonningii could be a promising source of novel bioactive compounds with pharmaceutical, agricultural and industrial importance. Keywords: Antimicrobial, Endophytic fungi, GC-MS, Piliostigma thonningii