Orthosporin, a major component of the fermentation product of Lasiodiplodia theobromae - an endophytic fungus of Musa paradisiaca as a potential antimicrobial agent

Abstract

Endophytic fungi remain an unexplored reservoir of chemical diversity, and have become the primary focus is several bio-prospecting programs. This study was carried out to detect the constituents and bioactivity of the secondary metabolites of an endophytic Lasiodiplodia theobromae associated with Musa paradisiaca. Following standard protocols, the axenic fungus was isolated from healthy leaves of Musa paradisiaca harvested from Agulu, Anambra State, Nigeria. The isolated fungus was characterized using a standard taxonomic identification procedure involving the amplification and sequencing of the ITS region of the DNA. The fungus was subjected to solid state fermentation in rice medium, followed by extraction, chromatographic separation and chemical characterization of its secondary metabolites. The antimicrobial, antioxidant, antiviral and cytotoxic activities of fungal extract was evaluated using standard methods. At a 1 mg/mL, the fungal extract demonstrated inhibitory potentials against Bacillus subtilis, Pseudomonas aeruginosa and Escherichia coli with inhibition zone diameters that ranged from 3-7 mm. The extract, at 100 μg/mL, exhibited antioxidant effect having an IC₅₀ of 65.8 µg/mL. The extract showed dose-dependent antiviral properties during the in vitro antiviral assay with 54% and 60% inhibition of reverse transcriptase observed at 0.5 and 1 mg/mL concentrations respectively. Following chromatographic separation and chemical analyses of the fungal metabolite, orthosporin was isolated. This widely known phytotoxic compound, together with other constituents of the fungal secondary metabolites, may have exhibited the observed bioactivities of the fungal extract recorded. Thus, our findings provide additional data on the potentials of endophytic fungi as producers of interesting bio-molecules.