Endophytic Fungal Biodiversity and Antimicrobial Bioprospecting of Penicillium citrinum KIB4 from Khaya ivorensis Bark

Abstract

Background: The emergence of pathogens that are resistant to antibiotics has raised serious concerns about public health, forcing the hunt for alternative antibacterial substances. Endophytes, particularly those from unscreened plants, may offer new sources of antibacterial substances. Hence, this research aimed to isolate antibiotic-producing fungi from Khaya ivorensis bark, a medicinal plant widely used in Nigeria. Methods: The fungal endophytes were isolated following conventional methods using potato dextrose agar (PDA). They were characterized by morpho-microscopical and sequencing of the internal transcribed spacer (ITS) of the fungal rDNA. The phylogenetic tree was drawn following the Neighbour-joining method and the tree was annotated using the Interactive Tree of Life (iTOL) version 6.0. The agar plug assay method was used to select putative antibiotic-producing isolate for further research. The antimicrobial activity of the fungal fermentation product was assessed by agar well diffusion while the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were estimated using the solid agar dilution technique. Results:Atotal of 12 endophytic fungi were isolated. They were noted to be mostly Aspergillus sp. (11 isolates) while only one isolate represented Penicillium species. Only isolate KIB4 showed good inhibitory activity against several bacterial pathogens tested in the preliminary study within 10 mm to 12 mm inhibition zone diameter (IZD) range. Molecular identification proved that strain KIB4 fell into the genus Penicillium and shared the highest ITS gene sequence similarity with Penicillium citrinum D112 (98.83%), and Penicillium sp. TWJL1743 (98.65%). The fermentation extract of Penicillium citrinium KIB4 showed specific inhibition against Escherichia coli ML475, Staphylococcus aureus LN001, Klebsiella pneumoniae ML602, Bacillus subtilis ML225, and Proteus sp. UR979 with an IZD range of 11mm to 23mm. Conclusion: We reported for the first time, the antimicrobial efficacy of fermentation extract from endophytic fungi isolated from Khaya ivorensis against several bacterial pathogens. Further fractionation of the crude extract is needed to isolate specific antimicrobial compounds.