UV-mediated enhancement of antibacterial secondary metabolites in endophytic Lasiodiplodia theobromae

In the science of drug discovery, ultraviolet (UV) irradiation has been applied to induce mutagenesis in fungi to provide possibilities for the stimulation or enhancement of fungal biosynthetic capabilities. This study was carried out to evaluate the effect of UV radiation on the biosynthesis of antibacterial secondary metabolites in an endophytic Lasiodiplodia theobromae. Using standard methods, the fungus was isolated from healthy leaves of Cola acuminata and identified based on PCR amplification and genomic sequencing of the internal transcribed spacer (ITS) region. Cultures of L. theobromae were exposed to UV radiation at different time intervals of 1, 2 and 5 min. The fungus was subjected to solid-state fermentation in rice medium before and after UV treatments. The fungal secondary metabolites were extracted and tested for antibacterial activity using the agar diffusion method. Compounds present in the obtained extracts were identified by HPLC and GC-MS analysis. At a concentration of 1 mg/ml, the extract of the wild type L. theobromae (untreated) was observed to only inhibit Staphylococcus aureus, with an IZD of 12 mm. However, the extract of UV-treated L. theobromae (2 min) inhibited S. aureus, Escherichia coli and Pseudomonas aeruginosa with an IZD of 10 and 4 mm respectively. A wide array of compounds in the phenolics, fatty acids, alkaloids and alkanes classes were identified in the UV-treated and untreated fungal extracts. Overall, UV treatments of L. theobromae stimulated the production of seventeen (17) new compounds that were not detected in the untreated strain. The study confirms UV irradiation as an effective method for stimulating microbial biosynthesis of new bioactive compounds, indicating a promising and potentially abundant source of new drug compounds from microorganisms

Antimicrobial and Antioxidant Activities of Secondary Metabolites of an Endophytic fungus of Azadirachta indica

Background: Recent upsurge in the mortality rate and long hospital stays as a result of antimicrobial resistance caused by multi-drug resistant bacteria is a huge burden to public health sector. Intensive search for more effective and newer agents to deal with these problems. Endophytes are a novel source of potentially useful medicinal compounds. Aim: The study aimed at evaluating the antimicrobial and antioxidant activities of an endophytic fungus isolated from Azadirachta indica against multi drug resistant bacteria species. Method: Endophytic fungus was isolated from fresh leaves of Azadirachta indica. The fungus was fermented in rice medium, and the secondary metabolites were extracted. The antimicrobial activity of the extract against laboratory strains of Staphylococcus aureus, Escherichia coli, Klebsiella pneumonia and Bacillus subtilis, Candida albicans, Aspergillus niger) was determined. The fungal extract was also evaluated for antioxidant activity using the DPPH assay method. Using GC-FID analysis, some constituents of the fungal extracted were identified. Result: At 1 and 0.5 mg/mL, the fungal extract demonstrated antibacterial activity against Klebsiella pneumoniae but no activity against the other test microbes. However, the fungal extract of A. indica showed excellent antioxidant activity due to possession of bioactive secondary metabolites. Conclusion: The result of GC-FID showed the presence of Rutin, Lunamarin, Anthocyanin, Catechin, Naringenin, Flavan 3 ol, Sapogernin, Tannin, Spartein, Naringin, Flavonones, Steroids, Kaemferol, Cyanogenic glycoside, Phytate, Epicatechin, Reseveratol, Cardic glycoside and Epihedrine at different concentrations. This study reveals the dynamic potentials of the endophytic fungus of A. indica as the bedrock of naturally occurring bioactive agent.  Keywords: Azadirachta indica, endophytes, GC-FID, secondary metabolites, medicinal plants, phytochemicals