SOURCE:

Faculty: Pharmaceutical Sciences
Department: Pharm. Microbio & Biotech

CONTRIBUTORS:

Eze, P. M.
Esimone, C. O.
Okoye, F. B. C.

ABSTRACT:

enhanced through modulation of their culture conditions. This study was aimed at the modulation of a lichen-associated fungus to improve its biosynthetic ability; and isolation of bioactive metabolites of endophytic fungi from Carica papaya. Specific objectives include: modulation of the culture conditions of the lichen-associated fungus for improved biosynthesis of secondary metabolites; isolation and identification of endophytic fungi from C. papaya; fermentation and extraction of secondary metabolites from endophytic fungi; bioassay of endophytic fungal secondary metabolites; and isolation of bioactive compounds from endophytic fungal extracts. Fungal isolation, identification, and fermentation, as well as the extraction of secondary metabolites were carried out using standardized methods. The fungal extracts were screened for bioactivities, and also subjected to several chromatographic separation methods. The resulting fractions were subjected to HPLC-DAD analysis. Detected compounds were then isolated and characterized using various techniques depending on the complexity of their structures. Co-cultivation of Apiosporamontagnei with bacterial strains; manipulation of cultural conditions of the fungus by addition of chemical agents; as well as cultivation of the fungus at different temperatures were carried out to improve the biosynthesis of identified bioactive compounds.Several undetected compounds were up-regulated after manipulation of the cultural conditions of A. montagnei. Expression of silent fungal genes was observed at 28oC, after co-cultivation with Bacillus subtilis, and after the addition of various sodium salts, nitrogen, and carbon sources. Co-cultivation with Streptomyces lividans, as well as the addition ofNaCl (5%) and NH4Cl (1%) induced the production of new compounds. Result of bioassays carried out on the endophytic fungal extracts showed that at 10 µg/ml,Aspergillus aculeatus’s extract recorded an excellent cytotoxic activity against mouse lymphoma cell lines (L5178Y), with a growth inhibition of 106.40%. The A. aculeatus’sextractalso showed good antioxidant activity at 500 µg/ml, with an inhibition of 75.84%. No cytotoxic or antioxidant activity was recorded for Fusariumequiseti’s extract. At 1 mg/ml, crude extracts from both A. aculeatusand F. equiseti showed antibacterial activity against the Gram positive test bacteria. Secalonic acid F, variecolactone, oxaline and JBIR-74 were isolated from A. aculeatus, while Equisetin and 5’-epiequisetin were isolated from F. equiseti. The study indicated that co-cultivation, as well as manipulation of cultural conditions can increase the yields of secondary metabolites and induce previously unexpressed pathways for bioactive constituents. The study suggested that endophytic fungi associated with Nigerian indigenous plants could be a potential source of novel compounds for pharmaceutical and industrial applications.