Attenuation of camptothecin production and negative relation between hyphal biomass and camptothecin content in endophytic fungal strains isolated from Nothapodytes nimmoniana Grahm (Icacinaceae)

Endophytic fungi, a group of fungi living inside the host plant tissues without causing visible symptoms of disease, are known to occur ubiquitously in plants. Existing in a mutualistic association with their host plants, they have been shown to enhance the plant’s ability to tolerate abiotic and biotic stresses3. In culture, many endophytic species have been shown to produce a number of important secondary metabolites including anticancer,antidiabetic, antifungal and immunosuppressant compounds. Many of these compounds closely mimic those produced by the respective host plants, suggesting that the fungi could in fact potentially serve as an alternative source of plant secondary metabolites. Notwithstanding these findings, to date, there has been no major breakthrough in commercially exploiting the endophytic fungi as a source of important secondary metabolites. Among the reasons attributed is the severe attenuation of production of the secondary metabolite by the fungi in culture. Li et al. showed that successive cultures of an endophytic fungi Pericornia sp. isolated from Torreya grandifolia, resulted in the attenuation of taxol production, though the fungal growth itself was unaffected. Although the reasons for such attenuation are not extensively studied, it is conjectured that it could be due to lack of host stimulus in the culture media