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 caus-ing visible symptoms of disease, are known to occur ubiquitously in plants1. Existing in a mutualistic association with their host plants, they have been shown to enhance the plant’s ability to tolerate abiotic2 and biotic stresses3. In culture,mmany endophytic species have been shown to produce a number of important secondary metabolites including anti- cancer, antidiabetic, antifungal and immunosuppressant compounds4,5. 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 metabolites4,6. Not- withstanding these findings, to date, there has been no major breakthrough in commercially exploiting the endophytic fungi as a source of important secondary metabolites7,8. Among the reasons attrib- uted is the severe attenuation of produc-tion of the secondary metabolite by the fungi in culture. Li et al.9 showed that successive cultures of an endophytic fungi Pericornia sp. isolated from Tor- reya grandifolia, resulted in the attenua- tion of taxol production, though the fungal growth itself was unaffected. Al- though the reasons for such attenuation are not extensively studied, it is conjec- tured that it could be due to lack of host stimulus in the culture media9.