Production and bioprocessing of camptothecin from Aspergillus terreus, an endophyte of Cestrum parqui, restoring their biosynthetic potency by Citrus limonum peel extracts

Abstract

The metabolic potency of fungi as camptothecin producer elevates their prospective use as an industrial platform for commercial production, however, the loss of camptothecin productivity by fungi with the storage and subculturing are the major obstacle. Thus, screening for endophytic fungal isolates inhabiting ethnopharmacological plants with an obvious metabolic stability and sustainability for camptothecin biosynthesis could be one of the most feasible paradigms. Aspergillus terreus ON908494.1, an endophyte of Cestrum parqui was morphologically and molecularly verified, displaying the most potent camptothecin biosynthetic potency. The chemical identity of A. terreus camptothecin was confirmed from the HPLC, FTIR and LC–MS/MS analyses, gave the same molecular structure and mass fragmentation patterns of authentic one. The purified putative camptothecin displayed a strong anticancer activity towards HepG-2 and MCF-7 with IC50 values 0.96 and 1.4 µM, respectively, with no toxicity to OEC normal cells. As well as, the purified camptothecin displayed a significant antifungal activity towards fungal human pathogen Candida albicans, Aspergillus flavus, and A. parasiticus, ensuring the unique structural activity relationships of A. terreus camptothecin, as a powerful dually active anticancer and antimicrobial agent. The camptothecin productivity of A. terreus was maximized by bioprocessing with Plackett–Burman design, with an overall 1.5 folds increment (170.5 µg/L), comparing to control culture. So, the optimal medium components for maximum yield of camptothecin by A. terreus was acid why (2.0 mL/L), Diaion HP20 (2.0 g/L), Amberlite XAD (2.0 g/L), dextrin (5.0 g/L), glucose (10.0 g/L), salicylic acid (2.0 g/L), serine (4.0 g/L), cysteine (4.0 g/L) and glutamate (10.0 g/L), at pH 6 for 15 days incubation. By the 5th generation of A. terreus, the camptothecin yield was reduced by 60%, comparing to zero culture. Interestingly, the productivity of camptothecin by A. terreus has been completely restored and over increased (210 µg/L), comparing to the 3rd generation A. terreus (90 µg/L) upon addition of methanolic extracts of Citrus limonum peels, revealing the presence of some chemical signals that triggers the camptothecin biosynthetic machinery. The feasibility of complete restoring of camptothecin biosynthetic-machinery of A. terreus for stable and sustainable production of camptothecin, pave the way for using this fungal isolate as new platform for scaling-up the camptothecin production.