Model based fed batch cultivation and elicitation for the overproduction of ajmalicine from hairy roots of Catharanthus roseus

Abstract

Batch cultivation of Catharanthus roseus hairy roots was attempted in a statistically optimized nutrient medium. This resulted in a biomass growth of 5.12 ± 0.46 g/l and ajmalicine content of 24.9 ± 1.2 mg/l on day 30 beyond which the product concentration declined. Using the observed batch kinetics data a mathematical model was developed which could describe the experimental observations to the extent of 99% accuracy as demonstrated by the statistical validity test. The model was thereafter extrapolated to fed-batch cultivation to identify suitable nutrient feeding strategies (by off-line simulations) for the overproduction of ajmalicine. Eventually the experimental implementation of three such feeding strategies and comparison with the model predictions further reinforced the efficacy of the mathematical model under dynamic fed batch conditions. A 60% increase in ajmalicine overall productivity and a 2.5 fold increase in volumetric yield was obtained by the “increasing feed rate strategy” as opposed to batch cultivation. To further improve the alkaloid accumulation a combination of statistically optimized mixture of elicitor(s) (jasmonic acid, methyl jasmonate and KCl) was added after the termination of model based increasing fed batch cultivation which resulted in a significantly high ajmalicine concentration of 123.2 ± 8.63 mg/l (a 4 fold increase compared to batch). This is the first report of such a strategy for overproduction of ajmalicine in rather complex hairy root cultivation.