Metabolite and hormonal status of hairy root cultures of Devil's claw ( Harpagophytum procumbens) in flasks and in a bubble column bioreactor

Abstract

Hairy root cultures of Devil's claw ( Harpagophytum procumbens), a plant with high medicinal value due to its bioactive metabolites, were cultivated in two different ways: (1) in conventional flasks with shaking and (2) in a 3-l bubble column bioreactor. We investigated parts of the metabolite profiles of both of these types of culture and identified the iridoid glycosides harpagide and harpagoside by HPLC analysis. The bioreactor cultures contained more harpagide than the flask cultures. In addition, several cinnamic acid derivatives, amino acids, sugars, phytosterols and carotenoids were identified as minor compounds of the Harpagophytum hairy roots by GC–MS analysis. A comparison between the flask and bioreactor cultures revealed both qualitative and quantitative differences in some major metabolites. The bioreactor cultures had higher levels of sugars and amino acids, probably due to their better nutrient status. Determination of the hormonal status of the cultures showed that the free indole-3-acetic acid content was similar in the two cultures, but the level of indole-3-acetic acid conjugates was higher in the shake-flasks than in the bioreactor cultures. Levels of abscisic acid, salicylic acid, and aminocyclopropane carboxylic acid were also significantly higher (and levels of jasmonic acid were very variable and non-significantly higher) in the shake-flask cultures. These findings are discussed with respect to relative stress levels in the two culture systems and the scope for using them for secondary metabolite production.