Formation of Forskolin by Suspension Cultures of Coleus forskohlii ¹

Abstract

Suspension cultures of Coleus forskohlii were established and cultivated on a medium containing the phytohormones 2,4-D and kinetin: no forskolin or other labdane diterpenoids were formed under these conditions. To start the biosynthesis of secondary metabolites, the cell aggregates were transferred into an induction medium containing indolebutyric acid (IBA) instead of 2,4-D. Within two cultivation periods of 14 days the amount of forskolin increased up to 0.2-1 g/kg dry cell weight. During this time the producing cells often showed macroscopically visible differentiation. Forskolin was isolated from a cell culture extract and its identity was verified by ¹H-NMR spectroscopy. The scale up of the procedure was performed in 20 l air-lift bioreactors. Forskolin production increased to a maximum of 730 mg/kg after 19 days of fermentation. Additionally, a semi-continuous fermentation run in a 200 l pilot reactor is described. The main diterpenoids, forskolin and 1,9-dideoxyforskolin (DDF), were monitored by HPLC after purification of the crude extract by mini-column chromatography.