Sparge gas composition affects biomass and ajmalicine production from immobilized cell cultures of Catharanthus roseus

Despite their low solubility in aqueous medium, dissolved gases play important roles in the cultivation and successful scale-up of plant cell cultures. In this paper, the effects of O2 and CO2 on growth and secondary metabolism were investigated using the production of ajmalicine from Catharanthus roseus cultures. The effects of gas composition were investigated using shear-protected alginate-immobilized cells (diameter < 2 mm) cultured in bubble columns sparged with premixed gases, including nine combinations of O2 and CO2. A wider range of concentrations (10–95% O2, 0.03–10% CO2 by mole) was studied to explore potential benefits or drawbacks. Sparge gas composition significantly altered growth and ajmalicine production. Low and high O2 concentrations (10, 90, 95% O2) were either inhibitory or toxic to growth and ajmalicine production. The effects of CO2 depended on O2 concentration. At lower O2 concentrations (21% O2), increasing the CO2 concentration decreased both growth and specific ajmalicine production. At higher O2 concentrations (78.4% O2), increasing the CO2 concentration decreased growth while specific ajmalicine production was not affected. In these studies, extracellular ajmalicine concentration was maximized with a gas mixture of 50% O2 + 0.03% CO2.