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 O-2 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 O-2 and CO2. A wider range of concentrations (10-95% 02, 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 O-2 concentrations (10, 90, 95% 02) were either inhibitory or toxic to growth,and ajmalicine production. The effects Of CO2 depended on O-2 concentration. At lower O-2 concentrations (21% 02), increasing the CO2 concentration decreased both growth and specific ajmalicine production. At higher O-2 concentrations (78.4% O-2), 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% 02 + 0.03% CO2. (c) 2005 Elsevier Inc. All rights reserved.