The productivity of a cell culture for the production of a secondary metabolite is defined by three factors: specific growth rate, specific product formation rate, and biomass concentration during production. The effect of scaling-up from shake flask to bioreactor on growth and production and the effect of increasing the biomass concentration were investigated for the production of ajmalicine by Catharanthus roseus cell suspensions. Growth of biomass was not affected by the type of culture vessel. Growth, carbohydrate storage, glucose and oxygen consumption, and the carbon dioxide production could be predicted rather well by a structured model with the internal phosphate and the external glucose concentration as the controlling factors. The production of ajmalicine on production medium in a shake flask was not reproduced in a bioreactor. The production could be restored by creating a gas regime in the bioreactor comparable to that in a shake flask. Increasing the biomass concentration both in a shake flask and in a stirred fermenter decreased the ajmalicine production rate. This effect could be removed partly by controlling the oxygen concentration in the more dense culture at 85% air saturation.@en

In Catharanthus roseus cell cultures the time courses of four enzyme activities, tryptophan decarboxylase (TDC), strictosidine synthase (SSS), geraniol-10-hydroxylase (G10H) and anthranilate synthase (AS), and alkaloid accumulation were compared under two different culture conditions (low-inoculum density and high-inoculum density on induction medium) and a control on growth medium. In growth medium a transient increase in TDC activity was first observed after which G10H reached its maximum activity; only tryptamine accumulated, no ajmalicine could be detected. Apparently, a concerted induction of enzyme activities is required for ajmalicine formation. Cells inoculated in induction medium showed such a concerted induction of AS, TDC and G10H activities. After 30 days the low-density culture had accumulated six times more ajmalicine (in μmoles/g) than the high-density culture. Thus, increase in biomass concentration (high-density cultures) did not enhance the total alkaloid production. The major differences observed in enzyme levels between high-and low-density cultures were in the AS and TDC activities, which were two to three times higher in the low-density culture, indicating that there is a positive correlation between ajmalicine formation and AS and TDC activities.@en

Proteases from Cynara cardunculus L. are used in cheese-making. The growth of C. cardunculus cell suspension culture and the production of proteases and phenols were studied in sucrose-limited chemostat cultures at two dilution rates. Biomass yields and biomass and protease productivities in chemostat cultures were compared with those in batch cultures. C. cardunculus cells showed a high ability to adapt to chemostat conditions. Phenolic production was not observed in the steady-state cultures of C. cardunculus cell cultures in contrast to batch cultures. Protease production was linked to the exponential growth phase and was higher and more stable in sucrose-limited chemostats than in batch culture.@en

The growth of plant cell suspension cultures of Catharanthus roseus in batch fermentors was studied at different initial phosphate levels of the medium. On the basis of the observations and existing knowledge with respect to phosphate metabolism in cultured C. roseus cells, a structured mathematical model was developed for the description of the kinetics of growth and intracellular accumulation of glucose and phosphate, as a function of glucose and phosphate supply. It was shown that the model offers not only good description of the growth of the cells in batch culture at different initial phosphate levels, but also provided a satisfactory description of the growth in glucose limited chemostats. © 1993 Wiley & Sons, Inc.@en