Cell Weight Kinetics Simulation in Chemostat and Batch Culture of the Rhodophyte Porphyridium cruentum

Experimental observations of cell size variations in the proliferating rhodophyte Porphyridium cruentum cul- tured under fully controlled conditions showed significant decreases from inoculation to a steady state in the che- mostat with 0.23 d � 1 dilution rate and to a minimum in batch, dropping in size by ratios of over 10. To numerically simulate these variations, we assumed that the cell is made up of two categories of components that behave differ- ently during the interphase and mitosis. These have been called essential (EC) and accessory (AC) components. It is assumed that the cell divides once the EC have doubled in size, regardless of the AC's state. The experimental cell weight time courses were correctly simulated by a model of synchronous cell kinetics based on these assumptions. The EC's specific growth rate was 1.5 times that of the whole cell, when no limitation occurred. The increase in cell weight observed during batch cultures after nutrient ex- haustion was suitably simulated by assuming that EC growth stops when a limiting nutrient is exhausted. Several parameters characterizing the cell kinetics were defined, particularly the minimum minimorum EC or cell weight (26 and 15 pg for chemostat and batch, respectively), which was influenced by the cultivation method, and the maximum whole cell weight (224 to 244 pg), which de- pended on the inoculum's age. The influence of culture conditions on the amount of essential and accessory com- ponents contained in a cell was examined. A new approach was developed with respect to these compartments to de- termine the most suitable strategy and conduct a predictive approach for valuable molecule production. B 2004 Wiley Periodicals, Inc.