A predictive model for the spontaneous synchronization of Saccharomyces cerevisiae grown in continuous culture. II. Experimental verification

Abstract

Oscillating chemostat cultures of S. cerevisiae in a high performance CSTR have been analyzed at various dilution rates and compared to the predictions of the model presented in the first part of this study (Strässle et al., 1988). The most important signals in the comparison between simulations and experiments were CO 2- and O 2-content in exhaust gas, ethanol- and biomass-concentration, flow rate of pH-controlling agent and percentage of cells in various cell cycle phases. On-line measurement techniques were used extensively in order to obtain much information about the time course of many signals while reducing the disturbances of the culture to a minimum. In both simulation and experiment cell division synchrony gives rise to oscillations in every observed signal. The frequency, permissive D range, amplitude and phase angle of most of the signals are in good agreement in simulation and experiment. A significant difference exists in the phase relationship between the percentage of cells in the various cell cycle phases and the macroscopic signals. This discrepancy together with the dependence of the oscillation period on the dilution rate cause some doubt about the assumed timing of the cell cycle. The constant duration of the budding phase and the coupling of bud emergence, S-phase and mobilization of storage carbohydrates seem to be too strict in the model cells. The model predicts many important properties of continuous cultures of S. cerevisiae This suggests that the assumed mechanism is probably correct (although not complete). Moreover, the experimental results demonstrate the principal possibility to establish permanent synchrony in microbial cultures.