A unified stoichiometric model for oxidative and oxidoreductive growth of yeasts

Yeasts degrade glucose through different metabolic pathways, where the choice of the pathway is dependent on the nature of the limitation in the various substrates. When oxygen is limiting in addn. to glucose, yeasts often grow according to a mixt. of oxidative and reductive metab. Oxygen may be limiting either by supply or by inherent biol. restrictions such as the respiratory bottleneck in Saccharomyces cerevisiae or by both. A unified model incorporating both supply and biol. limitations is proposed for the quant. prediction of growth rates, consumption and prodn. rates, as well as key metabolite concns. during mixed oxidoreductive metab. occurring as a result of such oxygen limitations. This simple unstructured model can be applied to different yeast strains while at the same time requiring a min. no. of measured parameters. Estimators are utilized in order to predict the presence of supply-side or biol. limitations. The values of these estimators also characterize the relative importance of oxidative to total metab. Results from the aerobic and oxygen-limited chemostat cultures were used to corroborate the model predictions. During these expts., the heat released by the yeast cultures was also monitored online. The model correctly predicted the over-all stoichiometry, steady-state concns., and rates including heat dissipation rates measured in the various situations of oxygen limitations. Direct continuous measurements such as heat can be used in conjunction with the unified model for online process control. [on SciFinder (R)]