Process analysis in disturbed environment during oscillatory metabolism of Saccharomyces cerevisiae

The yeast Saccharomyces cerevisiae exhibits sustained oscillations under noise-free controlled conditions in continuous cultures. The regular periodicity of the oscillations and synchrony between different metabolic variables may be described by mathematical models and model-based control. Large bioreactors, however, are prone to disturbances or noise in the feed stream, which may alter the oscillatory behaviour. This aspect has been investigated. Time-dependent Gaussian noise was applied to the substrate feed rate, and it was seen through simulations that while periodicity in the cell mass concentration was lost, other variables were less severely affected. A corollary observation was that the earlier synchrony among different variables, some intra-cellular and some extra-cellular, remained neither complete nor constant, indicating that intra-cellular processes are affected by external disturbances. Thus, deterministic models and control policies based on them may not be suitable in realistic industrial conditions, where intelligent heuristic approaches are more appropriate.