Substrate trajectory tracking for methionine production in a fed-batch bioreactor using nonlinear adaptive control

The metabolic pathway for the synthesis of methionine is strictly regulated in microorganisms. Consequently, only mutant strains having deregulated pathways are capable of producing methionine. Fed-batch fermentation has been found to be a suitable method for methionine production. However, there are many factors that make control of fed-batch fermentation difficult. These include changing process parameters, changing environmental conditions and lack of reliable sensors. In order to further enhance the productivity of such strains, it is necessary to implement controllers that can maintain the fermentation process along a desired trajectory. For this purpose we developed a specific control strategy based on experimental observations and implemented this using a nonlinear adaptive controller. The model used is a modification of the Leudeking-Piret model in which the oxygen dynamics has been incorporated and an exponential structure has been proposed for growth kinetics instead of the Monod-type kinetics. The stability of the controller is confirmed using the Meyer-Kalman-Yakubovich lemma. Simulations are carried out to demonstrate the performance of the controller.