A feedforward-feedback substrate controller based on a Kalman filter for a fed-batch cultivation of Escherichia coli producing phytase

For the feeding-phase of a batch/fed-batch cultivation of a recombinant Escherichia coli producing extracellular phytase, a controller has been developed. Based on the estimated process variables by a Kalman filter, a feedforward-feedback controller has been implemented in order to maximize the phytase production and to minimize acetate production. The Kalman filter was used to reduce the noise of the glucose measurements and to estimate the biomass concentration, the substrate (glucose) concentration, the maximal growth rate as well as the reaction broth volume, which are used to calculate the feedforward controller contribution. A PI controller was applied to adjust the glucose concentration to the desired set point of 0.2 g/L. The secretion of phytase into the medium is increased at low glucose concentration whereas the acetate production is reduced, due to a low concentration avoiding significant overflow metabolism. The glucose concentration, as the sole measured variable used by the controller, is determined using flow injection analysis (FIA). The operation of the controller as well as its application to the E. coli cultivation is presented. The average on-line measured glucose concentration is 0.208 g/L with a standard deviation of 0.066 g/L. During the cultivation a fault occurred in the measurement system. The response of the controller system with respect to this fault is discussed in detail. Compared to a controller based on oxygen measurements, the yield of phytase is the same with the presented system.