Generic model control of induced protein expression in high cell density cultivation of Escherichia coli using on-line GFP-fusion monitoring

Abstract

A model-based control algorithm (generic model control) is presented for fed-batch cultivation of recombinant Escherichia coli producing either transcriptional or translational fusion products. With the recent development of translational and operon fusions using green fluorescent protein (GFP) [Albano et al. (1998) Biotechnol Prog 14:351–354] along with an on-line GFP sensor [Randers-Eichhorn et al. (1997) Biotechnol Bioeng 55:921–926], real-time measurements of foreign protein level are now possible. A mathematical model is presented that is both accurate and simple so as to ensure that all state variables remain observable during cultivation. A balance between model accuracy and mathematical tractability was obtained to facilitate the formulation of the control algorithm. Generic model control (GMC) is a process model-based control algorithm incorporating a process model directly within the control structure. GMC was desirable since linearization of the process model was not necessary and robust performance could be obtained despite process disturbances or plant/model mismatch. Furthermore, a time-delay compensator was built into the control law to account for the observed 90-min lag associated with GFP fluorescence. The feasibility of the GMC algorithm was demonstrated by simulations.