A comparison of mathematical model predictions to experimental measurements for growth and recombinant protein production in induced cultures of Escherichia coli.

Recombinant cell growth and protein synthesis by a recombinant Escherichia coli under various inducing conditions are compared to the predictions of a mathematical model. The mathematical model used was a combination of two literature models: (1) an empirical kinetic model for recombinant growth and product formation and (2) a genetically structured model of the lac promoter-operator on a multicopy plasmid. The experimental system utilized was recombinant E. coli CSH22 bearing the temperature-sensitive plasmid pVH106/172, which codes for the synthesis of beta-galactosidase and the other lac operon genes under the control of a lac promoter. Mathematical model predictions for recombinant beta-galactosidase yield and specific growth rate were compared with fermentation measurements of these same quantities for conditions of chemical induction with cyclic AMP and IPTG, copy number amplification (by shifting culture temperature), and combined chemical induction and copy number amplification. The model successfully predicted experimental product yields for most cases of chemical induction even though the product yields varied from 0.34 x 10(3) to 1500 x 10(3) units/g cell mass. The kinetic model also correctly predicted a decline in the specific growth rate with increasing levels of plasmid and recombinant protein. The model was less successful at predicting product amplification at high copy numbers. A comparison of model predictions and experimental results was also used to investigate some of the assumptions used in constructing the mathematical models.