Transient metabolic modeling of Escherichia coli MG1655 and MG1655 DeltaackA-pta, DeltapoxB Deltapppc ppc-p37 for recombinant beta-galactosidase production.

Escherichia coli is one of the most widely used hosts for the production of recombinant proteins, among other reasons because its genetics are far better characterized than those of any other microorganism. To improve the understanding of recombinant protein synthesis in E. coli, the production of a model recombinant protein, beta-galactosidase, was studied in response to the constitutive overexpression of the anaplerotic reaction afforded by PEP carboxylase. To this end, an IPTG wash-in experiment was performed starting from a well-defined steady-state condition for both the wild-type E. coli and a mutant with a defective acetate pathway and a constitutively overexpressed ppc. In order to compare the dynamics of the fluxes over time during the wash-in experiment, a method referred to as transient metabolic flux analysis, which is based on steady-state metabolic flux analysis, was used. This allowed us to track the intracellular changes/fluxes in both strains. It was observed that the flux towards fermentation products was 3.6 times lower in the ppc overexpression mutant compared to the wild-type E. coli. In the former on the other hand, the PPC flux is in general higher. In addition, the flux towards beta-galactosidase was higher (12.4 times), resulting in five times more protein activity. These results indicate that by constitutively overexpressing the anaplerotic ppc gene in E. coli, the TCA cycle intermediates are increasingly replenished. The additional supply of these protein precursors has a positive result on recombinant protein production.