Modeling of inducer exclusion and catabolite repression based on a PTS-dependent sucrose and non-PTS-dependent glycerol transport systems in Escherichia coli K-12 and its experimental verification.

We used genetically engineered sucrose positive Escherichia coli K-12 derivatives as a model system for the modeling and experimental verification of regulatory processes in bacteria. These cells take up and metabolize sucrose by the phosphoenolpyruvate (PEP)-dependent sucrose phosphotransferase system (Scr-PTS). Expression of the scr genes, which cluster in two different operons (scrYAB and scrK), is negatively controlled by the ScrR repressor. Additionally, expression of the scrYAB operon, but not of the scrK operon is positively controlled by the cAMP-CRP complex. Modeling of sucrose transport and metabolism through the Scr-system and of the scr gene expression has been performed using a modular and object-orientated new approach. To verify the model and identify important model parameters we measured in a first set of experiments induction kinetics of the scr genes after growth on glycerol using strains with single copy lacZ operon fusions in the scrK or scrY genes, respectively. In a second set of experiments an additional copy of the complete scr-regulon was integrated into the chromosome to construct diplogenotic strains. Differences were observed in the induction kinetics of the cAMP-CRP-dependent scrY operon compared to the cAMP-CRP independent scrK operon as well as between the single copy and the corresponding diplogenotic strains.