Inactivation of the PTS as a Strategy to Engineer the Production of Aromatic Metabolites in Escherichia coli

Laboratory and industrial cultures of Escherichia coli employ media containing glucose which is mainly transported and phosphorylated by the phosphotransferase system (PTS). In these strains, 50% of the phosphoenolpyruvate (PEP), which results from the catabolism of transported glucose, is used as a phosphate donor for its phosphorylation and translocation by the PTS. This characteristic of the PTS limits the production of industrial biocommodities that have PEP as a precursor. Furthermore, when E. coli is exposed to carbohydrate mixtures, the PTS prevents expression of catabolic and non-PTS transport genes by carbon catabolite repression and inducer exclusion. In this contribution, we discuss the main strategies developed to overcome these potentially limiting effects in production strains. These strategies include adaptive laboratory evolution selection of PTS(-) Glc(+) mutants, followed by the generation of strains that recover their ability to grow with glucose as a carbon source while allowing the simultaneous consumption of more than one carbon source. We discuss the benefits of using alternative glucose transport systems and describe the application of these strategies to E. coli strains with specific genetic modifications in target pathways. These efforts have resulted in significant improvements in the production of diverse biocommodities, including aromatic metabolites, biofuels and organic acids.