Escherichia coli chromosome-based T7-dependent constitutive overexpression system and its application to generating a phenylalanine producing strain.

Many metabolic engineering approaches have been attempted to generate strains capable of producing valuable compounds. One of main goals is industrial application of these strains. Integration of synthetic pathway genes into the Escherichia coli chromosome enables generation of a plasmid-free strain that is stable and useful for industrial applications. Strains that do not require induction are advantageous in terms of cost. In the present study, we constructed a constitutive overexpression system in E. coli to generate plasmid-free and inducer-free strains. The T7 RNA polymerase/T7 promoter overexpression system, which is an isopropyl-β-d-thiogalactopyranoside (IPTG)-inducible gene overexpression system (T7-dependent inducible overexpression system), was modified to be a constitutive overexpression system. The constructed overexpression system, a "chromosome-based T7-dependent constitutive overexpression system", was applied in a metabolic engineering study to generate a plasmid-free and inducer-free phenylalanine producing strain of E. coli.