Engineered chromosome-based T7 RNA polymerase in Escherichia coli W3110 for orthogonal T7 promoter circuit as a cell factory

Abstract

Background Orthogonal T7 RNA polymerase (T7RNAP) and T7 promoter were powerful tools to mediate the protein expression. Moreover, Escherichia coli W3110 strain possesses more advantages than the B strain due to more heat shock proteins and higher tolerance to chemicals. Therefore, implementation of T7-based system in W3110 strain is a conceivable strategy to develop the cell factory. Results Three novel W3110 strains with chromosome-equipped T7RNAP (i.e W3110:IL5, W3110::L5 and W3110::pI) were engineered to demonstrate the feasibility on protein expression and chemical production. At first, the LacZ and T7RNAP with IPTG induction showed higher expression levels in W3110 derivatives than that in BL21(DE3). The plasmids with and without lacI/lacO repression were used to investigate the protein expression of super-fold green fluorescence protein (sfGFP), Cas9, carbonic anhydrase (CA) and lysine decarboxylase (CadA). All the proteins were expressed higher and enzymatic functions were better in W3110::L5 and W3110::pI. Moreover, the highest cadaverine production, lysine consumption and the yield were obtained in W3110::L5(+) strain with pET28a(+)-CadA which reached 32.2 g/L, 45 g/L and 91.7% at 24 h, while the W3110::pI(-) strain with pSU-T7-CadA achieved 36.9 g/L, 43.8 g/L and 103.4% at 12 h which is unnecessary of inducer. Conclusion Inducer and lacI/lacO regulators on chromosome and plasmid have been investigated in W3110 strains with T7RNAP. The newly engineered W3110::L5 and W3110:pI both possessed similar protein expression compared to commercial BL21(DE3). Furthermore, among all strains, W3110::pI displayed the greatest potential as cell factory in the future.