Escherichia coli W as a new platform strain for the enhanced production of L ‐Valine by systems metabolic engineering

A less frequently employed Escherichia coli strain W, yet possessing useful metabolic characteristics such as less acetic acid production and high L ‐valine tolerance, was metabolically engineered for the production of L ‐valine. The ilvA gene was deleted to make more pyruvate, a key precursor for L ‐valine, available for enhanced L ‐valine biosynthesis. The lacI gene was deleted to allow constitutive expression of genes under the tac or trc promoter. The ilvBN mut genes encoding feedback‐resistant acetohydroxy acid synthase (AHAS) I and the L ‐valine biosynthetic ilvCED genes encoding acetohydroxy acid isomeroreductase, dihydroxy acid dehydratase, and branched chain amino acid aminotransferase, respectively, were amplified by plasmid‐based overexpression. The global regulator Lrp and L ‐valine exporter YgaZH were also amplified by plasmid‐based overexpression. The engineered E. coli W (Δ lacI Δ ilvA ) strain overexpressing the ilvBN mut , ilvCED , ygaZH , and lrp genes was able to produce an impressively high concentration of 60.7 g/L L ‐valine by fed‐batch culture in 29.5 h, resulting in a high volumetric productivity of 2.06 g/L/h. The most notable finding is that there was no other byproduct produced during L ‐valine production. The results obtained in this study suggest that E. coli W can be a good alternative to Corynebacterium glutamicum and E. coli K‐12, which have so far been the most efficient L ‐valine producer. Furthermore, it is expected that various bioproducts including other amino acids might be more efficiently produced by this revisited platform strain of E. coli . Bioeng. 2011; 108:1140–1147. © 2010 Wiley Periodicals, Inc.