초록
<P><B>Abstract</B></P><P>A less frequently employed <I>Escherichia coli</I> strain W, yet possessing useful metabolic characteristics such as less acetic acid production and high <SMALL>L</SMALL>‐valine tolerance, was metabolically engineered for the production of <SMALL>L</SMALL>‐valine. The <I>ilvA</I> gene was deleted to make more pyruvate, a key precursor for <SMALL>L</SMALL>‐valine, available for enhanced <SMALL>L</SMALL>‐valine biosynthesis. The <I>lacI</I> gene was deleted to allow constitutive expression of genes under the <I>tac</I> or <I>trc</I> promoter. The <I>ilvBN</I><SUP><I>mut</I></SUP> genes encoding feedback‐resistant acetohydroxy acid synthase (AHAS) I and the <SMALL>L</SMALL>‐valine biosynthetic <I>ilvCED</I> 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 <SMALL>L</SMALL>‐valine exporter YgaZH were also amplified by plasmid‐based overexpression. The engineered <I>E. coli</I> W (Δ<I>lacI</I> Δ<I>ilvA</I>) strain overexpressing the <I>ilvBN</I><SUP><I>mut</I></SUP>, <I>ilvCED</I>, <I>ygaZH</I>, and <I>lrp</I> genes was able to produce an impressively high concentration of 60.7 g/L <SMALL>L</SMALL>‐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 <SMALL>L</SMALL>‐valine production. The results obtained in this study suggest that <I>E. coli</I> W can be a good alternative to <I>Corynebacterium glutamicum</I> and <I>E. coli</I> K‐12, which have so far been the most efficient <SMALL>L</SMALL>‐valine producer. Furthermore, it is expected that various bioproducts including other amino acids might be more efficiently produced by this revisited platform strain of <I>E. coli</I>. Bioeng. 2011; 108:1140–1147. © 2010 Wiley Periodicals, Inc.</P>