초록
<P>The production of <SMALL>L</SMALL>-leucine was improved by the disruption of <I>ltbR</I> encoding transcriptional regulator and overexpression of the key genes (<I>leuAilvBNCE</I>) of the <SMALL>L</SMALL>-leucine biosynthesis pathway in <I>Corynebacterium glutamicum</I> XQ-9. In order to improve <SMALL>L</SMALL>-leucine production, we rationally engineered <I>C. glutamicum</I> to enhance <SMALL>L</SMALL>-leucine production, by improving the redox flux. On the basis of this, we manipulated the redox state of the cells by mutating the coenzyme-binding domains of acetohydroxyacid isomeroreductase encoded by <I>ilvC</I>, inserting NAD-specific leucine dehydrogenase, encoded by <I>leuDH</I> from <I>Lysinibacillus sphaericus</I>, and glutamate dehydrogenase encoded by <I>rocG</I> from <I>Bacillus subtilis</I>, instead of endogenous branched-chain amino acid transaminase and glutamate dehydrogenase, respectively. The yield of <SMALL>L</SMALL>-leucine reached 22.62 ± 0.17 g·L<SUP>−1</SUP> by strain ΔLtbR-acetohydroxyacid isomeroreductase (AHAIR)<SUP>M</SUP>/ABNC<SUP>M</SUP>E, and the concentrations of the by-products (<SMALL>L</SMALL>-valine and <SMALL>L</SMALL>-alanine) increased, compared to the strain ΔLtbR/ABNCE. Strain ΔLtbR-AHAIR<SUP>M</SUP>LeuDH/ABNC<SUP>M</SUP>LDH accumulated 22.87±0.31 g·L<SUP>−1</SUP><SMALL>L</SMALL>-leucine, but showed a drastically low <SMALL>L</SMALL>-valine accumulation (from 8.06 ± 0.35 g·L<SUP>−1</SUP> to 2.72 ± 0.11 g·L<SUP>−1</SUP>), in comparison to strain ΔLtbR-AHAIR<SUP>M</SUP>/ABNC<SUP>M</SUP>E, which indicated that LeuDH has much specificity for <SMALL>L</SMALL>-leucine synthesis but not for <SMALL>L</SMALL>-valine synthesis. Subsequently, the resultant strain ΔLtbR-AHAIR<SUP>M</SUP>LeuDHRocG/ABNC<SUP>M</SUP>LDH accumulated 23.31 ± 0.24 g·L<SUP>−1</SUP><SMALL>L</SMALL>-leucine with a glucose conversion efficiency of 0.191 g·g<SUP>−1</SUP>.</P>