초록
<P>Exchange of the native <I>Corynebacterium glutamicum</I> promoter of the <I>aceE</I> gene, encoding the E1p subunit of the pyruvate dehydrogenase complex (PDHC), with mutated <I>dapA</I> promoter variants led to a series of <I>C. glutamicum</I> strains with gradually reduced growth rates and PDHC activities. Upon overexpression of the <SMALL>l</SMALL>-valine biosynthetic genes <I>ilvBNCE</I>, all strains produced <SMALL>l</SMALL>-valine. Among these strains, <I>C. glutamicum aceE</I> A16 (pJC4 <I>ilvBNCE</I>) showed the highest biomass and product yields, and thus it was further improved by additional deletion of the <I>pqo</I> and <I>ppc</I> genes, encoding pyruvate:quinone oxidoreductase and phosphoenolpyruvate carboxylase, respectively. In fed-batch fermentations at high cell densities, <I>C. glutamicum aceE</I> A16 Δ<I>pqo Δppc</I> (pJC4 <I>ilvBNCE</I>) produced up to 738 mM (i.e., 86.5 g/liter) <SMALL>l</SMALL>-valine with an overall yield (<I>Y</I><SUB>P/S</SUB>) of 0.36 mol per mol of glucose and a volumetric productivity (<I>Q<SUB>P</SUB></I>) of 13.6 mM per h [1.6 g/(liter × h)]. Additional inactivation of the transaminase B gene (<I>ilvE</I>) and overexpression of <I>ilvBNCD</I> instead of <I>ilvBNCE</I> transformed the <SMALL>l</SMALL>-valine-producing strain into a 2-ketoisovalerate producer, excreting up to 303 mM (35 g/liter) 2-ketoisovalerate with a <I>Y</I><SUB>P/S</SUB> of 0.24 mol per mol of glucose and a <I>Q<SUB>P</SUB></I> of 6.9 mM per h [0.8 g/(liter × h)]. The replacement of the <I>aceE</I> promoter by the <I>dapA</I>-A16 promoter in the two <I>C. glutamicum</I> <SMALL>l</SMALL>-lysine producers DM1800 and DM1933 improved the production by 100% and 44%, respectively. These results demonstrate that <I>C. glutamicum</I> strains with reduced PDHC activity are an excellent platform for the production of pyruvate-derived products.</P>