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