l -Valine Production with Pyruvate Dehydrogenase Complex-Deficient Corynebacterium glutamicum

Abstract

ABSTRACT Corynebacterium glutamicum was engineered for the production of l -valine from glucose by deletion of the aceE gene encoding the E1p enzyme of the pyruvate dehydrogenase complex and additional overexpression of the ilvBNCE genes encoding the l -valine biosynthetic enzymes acetohydroxyacid synthase, isomeroreductase, and transaminase B. In the absence of cellular growth, C. glutamicum Δ aceE showed a relatively high intracellular concentration of pyruvate (25.9 mM) and produced significant amounts of pyruvate, l -alanine, and l -valine from glucose as the sole carbon source. Lactate or acetate was not formed. Plasmid-bound overexpression of ilvBNCE in C. glutamicum Δ aceE resulted in an approximately 10-fold-lower intracellular pyruvate concentration (2.3 mM) and a shift of the extracellular product pattern from pyruvate and l -alanine towards l -valine. In fed-batch fermentations at high cell densities and an excess of glucose, C. glutamicum Δ aceE (pJC4ilvBNCE) produced up to 210 mM l -valine with a volumetric productivity of 10.0 mM h −1 (1.17 g l −1 h −1 ) and a maximum yield of about 0.6 mol per mol (0.4 g per g) of glucose.