Enhancing l-Isoleucine Production by thrABC Overexpression Combined with alaT Deletion in Corynebacterium glutamicum

l-isoleucine is synthesized from 2-ketobutyrate and pyruvate in Corynebacterium glutamicum, and the supplies of these two precursors are important for l-isoleucine synthesis. C. glutamicum YILW Delta alaT with alaT gene deletion (encoding alanine aminotransferase, a principal enzyme for l-alanine synthesis) was constructed to increase intracellular pyruvate availability, and the thrABC genes from Escherichia coli (encoding bifunctional aspartate kinase I-homoserine dehydrogenase I, homoserine kinase, and threonine synthetase) were overexpressed in C. glutamicum YILW and YILW Delta alaT to increase the supply of intracellular 2-ketobutyrate. In the fed-batch fermentation, YILWpXMJ19thrABC, YILW Delta alaT, and YILW Delta alaTpXMJ19thrABC exhibited 5.3, 17.6, and 8.4 % higher l-isoleucine production than the original strain, respectively. Both YILWpXMJ19thrABC and YILW Delta alaT excreted lower concentrations of l-lysine, l-alanine, and l-valine. YILW Delta alaTpXMJ19thrABC exhibited a cumulative reduction of these by-products excretion, which indicated that thrABC overexpression combined with alaT deletion resulted in the metabolic flux redistribution from 2-ketobutyrate and pyruvate to l-isoleucine synthesis, and decreased the fluxes to by-products synthesis accordingly.