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 YILWΔalaT 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 YILWΔalaT to increase the supply of intracellular 2-ketobutyrate. In the fed-batch fermentation, YILWpXMJ19thrABC, YILWΔalaT, and YILWΔalaTpXMJ19thrABC exhibited 5.3, 17.6, and 8.4 % higher L-isoleucine production than the original strain, respectively. Both YILWpXMJ19thrABC and YILWΔalaT excreted lower concentrations of L-lysine, L-alanine, and L-valine. YILWΔalaTpXMJ19thrABC 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.