Metabolic engineering of Corynebacterium glutamicum WM001 to improve l-isoleucine production

In this study, l-isoleucine production in Corynebacterium glutamicum WM001 was improved by deleting three genes in the genome, replacing the native promoter of ilvA in the genome, and overexpression of five genes in an alr-based auxotrophic complementation expression system. The three genes deleted in the genome are alaT, brnQ, and alr. Deletion of alaT improved l-isoleucine production by increasing the supply of pyruvate, whereas deletion of brnQ improved l-isoleucine production by blocking the uptake of extracellular l-isoleucine. Exchange of the native promoter of ilvA with promoter tac or tacM could contribute to l-isoleucine production by increasing 2-ketobutyric acid; tac is better than tacM for improving l-isoleucine yield. Different combinations of the genes ilvBN, ppnK, lrp, and brnFE were overexpressed in an alr-based auxotrophic complementation expression system to further improve l-isoleucine production, and the best yield after 72-H flask fermentation was obtained from the strain WM005/pYCW-1-ilvBN2-ppnK1. Without addition of any antibiotics, WM005/pYCW-1-ilvBN2-ppnK1 could produce 32.1 g/L l-isoleucine after 72-H fed-batch fermentation, which is 34.3% increase compared with the original strain WM001.