Disruption of genes for the enhanced biosynthesis of α-ketoglutarate in Corynebacterium glutamicum

The development of microbial strains for the enhanced production of alpha-ketoglutarate (alpha-KG) was investigated using a strain of Corynebacterium glutamicum that overproduces of L-glutamate, by disrupting three genes involved in the alpha-KG biosynthetic pathway. The pathways competing with the biosynthesis of alpha-KG were blocked by knocking out aceA (encoding isocitrate lyase, ICL), gdh (encoding glutamate dehydrogenase, L-gluDH), and gltB (encoding glutamate synthase or glutamate-2-oxoglutarate aminotransferase, GOGAT). The strain with aceA, gltB, and gdh disrupted showed reduced ICL activity and no GOGAT and L-gluDH activities, resulting in up to 16-fold more alpha-KG production than the control strain in flask culture. These results suggest that L-gluDH is the key enzyme in the conversion of alpha-KG to L-glutamate; therefore, prevention of this step could promote alpha-KG accumulation. The inactivation of ICL leads the carbon flow to alpha-KG by blocking the glyoxylate pathway. However, the disruption of gltB did not affect the biosynthesis of alpha-KG. Our results can be applied in the industrial production of alpha-KG by using C. glutamicum as producer.