Metabolic flux engineering of L-lysine production in Corynebacterium glutamicum--over expression and modification of G6P dehydrogenase.

In the present work, metabolic flux engineering of Corynebacterium glutamicum was carried out to increase lysine production. The strategy focused on engineering of the pentose phosphate pathway (PPP) flux by different genetic modifications. Over expression of the zwf gene, encoding G6P dehydrogenase, in the feedback-deregulated lysine-producing strain C. glutamicum ATCC 13032 lysC(fbr) resulted in increased lysine production on different carbon sources including the two major industrial sugars, glucose and sucrose. The additional introduction of the A243T mutation into the zwf gene and the over expression of fructose 1,6-bisphosphatase resulted in a further successive improvement of lysine production. Hereby the point mutation resulted in higher affinity of G6P dehydrogenase towards NADP and reduced sensitivity against inhibition by ATP, PEP and FBP. Overall, the lysine yield increased up to 70% through the combination of the different genetic modifications. Through strain engineering formation of trehalose was reduced by up to 70% due to reduced availability of its precursor G6P. Metabolic flux analysis revealed a 15% increase of PPP flux in response to over expression of the zwf gene. Overall a strong apparent NADPH excess resulted. Redox balancing indicated that this excess is completely oxidized by malic enzyme.