Abstract:The ppnk and gdh encoding NAD kinase (NADK) and glutamate dehydrogenase (GDH) were two important enzymes in the glutamate biosynthesis pathway. The two genes were amplified by polymerase chain reaction (PCR) from the glutamate-producing strain CN1021. The specific activity of NAD kinase in extracts was increased by 2.4-fold, and GDH, by 2.1-fold. When both genes were co-expressed in CN1021, the activity of NADK and GDH were increased by 2.0-fold and 1.5-fold, respectively. The flask fermentation results showed that the separate over-expression of ppnk and gdh in CN1021 approximately 7.9% higher and 1.4% more L-glutamate than the original strain, moreover, co-expressing the two genes strain exhibited 13.2% higher L-glutamate. Taken together, the results demonstrated that co-expression of gdh and ppnk genes can significantly improve the production of L-glutamate.
