串联表达NAD激酶和谷氨酸脱氢酶基因对L-谷氨酸产量的影响

Effect of Co-expression of ppnk and gdh on L-glutamate Production

由ppnk和gdh编码的NAD激酶和谷氨酸脱氢酶是L-谷氨酸合成途径中的两个重要酶。以谷氨酸生产菌CN1021基因组为模板PCR扩增ppnk和gdh基因并转化至该菌中,检测上述两个基因单独表达和串联表达对L-谷氨酸产量的影响。结果表明,当两个基因单独过表达时,其酶活性分别提高2.4和2.1倍,L-谷氨酸产量分别提高7.9%和1.4%。当将两个基因串联表达时,其酶活性分别提高2.0和1.5倍,L-谷氨酸的产量却提高了13.2%。说明过表达ppnk和gdh能够有效提高L-谷氨酸产量,且具有协同作用。

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.