Overexpression Of NAD Kinase In Corynebacterium Crenatum SYPA5-5and Its Impact On L-Arginine Biosynthesis

L-arginine is a commercially important amino acid for the food, feed, pharmaceuticals andcosmetics industries. NADPH is one of the cofactors required for L-arginine biosynthesis incorynebacterium sp. In C. glutamicum, NADPH is generated mainly through NADP+dependent dehydrogenases such as glucose-6-phosphate dehydrogenase (G6PDH/zwf) and6-phosphogluconate dehydrogenase (6PGDH/gnd) in oxidative route of pentose phosphatepathway (PPP). However, NAD kinase (ppnk) catalyzes the formation of NADP+through thephosphorylation of NAD~+. Due to the allosteric nature of NAD kinase, it is believed that theNAD(H) and NADP(H) balance might be directly regulated by NAD kinase. Altering thelevel of cofactor(s) such as NADP+may stimulate the Glucose-6-phosphate with concurrentproduction of NADPH and precursor metabolites, from PP pathway and thus may increase theproduction of L-arginine. In this work, we tried to improve L-arginine biosynthesis inCorynebacterium crenatum SYPA5-5by overexpressing homologous NAD kinase (ppnk) in ashuttle vector pJC1and further studied the impact in presence of high oxygen supply (HOS)and low oxygen supply (LOS). In HOS condition, NAD+kinase activity increased by116%,intracellular concentrations of NADP~+and NADPH increased by7.30%and36.84%respectively. Whereas, in LOS condition, NAD+kinase activity increased49%, with anincreased intracellular concentrations of NADP+and NADPH by14.67%and15%respectively. More importantly, recombinant strain could produce26.47g/L and11.36g/LL-arginine in HOS and LOS respectively, which is higher than control strain24.29g/L and7.58g/L respectively. These results suggest that altering the co-factors by NAD kinase is aneffective way to increase NADP~+with concurrent production of NADPH for enhancedL-arginine biosynthesis in both conditions of high oxygen and low oxygen supply.