Abstract
Some microorganisms, such as Escherichia coli, harbor transhydrogenases that catalyze the interconversion between NADPH and NADH. However, such transhydrogenase genes have not been found in the genome of a glutamic acid-producing bacterium Corynebacterium glutamicum. In this study, the E. coli transhydrogenase genes udhA and pntAB were introduced into the C. glutamicum wild-type strain ATCC 13032, and the metabolic characteristics of the recombinant strains under aerobic and microaerobic conditions were examined. No major metabolic changes were observed following the introduction of the E. coli transhydrogenase genes under aerobic conditions. Under microaerobic conditions, significant metabolic change was not observed following the introduction of the udhA gene. However, the specific production rates of lactic acid, acetic acid, and succinic acid, and the overall production levels of acetic acid and succinic acid were increased by introducing the E. coli pntAB gene. Moreover, the NADH/NAD+ ratio was increased by introduction of pntAB. Our results suggest that the E. coli PntAB transhydrogenase enhances the conversion of NADPH to NADH in C. glutamicum under microaerobic conditions, and the increased NADH/NAD+ ratio results in increased succinic acid production. In addition, acetic acid production might be enhanced to supply ATP to the anaplerotic reaction catalyzed by pyruvate carboxylase.
