P98: Regulation of NAD de novo biosynthesis genes in Corynebacterium glutamicum

Corynebacterium glutamicum, a Gram-positive soil bacterium, is widely used for the industrial production of amino acids. We have developed a bioprocess for production of lactate, succinate, and ethanol using C. glutamicum. Since NAD acts as a cofactor for numerous redox reactions in cellular metabolism, it is important to understand the regulation of NAD metabolism to enable optimal engineering of this industrially important microorganism. In this study, we focused on NAD de novo biosynthesis. NAD de novo biosynthesis genes, nadA and nadC, which are conserved in numerous bacterial species, are located in a gene cluster containing two other genes (ndnR-nadA-nadC-nadS) in the genome of C. glutamicum. nadS encodes a homologue of cysteine desulfurase supposed to be involved in the maturation of NadA, an Fe-S protein. ndnR encodes a member of the Nudix-related transcriptional regulator family. Mutant strains deficient in nadA, nadC, or nadS required exogenous nicotinate for growth, indicating that each of these genes is essential for growth in the absence of an exogenous source of NAD biosynthesis. The expression of all of the nad cluster genes was markedly and coordinately repressed by nicotinate. It was demonstrated that the nicotinate-responsive regulation of the NAD de novo biosynthesis genes is primarily mediated by NdnR. This work was partially supported by a grant from the New Energy and Industrial Technology Development Organization (NEDO).