LAUSR

BACKGROUND Nicotinamide mononucleotide (NMN), a key intermediate of nicotinamide adenine dinucleotide, plays an important in anti-aging and disease. Lactococcus lactis, an important probiotic lactic acid bacteria (LAB), has shown great potential for the biosynthesis of NMN, which will significantly affect the probiotic effects of the dairy products. RESULTS We used the CRISPR/nCas9 technique to knockout nadR gene of L. lactis NZ9000 to enhance the accumulation of NMN by 61%. The nadE* gene from Francisella tularensis with codon optimization was heterologous in L. lactis NZ9000ΔnadR and has a positive effect on NMN production. Combined with optimization of the concentration of substrate nicotinamide, a final intracellular NMN titer was 2289 μmol/L/mg with 10 g/L NAM supplement, which was 5.7-fold higher than that of control. The transcription levels of key genes (pncA, nadD, and prs1) involved in NMN biosynthesis were up-regulated by more than 2-fold, indicating that the increase of NMN titer was attributed to FtnadE* heterologous expression. CONCLUSION Our study provides a better understanding of the NMN biosynthesis pathway in L. lactis, and can facilitate NMN production in LAB via synthetic biology approaches. This article is protected by copyright. All rights reserved.