High-Level Production\nof Nicotinamide Mononucleotide\nby Engineered Escherichia Coli

Nicotinamide mononucleotide (NMN),\na key precursor of\nNAD<sup>+</sup>, is a promising nutraceutical due to its excellent\nefficacy in alleviating\naging and disease. The bioproduction of NMN faces challenges related\nto incomplete metabolic engineering and insufficient metabolic flux.\nHere, we constructed an NMN synthesis pathway in Escherichia\ncoli BW25113 by deleting the competitive pathway genes\nand introducing three heterologous genes encoding the key enzymes\nnicotinamide phosphoribosyltransferase (NAMPT), phosphoribosyl pyrophosphate\nsynthetase and an NMN transporter. Next, the identification of a highly\nactive NAMPT and optimization of gene expression markedly increased\nthe conversion of NAM to NMN, with a titer of 3503.85 mg/L in shake\nflasks. Furthermore, by facilitating the coutilization of glucose\nand xylose, more metabolic flux was diverted toward PRPP biosynthesis,\nresulting in an NMN titer of 15.66 g/L through whole-cell catalysis\nand 46.66 g/L in a 2-L bioreactor. This represents the highest NMN\nyield reported to date, exhibiting great potential for initiating\nsustainable industrial production of NMN.