Systematic engineering for efficient production of nicotinamide mononucleotide from d-xylose and nicotinamide in Escherichia coli

β-Nicotinamide mononucleotide (NMN) is a direct precursor of the important coenzyme NAD+ in the human body and has broad application prospects in healthcare. This study engineered an Escherichia coli BL21 (DE3) strain to efficiently biosynthesize NMN from nicotinamide (NAM) and xylose. Firstly, the nicotinamide phosphoribosyltransferase (Nampt) from Chitinophaga pinensis was selected and heterologous expressed to construct the NAD + remediation pathway for NMN synthesis from nicotinamide (NAM) and in vivo precursor phosphoribosyl pyrophosphate (PRPP). Then, the supply of PRPP was enhanced by constructing the metabolic flux from d-xylose. To facilitate NMN accumulation, the branch pathways, including PRPP competitive pathway, carbon flow competitive pathway, and NMN downstream metabolic decomposition pathway were fine-tuned using CRISPR/Cas9 editing tools. Combined with process optimization of whole-cell biocatalytic reaction, a NMN titre of 497.5 mg L−1 was obtained. Finally, the scale-up culture was carried out on a 5 L fermenter, and the yield reached 760.2 mg L−1. This work achieved green biosynthesis of NMN using xylose as substrate and enhanced the productivity by systematic engineering strategies, presenting more possibilities for the synthesis of NMN from a wide range of monosaccharides.