Whole-cell Catalytic Synthesis of β-nicotinamide Mononucleotide by the Recombinant Escherichia Coli

β-nicotinamide mononucleotide (NMN) was a naturally occurring active derivative of B vitamins, which had the function of improving the mammalian fertility ability and intestinal function. Escherichia coli BW25113 was used as the expression host, and according to the protein sequence of nicotinamide ribokinase (NRK) in the NCBI database, Nrk genes from different sources were synthesized by homologous alignment analysis. Then, a recombinant strain NRK-Gs/BW with high efficiency in converting nicotinamide ribose (NR) to NMN was screened. 43 mmol·L^-1 NMN could be synthesized in the reaction mixture containing 50 mmol·L^-1 NR and 10 mmol·L^-1 ATP. Polyphosphate kinase (PPK2) was further introduced to construct the ATP circulation system. The amount of ATP was reduced by 80%, and the AMP production in the reaction mixture was less than or equal to 3 mmol·L^-1. Finally, the reaction mixture was optimized by factorial design. In the reaction mixture of 50 mmol·L^-1 NR and 10 mmol·L^-1 ATP, the yield of NMN was 49.96 mmol·L^-1, with a molar yield of 99.96%. By constructing the NMN engineering bacteria synthesized by NR containing the ATP circulation system, the molar ratio of ATP was greatly reduced, which laid a foundation for the subsequent production of NMN.