Enhancing nicotinamide mononucleotide production in Escherichia coli through systematic metabolic engineering

Abstract

Nicotinamide mononucleotide (NMN) serves as a crucial precursor in the biosynthesis of NAD⁺ and has garnered significant attention in the food, dietary supplement, and cosmetic industries. This study engineered an Escherichia coli strain for enhancing NMN production. Firstly, the strain with reduced NMN degradation and the ability to transport NMN extracellularly was constructed. Meanwhile, the gene encoding nicotinamide phosphoribosyltransferase (pncA) was disrupted to minimize substrate nicotinamide (NAM) degradation. Then, the induction starting point was optimized to alleviate the metabolic burden on the engineered strain. Subsequently, systematic remodeling of E. coli's glucose metabolism was conducted to enhance its suitability for NMN production by overexpressing key enzymes of the pentose phosphate pathway (Zwf and Gnd), knocking out genes related to the Entner-Doudoroff pathway (gntR and edd), and further attenuating the glycolytic pathway. Then, we concentrated on optimizing the cellular metabolic state, meticulously balancing intracellular redox homeostasis. Finally, using glucose and 2 g/L of NAM as substrates, the extracellular NMN yield reached 4.96 g/L, which is the highest yield reported so far in similar research. These findings contribute to the commercial production of NMN and offer valuable insights for constructing efficient cell factories for other nucleotide compounds.