Efficient Production of N-Acetylneuraminic Acid in Escherichia coli Based on the UDP-N-Acetylglucosamine Biosynthetic Pathway

N-Acetylneuraminic acid (NeuAc) is thepredominantsialic acid found in human cells and a human-identical milk monosaccharide.Due to its numerous health benefits, it has great commercial potentialin the pharmaceutical, cosmetic, and food industries. Microbial synthesisvia metabolic engineering strategies is an important approach to itslarge-scale production. In this study, a NeuAc synthetic pathway wasconstructed in Escherichia coli BL21(DE3)by deleting the competitive pathway genes and introducing two genesencoding UDP-N-acetylglucosamine (GlcNAc) 2-epimerase(NeuC) and NeuAc synthase (NeuB). UDP-GlcNAc pathway genes, glmS, glmM, and glmU, wereoverexpressed to strengthen precursor supply for enhancement of NeuAcsynthesis. The microbial source of neuC and neuB was optimized, and their expression was fine-tuned.In addition, glycerol as the carbon source showed a much better effecton NeuAc synthesis than glucose. The final engineered strain produced7.02 g/L NeuAc by shake-flask cultivation. The titer was enhancedto 46.92 g/L by fed-batch cultivation, with the productivity of 0.82g/L/h and 1.05 g/g DCW.