Construction of an engineered Escherichia coli for effective synthesis of 2'-fucosyllactose via the salvage pathway.

2'-Fucosyllactose (2'-FL) is one of the important functional oligosaccharides in breast milk. So far, few attempts on biosynthesis of 2'-FL by the salvage pathway have been reported. Herein, the salvage pathway enzyme genes were introduced into the E. coli BL21star(DE3) for synthesis of 2'-FL. The 2'-FL titer increased from 1.56 to 2.13 g/L by deleting several endogenous genes on competitive pathways. The α-1,2-fucosyltransferase (WbgL) was selected, and improved the 2'-FL titer to 2.88 g/L. Additionally, the expression level of pathway enzyme genes was tuned through optimizing the plasmid copy number. Furthermore, the spatial distribution of WbgL was enhanced by fusing with the MinD C-tag. After optimizing the fermentation conditions, the 2'-FL titer reached to 7.13 g/L. The final strain produced 59.22 g/L of 2'-FL with 95% molar conversion rate of lactose and 92% molar conversion rate of fucose in a 5 L fermenter. These findings will contribute to construct a highly efficient microbial cell factory to produce 2'-FL or other HMOs.