2′-Fucosyllactose production in engineered Escherichia coli with deletion of waaF and wcaJ and overexpression of FucT2

2'-Fucosyllactose (2'-FL), a major oligosaccharide of human breast milk, and is currently supplemented into infant formula. For the overproduction of 2'-FL via fucosylation of lactose, conventional approaches have focused on the episomal overexpression of de novo or salvage GDP-L-fucose biosynthetic pathway and alpha-1,2-fucosyltransferase (FucT2) through T7 RNA polymerase expression system in engineered E. coli. However, these approaches have drawbacks of metabolic burden, plasmid instability, and inclusion body formation. In this study, a deletion mutant of waaF coding for ADP-heptose:LPS heptosyltransferase II was employed for 2'-FL production. As the waaF deletion induces accumulation of colanic acid, additional deletion of wcaJ coding for UDP-glucose-1-phosphate transferase in the waaF deletion mutant resulted in enhanced accumulation of GDP-L-fucose. Besides, 2'-FL yields and titers were drastically improved when T7 promoter was replaced with Trc promoter for alpha-1,2 fucosyltransferase expressions in the waaF and wcaJ deleted strain. As a result, when FucT2 was expressed under Trc promoter in the E. coli JM109(DE3) Delta waaF Delta wcaJ, 14.7 g/L of 2'-FL was produced with a productivity of 0.31 g/L/h in a fed-batch fermentation. We envision that the deletion-based metabolic design and decreased promoter strength for fucosyltransferase expression can resolve the drawbacks of T7 RNA polymerase-based expression design for 2'-FL production in E. coli.