Elimination of Byproduct Generation and Enhancement of 2′-Fucosyllactose Synthesis by Expressing a Novel α1,2-Fucosyltransferase in Engineered Escherichia coli

2'-Fucosyllactose (2'-FL) is a kind of fucosylated human milk oligosaccharide (HMO), representing the most abundant oligosaccharide in breast milk. We conducted systematic studies on three canonical α1,2-fucosyltransferases (WbgL, FucT2, and WcfB) to quantify the byproducts in a lacZ- and wcaJ-deleted Escherichia coli BL21(DE3) basic host strain. Further, we screened a highly active α1,2-fucosyltransferase from Helicobacter sp. 11S02629-2 (BKHT), which exhibits high in vivo 2'-FL productivity without the formation of byproducts difucosyl lactose (DFL) and 3-FL. The maximum 2'-FL titer and yield reached 11.13 g/L and 0.98 mol/mol of lactose, respectively, in shake-flask cultivation, both approaching the theoretical maximum value. In a 5 L fed-batch cultivation, the maximum 2'-FL titer reached 94.7 g/L extracellularly with a yield of 0.98 mol of 2'-FL/mol of lactose and productivity of 1.14 g L^-1 h^-1. Our reported 2'-FL yield is the highest from lactose reported to date.