Metabolic Engineering of De Novo Pathway for the Production of 2'-Fucosyllactose in Escherichia coli.

2'-Fucosyllactose (2'-FL), one of the most abundant oligosaccharides in human milk, has gained increased attention owing to its nutraceutical and pharmaceutical potential. However, limited availability and high-cost of preparation have limited its widespread application and in-depth investigation of its potential functions. Here, a modular pathway engineering was implemented to construct an Escherichia coli strain to improve the biosynthesis titer of 2'-FL. Before overexpression of manB, manC, gmd, wcaG, and heterologous expression of futC, genes wcaJ and lacZ encoding UDP-glucose lipid carrier transferase and β-galactosidase, respectively, were inactivated from E. coli BL21 (DE3) with the CRISPR-Cas9 system, which inhibited the production of 2'-FL. The results showed that final shake flask culture yielded a 3.8-fold increase in 2'-FL (0.98 g/L) from the engineered strain ELC07. Fed-batch fermentation conditions were optimized in a 3-L bioreactor. The highest titer of 2'-FL (18.22 g/L) was obtained, corresponding to a yield of 0.25 g/g glycerol and a substrate conversion of 0.88 g/g lactose.