Effect of Pathway Configurations on the Synthesis of 2'-Fucosyllactose in Escherichia coli

The de novo synthesis pathway of 2'-fucosyllactose (2'-FL) was established in Escherichia coli BL21 Star (DE3) in this study. The β-galactosidase gene lacZ M15 and the uridine diphosphate (UDP)-glucose lipid carrier transferase gene wcaJ were knocked out using the CRISPR/Cas9 gene editing system. The effects of three different pathway configurations, viz., operon, pseudo-operon, and monocistronic on the synthesis of 2'-FL were explored. The results showed that the concentration of 2'-FL produced in shake flasks was 0.34 g/L after overexpression of the de novo synthesis pathway related genes in E. coli BL21 Star (DE3). The concentration of 2'-FL was increased to 1.26 g/L by deleting the lacZ M15 and wcaJ genes. The highest concentration of 2'-FL of 1.92 g/L was observed in strain BS-7 when regulated by the operon expression. Fed-batch fermentation of strain BS-7 accumulated 14.04 g/L 2'-FL with a productivity of 0.59 g/(L·h) and a lactose conversion rate of 63%, respectively. This study suggested that lower gene expression levels not only increased 2'-FL production, but also could improve the conversion efficiency of substrate in engineered E. coli.