Microbial Synthesis of Lacto--fucopentaose I with High Titer and Purity by Screening of Specific Glycosyltransferase and Elimination of Residual Lacto--triose II and Lacto--tetraose.

Lacto--fucopentaose I (LNFP I) has recently been approved as generally recognized as safe, demonstrating its great commercial potential in the food industry. Microbial synthesis through metabolic engineering strategies is an effective approach for large-scale production of LNFP I. Biosynthesis of LNFP I requires consideration of two key points: high titer with low byproduct 2'-fucosyllactose (2'-FL) generation and high purity with low lacto--triose II (LNTri II) and lacto--tetraose (LNT) residues. Herein, α1,2-fucosyltransferase from sp. RBIITD was screened from 16 selected LNFP I-producing glycosyltransferase candidates, showing the highest in vivo LNFP I productivity. Chromosomal integration of enhanced the LNFP I production by improving the precursor conversion from LNTri II to LNT. The best engineered strain produced 4.42 and 35.1 g/L LNFP I in shake-flask and fed-batch cultivation, respectively. The residual LNTri II and LNT were eliminated by further cultivation with a recombinant strain coexpressing β--acetylhexosaminidase and lacto--biosidase. A strategy for LNFP I biosynthesis with high yield and purity was finally realized, providing support for its practical application in large-scale production.