Optimization of l-Fucose Biosynthesis in Escherichia coli through Pathway Engineering and Mixed Carbon Source Strategy

This study presents an engineered strain of Escherichia coli specifically designed to enhance the production of l-fucose while minimizing residues of 2′-fucosyllactose. The optimization strategies employed include the selection of key enzymes, optimization of gene copy numbers, and fermentation using mixed carbon sources. The metabolic flux was directed toward l-fucose synthesis by integrating preferred 1,2-fucosyltransferase and α-l-fucosidase into the genome. Furthermore, the gene copy numbers were optimized to enhance enzyme expression, thereby increasing l-fucose production. Additionally, the supply of guanosine 5′-triphosphate was improved, and cofactors were regenerated to better regulate metabolism. Modifications to transporter proteins effectively reduced the accumulation of 2′-fucosyllactose. The implementation of a glucose/glycerol co-fermentation strategy enhanced carbon flux distribution and strain efficiency. The optimized strain achieved a yield of 91.90 g/L of l-fucose in a 5 L bioreactor, representing an 80.01% increase over previous yields, with a productivity of 1.18 g L^–1 h^–1. This yield is the highest reported for l-fucose, demonstrating its potential for industrial production.