Host-Specific Metabolic Engineering for Microbial Production of Fucosyllactoses

Human milk oligosaccharides (HMOs) are a diverse group of bioactive glycans that play important roles in infant health by modulating the gut microbiota, inhibiting pathogen adhesion, and promoting immune development. Among them, 2'-fucosyllactose (2'-FL) and 3-fucosyllactose (3-FL) have attracted considerable attention owing to their established health benefits and increasing applications in infant formula and functional foods. Microbial biosynthesis has emerged as a sustainable and scalable alternative to chemical synthesis and enzymatic production. This review summarizes recent advances in microbial FL production using Escherichia coli, Saccharomyces cerevisiae, and Yarrowia lipolytica, with emphasis on host-specific metabolic engineering strategies. Key engineering approaches, including GDP-L-fucose biosynthesis, lactose uptake, fucosyltransferase (FT) optimization, transporter engineering, and fermentation process development, are systematically discussed and compared across microbial hosts. The review highlights the distinct advantages and limitations of bacterial and yeast platforms, including product secretion, intracellular FL accumulation, carbon flux distribution, and redox balance. Finally, current bottlenecks and future engineering opportunities are discussed, including transporter optimization, host-specific metabolic regulation, and industrial process development. These advances provide valuable insights into the development of efficient, safe, and economically viable microbial cell factories for the sustainable production of FL and other fucosylated HMOs.