De novo 2′-fucosyllactose bioproduction through modular engineering of a novel Escherichia coli K12-derived strain

The most abundant human milk oligosaccharide 2′-fucosyllactose (2′-FL) is a valuable component that has gained significant attention from the food industry. To biosynthesize 2′-FL, various Escherichia coli K12 derivatives have been genetically modified. To further enhance the application performance of E. coli K12, a novel E. coli K12 derivative BL27 was used as a chassis cell in this study, and modular pathway enhancement was performed to achieve de novo synthesis of 2′-FL. The futC gene encoding α-1,2-fucosyltransferase was introduced, and the wcaJ gene was knocked out to prevent the conversion of GDP- l-fucose to colanic acid. Next, the effects of overexpressing transcriptional regulators rcsA and rcsB and knocking out transcriptional regulators mcbR and waaF were evaluated to optimize the colanic acid pathway. The expression level, solubility, and activity of FutC were improved through genomic integration, TrxA-tag fusion, and double mutation in F40S/Q237S. Fermentation conditions were optimized to achieve maximum 2′-FL titers of 3.86 and 23.56 g/L in shake-flask and fed-batch cultivation, respectively. Over 85% of the products were successfully excreted into extracellular and almost no byproduct 2′,3-difucosyllactose was generated. This study has explored a new microbial platform and modification strategies for the synthesis of 2′-FL and provides opportunities for its commercial production.