Quercetin glycosylation by engineered Escherichia coli

Quercetin is a common flavonoid that are present with high concentrations in tea, wine, apples and onions. Quercetin glucoside not only exhibits antioxidant and anticancer activity, but also has much higher bioavailability than the aglycone form. Escherichia coli MG1655 expressing Arabidopsis thaliana UDP-glycosyltransferase produced 0.2 g/L quercetin-3-glucoside (yield about 9 mmol/mol glucose) during growth on D-glucose as a sole carbon source. Additional knockout in gene encoding phosphoglucose isomerase (E. coli MEC371) successfully diverted the carbon flux toward sugar donor accumulation and elevated the glucoside yield to 27 mmol/mol glucose.  Under optimized controlled batch conditions with 30 g/L D-glucose and 5 g/L quercetin, MEC371 generated 3.8 g/L quercetin-3-glucoside, with yield of 0.5 mol/mol quercetin and 45 mmol/mol glucose.  The results demonstrated an approach, including both genetic manipulation and process optimization, which enables, in high yields, the glycosylation using engineered Escherichia coli.

Key words:     UDP-glycosyltransferase, phosphoglucose isomerase, quercetin, glycosylation