Production of 3-O-xylosyl quercetin in Escherichia coli

Quercetin, a flavonol aglycone, is one of the most abundant flavonoids with high medicinal value. The bioavailability and pharmacokinetic properties of quercetin are influenced by the type of sugars attached to the molecule. To efficiently diversify the therapeutic uses of quercetin, Escherichia coli was harnessed as a production factory by the installation of various plant and bacterial UDP-xylose sugar biosynthetic genes. The genes encoding for the UDP-xylose pathway enzymes phosphoglucomutase (nfa44530), glucose-1-phosphate uridylyltransferase (galU), UDP-glucose dehydrogenase (calS8), and UDP-glucuronic acid decarboxylase (calS9) were overexpressed in E. coli BL21 (DE3) along with a glycosyltransferase (arGt-3) from Arabidopsis thaliana. Furthermore, E. coli BL21(DE3)/a dagger pgi, E. coli BL21(DE3)/a dagger zwf, E. coli BL21(DE3)/a dagger pgia dagger zwf, and E. coli BL21(DE3)/a dagger pgia dagger zwfa dagger ushA mutants carrying the aforementioned UDP-xylose sugar biosynthetic genes and glycosyltransferase and the galU-integrated E. coli BL21(DE3)/a dagger pgi host harboring only calS8, calS9, and arGt-3 were constructed to enhance whole-cell bioconversion of exogeneously supplied quercetin into 3-O-xylosyl quercetin. Here, we report the highest production of 3-O-xylosyl quercetin with E. coli BL21 (DE3)/a dagger pgia dagger zwfa dagger ushA carrying UDP-xylose sugar biosynthetic genes and glycosyltransferase. The maximum concentration of 3-O-xylosyl quercetin achieved was 23.78 mg/L (54.75 mu M), representing 54.75 % bioconversion, which was an similar to 4.8-fold higher bioconversion than that shown by E. coli BL21 (DE3) with the same set of genes when the reaction was carried out in 5-mL culture tubes with 100 mu M quercetin under optimized conditions. Bioconversion was further improved by 98 % when the reaction was scaled up in a 3-L fermentor at 36 h.