Efficient glucosylation of flavonoids by organic solvent-tolerant Staphylococcus saprophyticus CQ16 in aqueous hydrophilic media

• A DMSO-tolerant bacterium S. saprophyticus CQ16 capable of glucosylating daidzein was isolated.
• The glucosyltransferase from strain CQ16 showed broad substrate specificity to various kinds of flavonoids, and regio-selective glucosylation high activity in aqueous hydrophilic medium.
• The polar solvent DMSO significantly improved the glucosylation of daidzein and other substrates.

Glucosylation of flavonoids improves their bioavaibility and pharmacological properties. An organic solvent-tolerant bacterium Staphylococcus saprophyticus CQ16 was newly isolated and was found to glucosylate daidzein. Strikingly, the polar solvent 15% DMSO significantly improved the glucosylation of daidzein with 3.5 times yield, and glucosylation was further improved with the supplemental co-solvents. The most effective glucosylation of daidzein to daidzein-7-O-glucoside catalyzed by whole cells of strain CQ16 was achieved with a molar yield of 90% in a system with addition of 15% DMSO and 0.5% butyl acetate. The conversion process produced very few by-products, and therefore simplified purification of the glycoside product. The glucosyltransferase from strain CQ16 showed broad substrate specificity to the various flavonoids as well as flavonoid analogs, nonetheless an exquisite regioselectivity of the C-7 hydroxyl group of flavonoids. It would be substantive benefits for exploiting the new candidates with higher bioavailability for pharmaceuticals.

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