Quercetin Glucoside Production by Engineered Escherichia coli

Escherichia coli strains expressing the O-glucosyltransferases UGT73B3 or UGT84B1 were compared for the production of glucosides from quercetin supplied into a defined medium. The formation of quercetin-3-glucoside (Q3G) by UGT73B3 showed a maximum at 33 degrees C, while the formation of quercetin-7-glucoside by UGT84B1 increased with increasing temperature to 37 degrees C. The highest concentrations of Q3G were attained by strains having a deletion in the pgi gene-coding phosphoglucose isomerase, which effectively blocked the entry of glucose-6P into the Embden-Meyerhof-Parnas pathway. Formation of Q3G was improved in 1-L controlled bioreactors compared to shake flask cultures, a result attributed to the greater oxygen transfer rate in bioreactors. Under batch conditions with 30 g/L glucose as the sole carbon source, E. coli MEC367 (MG1655 pgi) expressing UGT73B3 generated 3.9 g/L Q3G in 56 h.