Abstract:Quercetin is a kind of important citrus flavonoid with antibacterial, anti-inflammatory and antioxidant activities, but with poor water solubility and lipid solubility. It has been proved that the metabolic stability and bioavailability of quercetin can be improved by methylation, and microbial transformation method is a good method to obtain methylated quercetin. In this study, 11 flavonoid O-methyltransferase(FOMT) from different sources were screened and classified according to methylation sites, and then the corresponding Escherichia coli engineering bacteria were constructed. Four mono O-methylated quercetin（tamarixetin, rhamnetin, isorhamnetin and 3-O-methylquercetin）were synthesized by fermentation with quercetin as substrate. The highest yields were 31.17, 11.17, 8.90, 52.95 mg/L, respectively. Then, the co-culture system of E.coli was constructed, and the whole cell catalyst containing MpOMT4 and OsNOMT was added step by step. By adjusting the proportion and biomass of the two bacteria in the system, it was finally determined that when the dry weight of cell was 24 g/L and the ratio of cell 1 and cell 2 was 1∶2, and the highest yields of 4′, 7-dimethoxyquercetin was 21.56 mg/L.
