Isolation and characterization of human intestinal Enterococcus avium EFEL009 converting rutin to quercetin

Quercetin is a flavonol believed to have beneficial effects on human health. Rutin, found in many plants, fruits and vegetables, is metabolized by human intestinal bacteria and converted to quercetin, where it is absorbed through the intestinal epithelium. This study aimed to isolate and characterize human intestinal bacteria capable of converting rutin to quercetin. A bacterium that can metabolize rutin was isolated from human faecal samples and identified by 16S rRNA gene sequencing. The whole-cell enzymatic activities on flavonoid glycoside and the conversion profiles of the isolate were also analysed. The bacterium was identified as Enterococcus avium EFEL009 and was shown to convert rutin to isoquercetin and then to quercetin under anaerobic conditions. Microscopic analysis revealed short chains of cocci with diameters of approx. 1 μm. β-Glucosidase was shown to be constitutively expressed in Ent. avium, while α-rhamnosidase was expressed following induction by rutin. Both enzymes were mainly localized to the cell surface. This study is the first report on the isolation of a quercetin-producing Ent. avium FEEL009, which could be a potential industrial starter bacterium.

Quercetin is a member of the flavonoids family reported to have better cytoprotective abilities, stronger inhibition of lipopolysaccharide-induced nitric oxide production, and better chemoprevention than rutin. This is the first report on the isolation and characterization of Enterococcus avium EFEL009 from the human intestine which is capable of converting rutin to quercetin.