Anaerobic degradation of flavonoids by Eubacterium ramulus
Eubacterium ramulus, a quercetin-3-glucoside-degrading anaerobic microorganism that occurs at numbers of approximately 108/g dry feces in humans, was tested for its ability to transform other flavonoids. The organism degraded luteolin-7-glucoside, rutin, quercetin, kaempferol, luteolin, eriodictyol, naringenin, taxifolin, and phloretin to phenolic acids. It hydrolyzed kaempferol-3-sorphoroside-7-glucoside to kaempferol-3-sorphoroside and transformed 3,4-dihydroxyphenylacetic acid, a product of anaerobic quercetin degradation, very slowly to non-aromatic fermentation products. Luteolin-5-glucoside, diosmetin-7-rutinoside, naringenin-7-neohesperidoside, (+)-catechin, and (–)-epicatechin were not degraded. Cell extracts of E. ramulus contained α- and β-d-glucosidase activities, but were devoid of α-l-rhamnosidase activity. Based on the degradation patterns of these substrates, a pathway for the degradation of flavonoids by E. ramulus is proposed.
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