Degradation of natural polyphenols by methanogenic consortia enriched fromdigested municipal sludge

Using digested municipal sludge as the inoculum and either rutin, quercetin or hesperidin as the sole external carbon source, methanogenic consortia w ere enriched which converted various flavonoids at initial concentration of 0.5-3.0 mM during stationary incubation at 37 degreesC in serum bottles wi th specific rates ranging from 0.025 to 0.073 mu mol min(-1) (mg protein)(- 1). In the culture fluid, several hydroxyaromatic metabolites as well as VF A (acetate. propionate, n-butyrate) were detected and biogas was formed in the headspace of the rest bottles. Most of these metabolites were identifie d. Based on their sequential appearance,:disappearance in the test cultures it was concluded that following initial hydrolysis of the glycosidic bond by cellular enzymes, ring C of the flavane skeleton was hydrolytically clea ved yielding an A- and B-ring fission product. In case of the flavonol quer cetin, phlorogiucinol (A-ring) and 3,4-dihydroxyphenylacetate (B-ring) were identified as the fission products whereas the flavanone hesperetin was cl eaved with formation of phloroglucinol (A-ring) and 3,4-dihydroxyphenylprop ionate (B-ring). In pre-adapted subcultures amended with either hesperidin or hesperetin, all of the: formed hydroxyaromatic metabolites disappeared w ithin 100 h of incubation whereas in the culture medium of rutin and querce tin degrading consortia m-cresol (3-methylphenol) was formed as the ultimat e hydroxyaromatic metabolite being detectable in considerable amounts even after prolonged incubation. (C) 2001 Elsevier Science Ltd. All rights reser ved.