6533b851fe1ef96bd12a975a

RESEARCH PRODUCT

Epimerization, oxidation and reduction of bile acids by Eubacterium lentum

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Summary Twenty-eight strains of Eubacterium lentum were divided into five groups on the basis of their ability to metabolize cholic acid and dehydrocholic acid: (I) Strains with 3α- and 3/β-dehydrogenating activities (1 strain), (II) strains with 12α-dehydrogenating activity (5 strains), (III) strains with 3α-, 3β-, 7α-, and 12α-dehydrogenating activities (8 isolates), (IV) transition stages between group II and III (1 strain), (V) strains devoid of any measurable bile acid metabolizing activities or with only trace activities (11 isolates). Using appropriate bile acids it was demonstrated that hydroxyl or keto groups at positions C 3 , C 7 , and C 12 did not influence bile acid transformations by E. lentum groups I, II, and III. A 7β-hydroxyl group was not oxidized by group III organisms. Oxidation of 7α-hydroxyl groups was considerably suppressed by oxygen, while oxidation of 3α-, and, to a lesser extent, 12α-hydroxyl groups was enhanced. Growth kinetics experiments with E. lentum groups I and III showed that during epimerization of 3-hydroxyl bile acids (group I: 3β-hydroxy acids; group III: 3α-hydroxy acids) the concentration of 3-keto acids passed through a distinct maximum, while 3-keto bile acid substrates were always reduced concomitantly to α- and β-hydroxyl groups. These results strongly point to an epimerization mechanism via the 3-keto intermediates. Groups of bacteria with a 12α-dehydrogenating activity only were also detected within the species' Bacteroides distasonis , B. eggerthii , B. vulgatus , Lactobacillus plantarum , L. salivarius and Peptococcus magnus . The metabolic peculiarities of E. lentum group III, however, were only found in one Eubacterium strain which could not be classified into a known species.