The effects of Bacteroides sp. strain T-40 isolated from human feces on the biotransformation of bile acids were examined in an anaerobic culture system. Bacteroides sp. T-40 oxidized cholic acid (CA) and chenodeoxycholic acid (CDCA) to 3α,12α-dihydroxy-7-oxo-5β-cholanoic acid and 3α-hydroxy-7-oxo-5β-cholanoic acid, and reduced these oxo-bile acids to CA and CDCA, respectively. However, the reduction activities were lower than the oxidation activities. Hyocholic acid was dehydrogenated, but to a lesser extent than CA or CDCA. On the other hand, α-muricholic acid, which has a hydroxyl group at the position of 7α, was not dehydrogenated. Glycocholic acid was converted to free 3α,12α-dihydroxy-7-oxo-5β-cholanoic acid but any glycine conjugated 7-oxo product was not detected. These data indicate that Bacteroides sp. T-40 possesses bile acid hydrolase and 7α-hydroxysteroid dehydrogenase, by which conjugated bile acids are initially deconjugated, and then undergo oxidization of the 7α-hydroxy group
