Aerobic and Anaerobic Biotransformation of Bile Acids by Escherichia coli (II): No Conversion of α-Muricholic Acid by 7α-Hydroxysteroid Dehydrogenase of E. coli

The effect of Escherichia coli K-12 on the transformation of hyocholic acid, α-muricholic acid, β-muricholic acid and 3α,7β,12α-trihydroxy-5β-cholanoic acid was examined in aerobic and anaerobic cultures for 4 days and the activities were compared with those on cholic acid and chenodeoxycholic acid. Hyocholic acid was dehydrogenated, but to a lesser extent than cholic acid or chenodeoxycholic acid. However, α-muricholic acid, which has a 7α-hydroxyl group, was not dehydrogenated even after 4 days. This was confirmed by experiments using a cell-free crude enzyme preparation and by gas chromatographic analysis of bile acids in the medium culture. β-Muricholic acid and 3α,7β,12α-trihydroxy-5β-cholanoic acid were not changed by Esherichia coli K-12.