[The significance of the bacterial steroid degradation for the etiology of large bowel cancer. IV. Deconjugation of glycocholic acid, oxidation, and reduction of cholic acid by saccharolytic Bacteroides species (author's transl)].

A total of 36-38 strains (depending on the test series) of the strictly anaerobic Bacteroides species V. bulgatus, B. fragilis, B. thetaiotamicron, and B. distasonis was tested for the ability of splitting the acide amide linkage of glycocholate and for a further degradation of cholate. We found 23 of 38 strains (60 per cent) to be able to deconjugate glycocholate, but as many as 18 (46 per cent) resulted in an intensive to complete degradation. On the other hand 32 of 36 strains (89 per cent) were able to degrade cholate when cultivated anaerobically. They normally formed 1 transformation product, however, occasionally 2-3. Using the aerobic incubation of resting cells as test system we observed 30 active strains of 37 (81 per cent), which as well produced 1 degradation product generally, but sometimes 2-4 compounds. 3 strains transformed cholate during growth only. Thin layer-, gas chromatography, and combined gas chromatography-mass spectrometry were used for the identification of transformation products. We proved the main degradation product of all active strains to be 3alpha,12alpha-dihydroxy-7-oxo-5beta-cholanoate, by anaerobic cultivation as well as by aerobic incubation of cell suspensions. Deoxycholate (3alpha,12alpha-dihydroxy-5beta-cholanoate), in vivo the main product of cholate transformation, was hitherto found to be formed by 3 strains only as main degradation product, it may probably be a by-product of the degradation with other strains. All these strains, however, may also oxidise the 7alpha-hydroxyl group beside dehydroxylating cholate. For this reason we assume that the conditions for the formation of deoxycholate are in general not existent in our experiments. The third degradation product, formed under anaerobic conditions, is probably a monohydroxy-monooxo-cholanoate, derived from deoxycholate. Structures of additional transformation products, occasionally found under aerobic incubation, which are all less polar than 3alpha,12alpha-dihydroxy-7-oxo-5beta-cholanoic acid, could not be elucidated on account of minor amounts available. Bacteroides species are unable to transform the side chain of cholate, either as anaerobically growing cultures, or as aerobically incubated resting cells.