[The significance of the bacterial steroid degradation for the etiology of large bowel cancer. V. Transformation of chenodeoxycholic acid by saccharolytic bacteroides-species (author's transl)].

We analysed a total of 36 strains of the obligately anaerobic Bacteroides species B. vulgatus, B. fragilis, B. thetaiotaomicron, and B. distasonis to test their faculties to metabolize chenodeoxycholate. For experiments with growing cultures, we used a synthetic medium with inorganic salts, glucose, citrate, amino acids, vitamins, and hemin. The same medium, but without amino acids and vitamins was used for experiments with resting cells, incubated aerobically. After preincubation in a medium containing bile and deoxycholate, we observed that 26 strains of 35 (74 per cent) could degrade this bile acid, when cultivated anaerobically, compared to 30 strains of 36 (83 per cent), when incubated aerobically. To sum up the number of active strains, there are 32, corresponding 89 per cent. With the exception of two strains, which formed two transformation products, all active strains formed one degradation product only. All strains but one, active when cultured anaerobically, belong to the species B. fragilis and B. thetaiotaomicron. As can be seen by the results of aerobic incubation most strains of the species B. vulgatus posses the degradative activity, found inactive, however, under anerobic conditions. We therefore suppose that its regulatory mechanism is different from the other species. Thin-layer, gas chromatography, and combined gas chromatography-mass spectrometry were used for the identification of transformation products. With these methods, we were able to demonstrate the bacteria to metabolize chenodeoxycholate to 3 alpha-hydroxy-7-oxo-5 beta-cholanoate, either if growing anaerobically or incubated aerobically. The second degradation products of two strains, found in traces or as by-product, could not be identified on account of minor amounts.