Tauroconjugation of cholic acid stimulates 7α-dehydroxylation by fecal bacteria

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Abstract

We examined the effect of the type of cholic acid conjugation (taurine- conjugated, glycine-conjugated, or unconjugated cholic acid) on cholic acid 7α-dehydroxylation by intestinal flora. Cholic acid 7α-dehydroxylation in fecal cultures, in cultures of a defined limited flora consisting of a mixture of seven bacterial species isolated from the intestinal tract, and in a binary culture of a 7α-dehydroxylating Clostridium species plus a cholic acid-deconjugating Bacteroides species was studied. We found that tauroconjugation of cholic acid significantly (P < 0.05) increased bacterial 7α-dehydroxylation of cholic acid into deoxycholic acid from 34 to 55% in fecal cultures, from 45 to 60% in defined limited fecal cultures, and from 75 to 100% in binary cultures. Equimolar concentrations of free taurine did not stimulate 7α-dehydroxylation in fecal cultures or in the defined limited flora, but free taurine did stimulate 7α-dehydroxylation in the binary culture. In the binary culture of Clostridium species strain 9/1 plus Bacteroides species strain R1, the minimal flora capable of increased 7α- dehydroxylation of taurocholic acid, strain R1 deconjugated taurine and rapidly reduced it to H2S. Bacteroides species strain R1 did not grow unless taurine or another appropriate reducible sulfur source was present. Clostridium species strain 9/1 did not grow or 7α-dehydroxylate unless H2S or another source of reduced sulfur was present. We conclude that the increased 7α-dehydroxylation of tauroconjugated cholic acid depends on the reduction of taurine to H2S, which is a necessary growth factor for the 7α- dehydroxylating bacteria.

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Van Eldere, J., Celis, P., De Pauw, G., Lesaffre, E., & Eyssen, H. (1996). Tauroconjugation of cholic acid stimulates 7α-dehydroxylation by fecal bacteria. Applied and Environmental Microbiology, 62(2), 656–661. https://doi.org/10.1128/aem.62.2.656-661.1996

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