TAUROCONJUGATION OF CHOLIC-ACID STIMULATES 7-ALPHA-DEHYDROXYLATION BYFECAL BACTERIA

We examined the effect of the type of cholic acid conjugation (taurine -conjugated, glycine-conjugated, or unconjugated cholic acid) on choli c acid 7 alpha-dehydroxylation by intestinal flora. Cholic acid 7 alph a-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 7 alpha-dehydroxyl ating Clostridium species plus a cholic acid-deconjugating Bacteroides species was studied. We found that tauroconjugation of cholic acid si gnificantly (P < 0.05) increased bacterial 7 alpha-dehydroxylation of cholic acid into deoxycholic acid from 34 to 55% in fecal cultures, fr om 45 to 60% in defined limited fecal cultures, and from 75 to 100% in binary cultures. Equimolar concentrations of free taurine did not sti mulate 7 alpha-dehydroxylation in fecal cultures or in the defined lim ited flora, but free taurine did stimulate 7 alpha-dehydroxylation in the binary culture. In the binary culture of Clostridium species strai n 9/1 plus Bacteroides species strain R1, the minimal flora capable of increased 7 alpha-dehdroxylation of taurocholic acid, strain R1 decon jugated taurine and rapidly reduced it to H2S. Bacteroides species str ain R1 did not grow unless taurine or another appropriate reducible su lfur source was present. Clostridium species strain 9/1 did not grow o r 7 alpha-dehydroxylate unless H2S or another source of reduced sulfur was present. We conclude that the increased 7 alpha-dehydroxylation o f tauroconjugated cholic acid depends on the reduction of taurine to H 2S, which is a necessary growth factor for the 7 alpha-dehydroxylating bacteria.