Department of Chemistry
Master of Science
Bile acids are C24 steroids that are derived in the liver from cholesterol and secreted into the intestinal lumen to aid in emulsification of dietary lipids and lipid-soluble vitamins. The indigenous intestinal microflora modify bile acids, producing up to 20 unique bile acid metabolites. The 7α-dehydroxylation of the bile acids is the most physiologically important bile acid biotransformation. All known intestinal bacteria capable of bile acid 7α-dehydroxylation are anaerobic, gram-positive rods of the genera Clostridium and Eubcicterium. Bile acid 7α-dehydroxylating bacteria often contain bile salt hydrolase, which hydrolyzes the peptide bond in taurine-conjugated bile acids to yield a free bile acid and taurine. Taurine is an organosulfonate containing a sulfite moiety. There have been no published reports indicating whether 7α-dehydroxylating bacteria can utilize taurine. Given that taurine and taurine-conjugated bile acids are found at great concentrations in the intestine, the ability to utilize the compound would confer a competitive advantage to these bacteria. In this study, the ability of 7α-dehydroxylating bacteria to dissimilate taurine and taurine-conjugated bile acids produce hydrogen sulfide was investigated. First, hydrogen sulfide produced by bile acid 7α-dehydroxylating bacteria cultured in tryptic soy broth and semi-defined media from taurine and taurine-conjugated bile acids was qualitatively detected by inclusion of ferric ammonium citrate in the media. The results obtained from trials utilizing anaerobic tryptic soy broth and from semi-defined medium were not consistent, suggesting that qualitative determination of sulfide by inclusion of ferric ammonium citrate is inconclusive. Then hydrogen sulfide produced by bile acid 7α-dehydroxylating bacteria cultured in modified semi-defined medium (not containing a reducing agent) over time in the presence or absence of taurine-conjugated bile acids was quantified using the methylene blue method. Sulfide concentrations in medium cultured with two different strains of bile acid 7α-dehydroxylating bacteria, Eubcicterium sp. 12708 and Clostridium sp. HD-17, in presence of 100 |j.M or 5 mM sulfonates were not significantly higher than those in the absence of sulfonate. In addition, the highest sulfide concentration determined from medium cultured with two different strains of bile acid 7α-dehydroxylating bacteria for a period of five days was not above backgroud level. These data demonstrated that these two bile acid 7α-dehydroxylating bacteria, Eubcicterium sp. 12708 and Clostridium sp. HD-17, are not capable of desulfonating taurine and taurineconjugated bile acids to produce hydrogen sulfide under the conditions tested.
Qian, Jiang, "Studies of Sulfur Reduction of Taurine and Taurine-Conjugated Bile Acids by Bile acid 7α-Dehydroxylating Bacteria" (2000). Masters Theses & Specialist Projects. Paper 694.