Publications

• Formation of ursodeoxycholic acid from chenodeoxycholic acid by a 7 beta-hydroxysteroid dehydrogenase-elaborating Eubacterium aerofaciens strain cocultured with 7 alpha-hydroxysteroid dehydrogenase-elaborating organisms.

  MacDonald I.A., Rochon Y.P., Hutchison D.M., Holdeman L.V.

  A gram-positive, anaerobic, chain-forming, rod-shaped anaerobe (isolate G20-7) was isolated from normal human feces. This organism was identified by cellular morphology as well as fermentative and biochemical data as Eubacterium aerofaciens. When isolate G20-7 was grown in the presence of Bacteroi ... >> More

  A gram-positive, anaerobic, chain-forming, rod-shaped anaerobe (isolate G20-7) was isolated from normal human feces. This organism was identified by cellular morphology as well as fermentative and biochemical data as Eubacterium aerofaciens. When isolate G20-7 was grown in the presence of Bacteroides fragilis or Escherichia coli (or another 7 alpha-hydroxysteroid dehydrogenase producer) and chenodeoxycholic acid, ursodeoxycholic acid produced. Time course curves revealed that 3 alpha-hydroxy-7-keto-5 beta-cholanoic acid produced by B. fragilis or E. coli or introduced into the medium as a pure substance was reduced by G20-7 specifically to ursodeoxycholic acid. The addition of glycine- and taurine-conjugated primary bile acids (chenodeoxycholic and cholic acids) and other bile acids to binary cultures of B. fragilis and G20-7 revealed that (i) both conjugates were hydrolyzed to give free bile acids, (ii) ursocholic acid (3 alpha, 7 beta, 12 alpha-trihydroxy-5 beta-cholanoic acid) was produced when conjugated (or free) cholic acid was the substrate, and (iii) the epimerization reaction was at least partially reversible. Corroborating these observations, an NADP-dependent 7 beta-hydroxysteroid dehydrogenase (reacting specifically with 7 beta-OH-groups) was demonstrated in cell-free preparations of isolate G20-7; production of the enzyme was optimal at between 12 and 18 h of growth. This enzyme, when measured in the oxidative direction, was active with ursodeoxycholic acid, ursocholic acid, and the taurine conjugate of ursodeoxycholic acid (but not with chenodeoxycholic, deoxycholic, or cholic acids) and displayed an optimal pH range of 9.8 to 10.2 << Less

  Appl Environ Microbiol 44:1187-1195(1982) [PubMed] [EuropePMC]

• Contribution of the 7beta-hydroxysteroid dehydrogenase from Ruminococcus gnavus N53 to ursodeoxycholic acid formation in the human colon.

  Lee J.Y., Arai H., Nakamura Y., Fukiya S., Wada M., Yokota A.

  Bile acid composition in the colon is determined by bile acid flow in the intestines, the population of bile acid-converting bacteria, and the properties of the responsible bacterial enzymes. Ursodeoxycholic acid (UDCA) is regarded as a chemopreventive beneficial bile acid due to its low hydrophob ... >> More

  Bile acid composition in the colon is determined by bile acid flow in the intestines, the population of bile acid-converting bacteria, and the properties of the responsible bacterial enzymes. Ursodeoxycholic acid (UDCA) is regarded as a chemopreventive beneficial bile acid due to its low hydrophobicity. However, it is a minor constituent of human bile acids. Here, we characterized an UDCA-producing bacterium, N53, isolated from human feces. 16S rDNA sequence analysis identified this isolate as Ruminococcus gnavus, a novel UDCA-producer. The forward reaction that produces UDCA from 7-oxo-lithocholic acid was observed to have a growth-dependent conversion rate of 90-100% after culture in GAM broth containing 1 mM 7-oxo-lithocholic acid, while the reverse reaction was undetectable. The gene encoding 7β-hydroxysteroid dehydrogenase (7β-HSDH), which facilitates the UDCA-producing reaction, was cloned and overexpressed in Escherichia coli. Characterization of the purified 7β-HSDH revealed that the kcat/Km value was about 55-fold higher for the forward reaction than for the reverse reaction, indicating that the enzyme favors the UDCA-producing reaction. As R. gnavus is a common, core bacterium of the human gut microbiota, these results suggest that this bacterium plays a pivotal role in UDCA formation in the colon. << Less

  J. Lipid Res. 54:3062-3069(2013) [PubMed] [EuropePMC]

  This publication is cited by 1 other entry.

• Bile induction of 7 alpha- and 7 beta-hydroxysteroid dehydrogenases in Clostridium absonum.

  MacDonald I.A., Roach P.D.

  Eight strains of Clostridium absonum grown in the presence of 4 . 10(-4) M deoxycholate contained both NADP-dependent 7 alpha- and 7 beta-hydroxysteroid dehydrogenase activities. In one strain studied in detail, significant amounts of NADP-dependent 7 alpha- and 7 beta-hydroxysteroid dehydrogenase ... >> More

  Eight strains of Clostridium absonum grown in the presence of 4 . 10(-4) M deoxycholate contained both NADP-dependent 7 alpha- and 7 beta-hydroxysteroid dehydrogenase activities. In one strain studied in detail, significant amounts of NADP-dependent 7 alpha- and 7 beta-hydroxysteroid dehydrogenase and NAD-dependent 7 alpha-hydroxysteroid dehydrogenase activities were demonstrated only when cells were grown in the presence of deoxycholate or chenodeoxycholate, both optimal at 4 . 10(-4) M. When the bile salt was deleted from the medium, only a trace of 7 alpha-hydroxysteroid dehydrogenase was present and 7 beta-hydroxysteroid dehydrogenase was absent. Other bile salts including cholate, ursodeoxycholate and keto bile salts were less effective as inducers. Addition of cholate to medium already containing deoxycholate at a suboptimal concentration enhanced the induction, while addition of ursodeoxycholate suppressed the induction. Further enhancement of 7 alpha- and 7 beta-hydroxysteroid dehydrogenase could be obtained by additions of deoxycholate (up to a total of 6 . 10(-4) M) during the growth of the organisms (in log phase). As enzyme enhancement is blocked by addition of rifampicin to the medium, the authors conclude that the enzymes are bile salt-inducible. Growth curve studies revealed an optimal enzyme yield at a harvest time of approx. 6-9 h. We have preliminarily characterized several inducible enzyme components: an NADP-dependent 7 beta-hydroxysteroid dehydrogenase as well as both NAD- and NADP-dependent 7 alpha-hydroxysteroid dehydrogenases. << Less

  Biochim. Biophys. Acta 665:262-269(1981) [PubMed] [EuropePMC]

• Characterization of NADP-dependent 7 beta-hydroxysteroid dehydrogenases from Peptostreptococcus productus and Eubacterium aerofaciens.

  Hirano S., Masuda N.

  Peptostreptococcus productus strain b-52 (a human fecal isolate) and Eubacterium aerofaciens ATCC 25986 were found to contain NADP-dependent 7 beta-hydroxysteriod dehydrogenase activity. The enzyme was synthesized constitutively by both organisms, and the enzyme yields were suppressed by the addit ... >> More

  Peptostreptococcus productus strain b-52 (a human fecal isolate) and Eubacterium aerofaciens ATCC 25986 were found to contain NADP-dependent 7 beta-hydroxysteriod dehydrogenase activity. The enzyme was synthesized constitutively by both organisms, and the enzyme yields were suppressed by the addition of 0.5 mM 7 beta-hydroxy bile acid to the growth medium. Purification of the enzyme by chromatography resulted in preparations with 3.5 (P. productus b-52, on Sephadex G-200) and 1.8 (E. aerofaciens, on Bio-Gel A-1.5 M) times the activity of the crude cell extracts. A pH optimum of 9.8 and a molecular weight of approximately 53,000 were shown for the enzyme of strain b-52, and an optimum pH at 10.5 and a molecular weight of 45,000 was shown for that from strain ATCC 25986. Kinetic studies revealed that both enzyme preparations oxidized the 7 beta-hydroxy group in unconjugated and conjugated bile acids, a lower Km value being demonstrated with free bile acid than with glycine and taurine conjugates. No measureable activity against 3 alpha-, 7 alpha-, or 12 alpha-hydroxy groups was detected in either enzyme preparation. When tested with strain ATCC 25986, little 7 beta-hydroxy-steroid dehydrogenase activity was detected in cells grown in the presence of glucose in excess. The enzyme from strain b-52 was found to be heat labile (90% inactivation at 50 degrees C for 3 min) and highly sensitive to sulfhydryl inhibitors. << Less

  Appl. Environ. Microbiol. 43:1057-1063(1982) [PubMed] [EuropePMC]