Formation of hyodeoxycholic acid from muricholic acid and hyocholic acid by an unidentified gram-positive rod termed HDCA-1 isolated from rat intestinal microflora

From the rat intestinal microflora we isolated a gram-positive rod, termed HDCA-1, that is a member of a not previously described genomic species and that is able to transform the 3 alpha,6 beta,7 beta-trihydroxy bile acid be ta-muricholic acid into hyodeoxycholic acid (3 alpha,6 alpha-dihydroxy acid ) by dehydroxylation of the 7 beta-hydroxy group and epimerization of the 6 beta-hydroxy group into a 6 alpha-hydroxy group. Other bile acids that wer e also transformed into hyodeoxycholic acid were hyocholic acid (3 alpha,6 alpha,7 alpha-trihydroxy acid), alpha-muricholic acid (3 alpha,6 beta,7 alp ha-trihydroxy acid), and omega-muricholic acid (3 alpha,6 alpha,7 beta-trih ydroxy acid). The strain HDCA-1 could not be grown unless a nonconjugated 7 -hydroxylated bile acid and an unidentified growth factor produced by a Rum inococcus productus strain that was also isolated from the intestinal micro flora were added to the culture medium. Germfree rats selectively associate d with the strain HDCA-1 plus a bile acid-deconjugating strain and the grow th factor-producing R. productus strain converted beta-muricholic acid almo st completely into hyodeoxycholic acid.