Absence of Cholic Acid 7α-Dehydroxylase Activity in the Strains of Lactobacillus and Bifidobacterium

Abstract

To investigate the presence of 7α-dehydroxylase activity on bile acids in the bacterial strains of fermented milk products, 46 strains of Lactobacillus casei, Lactobacillus paracasei, Lactobacillus rhamnosus, Lactobacillus acidophilus, Lactobacillus gasseri, Bifidobacterium adolescentis, Bifidobacterium bifidum, Bifidobacterium breve, Bifidobacterium infantis, Bifidobacterium longum, Lactococcus lactis spp. lactis, and Streptococcus salivarius spp. thermophilus were tested for their ability to produce deoxycholic acid from cholic acid. The production of deoxycholic acid was quantitatively measured by radio-chromatographic analysis in anaerobically prepared washed whole resting cells and by HPLC analysis in growing cultures. Resting whole cells from a positive control strain, Eubacterium lentum-like strain c-25, converted 81.7% of .2mM cholic acid to deoxycholic acid and 3.7% to 7-keto-deoxycholic acid, when the cell suspension was incubated anaerobically at a concentration of 2mg of protein/ml for 4h at pH 7.3. However, none of the test strains investigated in this study was able to transform cholic acid under the same conditions. In growing cultures, 91.5% of 150µg/ml of cholic acid was transformed to deoxycholic acid and 1.1% to 7-ketodeoxycholic acid by E. lentum-like c-25 after a 7-d anaerobic incubation. None of the test strains showed production of either deoxycholic acid or 7-ketodeoxycholic acid as growing cultures.