Diversity Of BSH Activities In Different Lactobacilli Towards Human Bile Salts

In this paper, we draw attention to the diversity of BSH activities in eight species of lactobacilli. The BSH activities of sixteen strains were quantified by the amount of taurine or glycine liberated from bile salts mixture that resembled the human bile and six main human bile salts (GC, GDC, GCDC, TC, TCDC, and TDC )respectively. The eight species had different characteristics: It was found for the first time that the L.helveticus, L.fermentum, and L.galllinarum strains only had taurine-congjugated bile salts deconjugation ability but not glycine-conjugated bile salts deconjugation ability. It suggested that these BSHs recognized the amino acid moiety of bile salts, which further proved that microbial BSHs recognized bile salts on not only the cholate steroid nucleus but also the amino acid moiety. Among eight species, the L.acidophilus strains exhibited the highest specific BSH activity towards bile salts mixture and five human bile salts except of TC. The L.acidophilus specific BSH activity towards glycine-congjugated bile salts was ten times higher than that towards taurine-congjugated bile salts. And the specific BSH activities of the four L. acidophilus strains towards the bile mixture ranged from 336.5 to 776.4Umg-1, which was obviously various. Unlike L.acidophilus, there was no obvious difference of specific BSH activity among the different L.plantarum strains. And the specific BSH activity of L.plantarum did not vary significantly towards different bile salts. The L.gasseri Am1 exhibited higher specific BSH activity towards TC than other lactobacilli strains. The BSH activity of L.gasseri depended on not only the amino acid moiety but also the steroid core of bile salt. Strains of L.casei and L.salivarius did not show any BSH activity. It was also found that the specific BSH activity of L.gasseri and L.acidophilus diminished dramatically (maximum 80%) in MRSB (MRS supplied with 0.15% oxgall) compared with that in MRS. The other strains did not show obvious difference of BSH activity between in MRSB and in MRS. Comparison of different bsh genes indicated that LA-bshA, LA-bshB, LG-bsh and LP-bsh1 genes had high similarities (higher than 45%) between each other, while LP-bsh2, LP-bsh3 and LP-bsh4 genes which might not encode BSH enzymes had lower similarities (lower than 26.3%) with the other bsh genes (LA-bshA, LA-bshB, LG-bsh and LP-bsh1) which encoded BSH enzymes with deconjugation abilities. The alignment of the bsh genes in our study indicated that the predicted active residues were strictly conserved while the residues of the substrate binding pocket were not.