Functional analysis of four bile salt hydrolase and penicillin acylase family members in Lactobacillus plantarum WCFS1.

Abstract

Bile salts play an important role in the digestion of lipids in vertebrates and are synthesized and conjugated to either glycine or taurine in the liver. Following secretion of bile salts into the small intestine, intestinal microbes are capable of deconjugating the glycine or taurine from the bile salts, using an enzyme called bile salt hydrolase (Bsh). Intestinal lactobacilli are regarded as major contributors to bile salt hydrolysis in vivo. Since the bile salt-hydrolyzing strain Lactobacillus plantarum WCFS1 was predicted to carry four bsh genes (bsh1, bsh2, bsh3, and bsh4), the functionality of these bsh genes was explored using Lactococcus lactis heterologous overexpression and multiple bsh deletion strains. Thus, Bsh1 was shown to be responsible for the majority of Bsh activity in L. plantarum WCFS1. In addition, bsh1 of L. plantarum WCFS1 was shown to be involved in conferring tolerance to specific bile salts (i.e., glycocholic acid). Northern blot analysis established that bsh1, bsh2, bsh3, and bsh4 are all expressed in L. plantarum WCFS1 during the exponential growth phase. Following biodiversity analysis, bsh1 appeared to be the only bsh homologue that was variable among L. plantarum strains; furthermore, the presence of bsh1 correlated with the presence of Bsh activity, suggesting that Bsh1 is commonly responsible for Bsh activity in L. plantarum strains. The fact that bsh2, bsh3, and bsh4 genes appeared to be conserved among L. plantarum strains suggests an important role of these genes in the physiology and lifestyle of the species L. plantarum. Analysis of these additional bsh-like genes in L. plantarum WCFS1 suggests that they might encode penicillin acylase rather than Bsh activity, indicating their implication in the conversion of substrates other than bile acids in the natural habitat.