Genetic Characterization and Gene Expression of Bile Salt Hydrolase (bsh ) from Lactobacillus reuteri CRL 1098, a Probiotic Strain

Abstract

Intestinal microbes containing the bile salt hydrolase (BSH) enzyme, releases free BA plus amino acids from conjugated BA. BSH activity triggers cholesterol consumption in liver to synthesize BA de novo leading to consequential cholesterol lowering. Lactobacillus (L.) reuteri CRL 1098 is a probiotic bacterium with a proven hypocholesterolemic effect associated to its ability to hydrolyze BA. In this work we characterized the bile salt hydrolase (bsh) operon of CRL 1098 strain as a single open reading frame of 978 nucleotides that encodes a predicted protein of 325 amino acids, with a calculated mass of 36098.1 Da and a theoretical pI of 4.81. Moreover, deduced BSH protein had high similarity with BSHs of other L. reuteri strain and also exhibited similarity to the Pencillin V amidases of Listeria and Bacillus strains. Five catalytically important amino acids were highly conserved in Lactobacillus, Enterococcus and Bifidobacterium strains while four amino acid motifs around these active sites, were only partially conserved. After the bsh gene product was expressed in the heterologous host Lactococcus lactis NZ9000. The activity was specific towards bile acids but not against alternative substrates. Finally, a significant up-regulation of the bsh gene was observed at pH 5.2 (optimal pH of BSH activity). Our studies suggest that BSHs would have an important but so far unknown role in the physiology and lifestyle of L. reuteri strains. The present work would be useful to unravel the ecological role of the BSH and to deepen their influence in the reduction of blood cholesterol levels