Study of the physiological role of bile salt hydrolase from Lactobacilli

BUSTOS, ANA YANINA; FONT DE VALDEZ, GRACIELA; MOZZI, FERNANDA; RAYA, RAUL; TARANTO, MARIA PIA

Holanda

Simposio; 9th symposium on Lactic Acid Bacteria; 2008

Conjugated Bile Acids (BA), which facilitates lipid digestion and absorption in the intestine, are modified by numerous microbial transformations. One of these transformations is the hydrolysis of the amide bond by the enzyme Bile Salt Hydrolase (BSH) to release free amino acid (taurine or glycine) and the unconjugated BA. Several hypotheses have been proposed to explain the significance of BSH activity: nutritional role, detoxification bile, gastrointestinal persistence, etc. Nevertheless the precise function(s) of microbial BSHs is currently unknown. In this work, the effect of the conjugated BA on the microbial internal pH (pHi) values in several probiotic strains was evaluated to determine a potential relationship between the BSH activity and the pHi regulation. The pHi assays were performed in resting cells at an external pH of 5.2 (optimal pH of the BSH) in the presence of the conjugated BA (TDCA and GDCA). The pHi values were measured with the internally conjugated fluorescent pH probe 5,6-carboxyfluorescein succinimidyl ester. The pHi values of the BSH+ strains (Lactobacillus (L.) reuteri CRL1098, L. reuteri CRL1100, L. reuteri CRL1101) showed a gradual increase following the addition of conjugated BA; this behavior was more pronounced with GDCA than that TDCA probably by the higher affinity of BSH for glyco-conjugates. Conversely, the BSH- strains (L. acidophilus CRL1072, L. coryneiforme CRL1001, Enterococcus mundtii CRL35) showed a decrease in internal pH probably as a consequence of weak acid accumulation. The results suggest that the BSH activity would confer an adaptive advantage to the BSH+ strain to maintain pH homeostasis under stress acid conditions, which would be a competitive advantage over some other bacteria for surviving in the small bowel.