Evaluation of the relationship between the bsh activity and the internal ph regulation in probiotic lactic acid bacteria

BUSTOS, ANA YANINA; FONT DE VALDEZ, GRACIELA; MOZZI, FERNANDA; RAYA, RAUL; TARANTO, MARÍA PÍA

Holanda

Simposio; 9th symposium on Lactic Acid Bacteria; 2008

Bile acids (BA) are synthesized from cholesterol in the liver; conjugated to either glycine or taurine and released into the intestines, where facilitate lipid digestion and absorption by emulsifying lipids. These BA are modified by numerous microbial biotransformations in the gut. The first of these reactions   is the hydrolysis of the amide bond to release free amino acid and the unconjugated BA, which is catalyzed by the enzyme bile salt hydrolase (BSH). Although BSH activity is a commonly observed phenomenon, its significance is far from understood. The aims of this work was evaluated the relationship between the BSH activity and the internal pH (pHi) regulation in probiotic Lactic Acid Bacteria under stress acid conditions to establish the physiological role of this activity. The assays were performed in resting cells of Lactobacillus (L.) reuteri CRL 1098, L. reuteri CRL 1100 y L. reuteri CRL 1101 (BSH + strains), L. acidophilus CRL 1072, L. coryneiforme CRL 1001 and Enterococcus mundtii CRL 35 (BSH - strains) an acid external of pH 5.2 in the presence of conjugated bile acids (TDCA y GDCA). The pH values of the lactobacilli was measured with the internally conjugated fluorescent pH probe5, 6-carboxyfluorescein succinimidyl ester (cFDASE) according the protocols of Kurdi et al.with modification. The BSH (+) strain showed a gradual increase in the pHi following the addition of BA, ranged from 5.1 to 5.8, and from 5.2 to 5.5 with GDCA and TDCA respectively.This behaviour was more evident in the presence of GDCA that TDCA probably due to the higher affinity for glycoconjugated acid (Taranto et al. 1999). On the contrary, the BSH (-) strains showed an internal ph decrease (ranged from 5.2 to 5.0 ) probably due to the BA (weak acid) accumulation. These 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.