Bile salt deconjugation by Lactobacillus plantarum 80 and its implication for bacterial toxicity

Abstract

. 1999. The effects of bile salts on the survival of lactobacilli were investigated using glycocholic acid, cholic acid and deoxycholic acid as model compounds and the bile salt hydrolase active Lactobacillus plantarum 80 (BSH + ) and its BSH negative mutant. The detrimental effects of cholic acid, i.e. growth inhibition and cytotoxicity at a concentration of 1 and 5 mmol l , respectively, were considered to be due to the hydrophobic protonated form of the molecule, which brings about membrane damage. The conversion of glycocholic acid to cholic acid by the BSH active L. plantarum 80 caused a growth inhibition which was comparable with the inhibition observed in the broth supplemented with 1 mmol l −1 cholic acid. Deoxycholic acid caused toxicity through membrane damage when the compound was in solution. Its toxicity disappeared in the culture broth as the molecule precipitated. In case of cholic acid, the toxicity could be removed by buffering the solution at pH 7·0. It was calculated that at this pH most of the cholic acid molecules were ionized. The results led to the formulation of an extended hypothesis about the ecological significance of bile salt transformations. Primary deconjugation is carried out to counteract intracellular acidification. Yet, the deconjugated molecule can be harmful at moderately acidic pH-values. In this case, the BSH + strains could effectively profit from their activity in case they are associated with 7a-dehydroxylating bacteria which dehydroxylate the deconjugated bile salts. The dehydroxylated molecule has a low solubility and precipitates at moderately acidic pH.

Bile salt biotransformations by human intestinal bacteria

“…The presence of a functional BSH results in the intracellular accumulation of free bile acids, which become protonated in a stoichiometric manner, decreasing energydependent H 1 -ATPase-driven proton efflux. BSHs from human intestinal lactobacilli generally have higher affinity for glycine conjugates (26)(27)(28)(29). This observation may lend weight to the hypothesis of De Smet et al (26), or the higher affinity of BSHs for glycine conjugates may have evolved because glycine conjugates are generally higher in proportion (3:1) than taurine conjugates in human bile (6).…”

Genetic Characterization of the Bile Salt Response in Lactobacillus plantarum and Analysis of Responsive Promoters In Vitro and In Situ in the Gastrointestinal Tract

“…Therefore, a porcine bile concentration of 0.1% was chosen for identification of bile-inducible promoter elements in L. plantarum. Notably, 0.1% bile is in the physiological concentration range that occurs in the GI tract (2,8).…”

Optimization of a yeast estrogen screen and its applicability to study the release of estrogenic isoflavones from a soygerm powder.

“…Bile salts occur in the intestine in a concentration ranging from 0.1 to 5 mmol/L, and they play an important role in solubilization of dietary lipids. However, bile salts in this concentration range also disrupt membrane integrity and are toxic to bacteria, isolated hepatocytes, and colonic mucosa (48)(49)(50)(51). The extracts obtained from samples of digested soygerm powder incubated with a microbial suspension exhibited a significantly higher (p ≤ 0.05) absorbance at 575 nm compared to the control with ethanol, which points to estrogenic activity.…”