Significance of bile salt hydrolytic activities of lactobacilli

Abstract

Bile salt hydrolase (BSH) activity was shown to be constitutive and substrate-specific: the BSH isogenic Lactobacillus plantarum wild type (LP80 WT) and BSH overproducing LP80 (pCBH1) strains preferentially hydrolysed glycodeoxycholic acid (GDCA), whereas the hamster Lact. animalis isolates H362 and H364 showed a higher affinity for taurodeoxycholic acid (TDCA). In viability studies in the presence of nutrients, it was demonstrated that GDCA exerted a higher toxicity than TDCA in a pH-dependent manner. This toxicity was inversely proportionate to the BSH activity level of the strains tested, indicating that BSH activity contributed towards bile salt resistance when appropriate nutrients were available. The high toxicity of GDCA relative to TDCA was suggested to be caused by their weak and strong acid properties respectively. It was therefore hypothesized that the protonated form of bile salts exhibited toxicity as it imported protons in the cell. This puts an energy-burden on BSH- lactobacilli which undergo intracellular acidification. BSH+ cells primarily protect themselves through the formation of the weaker DCA compound, which can help negate the pH-drop by recapturing and exporting the co-transported proton. However, since DCA is more toxic than its conjugated counterparts, an additional energy-dependent detoxification of DCA is suggested.

Consequences of bile salt biotransformations by intestinal bacteria

“…8 BSH activity is widespread in commensal bacteria inhabiting both the small intestine and large bowel. Grampositive gut bacteria have the most diverse distribution of BSH including; Clostridium, 12,13 Enterococcus, 14 Bifidobacterium, 15,16 and Lactobacillus, 17,18 while the distribution of BSH in Gram-negatives is, so far, detected only in members of the genus Bacteroides. 19 Species of human intestinal archaea such as Methanobrevibacter smithii and Methanosphera stadmanae were both shown to encode BSH capable of hydrolyzing both taurine-and glycine-conjugates.…”

In Vitro Study on Release of Bioactive Antimicrobial Compounds From Dairy Products by Certain Promising Probiotic Lactobacillus Strains

“…The isolated strains tolerated up to 0.6% which showed a good tolerance to bile salt. Bsh activity is a relevant property for probiotic strains to survive the toxicity of conjugated bile salts in the duodenum [19]. During the study, R1 and R7 produced Bsh activity specific to bile salt (sodium cholate) hydrolysis.…”

Hypocholesterolaemic Effects of Probiotics

“…To maintain bile salt homeostasis, more bile acids need to be synthesised and this in turn will reduce cholesterol in the body pool as cholesterol is the precursor for bile acids. The hypocholesterolaemic effect of lactic acid bacteria in this manner is comparable with that of cholestyramine treatment, which like other bile salt sequestrants, binds bile salts and prevents them from being reabsorbed [97]. Intestinal microflora plays a major role in interfering with the reabsorption of bile acid from the intestine, thus, promoting their excretion [97].…”

“…However, in the intestine, the bile salts may also be deconjugated by probiotics strains through bile salt hydrolase activity resulting in free bile salts. Free bile salts are more likely to be excreted via the faeces than the conjugated ones [96][97][98].…”