Overview
Bile salt hydrolase (BSH) is the microbial enzyme that deconjugates primary bile acids (taurocholate, glycocholate) by cleaving the amino acid (taurine or glycine) from the steroid core. This is the first and rate-limiting step in microbial bile acid transformation — without BSH, the entire secondary bile acid pool and its signaling functions would not exist.
BSH is found in Lactobacillus, Bifidobacterium, Bacteroides, Clostridium, and Enterococcus — among the most widely distributed microbial enzyme activities in the human gut.
Downstream Consequences
Deconjugated bile acids undergo further microbial transformation (7α-dehydroxylation) to produce secondary bile acids (deoxycholic acid, lithocholic acid), which:
- Activate FXR and TGR5 nuclear receptors → regulate cholesterol metabolism, gluconeogenesis, and energy expenditure.
- Are directly antimicrobial — secondary bile acids inhibit C. difficile germination (basis of colonization resistance).
- At high concentrations, are pro-carcinogenic — DCA promotes CRC by generating ROS and activating Wnt/β-catenin [1].
WikiBiome Relevance
- BSH activity determines the balance between primary and secondary bile acids — a balance disrupted by dysbiosis.
- Antibiotic-induced loss of BSH-producing bacteria → primary bile acid accumulation → C. difficile spore germination (primary bile acids promote it; secondary bile acids inhibit it).
- BSH is a target for probiotic engineering — enhancing BSH activity could improve cholesterol metabolism.
Cross-References
- bile acid metabolism — broader bile acid context
- colonization resistance — secondary bile acids inhibit C. difficile
- clostridioides difficile — BSH loss enables C. difficile
- lipid metabolism — FXR-mediated cholesterol regulation
- taurine — released by BSH deconjugation