A Screening Assay for Bile Acid-Transforming Microorganisms Using Engineered Bacterial Biosensors

Area of Science:

• Microbiology
• Biochemistry
• Enzymology

Background:

• Bile salt hydrolase (BSH) is key to microbial bile acid (BA) metabolism in the gut.
• BA pool dysregulation links to various human and animal diseases, necessitating BSH activity identification.
• Existing BSH screening methods are often costly, insensitive, or complex.

Purpose of the Study:

• To develop a novel, accessible, and sensitive assay for screening microbial BSH activity.
• To utilize a bacterial biosensor reporting BA concentrations via fluorescence for BSH detection.
• To ensure assay specificity by testing primary BAs within controlled ranges and addressing matrix effects.

Main Methods:

• Development of a bacterial biosensor for detecting bile acids (BAs).
• Implementation of a screening assay using the biosensor for microbial BSH activity.
• Evaluation of the assay on recombinant *Escherichia coli* strains expressing BSH genes from *Lactobacillus johnsonii* PF01 and *Lactobacillus rhamnosus* GG.
• Assessment of the matrix effect of microbial growth media on biosensor output.

Main Results:

• The assay successfully detected BSH activity in tested microbial strains.
• Results were consistent with previous BSH activity assays for the evaluated enzymes.
• The assay demonstrated robustness in addressing the matrix effect of growth media.

Conclusions:

• The developed biosensor assay provides a reproducible and accessible method for screening BSH activity in cultivated microbes.
• This assay supports the identification of BSH-producing strains relevant to healthcare and agroindustry.
• The assay is compatible with automated protocols, enhancing its utility.