PNNL

Abstract

ABSTRACT: The gut microbiome has a profound influence on human physiology, both in health and in disease. Bile acid biotransformation is one of the most prominent metabolic pathways through which the gut microbiome impacts host health. Bile salt hydrolases (BSH) are microbial enzymes that regulate the magnitude of bile acid metabolism in the gut. However, a complete understanding of how BSH directly impacts the host remains elusive due to the paucity of simple methods for detecting its activity, especially in clinically relevant and easy to obtain stool samples. Herein, we have de-veloped a simple, rapid, and inexpensive assay to detect BSH enzyme activity using a turn-on fluorescence probe with the concentration as low as 6-25 µM, which is considerably more robust than prior approaches. We have successfully ap-plied this rhodamine-based assay to the detection of BSH activity in a wide range of biological samples such as recombi-nant protein, whole cells, fecal samples, and gut lumen content from mice. We were able to detect significant BSH activity in small amounts of mouse fecal/gut content (20-50 mg) within 2 h, which illustrates its potential to use in various bio-logical/clinical applications. Using this assay, we investigated the diurnal fluctuations of BSH activity in the large intes-tine of mice. By using time restricted feeding conditions, we provided direct evidence of 24 h rhythmicity in microbiome BSH activity levels and showed that this rhythmicity is influenced by feeding patterns. Taken together, we have devel-oped a novel function-centric approach that can be easily applied to aid in the discovery of therapeutic, diet, or lifestyle interventions in the gut microbiome for correction of homeostatic perturbations of host bile metabolism.