Fiber consumption stimulates microbial bile salt hydrolase activity

Previously, we reported a microbiota-dependent increase in the levels of bile acids (BA), taurine, and taurine conjugates in the intestinal mucosa that takes place during caloric restriction (CR). Now, we investigated the molecular regulation behind this process. Male mice were submitted to restrictive diets, housing with different types of cage bedding or without bedding. Fecal transplants were performed to assess the involvement of microbiota. Bile salt hydrolase activity (BSH) was inhibited and diets high in fiber were applied. Restrictive diets, including intermittent fasting and fasting-mimicking diet, have a similar impact to CR in terms of taurine level modulation. The type of cage bedding with which mice were housed during CR affected the levels of BAs and taurine in the intestinal mucosa. Complete removal of cage bedding prevented CR-specific increase in the levels of taurine and taurine conjugates in the mucosa. Accordingly, lack of bedding during CR resulted in increased taurine-conjugated BAs levels in the intestine mucosa implying decreased BAs deconjugation capacity of the gut microbiota. At the same time, fecal microbiota transplants from CR mice housed with bedding increased BAs deconjugation in ad libitum-fed mice. Next, inhibition of BSH prevented the increase in free taurine concentration while increasing taurine-conjugated BAs levels in the intestine mucosa of CR mice. Finally, ad libitum consumption of diets high in fiber increased the levels of taurine conjugates but did not elevate the levels of BAs. Dietary restriction is required to stimulate BAs secretion into the gut, while ingestion of fiber stimulates the deconjugation capacity of the intestinal microbiota. Sequencing was performed at the Joint Microbiome Facility of the Medical University of Vienna and the University of Vienna under the project ID JMF-2206-08.