Clostridium Hiranonis, a Bile Acid 7α-Dehydroxylating Bacterium in Dogs

Bile acids (BAs) are bioactive molecules that are crucial for the absorption of fat-soluble nutrients and regulation of host metabolism, including glucose, lipid, and energy homeostasis. BAs are synthesized in the liver and are further metabolized by microbiota in the gut. Previous studies have shown that an alteration of gastrointestinal microbiota, referred to as dysbiosis, can alter the bile acid profiles. This aim of this project was to identify and characterize Clostridium hiranonis, a bile acid 7α-dehydroxylating bacterium from canine feces, and to study the association between C. hiranonis and secondary bile acids (SBAs). Firstly, this study evaluated the fecal microbiome of dogs with exocrine pancreatic insufficiency (EPI) based on 16S rRNA sequencing. The fecal microbiota of dogs with EPI was different when compared to healthy control dogs. In dogs with EPI, the bacterial families, Lachnospiraceae and Ruminococcaceae were decreased, while Lactobacillus, Bifidobacterium, and Enterococcus were increased in dogs with EPI. At the species level, Blautia producta, Clostridium hiranonis, Faecalibacterium prausnitzii, Ruminoccocus gnavus, and Collinsella stercoris were decreased in dogs with EPI. Secondly, this study isolated, identified, and characterized C. hiranonis from canine feces. The canine isolates were similar to the reference strain C. hiranonis DSM 13275 based on morphological, biochemical, and fatty acid profiles. Based on whole genome sequencing results, these isolates possess genes for the enzymes choloylglycine hydrolase, and bile acid 7α- dehydratase, which are essential for deconjugation and bile acid 7α-dehydroxylation of primary bile acids. Finally, this study examined the correlation between C. hiranonis and SBAs in canine fecal samples. Results show that C. hiranonis and SBA concentrations are significantly correlated in canine feces. The ROC analysis showed that the fecal abundance of C. hiranonis can be used to discern between normal and low fecal SBAs with a sensitivity of 88% and specificity of 90% in dogs. In conclusion, this is the first study to isolate and characterize C. hiranonis from canine feces and to find a significant correlation between SBA concentrations and abundance of C. hiranonis in canine feces