Bacteria from theTuricibactergenus are prominent members of the mammalian gut microbiota and correlate with alterations in dietary fat and body weight, but the specific connections between these symbionts and host physiology are poorly understood. To address this knowledge gap, we characterize a diverse set of mouse- and human-derivedTuricibacterisolates, and find they group into clades that differ in their transformations of specific bile acids. We identifyTuricibacterbile salt hydrolases that confer strain-specific differences in bile deconjugation. Using male and female gnotobiotic mice, we find colonization with individualTuricibacterstrains leads to changes in host bile acid profiles, generally aligning with those produced in vitro. Further, colonizing mice with another bacterium exogenously expressing bile-modifying genes fromTuricibacterstrains decreases serum cholesterol, triglycerides, and adipose tissue mass. This identifies genes that enableTuricibacterstrains to modify host bile acids and lipid metabolism, and positionsTuricibacterbacteria as modulators of host fat biology.