*Article* **Impact of Fecal Microbiota Transplantation on Gut Bacterial Bile Acid Metabolism in Humans**

**Jessica-Miranda Bustamante 1,†, Tyson Dawson 2,†, Caitlin Loeffler 2, Zara Marfori 1, Julian R. Marchesi 3, Benjamin H. Mullish 3, Christopher C. Thompson 4, Keith A. Crandall 2,5, Ali Rahnavard 2,5, Jessica R. Allegretti 4,\* and Bethany P. Cummings 1,\***


**Abstract:** Fecal microbiota transplantation (FMT) is a promising therapeutic modality for the treatment and prevention of metabolic disease. We previously conducted a double-blind, randomized, placebo-controlled pilot trial of FMT in obese metabolically healthy patients in which we found that FMT enhanced gut bacterial bile acid metabolism and delayed the development of impaired glucose tolerance relative to the placebo control group. Therefore, we conducted a secondary analysis of fecal samples collected from these patients to assess the potential gut microbial species contributing to the effect of FMT to improve metabolic health and increase gut bacterial bile acid metabolism. Fecal samples collected at baseline and after 4 weeks of FMT or placebo treatment underwent shotgun metagenomic analysis. Ultra-high-performance liquid chromatography-mass spectrometry was used to profile fecal bile acids. FMT-enriched bacteria that have been implicated in gut bile acid metabolism included *Desulfovibrio fairfieldensis* and *Clostridium hylemonae*. To identify candidate bacteria involved in gut microbial bile acid metabolism, we assessed correlations between bacterial species abundance and bile acid profile, with a focus on bile acid products of gut bacterial metabolism. *Bacteroides ovatus* and *Phocaeicola dorei* were positively correlated with unconjugated bile acids. *Bifidobacterium adolescentis*, *Collinsella aerofaciens*, and *Faecalibacterium prausnitzii* were positively correlated with secondary bile acids. Together, these data identify several candidate bacteria that may contribute to the metabolic benefits of FMT and gut bacterial bile acid metabolism that requires further functional validation.

**Keywords:** bile salt hydrolase (BSH); bile acids; gut microbiota; metagenomics; fecal microbiome transplant (FMT)
