Identification and characterization of <i>Dorea ammoniilytica</i> as a novel deoxycholic acid-producing bacterial species in the human gut microbiota

Deoxycholic acid (DCA), a representative secondary bile acid, is produced by specific gut bacteria through bile acid 7α-dehydroxylation of cholic acid, catalyzed by enzymes encoded in the bai gene operon. Exploration of diversity and functional characteristics of DCA-producing bacteria is crucial for understanding the "in vivo" mechanisms of DCA production in the human intestine. Here, we have identified and characterized two strains derived from human feces as a novel DCA-producing species, Dorea ammoniilytica. These strains harbored segmented bai gene operons in their complete genome sequences and showed high DCA production activity from cholic acid in the culture experiments. Biochemical, phylogenetic, and average nucleotide identity analyses categorized them as D. ammoniilytica, which belongs to a distinct lineage from other known DCA producers and Dorea species. These findings expand the diversity of secondary bile acid-producing bacteria in the human gut microbiota and provide clues for clarifying the in vivo DCA production mechanisms.