CK-1C4-19 taxa are phylogenetically distributed by host and habitat. The V3-V4 regions from publically available 16S rDNA sequences assigned to the candidate division CK-1C4-19 were aligned with CK-1C4-19 sequences found in the fathead minnow gut (OTU4, OTU711), and a phylogenetic tree was constructed. OTUs found in the fathead minnow gut are most closely related to sequences reported from other fish in the family Cyprinidae. Scale bar changes per site. Inset: relative abundances by time and treatment of the dominant CK-1C4-19 OTU4.