Redefining the phylogenetic and metabolic diversity of phylum Omnitrophota

The candidate phylum Omnitrophica-recently termed Omnitrophota, and originally known as OP3-is an understudied bacterial clade that has primarily been found in aquatic ecosystems. To characterize the diversity and ecology of this phylum, we reconstructed 55 Omnitrophota metagenome-assembled genomes (MAGs) from a well-characterized groundwater system within central Germany and placed them within the context of publicly available genomes. Seven clades were identified, four of which contained novel genomes obtained from our groundwater system. All clades exhibited the capacity for type IV pili, type II secretion systems, glycogen storage, and carbohydrate degradation. Only the characterized Cand. Omnitrophus magneticus genome exhibited functions associated with magnetosome construction. Clades were characterized by sets of traits rather than unique pathways, which were then used to infer ecological strategies. These lifestyles consisted of mixotrophs, obligate fermenters, and versatile respiratory heterotrophs. Patterns in 16S rRNA gene amplicons from a 6 years, monthly sampled groundwater time-series dataset reflected the persistent and widespread occurrence of Clade 7 Wood-Ljungdahl utilizing mixotrophs and highlight this group as a core member of the groundwater community. Overall, this study uncovered, characterized, and contextualized the metabolic and phylogenetic diversity within phylum Omnitrophota, and predicts that environmental populations may mediate both nitrogen and sulfur cycling, along with organic matter production and degradation within aquatic ecosystems.