Growth of candidate phyla radiation bacteria in groundwater incubations reveals widespread adaptations to oxic conditions.

The candidate phyla radiation (CPR) comprises a widespread but poorly understood group of bacteria with limited cultured representatives, largely due to their metabolic dependencies on microbial hosts. In laboratory incubations, CPR often decline sharply in relative abundance, even when samples originate from natural environments where they dominate, such as groundwater, where they can represent over 50% of the microbiome. Suitable enrichment conditions and host interactions remain poorly defined.