biostudies-literatureGios EMinistry of Business, Innovation and EmploymentMinistry of Business, Innovation and Employment (MBIE)13https://www.ebi.ac.uk/biostudies/studies/S-EPMC9938205biostudies-literatureUnknown3(1)Aquifers are populated by highly diverse microbial communities, including unusually small bacteria and archaea. The recently described Patescibacteria (or Candidate Phyla Radiation) and DPANN radiation are characterized by ultra-small cell and genomes sizes, resulting in limited metabolic capacities and probable dependency on other organisms to survive. We applied a multi-omics approach to characterize the ultra-small microbial communities over a wide range of aquifer groundwater chemistries. Results expand the known global range of these unusual organisms, demonstrate the wide geographical range of over 11,000 subsurface-adapted Patescibacteria, Dependentiae and DPANN archaea, and indicate that prokaryotes with ultra-small genomes and minimalistic metabolism are a characteristic feature oISME communicationsUltra-small bacteria and archaea exhibit genetic flexibility towards groundwater oxygen content, and adaptations for attached or planktonic lifestyles.PMC9938205UOAX1720Mosley OEGios EHandley KMClose MWeaver LDaughney CfalseUltra-small bacteria and archaea exhibit genetic flexibility towards groundwater oxygen content, and adaptations for attached or planktonic lifestyles.Aquifers are populated by highly diverse microbial communities, including unusually small bacteria and archaea. The recently described Patescibacteria (or Candidate Phyla Radiation) and DPANN radiation are characterized by ultra-small cell and genomes sizes, resulting in limited metabolic capacities and probable dependency on other organisms to survive. We applied a multi-omics approach to characterize the ultra-small microbial communities over a wide range of aquifer groundwater chemistries. Results expand the known global range of these unusual organisms, demonstrate the wide geographical range of over 11,000 subsurface-adapted Patescibacteria, Dependentiae and DPANN archaea, and indicate that prokaryotes with ultra-small genomes and minimalistic metabolism are a characteristic feature o2023-01-01T00:00:00Z2023 Feb2025-04-18T14:12:08.321Z2025-04-07T00:15:11.561ZS-EPMC99382053680814710.1038/s43705-023-00223-x