A groundwater microbial community framework combining genome-resolved metagenomics from one agricultural and seven pristine groundwater sites, yielding 746 Candidate Phyla Radiation (CPR) bacterial and DPANN archaeal genomes. Pristine sites, which serve as local sources of drinking water, contained up to 31 percent CPR bacteria and 4 percent DPANN archaea. Little species-level overlap of metagenome-assembled genomes was observed across the sites, indicating that CPR and DPANN communities are differentiated according to physicochemical conditions and host populations. Cryogenic transmission electron microscopy and genomic analysis identified CPR and DPANN lineages that reproducibly attach to host cells, with attachment apparently stimulating CPR bacterial growth.
Taxonomy
| Taxon | Ontology ID | Functional Roles | Abundance |
|---|---|---|---|
| groundwater CPR (Candidate Phyla Radiation) bacteria — ontology label: Patescibacteria group | NCBITaxon:1783273 · TaxonMech · TraitMech |
SYNTROPHIC_PARTNER
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DOMINANT |
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| groundwater DPANN archaea — ontology label: Nanobdellati | NCBITaxon:1783276 · TaxonMech · TraitMech |
SYNTROPHIC_PARTNER
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ABUNDANT |
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| groundwater CPR/DPANN host bacteria and archaea — ontology label: cellular organisms | NCBITaxon:131567 · TaxonMech · TraitMech |
PRIMARY_DEGRADER
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N/A |
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Ecological Interactions
The graph shows only explicitly linked interaction participants. Community members without an asserted participant link are omitted; membership alone does not imply an interaction.
Groundwater CPR/DPANN-Host Coexistence
Genome-resolved surveys recovered 746 CPR and DPANN genomes across eight Northern California groundwater sites. This framework pools distinct environmental communities, not one defined three-member culture. The canonical participants are broad lineage/host categories; genome recovery and coexistence do not establish colonization facilitation or every possible host association.
Participating Taxa: groundwater CPR (Candidate Phyla Radiation) bacteria, groundwater DPANN archaea, groundwater CPR/DPANN host bacteria and archaea
Evidence
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PMID:33495623 - SUPPORT (COMPUTATIONAL)"recovered 746 CPR and DPANN genomes in total"
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PMID:33495623 - SUPPORT (COMPUTATIONAL)"site-specific diversity of CPR bacteria and DPANN archaea that coexist with diverse hosts in groundwater aquifers"
Site-Specific CPR/DPANN Differentiation
Most site pairs had little species-level genome overlap. Hydrogeochemistry, host composition, dispersal history, founder effects and sampling can contribute to this pattern; the comparison does not selectively demonstrate physiological niche partitioning or a universal interspecies mechanism.
Participating Taxa: groundwater CPR (Candidate Phyla Radiation) bacteria, groundwater DPANN archaea, groundwater CPR/DPANN host bacteria and archaea
Evidence
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PMID:33495623 - SUPPORT (COMPUTATIONAL)"little species-level overlap of metagenome-assembled genomes (MAGs) across the groundwater sites"
Size-Fraction CPR/DPANN Host-Attachment Signal
Larger size fractions contained CPR/DPANN genome signals consistent with some ultrasmall cells retaining host attachment. This is a size-fraction proxy, not direct taxonomic identification of cell pairs. Estimated cell counts used DNA yield and genome-size corrections, not direct cell counting; attachment disruption and other size-associated effects limit the interpretation.
Participating Taxa: groundwater CPR (Candidate Phyla Radiation) bacteria, groundwater DPANN archaea, groundwater CPR/DPANN host bacteria and archaea
Evidence
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PMID:33495623 - PARTIAL (COMPUTATIONAL)"indicate that a fair number of CPR/DPANN cells retain host attachment throughout the filtration process"
CPR/DPANN Episymbiotic Attachment to Hosts
The authors report cryo-TEM observations of ultrasmall cells attached to larger cells in concentrated Ag groundwater, with pili-like appendages at some interfaces. Their assignment to CPR or DPANN is inferred from size and community context, not a resolved taxonomic identity for each imaged pair. These observations do not establish a necessary attachment protein, transferred resource or host fitness effect.
Participating Taxa: groundwater CPR (Candidate Phyla Radiation) bacteria, groundwater DPANN archaea, groundwater CPR/DPANN host bacteria and archaea
Biological Processes:
- cell adhesion (GO:0007155 · PathwayMech)
HYPOTHESIZED - access to host-associated resources could stimulate CPR replication. Attached-cell images and higher CPR iRep in larger fractions support this interpretation, but attachment was not selectively perturbed and the putative resource transfer was not measured. The replication comparison does not include DPANN archaea.
Evidence
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PMID:33495623 - PARTIAL (IN_VIVO)"CPR and DPANN lineages that reproducibly attach to host cells"
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PMID:33495623 - SUPPORT (IN_VIVO)"attaching through pili-like structures"
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PMID:33495623 - PARTIAL (IN_VIVO)"likely to be CPR or DPANN organisms"
Host-Attached CPR Replication Stimulation
At three of four size-fraction sampling points in Ag groundwater, CPR populations had significantly higher iRep in the 0.65-2.5 micrometer fraction than in the 0.1-0.2 micrometer fraction. iRep is average genome-replication state, not a single-cell growth rate or doubling time. Archaea were excluded from this analysis. An association with probable attachment does not establish causation or commensalism because host fitness was not measured.
Participating Taxa: groundwater CPR (Candidate Phyla Radiation) bacteria, groundwater CPR/DPANN host bacteria and archaea
Evidence
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PMID:33495623 - PARTIAL (COMPUTATIONAL)"host-attached CPR bacteria consistently exhibit a higher replication rate than non-host-attached CPR bacteria"
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PMID:33495623 - PARTIAL (COMPUTATIONAL)"the growth of CPR bacteria seems to be stimulated by attachment to host-cell surfaces"
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PMID:33495623 - SUPPORT (COMPUTATIONAL)"archaeal genomes were excluded"
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PMID:33495623 - SUPPORT (COMPUTATIONAL)"average replication state of the cell population"
Knowledge gaps & discussions (1)
KNOWLEDGE_GAP OPEN Which hosts, resources and attachment mechanisms explain the CPR replication association?
The only arrow remains HYPOTHESIZED. Size fractions are imperfect proxies, imaged ultrasmall-cell taxonomy is inferred, and iRep describes CPR population replication state; DPANN archaea were excluded. Host fitness and transferred resources were not measured, so commensalism and syntrophic flux are not established. Preserve the three workflow-edge removals in the 2026-10-02 history. The eight-site framework is not a single reconstructed community. PMID:32252814 concerns separate Oak Ridge groundwater rather than the same California sites; non-graph provenance and role claims remain #1442. No new partner-specific structure is supported by these observations alone.
Attaches to: ecological_interactions#Groundwater CPR/DPANN-Host Coexistence, ecological_interactions#Site-Specific CPR/DPANN Differentiation, ecological_interactions#Size-Fraction CPR/DPANN Host-Attachment Signal, ecological_interactions#CPR/DPANN Episymbiotic Attachment to Hosts, ecological_interactions#Host-Attached CPR Replication Stimulation
External Resources
| Name | Repository | Resource ID |
|---|---|---|
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Primary publication for the episymbiotic CPR/DPANN groundwater community
PubMed record for the He et al. 2021 Nature Microbiology paper. |
OTHER | PMID:33495623 |
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DOI landing page
DOI link to the Nature Microbiology paper. |
OTHER | doi:10.1038/s41564-020-00840-5 |
Environmental Factors
| Factor | Value | Unit |
|---|---|---|
| Site land use | one agricultural and seven pristine groundwater sites | N/A |
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