A deep CO2-rich subsurface aquifer community below the Colorado Plateau, sampled from groundwater brought to the surface by eruptions of Crystal Geyser. Coupled lipidomic and metagenomic analyses show that bacterial and archaeal CO2 fixation in the deep subsurface provides the organic carbon pool, supporting an autotrophy-based deep biosphere. Candidate Phyla Radiation (CPR) bacterial putative symbionts lack complete lipid biosynthesis pathways but still possess regular lipid membranes, which may originate from other community members; these other members also adapt to high in situ pressure by increasing fatty acid unsaturation. An unusually high abundance of lysolipids attributed to CPR bacteria may represent an adaptation to membrane curvature stress induced by their small cell sizes.
Taxonomy
| Taxon | Ontology ID | Functional Roles | Abundance |
|---|---|---|---|
| deep-aquifer CPR bacteria — ontology label: Patescibacteria group | NCBITaxon:1783273 · TaxonMech · TraitMech |
SYNTROPHIC_PARTNER
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N/A |
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| deep-aquifer CO2-fixing bacteria and archaea — ontology label: cellular organisms | NCBITaxon:131567 · TaxonMech · TraitMech |
PRIMARY_PRODUCER
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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.
Predominantly Autotrophic Carbon Supply
Stable carbon isotope compositions, community metagenomes and geological constraints support a predominantly autotrophic origin of biomass across the sampled aquifers. Bacterial and archaeal carbon fixation supplies the community organic-carbon pool; isotope mass-balance estimates depend on fractionation assumptions and allow heterotrophic reuse. This does not trace a particular producer-to-CPR carbon or lipid transfer.
Participating Taxa: deep-aquifer CO2-fixing bacteria and archaea
Metabolites: carbon dioxide (CHEBI:16526 · MediaIngredientMech · CMMMech)
Biological Processes:
- carbon fixation (GO:0015977 · PathwayMech)
HYPOTHESIZED - autotrophically fixed carbon can supply bacterial lipid production and the community material available for CPR acquisition. The isotope, lipid and genomic observations support this proposed carbon route but do not trace transfer from a particular producer to CPR cells.
Evidence
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PMID:32203118 - SUPPORT (IN_VIVO)"bacterial and archaeal CO2 fixation ongoing in the deep subsurface provides organic carbon for the complex communities that reside there"
Putative CPR Lipid Acquisition
CROSS_FEEDINGHYPOTHESIZED - CPR-associated membrane lipids together with missing known complete lipid-biosynthesis pathways support acquisition of lipids or precursors from coexisting bacteria. Scavenging degraded biomass and direct host-derived acquisition remain alternatives; neither a donor nor uptake flux was resolved. The broad producer participant represents community context, not proof of archaeal-to-CPR donation. Some Nealsonbacteria retain near-complete pathways, so unknown ACP-independent biosynthesis cannot be excluded. Product-removal syntrophy was not demonstrated.
Participating Taxa: deep-aquifer CPR bacteria, deep-aquifer CO2-fixing bacteria and archaea
Metabolites: lipid (CHEBI:18059 · MediaIngredientMech · CMMMech), fatty acid (CHEBI:35366 · MediaIngredientMech · CMMMech)
Biological Processes:
- lipid metabolic process (GO:0006629 · PathwayMech)
HYPOTHESIZED - acquired community lipids or precursors could provide material for CPR-associated lysolipid membranes and their proposed curvature adaptation. Lipid correlations and mixed-fraction spectroscopy do not demonstrate that acquisition causes lysolipid enrichment or that enrichment improves curvature tolerance.
Evidence
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PMID:32203118 - PARTIAL (IN_VIVO)"CPR bacteria lack complete lipid biosynthesis pathways but still possess regular lipid membranes"
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PMID:32203118 - PARTIAL (IN_VIVO)"the redistribution of lipids into putative symbionts within this community"
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PMID:32203118 - PARTIAL (OTHER)"Thus, we suggest that most CPR bacteria derive their membrane lipids, including lysolipids, from coexisting bacteria."
CPR-Associated Lysolipids and Proposed Curvature Adaptation
Lipidomics, organism-lipid correlations and FTIR of CPR-enriched size fractions support lysolipid-rich membranes in some CPR bacteria. These fractions are mixed communities, not purified CPR isolates; the initial fraction also contained abundant Sulfurimonas. Reduced curvature stress in small cells is a proposed adaptive explanation, not a tested membrane-mechanical or fitness effect. No unaffected-donor relationship is established.
Participating Taxa: deep-aquifer CPR bacteria
Metabolites: lipid (CHEBI:18059 · MediaIngredientMech · CMMMech)
Biological Processes:
- lipid metabolic process (GO:0006629 · PathwayMech)
Evidence
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PMID:32203118 - PARTIAL (IN_VIVO)"An unusually high abundance of lysolipids attributed to CPR bacteria may represent an adaptation to membrane curvature stress induced by their small cell sizes"
Knowledge gaps & discussions (1)
KNOWLEDGE_GAP OPEN Which sources and uptake routes supply CPR lipids, and do lysolipids causally relieve membrane curvature stress?
The complete primary main body supports mostly autotrophic community carbon, missing known biosynthesis pathways and CPR-associated lysolipids. Correlated relative abundances, mixed size fractions and FTIR do not resolve donors or transfer rates. Degraded-biomass scavenging, direct host acquisition and unknown biosynthetic routes remain distinguishable hypotheses. Selective uptake/biosynthesis perturbations, tracing and membrane-mechanical measurements would test the proposed chain. The separate archaeal lipid discussion must not establish archaeal donation to CPR. No figure images or supplementary files were inspected. Non-graph taxon-role and pressure-adaptation overstatements remain in #1366.
Attaches to: ecological_interactions#Predominantly Autotrophic Carbon Supply, ecological_interactions#Putative CPR Lipid Acquisition, ecological_interactions#CPR-Associated Lysolipids and Proposed Curvature Adaptation
External Resources
| Name | Repository | Resource ID |
|---|---|---|
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Primary publication for the Crystal Geyser CPR lipid community
PubMed record for the Probst et al. 2020 ISME J paper. |
OTHER | PMID:32203118 |
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DOI landing page
DOI link to the ISME J paper. |
OTHER | doi:10.1038/s41396-020-0624-4 |
Environmental Factors
| Factor | Value | Unit |
|---|---|---|
| Aquifer chemistry | CO2-rich Colorado Plateau aquifers | N/A |
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| Sampling vehicle | Crystal Geyser eruptions | N/A |
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