A defined laboratory coculture in which the phototrophic Fe(II)-oxidizing bacterium Rhodopseudomonas palustris TIE-1 and the anaerobic Fe(III)-reducing bacterium Geobacter sulfurreducens cycle electrons through magnetite. The system demonstrates that mixed-valence magnetite can act as a recyclable electron donor and electron acceptor, effectively functioning as a naturally occurring biogeochemical battery under changing light and redox conditions. This community is DOE-relevant because mineral-mediated electron flow shapes subsurface elemental cycling and can influence contaminant fate in sediments, aquifers, and engineered remediation settings.
Taxonomy
| Taxon | Ontology ID | Functional Roles | Abundance |
|---|---|---|---|
| Rhodopseudomonas palustris TIE-1 | NCBITaxon:395960 · TaxonMech · TraitMech |
PRIMARY_PRODUCER
CROSS_FEEDER
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ABUNDANT |
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| Geobacter sulfurreducens | NCBITaxon:35554 · TaxonMech · TraitMech |
CROSS_FEEDER
SYNTROPHIC_PARTNER
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ABUNDANT |
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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.
Magnetite-Mediated Electron Sharing
The two recorded bacteria exchange electrons with a shared mixed-valence magnetite reservoir: R. palustris TIE-1 withdraws electrons during phototrophic Fe(II) oxidation, whereas G. sulfurreducens supplies electrons during Fe(III) reduction. This is mineral-mediated redox cycling, not a direct nutrient transfer from TIE-1 to Geobacter.
Participating Taxa: Rhodopseudomonas palustris TIE-1, Geobacter sulfurreducens
Metabolites: magnetite (CHEBI:50821 · MediaIngredientMech · CMMMech), Fe(II) (CHEBI:29033 · MediaIngredientMech · CMMMech), Fe(III) (CHEBI:29034 · MediaIngredientMech · CMMMech)
Opposed microbial electron withdrawal and supply allow magnetite to function as the shared redox reservoir under the tested externally controlled conditions.
Evidence
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PMID:25814583 - SUPPORT (IN_VITRO)"sharing of electrons in mixed-valent iron oxides between bacteria with different metabolisms"
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PMID:25814583 - SUPPORT (IN_VITRO)"bioavailable as electron sinks and electron sources"
Phototrophic Magnetite Fe(II) Oxidation
Under light, R. palustris TIE-1 oxidizes magnetite Fe(II), withdrawing stored electrons and discharging the mineral. In the coculture cycle this is one community redox step, not a demonstrated pairwise fitness benefit or resource-partitioning experiment.
Participating Taxa: Rhodopseudomonas palustris TIE-1, Geobacter sulfurreducens
Metabolites: magnetite (CHEBI:50821 · MediaIngredientMech · CMMMech), Fe(II) (CHEBI:29033 · MediaIngredientMech · CMMMech)
Biological Processes:
- photosynthesis (GO:0015979 · PathwayMech)
Oxidation regenerates magnetite Fe(III) that Geobacter can subsequently reduce when electron donor is supplied under the tested reducing conditions; the observed cycle depends on external conditions.
Phototrophic Fe(II) oxidation withdraws electrons from magnetite and discharges the mineral reservoir; it does not charge an oxidized electron store.
Evidence
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PMID:25814583 - SUPPORT (IN_VITRO)"Rhodopseudomonas palustris TIE-1 oxidizes magnetite (Fe3O4) nanoparticles using light energy"
Anaerobic Magnetite Fe(III) Reduction
G. sulfurreducens reduces magnetite Fe(III), storing supplied electrons as reduced Fe(II) and charging the mineral. The demonstrated reversal requires suitable electron-donor and environmental conditions; it is not evidence of direct reciprocal nutrient exchange.
Participating Taxa: Rhodopseudomonas palustris TIE-1, Geobacter sulfurreducens
Metabolites: magnetite (CHEBI:50821 · MediaIngredientMech · CMMMech), Fe(III) (CHEBI:29034 · MediaIngredientMech · CMMMech), Fe(II) (CHEBI:29033 · MediaIngredientMech · CMMMech)
Reduction regenerates magnetite Fe(II) that TIE-1 can oxidize during a subsequent illuminated phase, closing the experimentally demonstrated conditional redox cycle.
Fe(III) reduction charges magnetite with electrons and restores the reduced electron reservoir for later phototrophic discharge.
Evidence
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PMID:25814583 - SUPPORT (IN_VITRO)"reversible in co-cultures by the anaerobic Fe(III)-reducing bacterium Geobacter sulfurreducens"
Biogeochemical Battery Function
Repeated microbial reduction and oxidation make magnetite a reusable electron reservoir in the tested cocultures: reduction charges it and oxidation discharges it. External light and electron-donor supply drive the cycle; this is not a self-sustaining loop or a demonstrated syntrophic fitness relationship.
Participating Taxa: Rhodopseudomonas palustris TIE-1, Geobacter sulfurreducens
Metabolites: magnetite (CHEBI:50821 · MediaIngredientMech · CMMMech)
Evidence
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PMID:25814583 - SUPPORT (IN_VITRO)"effectively rendering magnetite a naturally occurring battery"
Associated Datasets
| Dataset | Type | Repository | Accession |
|---|---|---|---|
|
Magnetite redox cycling primary publication
Primary Science publication reporting magnetic and spectroscopic measurements of reversible magnetite redox cycling by R. palustris TIE-1 and G. sulfurreducens cocultures. |
PHENOTYPE | OTHER | PMID:25814583 |
Knowledge gaps & discussions (1)
KNOWLEDGE_GAP OPEN Which ecological benefits follow from the demonstrated mineral redox cycle?
The full primary paper supports repeated coculture redox reversals with externally controlled light and electron-donor conditions. Preserve the real feedback directions, but distinguish mineral electron storage from direct nutrient cross-feeding, competition-based niche partitioning and product-removal syntrophy. Current SYNTROPHY does not require obligacy; the missing evidence is the relevant metabolic/fitness feedback. Redox chemistry is not iron-ion transport. The DOI cache contains an editorial summary, so graph evidence now uses the primary PMID abstract. Non-graph functional roles remain for issue1759.
Attaches to: ecological_interactions#Magnetite-Mediated Electron Sharing, ecological_interactions#Phototrophic Magnetite Fe(II) Oxidation, ecological_interactions#Anaerobic Magnetite Fe(III) Reduction, ecological_interactions#Biogeochemical Battery Function
1 evidence item(s)
This process is reversible in co-cultures
Primary abstract supports reversal, not direct nutrient exchange or self-sustaining reciprocal fitness.
External Resources
| Name | Repository | Resource ID |
|---|---|---|
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DOE BER Science Highlight - Microbes Use Tiny Magnets as Batteries
DOE Biological and Environmental Research highlight describing the subsurface electron-flow relevance of the R. palustris TIE-1 and G. sulfurreducens magnetite battery study. |
OTHER | BER-2015-microbes-use-tiny-magnets |
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Environmental Factors
| Factor | Value | Unit |
|---|---|---|
| Magnetite nanoparticles | mixed-valence Fe3O4 mineral substrate | N/A |
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| Light energy | required for phototrophic Fe(II) oxidation by TIE-1 | N/A |
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| Changing redox conditions | varying environmental conditions | N/A |
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Growth Media
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