A defined electroactive syntrophic coculture pairing Geobacter sulfurreducens with Pseudomonas aeruginosa in a restricted formate-fumarate medium. The community was used to study interspecies electron transfer and adaptive shifts from syntrophy toward competition. Early coculture growth depends on cooperative metabolism and direct interspecies electron transfer associated with Geobacter cytochromes, while adapted cocultures show increased Geobacter dominance and hydrogen/formate-linked electron-transfer features. The system is relevant to DOE biogeochemistry and bioelectrochemical applications because Geobacter-Pseudomonas interactions connect extracellular electron transfer, metal cycling, and microbial community modeling.
Taxonomy
| Taxon | Ontology ID | Functional Roles | Abundance |
|---|---|---|---|
| Geobacter sulfurreducens | NCBITaxon:35554 · TaxonMech · TraitMech |
SYNTROPHIC_PARTNER
CROSS_FEEDER
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DOMINANT |
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| Pseudomonas aeruginosa | NCBITaxon:287 · TaxonMech · TraitMech |
SYNTROPHIC_PARTNER
CROSS_FEEDER
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COMMON |
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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.
Restricted-Medium Cooperative Growth
Initial Geobacter sulfurreducens and Pseudomonas aeruginosa cocultures grew substantially in restricted formate-fumarate medium, whereas the corresponding pure cultures did not show significant growth. Formate serves as the donor preferentially used by Pseudomonas and fumarate as the acceptor used by Geobacter. This supports early cooperative metabolism under the tested conditions, not universal inability of either species to grow alone or complete partner independence after adaptation. The observation is a community growth outcome, not a Geobacter-to-Pseudomonas electron flux.
Participating Taxa: Geobacter sulfurreducens, Pseudomonas aeruginosa
Metabolites: formate (CHEBI:15740 · MediaIngredientMech · CMMMech), fumarate (CHEBI:29806 · MediaIngredientMech · CMMMech)
Biological Processes:
- electron transport chain (GO:0022900 · PathwayMech)
Evidence
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PMID:28992596 - SUPPORT (IN_VITRO)"preferential utilization of formate and fumarate by P. aeruginosa and G. sulfurreducens respectively"
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PMID:28992596 - SUPPORT (IN_VITRO)"Pure cultures did not yield significant growth while substantial growth was observed in cocultures"
Cytochrome-Associated Interspecies Electron Transfer
SYNTROPHYInitial cocultures showed increased DIET-associated cytochrome abundance, and the primary abstract reports stunted growth in Geobacter omcZ- and omcS-deficient cocultures while phenazine-deficient Pseudomonas cocultures still grew. These observations support cytochrome-associated syntrophy and the authors' DIET interpretation. Pseudomonas is the inferred electron donor and Geobacter the recipient in the formate-donor/fumarate-acceptor system, not the reverse. Protein abundance is not direct electron-flux measurement, and the accessible evidence does not establish an exclusive transfer route or rule out pleiotropic mutant effects. The 2018 full Methods and perturbation controls were unavailable for this review; the 2020 primary Results explicitly describe Geobacter reliance on Pseudomonas electron donation.
Source Taxon: Pseudomonas aeruginosa
Target Taxon: Geobacter sulfurreducens
Metabolites: formate (CHEBI:15740 · MediaIngredientMech · CMMMech), fumarate (CHEBI:29806 · MediaIngredientMech · CMMMech)
Biological Processes:
- electron transport chain (GO:0022900 · PathwayMech)
PARTIAL: Pseudomonas-to-Geobacter electron transfer could couple Pseudomonas formate use to Geobacter fumarate respiration and thereby support initial cooperative growth. Cytochrome-deficient cocultures showed impaired growth and initial cytochrome abundance was elevated, supporting this direction; the accessible evidence does not selectively establish an exclusive DIET route or exclude pleiotropic mutant effects. This is not a causal claim that protein upregulation itself creates electron transfer.
Evidence
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PMID:28992596 - PARTIAL (IN_VITRO)"upregulation in DIET-associated cytochromes"
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PMID:28992596 - PARTIAL (IN_VITRO)"DIET plays a critical role in the establishment of syntrophy"
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PMID:28992596 - SUPPORT (IN_VITRO)"syntrophy was not reliant on phenazine"
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PMID:28992596 - SUPPORT (IN_VITRO)"however appeared to rely on cytochromes as evidenced from the stunted growth"
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PMID:32265334 - PARTIAL (IN_VITRO)"reliance on Pseudomonas spp. for providing electron donors through DIET"
Geobacter-Dominated Coculture Adaptation
Across the tested Pseudomonas strains, Geobacter dominance increased between initial cocultures and the thirteenth transfer, as supported by qPCR and FISH. Geobacter fabI and tetR variants increased in frequency, with tetR-associated CyaE and RND-efflux protein changes. These are population and molecular observations, not proof that either variant causes dominance or that Geobacter directly inhibits or preys on Pseudomonas. The authors interpret a shift toward competition, but Geobacter could not be isolated from either early or adapted cocultures under the tested conditions, so complete loss of partner dependence was not established. qPCR can include inactive cells or extracellular DNA; FISH supports the abundance contrast. Adapted HybA and FdnG increases motivate hydrogen-transfer and increased direct formate-use interpretations; protein abundance alone does not quantify their fluxes, distinguish every transfer route or show that either mediates dominance.
Participating Taxa: Geobacter sulfurreducens, Pseudomonas aeruginosa
Evidence
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PMID:32265334 - PARTIAL (IN_VITRO)"transition from syntrophy to competition"
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PMID:32265334 - SUPPORT (IN_VITRO)"fabI and tetR genes emerged that were strongly selected for throughout coculture evolution"
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PMID:32265334 - SUPPORT (IN_VITRO)"Geobacter sp. dominance increases with adaptation within the cocultures"
Inhibitory Response to Added Phenazine-1-Carboxylic Acid
Added commercial phenazine-1-carboxylic acid inhibited growth in Geobacter pure-culture and coculture MIC assays conducted in their respective media. This demonstrates inhibitory capacity, not endogenous Pseudomonas-to-Geobacter chemical pressure in the studied cocultures: PHZ-1-CA was below detection in all cocultures. The tested PHZ-1-CA exposure did not select the coculture-associated tetR/fabI variants at the reported frequency threshold, and those variants also arose with phenazine-deficient Pseudomonas. Other antibiotics or non-antibiotic functions remain possible. No selection or dominance arrow is assigned to this measured added-compound response; a negative result for this compound and test does not exclude every phenazine derivative or exposure condition.
Source Taxon: Geobacter sulfurreducens
Metabolites: phenazine-1-carboxylic acid (CHEBI:62412 · MediaIngredientMech · CMMMech)
Evidence
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PMID:32265334 - SUPPORT (IN_VITRO)"Pseudomonas-derived phenazine-1-carboxylic acid (PHZ-1-CA) for its potential to inhibit Geobacter growth"
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PMID:32265334 - SUPPORT (IN_VITRO)"Despite its inhibitory properties, PHZ-1-CA did not drive variant selection"
Knowledge gaps & discussions (2)
KNOWLEDGE_GAP OPEN Which electron-transfer routes support early and adapted cocultures?
Preserve the reported omcZ/omcS growth defect and phz-mutant growth while distinguishing the authors' DIET interpretation from selective route proof. Primary full 2018 perturbation controls, flux measurements, complementation and route-specific tests would resolve cytochrome pleiotropy and the inferred later HybA/FdnG roles. Pseudomonas supplies electrons to Geobacter in the described model. Later hydrogen-transfer and formate-use hypotheses are bounded in the existing adaptation node; no unsupported new transfer arrow or experimentally resolved route switch is added.
Attaches to: ecological_interactions#Restricted-Medium Cooperative Growth, ecological_interactions#Cytochrome-Associated Interspecies Electron Transfer, ecological_interactions#Geobacter-Dominated Coculture Adaptation
KNOWLEDGE_GAP OPEN What causes increased Geobacter dominance during coculture adaptation?
Abundance, sequence variants and protein changes do not selectively establish competition, killing, or a variant-to-dominance mechanism. PHZ-1-CA inhibition used added commercial material; coculture concentrations were below detection and this exposure did not select the observed variants. Test endogenous concentrations, alternative mediators, matched media and complemented variants while measuring both partners' viable growth. Do not infer complete Geobacter independence from dominance: isolation attempts failed. Results/Table 2 and main Methods differ on the MIC duration units; no precise duration is asserted here. The initial-growth-to-later-dominance arrow is removed as serial-transfer chronology, not restored as biological causation.
Attaches to: ecological_interactions#Geobacter-Dominated Coculture Adaptation, ecological_interactions#Inhibitory Response to Added Phenazine-1-Carboxylic Acid
External Resources
| Name | Repository | Resource ID |
|---|---|---|
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Exact-system proteomics publication - Geobacter/Pseudomonas electroactive coculture
Primary SWATH-MS proteomics study establishing and evolving Geobacter sulfurreducens and Pseudomonas aeruginosa syntrophic cocultures. |
OTHER | PMID:28992596 |
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Exact-system adaptive-evolution publication - Geobacter/Pseudomonas coculture
Open-access adaptive-evolution study of G. sulfurreducens with P. aeruginosa. |
OTHER | PMID:32265334 |
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Environmental Factors
| Factor | Value | Unit |
|---|---|---|
| Restricted formate-fumarate medium | formate and fumarate | N/A |
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| Serial-transfer adaptation | adaptive evolution | N/A |
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Growth Media
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