A microbial community stimulated for in situ bioremediation of uranium-contaminated groundwater at the Old Rifle site in Rifle, Colorado. This aquifer community demonstrates sequential reduction processes following acetate biostimulation at 1-3 mM concentrations. The community transitions through distinct metabolic phases: Phase I (days 0-50) dominated by Geobacter species (up to 89% of community) performing Fe(III) reduction coupled to U(VI) reduction, achieving 70% uranium removal within 50 days and reducing concentrations below the EPA treatment goal of 0.18 μM in some wells. Phase II (>50 days) shifts to sulfate-reducing bacteria including Desulfobacteraceae (45% by day 80), Desulfosporosinus, and Desulfotomaculum acetoxidans as Fe(III) becomes depleted. Geobacter metallireducens and Anaeromyxobacter dehalogenans reduce soluble U(VI) to insoluble U(IV), forming biogenic uraninite nanoparticles that immobilize uranium. Desulfovibrio species contribute to uranium reduction through enzymatic pathways while generating hydrogen sulfide that can chemically reduce uranium. This represents the first successful field demonstration of uranium bioremediation via stimulating subsurface Geobacter populations, providing an alternative to pump-and-treat remediation. Groundwater flow rate is 0.82 m/day, creating dynamic conditions where microbial metabolism must outpace uranium advection.
Taxonomy
| Taxon | Ontology ID | Functional Roles | Abundance |
|---|---|---|---|
| Geobacter species — ontology label: Geobacter metallireducens | NCBITaxon:28232 · TaxonMech · TraitMech |
PRIMARY_DEGRADER
SYNTROPHIC_PARTNER
|
DOMINANT |
|
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| Anaeromyxobacter dehalogenans | NCBITaxon:161493 · TaxonMech · TraitMech |
SYNTROPHIC_PARTNER
|
COMMON |
|
|||
| Desulfovibrio vulgaris — ontology label: Nitratidesulfovibrio vulgaris | NCBITaxon:881 · TaxonMech · TraitMech |
SECONDARY_FERMENTER
SYNTROPHIC_PARTNER
|
COMMON |
|
|||
| Desulfosporosinus species — ontology label: Desulfosporosinus | NCBITaxon:79206 · TaxonMech · TraitMech |
SECONDARY_FERMENTER
|
COMMON |
|
|||
| Desulfobacteraceae family — ontology label: Desulfobacterales | NCBITaxon:213118 · TaxonMech · TraitMech |
PRIMARY_DEGRADER
|
DOMINANT |
|
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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.
Geobacter Enrichment and Coincident Metal Reduction
During the initial Rifle field response to acetate amendment, Geobacter enrichment accompanied groundwater uranium loss and increasing Fe(II). This supports coincident community metal reduction, not a measured G. metallireducens-specific flux, a demonstrated cytochrome mechanism or cross-feeding between named members.
Metabolites: acetate (CHEBI:30089 · MediaIngredientMech · CMMMech), uranium(VI) (CHEBI:32992 · MediaIngredientMech · CMMMech), Fe(III) (CHEBI:29034 · MediaIngredientMech · CMMMech), Fe(II) (CHEBI:29033 · MediaIngredientMech · CMMMech)
Biological Processes:
- acetate catabolic process (GO:0045733 · PathwayMech)
PARTIAL: acetate-stimulated Geobacter-associated metal reduction is the proposed contributor to the observed initial groundwater uranium decline. Field covariation does not apportion species-specific flux or establish the mineral product and nanoparticle size.
Evidence
-
PMID:14532040 - SUPPORT (IN_VIVO)"the initial loss of uranium from the groundwater was associated with an enrichment of Geobacter species"
-
PMID:14532040 - PARTIAL (IN_VIVO)"suggesting that U(VI) reduction was coincident with Fe(III) reduction"
Initial Groundwater Uranium Removal
Groundwater U(VI) decreased during the initial acetate-amended field phase and fell below the prescribed treatment level in some monitoring wells. This is a measured removal outcome, not a direct characterization of 2-5 nm uraninite or a demonstrated Geobacter-Anaeromyxobacter mutualism. Later sulfate reduction coincided with increasing groundwater uranium, not sustained removal at the initial effectiveness.
Evidence
-
PMID:14532040 - SUPPORT (IN_VIVO)"within 50 days uranium had declined below the prescribed treatment level"
Later Sulfate Reduction and Sulfide Accumulation
The later field phase showed sulfate loss and sulfide accumulation as sulfate-reducer-related sequences became predominant. Groundwater uranium increased during this transition. These observations do not establish sulfide-mediated U(VI) reduction, a uraninite/uranium-sulfide product or pairwise nutrient exchange in this field system.
Metabolites: sulfate (CHEBI:16189 · MediaIngredientMech · CMMMech), hydrogen sulfide (CHEBI:16136 · MediaIngredientMech · CMMMech)
Biological Processes:
- sulfate reduction (GO:0019420 · PathwayMech)
Evidence
-
PMID:14532040 - SUPPORT (IN_VIVO)"there was a loss of sulfate from the groundwater and an accumulation of sulfide"
-
PMID:14532040 - SUPPORT (IN_VIVO)"associated with an increase in uranium concentration in the groundwater"
Community Succession from Metal to Sulfate Reduction
The groundwater community shifted from Geobacter enrichment toward sulfate-reducer-related sequences during continued amendment. HYPOTHESIZED: depletion of accessible Fe(III) near the amendment zone and local acetate consumption may have favored this transition. The primary discussion calls this explanation a hypothesis requiring verification; succession alone does not establish reciprocal harm, exact species replacement or the sediment-attached community composition.
Metabolites: Fe(III) (CHEBI:29034 · MediaIngredientMech · CMMMech), sulfate (CHEBI:16189 · MediaIngredientMech · CMMMech)
PARTIAL: the shift toward sulfate-reducer-related populations is proposed to accompany a change in the dominant acetate-oxidizing process, contributing to sulfate consumption and sulfide accumulation. The Fe(III)-depletion and donor-consumption explanation remains a field hypothesis, not independently established mediation or continued uranium immobilization.
Evidence
-
PMID:14532040 - SUPPORT (IN_VIVO)"Organisms with 16S rDNA sequences most closely related to those of sulfate reducers became predominant"
Knowledge gaps & discussions (1)
KNOWLEDGE_GAP OPEN Which organisms and mechanisms explain the two field phases?
Fresh primary abstracts and the cached Rifle main text were checked. PMID18843300 studies G. uraniireducens, while PMID19346346 and PMID18456853 concern Oak Ridge. High-salinity enrichment and D. hippei isolate evidence do not establish the removed Rifle mechanisms. The cached field discussion reports low-identity sulfate-reducer-related clones and a proposed Fe(III)/acetate explanation requiring verification. Field uranium loss does not measure nanoparticle identity or size. Unspecified COMMUNITY_LEVEL participants must not be interpreted as evidence for every canonical member; non-graph membership, family/species grounding, clone percentages and later-removal claims remain issue1770. No inference that these taxa or reactions can never occur is intended.
Attaches to: ecological_interactions#Geobacter Enrichment and Coincident Metal Reduction, ecological_interactions#Initial Groundwater Uranium Removal, ecological_interactions#Later Sulfate Reduction and Sulfide Accumulation, ecological_interactions#Community Succession from Metal to Sulfate Reduction
2 evidence item(s)
were inoculated with Geobacter uraniireducens
Identifies the organism of the transcriptome study formerly misassigned to Anaeromyxobacter.
site near Oak Ridge, TN
The Anaeromyxobacter field evidence is from another site.
Environmental Factors
| Factor | Value | Unit |
|---|---|---|
| pH | ~7 | pH units |
|
||
| Oxygen Availability | Anaerobic after acetate amendment | qualitative |
|
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| Acetate Concentration | 1-3 | mM |
|
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| Groundwater Flow Rate | 0.82 | m/day |
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| Initial Uranium Concentration | 0.4-1.4 | μM |
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| Time to Uranium Removal | 9-50 | days |
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Growth Media
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