An enrichment consortium in which microbial chromate reduction is coupled to anaerobic oxidation of inorganic electron donors. A 60-day cultivation study showed that sludge enrichments supplied with elemental sulfur, S(0), or zerovalent iron, Fe(0), as sole electron donors biologically reduced Cr(VI), deposited Cr(III) as the main reduction product, and achieved high chromate removal in both independent donor systems. High-throughput 16S rRNA sequencing linked this transformation to a consortium-level division of labor in which S(0)- or Fe(0)-oxidizing bacteria such as Thiobacillus or Ferrovibrio generated volatile fatty acids that chromate-reducing bacteria such as Geobacter or Desulfovibrio could further use to reduce chromate.
Taxonomy
| Taxon | Ontology ID | Functional Roles | Abundance |
|---|---|---|---|
| Thiobacillus | NCBITaxon:919 · TaxonMech · TraitMech |
PRIMARY_DEGRADER
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N/A |
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| Geobacter | NCBITaxon:28231 · TaxonMech · TraitMech |
PRIMARY_DEGRADER
CROSS_FEEDER
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N/A |
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| Desulfovibrio | NCBITaxon:872 · TaxonMech · TraitMech |
PRIMARY_DEGRADER
CROSS_FEEDER
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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.
Inorganic-Donor Oxidation to Volatile Fatty Acids
CROSS_FEEDINGHYPOTHESIZED - in separate S(0)-fed and Fe(0)-fed sludge enrichments, the authors propose that inorganic-donor oxidizers generate volatile fatty acids usable by chromate reducers. Thiobacillus and Ferrovibrio are example oxidizers in the primary abstract, not proof of one defined community shared by both systems. The accessible abstract and supplement do not establish exact VFA molecules or taxon-resolved production and transfer.
Participating Taxa: Thiobacillus
Metabolites: elemental sulfur (CHEBI:33403 · MediaIngredientMech · CMMMech)
HYPOTHESIZED - VFA production by donor-oxidizing members could provide organic electron donors to chromate reducers. This author-proposed substrate link is not direct tracing between the named genera, and exact molecules and system-specific producers/consumers remain unresolved in the accessible evidence.
Evidence
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doi:10.1021/acs.est.8b05053 - PARTIAL (IN_VITRO)"S(0)- or Fe(0)-oxidizing bacteria (e.g., Thiobacillus or Ferrovibrio) could generate volatile fatty acids as metabolites "
VFA-Fed Chromate Reduction
CROSS_FEEDINGPARTIAL - separate S(0)-fed and Fe(0)-fed sludge systems removed Cr(VI), with deposited Cr(III) reported as the main reduction product. The authors propose VFA use by reducers such as Geobacter or Desulfovibrio from community-composition evidence. This does not demonstrate one three-member defined consortium, acetate transfer, or exclusive VFA mediation. Supplemental controls distinguish biotic and abiotic systems and show some early abiotic Fe-associated Cr(VI) loss.
Participating Taxa: Thiobacillus, Geobacter, Desulfovibrio
Metabolites: chromate (CHEBI:35404 · MediaIngredientMech · CMMMech)
Reduction of Cr(VI) yields Cr(III), reported by XPS as the main deposited product in these enrichments. This supported transformation/product relationship does not establish that the upstream VFA mechanism uniquely caused deposition or that all removal is biological under every operating condition.
Evidence
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doi:10.1021/acs.est.8b05053 - PARTIAL (IN_VITRO)"volatile fatty acids as metabolites, which were further utilized by chromate-reducing bacteria "
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doi:10.1021/acs.est.8b05053 - PARTIAL (IN_VITRO)"Cr(VI) reduction coupled to S(0) or Fe(0) oxidation was mediated synergically by a microbial consortia "
Cr(III) Deposition and Immobilization
The primary abstract identifies deposited Cr(III) as the main Cr(VI)-reduction product by X-ray photoelectron spectroscopy. This is a bulk product/retention observation, not cross-feeding, demonstrated cellular detoxification, free chromium(3+) speciation or tested long-term immobilization stability.
Metabolites: chromate (CHEBI:35404 · MediaIngredientMech · CMMMech)
Evidence
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doi:10.1021/acs.est.8b05053 - SUPPORT (IN_VITRO)"The deposited Cr(III) was identified as the main reduction product based on X-ray photoelectron spectroscopy "
Knowledge gaps & discussions (1)
KNOWLEDGE_GAP OPEN Which exact donor-derived metabolites and taxa mediate Cr(VI) reduction in each enrichment?
The main subscription body was unavailable. The primary abstract proposes class-level VFA exchange, while accessible SI supplies reactor controls, solid analyses and bulk pH/bicarbonate dynamics, not taxon-resolved carbon/electron tracing. Literature acetate-fed comparator rows in SI Table S2 are not measurements in this system. Exact membership, VFA identity, biological versus abiotic contributions over time and deposited-species stability require full-system evidence. Existing taxonomy and related-ingredient metadata need separate review.
Attaches to: ecological_interactions#Inorganic-Donor Oxidation to Volatile Fatty Acids, ecological_interactions#VFA-Fed Chromate Reduction, ecological_interactions#Cr(III) Deposition and Immobilization
External Resources
| Name | Repository | Resource ID |
|---|---|---|
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Primary publication - microbial chromate reduction coupled to S(0) or Fe(0) oxidation
Environmental Science & Technology paper reporting chromate reduction by microbial consortia coupled to anaerobic oxidation of elemental sulfur or zerovalent iron. |
OTHER | doi:10.1021/acs.est.8b05053 |
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Environmental Factors
| Factor | Value | Unit |
|---|---|---|
| Inorganic electron donor | Elemental sulfur or zerovalent iron | N/A |
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| Cultivation duration | 60 | days |
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| Chromate removal efficiency | 92.9 and 98.1 | percent |
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Cross-Mech Suite Links
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