A laboratory bioreactor microbial community derived from consortia used to treat thiocyanate-contaminated water, perturbed by systematically increased SCN- input loading and the presence or absence of molasses as organic carbon. Five experiments over 790 days with genome-resolved metagenomics showed that a single Thiobacillus strain proliferated in all reactors at high SCN- loading, while a single Afipia variant dominated the molasses- free reactor at moderate loadings. The Afipia variant is predicted to degrade SCN- via a novel thiocyanate desulfurase, oxidize the resulting reduced sulfur, degrade the cyanate product to ammonia and CO2 via cyanate hydratase, and fix CO2 via the Calvin-Benson-Bassham cycle. Removal of molasses reproducibly selects for this autotrophic strain, although molasses-free reactors did not sustain high-loading SCN- degradation, possibly due to loss of biofilm-associated niche diversity.
Taxonomy
| Taxon | Ontology ID | Functional Roles | Abundance |
|---|---|---|---|
| Thiobacillus thiocyanate-degrader strain — ontology label: Thiobacillus | NCBITaxon:919 · TaxonMech · TraitMech |
PRIMARY_DEGRADER
PRIMARY_PRODUCER
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DOMINANT |
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| Afipia thiocyanate-degrader variant — ontology label: Afipia | NCBITaxon:1033 · TaxonMech · TraitMech |
PRIMARY_DEGRADER
PRIMARY_PRODUCER
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DOMINANT |
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| Rhizobiales background strains — ontology label: Hyphomicrobiales | NCBITaxon:356 · TaxonMech · TraitMech |
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.
Predicted Afipia Thiocyanate Metabolism and CO2 Fixation
PARTIAL: the Afipia_64_1782 genome and protein structural models predict thiocyanate desulfurase, cyanate hydratase, sulfur oxidation and Calvin-Benson-Bassham CO2 fixation. Reactor chemistry demonstrates community-level SCN degradation, not measured flux through this exact strain or biochemical validation of its novel enzyme. These are predicted intrinsic capacities, not cross-feeding from Afipia to another canonical member.
Participating Taxa: Afipia thiocyanate-degrader variant
Metabolites: thiocyanate (CHEBI:18022 · MediaIngredientMech · CMMMech), cyanate (CHEBI:29195 · MediaIngredientMech · CMMMech), ammonia (CHEBI:16134 · MediaIngredientMech · CMMMech), carbon dioxide (CHEBI:16526 · MediaIngredientMech · CMMMech)
Biological Processes:
- carbon fixation (GO:0015977 · PathwayMech)
Evidence
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PMID:33897653 - PARTIAL (COMPUTATIONAL)"predicted to break down SCN- using a novel thiocyanate desulfurase, oxidize resulting reduced sulfur, degrade product cyanate to ammonia and CO2 via cyanate hydratase, and fix CO2 via the Calvin-Benson-Bassham cycle"
Molasses Removal Selects for Afipia
Molasses withdrawal reproducibly favored Afipia_64_1782 at the studied moderate loadings within a complex community. R2 and R3 were held at 250 mg/L SCN, with R3 switched to no molasses; other reactors continued ramping. Community history and loading also affected composition. The canonical taxa list is a recorded subset, not a defined three-member consortium or proof that each background strain competes pairwise with Afipia.
Participating Taxa: Thiobacillus thiocyanate-degrader strain, Afipia thiocyanate-degrader variant, Rhizobiales background strains
PARTIAL: selection increases the representation of Afipia carrying the predicted SCN-degradation and carbon-fixation machinery. This links composition to enriched functional potential, not induction of the pathway or demonstration of strain-specific SCN flux.
Evidence
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PMID:33897653 - SUPPORT (IN_VITRO)"Removal of molasses from input feed solutions reproducibly led to dominance of this strain"
Unstable High-Loading SCN Degradation Without Molasses
SCN degradation became incomplete or erratic as high SCN inputs were imposed on molasses-free reactors R4 and R5, whereas R3 stably degraded the fixed 250 mg/L input after molasses withdrawal. HYPOTHESIZED: reduced biofilm-associated niche diversity contributes to instability, alongside altered nitrogen processing, ammonia accumulation and cofactor provision. Thin biofilms were observed, but selective loss of niche diversity was not established as the mediator, nor was the outcome shown to be caused by Afipia dominance. Canonical participants are a subset of the assayed microbiome, not identical functional roles.
Participating Taxa: Thiobacillus thiocyanate-degrader strain, Afipia thiocyanate-degrader variant, Rhizobiales background strains
Biological Processes:
- biofilm formation (GO:0042710 · PathwayMech)
Evidence
-
PMID:33897653 - PARTIAL (IN_VITRO)"reactors without molasses did not stably degrade SCN- at high loading rates, perhaps due to loss of biofilm-associated niche diversity"
Knowledge gaps & discussions (1)
KNOWLEDGE_GAP OPEN What mediates high-loading instability after molasses removal?
Composition shifts, biofilm changes and performance can share an environmental cause. Neither Afipia pathway induction nor selective niche-diversity mediation was measured. Strain assays and matched biofilm/cofactor/nitrogen perturbations would distinguish them. Preserve the correct startup/HRT history while repairing the separate loading metadata under issue #1897.
Attaches to: ecological_interactions#Predicted Afipia Thiocyanate Metabolism and CO2 Fixation, ecological_interactions#Molasses Removal Selects for Afipia, ecological_interactions#Unstable High-Loading SCN Degradation Without Molasses
1 evidence item(s)
reactors without molasses did not stably degrade SCN- at high loading rates, perhaps due to loss of biofilm-associated niche diversity
High-loading instability was observed; the snippet explicitly labels the niche-diversity explanation as tentative.
External Resources
| Name | Repository | Resource ID |
|---|---|---|
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Primary publication for the Afipia/Thiobacillus thiocyanate community
PubMed record for the Huddy et al. 2021 Frontiers in Microbiology paper. |
OTHER | PMID:33897653 |
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DOI landing page
DOI link to the Frontiers in Microbiology paper. |
OTHER | doi:10.3389/fmicb.2021.643368 |
Environmental Factors
| Factor | Value | Unit |
|---|---|---|
| Thiocyanate loading | systematically increased SCN- input concentration | N/A |
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| Molasses amendment | molasses-amended vs molasses-free | N/A |
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Cross-Mech Suite Links
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