A two-member consortium consisting of Geobacter sulfurreducens and Clostridium pasteurianum in which interspecies electron transfer modulates glycerol fermentation. G. sulfurreducens acts as an exoelectrogen and grows using C. pasteurianum as its sole electron acceptor; the resulting electron uptake induces a metabolic shift in C. pasteurianum's glycerol fermentation pathway, redirecting carbon flux away from ethanol and butanol production toward increased 1,3-propanediol (PDO) and butyrate production (+37% and +38% respectively). The shift is driven by a strikingly small electron uptake - under 0.6% of the electrons consumed by C. pasteurianum - and the relationship between G. sulfurreducens growth and the metabolite shift is non-linear. MECHANISM CONTESTED - do not read this record as establishing contact-dependent DIET. The discovery study (PMID:28287150) did not demonstrate physical contact, conductive pili, or nanowires in this coculture; its own discussion reports heterogeneous nanowire-rich and nanowire-poor cells and proposes growth on conductive materials as a future way to "ensure electrical connections", i.e. connection was not established. The same group's mechanistic follow-up (PMID:34939136) concluded the interaction is MEDIATED, proposing a diffusible cobamide acting on glycerol dehydratase, with a transmembrane flavin-bound polyferredoxin / cytochrome b5-rubredoxin electron-entry route offered only as a putative reinforcement. Both mechanisms remain putative; see discussion kg-geobacter-clostridium-contact-dependence-contested.
Taxonomy
| Taxon | Ontology ID | Functional Roles | Abundance |
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| Geobacter sulfurreducens | NCBITaxon:35554 · TaxonMech · TraitMech |
SYNTROPHIC_PARTNER
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N/A |
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| Clostridium pasteurianum | NCBITaxon:1501 · TaxonMech · TraitMech |
PRIMARY_DEGRADER
SYNTROPHIC_PARTNER
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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.
Proposed Acetate Oxidation and Interspecies Electron Transfer
HYPOTHESIZED: Geobacter sulfurreducens growth in responsive cocultures, but not in the corresponding monoculture without a known electron acceptor, supports the authors' proposed transfer of acetate-derived electrons to Clostridium pasteurianum. qPCR estimates cell growth; it does not directly measure electron uptake or current. The less-than-0.6% electron estimate assumes acetate as the Geobacter donor, 10% electron allocation to biomass and transfer of the remaining 90%; it is an inferred balance, not a measured flux. Significant Geobacter growth occurred in only two of four initial and eight of twelve subsequent cocultures. Contact-dependent transfer was not established. Nanowire-rich versus planktonic inoculum heterogeneity was a proposed explanation of variability, not a measured wiring result. The follow-up abstract calls the original IET interpretation an assumption and proposes a putative cobamide mechanism; neither that mechanism nor a specific electron-entry route is demonstrated here.
Participating Taxa: Geobacter sulfurreducens, Clostridium pasteurianum
Metabolites: acetate (CHEBI:30089 · MediaIngredientMech · CMMMech)
Biological Processes:
- acetate catabolic process (GO:0045733 · PathwayMech)
HYPOTHESIZED: Acetate-derived electron transfer could alter Clostridium redox regulation and thereby its glycerol-fermentation product profile. Growth/product associations and an assumed electron balance motivate this direction, but do not selectively establish electron uptake as the mediator. The follow-up proposes cobamides and possible electron entry as alternatives or contributors, not verified replacements.
Evidence
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PMID:28287150 - PARTIAL (IN_VITRO)"it was shown that Geobacter sulfurreducens was able to grow using Clostridium pasteurianum as sole electron acceptor"
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PMID:28287150 - PARTIAL (IN_VITRO)"This metabolic shift was clearly induced by a small electron uptake that represented less than 0.6% of the electrons consumed by C. pasteurianum"
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PMID:34939136 - PARTIAL (IN_VITRO)"It was assumed that this metabolic shift of the fermentative species resulted from an interspecies electron transfer"
Coculture-Associated Glycerol Fermentation Product Shift
At 72 h, the two responsive cultures among four initial cocultures had higher 1,3-propanediol and butyrate yields than Clostridium pasteurianum monocultures: 241 +/- 8 versus 176 +/- 13 and 105 +/- 6 versus 76 +/- 7 mmol/mol glycerol, respectively. Butanol and ethanol yields were lower: 188 +/- 9 versus 225 +/- 5 and 43 +/- 4 versus 54 +/- 2 mmol/mol glycerol. These correspond to +37%, +38%, -16% and -20%; they are not averages over all four initial cocultures or universal coculture responses. Significant Geobacter growth occurred in eight of twelve later cultures, and the reported growth/product regressions use those responders. Clostridium growth was reduced, so useful product yields do not establish mutual benefit. The measured conditional product shift is retained independently of its unresolved electron-transfer or cobamide mediator.
Participating Taxa: Geobacter sulfurreducens, Clostridium pasteurianum
Metabolites: glycerol (CHEBI:17754 · MediaIngredientMech · CMMMech), 1,3-propanediol (CHEBI:16109 · MediaIngredientMech · CMMMech), butyrate (CHEBI:30772 · MediaIngredientMech · CMMMech), butanol (CHEBI:28885 · MediaIngredientMech · CMMMech), ethanol (CHEBI:16236 · MediaIngredientMech · CMMMech)
Biological Processes:
- glycerol catabolic process (GO:0019563 · PathwayMech)
- fermentation (GO:0006113 · PathwayMech)
Evidence
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PMID:28287150 - SUPPORT (IN_VITRO)"pasteurianum metabolic pattern was significantly altered towards improved 1,3-propanediol and butyrate production (+37% and +38% resp.) at the expense of butanol and ethanol production (-16% and -20% resp.)"
Knowledge gaps & discussions (2)
CONTROVERSY OPEN Is the G. sulfurreducens-induced metabolic shift in C. pasteurianum actually caused by contact-dependent direct interspecies electron transfer along conductive pili, or by a diffusible mediator (candidate: a cobamide) released by G. sulfurreducens?
The prior contact-dependent DIET assertion was withdrawn in #256/#262; #295 corrected a remaining generic-background citation. This review also qualifies the broader IET interpretation: qPCR growth and an assumed electron balance do not directly measure uptake or selectively prove its mediation of the product shift. The 2017 Discussion proposes, rather than measures, nanowire-rich/planktonic inoculum heterogeneity and suggests conductive biofilms as future work. The record name and filename already use interspecies electron transfer rather than DIET, so the former pending-rename note is obsolete. The 2022 abstract describes mediated interaction and a putative cobamide model, with possible electron entry as reinforcement. Its full body remains inaccessible subscription content; the previously reported 0.22-um-filtered spent-medium result was not verified here and is not evidence for these graph decisions. Neither contact-dependent wiring, cobamide transfer nor a particular entry protein is asserted as established. Non-graph environmental, ingredient and overview text is preserved by this graph-scoped repair and is not scientifically certified by it.
Attaches to: ecological_interactions#Proposed Acetate Oxidation and Interspecies Electron Transfer, ecological_interactions#Coculture-Associated Glycerol Fermentation Product Shift
3 evidence item(s)
It was assumed that this metabolic shift of the fermentative species resulted from an interspecies electron transfer
The follow-up study characterizes the interspecies-electron-transfer reading of the original experiment as an assumption, not a demonstrated mechanism.
C. pasteurianum-G. sulfurreducens interaction inducing a metabolic shift is mediated
The abstract calls the interaction mediated, but the full experimental details were unavailable. This does not identify or verify the specific mediator, and is not treated as a selective contact-removal assay.
a putative interaction model was proposed: G. sulfurreducens produces cobamide molecules that possibly modify C. pasteurianum metabolic pathway at the key enzyme glycerol dehydratase
Supports a putative cobamide model stated in the abstract, not demonstrated cobamide transfer or a new verified interaction.
KNOWLEDGE_GAP OPEN Which mediator causes the conditional glycerol product shift?
Quantify all cultures rather than only responders, directly trace transferred electrons or metabolites, and selectively perturb the proposed mediator while measuring both organisms' growth. The measured product shift does not establish mutualism: Clostridium biomass decreased. Merge the duplicate product-output node into the measured fermentation response and remove its restatement arrow; retain only the explicitly HYPOTHESIZED upstream model arrow. The full 2022 study, including its reported cell-free assay, needs primary verification. No new causal node or arrow is added.
Attaches to: ecological_interactions#Proposed Acetate Oxidation and Interspecies Electron Transfer, ecological_interactions#Coculture-Associated Glycerol Fermentation Product Shift
Environmental Factors
| Factor | Value | Unit |
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| Anaerobic Conditions | Strict anaerobic | N/A |
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| Temperature | 35°C | N/A |
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| Electrical Connection Between Cells | Not established in the cited experiments | N/A |
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| Electron Transfer Monitoring | qPCR of 16S rRNA genes | N/A |
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Growth Media
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