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 |
|---|---|---|---|
| Geobacter sulfurreducens | NCBITaxon:35554 |
SYNTROPHIC_PARTNER
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N/A |
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| Clostridium pasteurianum | NCBITaxon:1501 |
PRIMARY_DEGRADER
SYNTROPHIC_PARTNER
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N/A |
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Ecological Interactions
Acetate Oxidation and Interspecies Electron Transfer
SYNTROPHYSource Taxon: Geobacter sulfurreducens
Metabolites: acetate (CHEBI:30089)
Biological Processes:
- acetate catabolic process (GO:0045733)
- electron transfer activity (GO:0009055)
Evidence
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PMID:28287150 - SUPPORT (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 - SUPPORT (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:28287150 - PARTIAL (IN_VITRO)"Direct interspecies electron transfer (DIET) mechanism has been recently characterised with Geobacter species which couple the electron balance with other species through physical contacts"
Glycerol Fermentation with Electron-Transfer-Induced Metabolic Shift
MUTUALISMSource Taxon: Clostridium pasteurianum
Metabolites: glycerol (CHEBI:17754), 1,3-propanediol (CHEBI:16109), butyrate (CHEBI:30772), butanol (CHEBI:28885), ethanol (CHEBI:16236)
Biological Processes:
- glycerol catabolic process (GO:0019563)
- fermentation (GO:0006113)
- electron transfer activity (GO:0009055)
Evidence
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PMID:28287150 - SUPPORT (IN_VITRO)"The present study deals with a co-culture of Geobacter sulfurreducens and Clostridium pasteurianum during glycerol fermentation"
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PMID:28287150 - SUPPORT (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:28287150 - PARTIAL (IN_VITRO)"Direct interspecies electron transfer (DIET) mechanism has been recently characterised with Geobacter species which couple the electron balance with other species through physical contacts"
Knowledge gaps & discussions (1)
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?
RE-SCOPED (was: this record asserted contact-dependent DIET as established). Caching the open-access full text of the discovery study (PMID:28287150, PMC5347079) showed the contact/nanowire mechanism was never supported by it. "Pili" and "nanowires" appear there only as general background about Geobacter species, and its own discussion states the opposite of what this record claimed: pre-cultures were "constituted of both nanowire-rich aggregates and nanowire-poor planktonic cells", and growing G. sulfurreducens on conductive material is offered as a future option "to ensure electrical connections" - i.e. electrical connection was NOT established in these experiments. Several evidence items had also cited that generic background sentence, or the unrelated "sole electron acceptor" sentence, as if they demonstrated contact-mediated transfer between these two organisms. Accordingly: `community_category` moved DIET -> SYNTROPHY (the schema defines DIET specifically as "Direct interspecies electron transfer", a mechanism claim no source supports here); pili/nanowire assertions were removed from the description, environment notes, taxon notes, and the interaction; the interactions were renamed to mechanism-neutral forms; and the "Cell Contact and Nanowire Formation" environmental factor became "Electrical Connection Between Cells", recording that connection was not established. The competing mechanism is NOT asserted in its place. The follow-up (PMID:34939136) concludes the interaction "is mediated" and proposes a diffusible cobamide acting on glycerol dehydratase, with a transmembrane flavin-bound polyferredoxin / cytochrome b5-rubredoxin electron-entry route offered only as putative reinforcement - and that paper calls its own model "putative". It is not open access, so only its abstract is snippet-verifiable here; its reported 0.22-um-filtered cell-free spent-medium result, which would show Geobacter cells are unnecessary for the shift, remains unverified against full text. STILL OPEN: which route actually carries the electrons, and whether the record's `name` and filename (both still say "DIET") should be changed - those affect external references and were left to a curator.
Attaches to: ecological_interactions#Acetate Oxidation and Interspecies Electron Transfer, ecological_interactions#Glycerol Fermentation with Electron-Transfer-Induced Metabolic 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
Key-point conclusion that the interaction is mediated (via a diffusible molecule), contradicting the contact-dependent nanowire mechanism asserted by this record.
a putative interaction model was proposed: G. sulfurreducens produces cobamide molecules that possibly modify C. pasteurianum metabolic pathway at the key enzyme glycerol dehydratase
States the competing diffusible-cobamide mechanism, and marks it as putative - so it must not be asserted as an interaction in place of the current one.
Environmental Factors
| Factor | Value | Unit |
|---|---|---|
| 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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