A defined anaerobic synthetic coculture that combines the acetogenic syngas fermenter Clostridium ljungdahlii with the chain-elongating bacterium Clostridium kluyveri in a continuously fed syngas bioprocess with in-line product extraction. C. ljungdahlii converts syngas into ethanol and acetate, while C. kluyveri uses ethanol for reverse-beta-oxidation chain elongation to butyrate and caproate. The same community also produced longer-chain alcohols including butanol, hexanol, and traces of octanol within a narrow pH range. The system is relevant to DOE carbon utilization and renewable fuels because it converts C1 gases into C4-C8 fuels and chemicals through microbial cross-feeding.
Taxonomy
| Taxon | Ontology ID | Functional Roles | Abundance |
|---|---|---|---|
| Clostridium ljungdahlii | NCBITaxon:1538 · TaxonMech · TraitMech |
PRIMARY_PRODUCER
CROSS_FEEDER
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ABUNDANT |
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| Clostridium kluyveri | NCBITaxon:1534 · TaxonMech · TraitMech |
CROSS_FEEDER
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ABUNDANT |
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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.
Syngas Fermentation to Ethanol and Acetate
CROSS_FEEDINGC. ljungdahlii converts syngas to ethanol and acetate that support C. kluyveri chain elongation in the tested continuous reactor. The gases are feed substrates and the C2 compounds are the proposed exchanged products. Product balances support this division of labor; the estimate that roughly two-thirds of ethanol production supported chain elongation is calculated from stoichiometry rather than directly traced partner flux.
Source Taxon: Clostridium ljungdahlii
Target Taxon: Clostridium kluyveri
Metabolites: carbon monoxide (CHEBI:17245 · MediaIngredientMech · CMMMech), carbon dioxide (CHEBI:16526 · MediaIngredientMech · CMMMech), hydrogen (CHEBI:18276 · MediaIngredientMech · CMMMech), acetate (CHEBI:30089 · MediaIngredientMech · CMMMech), ethanol (CHEBI:16236 · MediaIngredientMech · CMMMech)
Biological Processes:
- fermentation (GO:0006113 · PathwayMech)
C. ljungdahlii syngas fermentation produces ethanol and acetate that C. kluyveri uses for reverse beta-oxidation chain elongation.
Evidence
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PMID:27877166 - SUPPORT (IN_VITRO)"syngas-fermentation process with Clostridium ljungdahlii and Clostridium kluyveri"
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PMID:27877166 - SUPPORT (IN_VITRO)"These products were used as substrates by C. kluyveri to chain-elongate them into longer-chain carboxylates."
Ethanol-Driven Chain Elongation
CROSS_FEEDINGC. kluyveri uses ethanol and acetate supplied by C. ljungdahlii to form butyrate and hexanoate by chain elongation. PARTIAL - the C. kluyveri-to-C. ljungdahlii direction denotes proposed carboxylate supply for subsequent reduction, not ethanol transfer in that direction. Bulk products and stoichiometric calculations do not directly resolve all partner fluxes.
Source Taxon: Clostridium kluyveri
Target Taxon: Clostridium ljungdahlii
Metabolites: ethanol (CHEBI:16236 · MediaIngredientMech · CMMMech), acetate (CHEBI:30089 · MediaIngredientMech · CMMMech), butyrate (CHEBI:17968 · MediaIngredientMech · CMMMech), hexanoate (CHEBI:17120 · MediaIngredientMech · CMMMech)
Biological Processes:
- fermentation (GO:0006113 · PathwayMech)
PARTIAL - chain elongation supplies the carboxylate precursors for the observed longer-chain alcohols. The primary study proposes that C. ljungdahlii reduces them, but does not selectively establish the reducing organism or quantify donor-resolved precursor flux.
Evidence
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PMID:27877166 - SUPPORT (IN_VITRO)"utilized by C. kluyveri to chain elongate"
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PMID:27877166 - SUPPORT (IN_VITRO)"resulting in n-butyrate and n-caproate"
Proposed Carboxylate Reduction and Observed Longer-Chain Alcohols
PARTIAL - the coculture produced butanol, hexanol and trace octanol. The proposed mechanism is reduction of chain-elongated carboxylates, most likely by C. ljungdahlii using syngas-derived reducing power. The reducing partner was not selectively resolved, and the paper does not exclude a C. kluyveri contribution. These are community products, not demonstrated alcohol donation from C. ljungdahlii to C. kluyveri. Named carboxylate pools coexist with pH-dependent undissociated acids relevant to the proposed reduction.
Participating Taxa: Clostridium ljungdahlii, Clostridium kluyveri
Metabolites: butyrate (CHEBI:17968 · MediaIngredientMech · CMMMech), hexanoate (CHEBI:17120 · MediaIngredientMech · CMMMech), butanol (CHEBI:28885 · MediaIngredientMech · CMMMech)
Biological Processes:
- fermentation (GO:0006113 · PathwayMech)
Evidence
-
PMID:27877166 - PARTIAL (IN_VITRO)"likely reduced the produced carboxylates to their corresponding alcohols"
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PMID:27877166 - SUPPORT (IN_VITRO)"longer-chain alcohols n-butanol, n-hexanol, and n-octanol"
pH-Dependent Process Performance
Longer-chain products were observed across the tested pH range of 5.7-6.4 in phases of one continuously operated reactor. The phase comparisons, altered medium flow and operational disturbances support condition-dependent process tradeoffs, not a universal optimum or independent replicated pH treatments. Competition between chain elongation and reduction for carboxylate intermediates is a process-allocation model, not measured reciprocal ecological harm to both organisms.
Participating Taxa: Clostridium ljungdahlii, Clostridium kluyveri
Metabolites: acetate (CHEBI:30089 · MediaIngredientMech · CMMMech), ethanol (CHEBI:16236 · MediaIngredientMech · CMMMech)
Biological Processes:
- fermentation (GO:0006113 · PathwayMech)
Evidence
-
PMID:27877166 - SUPPORT (IN_VITRO)"narrow pH spectrum of 5.7-6.4"
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PMID:27877166 - PARTIAL (IN_VITRO)"two bioprocesses compete for intermediates"
Knowledge gaps & discussions (1)
KNOWLEDGE_GAP OPEN Which partner reduces each carboxylate, and how do pH and operating conditions partition flux between elongation and reduction?
PMID:27877166 reports products and condition responses from one reactor. Intermediate production and ethanol utilization are reconstructed from stoichiometry; reducing-organism attribution and several pH mechanisms remain proposed. Partner-selective or isotope-resolved experiments and replicated matched-flow pH comparisons would separate these mechanisms. Do not equate competing process routes with reciprocal organismal fitness harm.
Attaches to: ecological_interactions#Syngas Fermentation to Ethanol and Acetate, ecological_interactions#Ethanol-Driven Chain Elongation, ecological_interactions#Proposed Carboxylate Reduction and Observed Longer-Chain Alcohols, ecological_interactions#pH-Dependent Process Performance
External Resources
| Name | Repository | Resource ID |
|---|---|---|
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Exact-system primary publication - continuous syngas alcohol coculture
Primary open-access study of continuous syngas conversion by C. ljungdahlii and C. kluyveri with in-line product extraction. |
OTHER | PMID:27877166 |
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DOI landing page - Frontiers in Microbiology article
DOI landing page for the primary exact-composition coculture article. |
OTHER | doi:10.3389/fmicb.2016.01773 |
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Environmental Factors
| Factor | Value | Unit |
|---|---|---|
| Syngas feed | 60% CO, 35% H2, and 5% CO2 | N/A |
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| pH window | pH 5.7-6.4 | N/A |
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| Product extraction | gas stripping and product condensing | N/A |
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