A purified two-member anaerobic syntrophic coculture in which Syntrophorhabdus aromaticivorans strain UI(T) oxidizes phenol, p-cresol, 4-hydroxybenzoate, isophthalate, and benzoate in association with the hydrogenotrophic methanogen Methanospirillum hungatei DSM 864. The M. hungatei partner supplies the H2-scavenging methanogenic sink needed for strain UI(T) to mineralize aromatic substrates to acetate and methane, and blocking methanogenesis or raising hydrogen partial pressure halts phenol and 4-hydroxybenzoate degradation.
Taxonomy
| Taxon | Ontology ID | Functional Roles | Abundance |
|---|---|---|---|
| Syntrophorhabdus aromaticivorans strain UI(T) — ontology label: Syntrophorhabdus aromaticivorans | NCBITaxon:328301 · TaxonMech · TraitMech |
PRIMARY_DEGRADER
SYNTROPHIC_PARTNER
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N/A |
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| Methanospirillum hungatei | NCBITaxon:2203 · TaxonMech · TraitMech |
SYNTROPHIC_PARTNER
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.
Phenol Oxidation by Syntrophorhabdus
SYNTROPHYS. aromaticivorans UI(T) oxidized phenol in coculture with M. hungatei. Transient 4-hydroxybenzoate and benzoate were measured and subsequently consumed. PARTIAL - These intermediates support a proposed carboxylation/dehydroxylation route, but the paper explicitly leaves the actual enzymes and mechanism unresolved; they are not demonstrated interspecies carbon cargo.
Source Taxon: Syntrophorhabdus aromaticivorans strain UI(T)
Target Taxon: Methanospirillum hungatei
Metabolites: phenol (CHEBI:15882 · MediaIngredientMech · CMMMech), benzoic acid (CHEBI:30746 · MediaIngredientMech · CMMMech), 4-hydroxybenzoate (CHEBI:17879 · MediaIngredientMech · CMMMech)
Biological Processes:
- phenol-containing compound metabolic process (GO:0018958 · PathwayMech)
Phenol conversion by UI(T), coupled to partner electron disposal, supplies the measured coculture acetate/methane endpoint. Preserve this positive direction without asserting transfer of aromatic intermediates to the methanogen or complete substrate disappearance in the 100-day assay.
Evidence
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PMID:18281436 - SUPPORT (IN_VITRO)"During the degradation of phenol, a small amount of 4-hydroxybenzoate (a maximum of 4 microM) and benzoate (a maximum of 11 microM) were formed as transient intermediates."
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PMID:18281436 - SUPPORT (IN_VITRO)"This isolate is the first tangible, obligately anaerobic, syntrophic substrate-degrading organism capable of oxidizing phenol in association with an H(2)-scavenging methanogen partner"
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PMID:18281436 - PARTIAL (IN_VITRO)"The actual mechanisms employed by strain UIT cells for the metabolism of phenol remain unclear"
M. hungatei H2 Scavenging and Methanogenesis
SYNTROPHYM. hungatei supplied a methanogenic electron sink: 5 mM 2-BES blocked aromatic degradation, and elevated H2 stopped phenol and 4-hydroxybenzoate degradation. These perturbations support low-H2 syntrophy under the methanogenic conditions, not merely co-occurrence. Hydrogen was detected, while the authors did not exclude formate or other carriers. Dependence is conditional: AQDS enabled acetate production without methane in BES-treated culture; attempts at axenic isolation with AQDS failed.
Source Taxon: Methanospirillum hungatei
Target Taxon: Syntrophorhabdus aromaticivorans strain UI(T)
Metabolites: dihydrogen (CHEBI:18276 · MediaIngredientMech · CMMMech), methane (CHEBI:16183 · MediaIngredientMech · CMMMech), carbon dioxide (CHEBI:16526 · MediaIngredientMech · CMMMech)
Biological Processes:
- methane biosynthetic process (GO:0015948 · PathwayMech)
Methanogenic electron disposal maintains conditions allowing UI(T) phenol oxidation; BES inhibition and high-H2 inhibition support this direction. This applies to the methanogenic treatment, not an absolute requirement for this partner when an alternative acceptor such as AQDS is supplied.
The active methanogenic sink allows aromatic conversion to continue and supplies the methane component of the acetate/methane endpoint. AQDS-treated inhibited cultures produced acetate without methane, separating conversion from the methanogenic product.
Evidence
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PMID:18281436 - SUPPORT (IN_VITRO)"The addition of 5 mM 2-BES to a coculture with M. hungatei completely inhibited the degradation of isophthalate, phenol, and 4-hydroxybenzoate."
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PMID:18281436 - SUPPORT (IN_VITRO)"degradation of phenol and 4-hydroxybenzoate was completely stopped when the cultures were exposed to a gas phase containing a high partial pressure of hydrogen"
Community Aromatic Conversion to Acetate and Methane
SYNTROPHYThe defined UI(T)-M. hungatei coculture utilized phenol, p-cresol, isophthalate, 4-hydroxybenzoate and benzoate for growth and produced acetate and methane. Preserve these positive conversion and product measurements. Acetate remains an organic product, and Table 2 reports residual substrate at 100 days; this is not complete mineralization or universal complete removal. Absence of fermentative growth in the tested inhibited cultures does not negate the AQDS alternative-electron-acceptor result.
Participating Taxa: Syntrophorhabdus aromaticivorans strain UI(T), Methanospirillum hungatei
Metabolites: phenol (CHEBI:15882 · MediaIngredientMech · CMMMech), p-cresol (CHEBI:17847 · MediaIngredientMech · CMMMech), isophthalate (CHEBI:30803 · MediaIngredientMech · CMMMech), 4-hydroxybenzoate (CHEBI:17879 · MediaIngredientMech · CMMMech), benzoic acid (CHEBI:30746 · MediaIngredientMech · CMMMech), acetate (CHEBI:30089 · MediaIngredientMech · CMMMech), methane (CHEBI:16183 · MediaIngredientMech · CMMMech)
Biological Processes:
- phenol-containing compound metabolic process (GO:0018958 · PathwayMech)
- benzoate metabolic process (GO:0018874 · PathwayMech)
- methane biosynthetic process (GO:0015948 · PathwayMech)
Evidence
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PMID:18281436 - SUPPORT (IN_VITRO)"In syntrophic coculture with M. hungatei , strain UIT could utilize isophthalate, benzoate, phenol, p -cresol, and 4-hydroxybenzoate for growth and produce acetate and methane as end products."
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PMID:18281436 - SUPPORT (IN_VITRO)"No substrates that support the fermentative growth of strain UIT in pure culture (in the presence of 2-BES) were found"
Knowledge gaps & discussions (1)
KNOWLEDGE_GAP OPEN Which enzymes and electron carriers implement the observed syntrophic phenol conversion?
Preserve all three existing positive causal arrows and the BES/high-H2 perturbations. Intermediates suggest a route but do not identify its enzymes; the authors allow hydrogen and/or formate transfer. AQDS replaces the methanogenic electron sink under the tested inhibited condition, without establishing a pure isolate. Acetate/methane conversion is not complete carbon mineralization. The alternative Desulfovibrio culture is a separate experimental condition, not a third member of this canonical pair; no new topology is required for these repairs.
Attaches to: ecological_interactions#Phenol Oxidation by Syntrophorhabdus, ecological_interactions#M. hungatei H2 Scavenging and Methanogenesis, ecological_interactions#Community Aromatic Conversion to Acetate and Methane
2 evidence item(s)
The actual mechanisms employed by strain UIT cells for the metabolism of phenol remain unclear
Primary Discussion distinguishes intermediate measurements from the unresolved enzymatic route.
The addition of 5 mM 2-BES to a coculture with M. hungatei completely inhibited the degradation of isophthalate, phenol, and 4-hydroxybenzoate.
Blocking methanogenesis stopped aromatic-substrate degradation in the M. hungatei coculture.
Environmental Factors
| Factor | Value | Unit |
|---|---|---|
| Strict anaerobic cultivation | 50-ml serum vials; 20 ml medium; 37 C; no shaking | N/A |
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| Methanogenesis and hydrogen partial pressure | obligate | N/A |
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| AQDS terminal electron acceptor | AQDS can replace the methanogen under 2-BES | N/A |
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