An engineered mixed microbial culture for ex-situ thermophilic biomethanation that was enriched from autoclaved anaerobic digested sewage sludge in a 0.4 L working-volume continuously stirred tank reactor. The proof-of-concept reactor was conditioned with intermittent washouts and reached sustained H2/CO2 4:1 throughput of 500 L/L/d at 50 C in the final phase, where Euryarchaeota, Firmicutes, and Coprothermobacterota dominated the 16S phylum profile and Methanobacteria, Methanosarcina, and Methanosaeta were tracked by qPCR as methane content rose to 86% by day 69.
Taxonomy
| Taxon | Ontology ID | Functional Roles | Abundance |
|---|---|---|---|
| Euryarchaeota — ontology label: Methanobacteriota | NCBITaxon:28890 · TaxonMech · TraitMech |
SYNTROPHIC_PARTNER
CROSS_FEEDER
|
DOMINANT |
|
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| Firmicutes — ontology label: Bacillota | NCBITaxon:1239 · TaxonMech · TraitMech |
SECONDARY_FERMENTER
SYNTROPHIC_PARTNER
|
ABUNDANT |
|
|||
| Coprothermobacterota | NCBITaxon:2138240 · TaxonMech · TraitMech |
SYNTROPHIC_PARTNER
CROSS_FEEDER
|
COMMON |
|
|||
| Methanobacteria | NCBITaxon:183925 · TaxonMech · TraitMech |
SYNTROPHIC_PARTNER
CROSS_FEEDER
|
COMMON |
|
|||
| Methanosarcina | NCBITaxon:2207 · TaxonMech · TraitMech |
SYNTROPHIC_PARTNER
CROSS_FEEDER
|
RARE |
|
|||
| Methanosaeta qPCR target (Methanothrix) — ontology label: Methanothrix | NCBITaxon:2222 · TaxonMech · TraitMech |
SYNTROPHIC_PARTNER
CROSS_FEEDER
|
COMMON |
|
|||
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.
Thermophilic H2/CO2 Biomethanation
A conditioned mixed culture converted externally supplied H2/CO2 to methane in a single proof-of-concept CSTR. Output methane content reached 86% by day 69 in the final thermophilic phase; exceeding 90% was proposed, not observed. Cylinder-fed gas conversion is not itself interspecies cross-feeding. Methanobacteria enrichment and contributions by Methanosarcina are source interpretations informed by group-specific qPCR and community profiles, not taxon-resolved flux measurements. The listed phylum, class and genus are overlapping taxonomic summaries rather than independent strain members. Sequential conditioning and washout changes do not independently isolate temperature as the cause of every performance difference.
Participating Taxa: Euryarchaeota, Methanobacteria, Methanosarcina
Metabolites: dihydrogen (CHEBI:18276 · MediaIngredientMech · CMMMech), carbon dioxide (CHEBI:16526 · MediaIngredientMech · CMMMech), methane (CHEBI:16183 · MediaIngredientMech · CMMMech)
Biological Processes:
- methanogenesis (GO:0015948 · PathwayMech)
Evidence
-
PMID:42293522 - SUPPORT (IN_VITRO)"H₂ and CO₂ gases were supplied from pressurised gas cylinders"
-
PMID:42293522 - SUPPORT (IN_VITRO)"CH₄ levels in the output gas steadily increased with each washout, reaching 86% by day 69"
-
PMID:42293522 - PARTIAL (OTHER)"favoured hydrogenotrophic Methanobacteria"
VFA dynamics and inferred interspecies turnover
The measured VFA pool fell from approximately 5 to 3.5 g/L during the final phase and ended with 73% acetate, 16% propionic acid and 10% n-butyric acid. These are pool measurements during washout-managed operation, not direct rates of metabolite exchange. PARTIAL: the authors interpret Firmicutes as VFA producers, Coprothermobacterota as acetate oxidizers and Methanosaeta/Methanothrix as acetoclastic methanogens, with Methanosarcina potentially using both substrates. Group abundance and gene copies do not demonstrate those exact taxa executing each route, metabolic activity per cell, or product-removal-dependent thermodynamic cooperation. Washout and substrate-pool changes remain alternatives to attributing every VFA decrease to consumption.
Participating Taxa: Firmicutes, Coprothermobacterota, Methanosarcina, Methanosaeta qPCR target (Methanothrix)
Metabolites: acetate (CHEBI:30089 · MediaIngredientMech · CMMMech), propionate (CHEBI:17272 · MediaIngredientMech · CMMMech), butyrate (CHEBI:17968 · MediaIngredientMech · CMMMech), dihydrogen (CHEBI:18276 · MediaIngredientMech · CMMMech), carbon dioxide (CHEBI:16526 · MediaIngredientMech · CMMMech), methane (CHEBI:16183 · MediaIngredientMech · CMMMech)
Biological Processes:
- methanogenesis (GO:0015948 · PathwayMech)
Evidence
-
PMID:42293522 - SUPPORT (IN_VITRO)"At this point, the VFAs comprised 73% acetate, 16% propionic acid, and 10% n-butyric acid"
-
PMID:42293522 - PARTIAL (OTHER)"Overall, in the final phase, the system exhibited a balanced microbial community"
-
PMID:42293522 - PARTIAL (OTHER)"Coprothermobacterota converting acetate"
-
PMID:42293522 - PARTIAL (OTHER)"Methanosaeta converting acetate"
-
PMID:42293522 - SUPPORT (IN_VITRO)"VFA concentrations were measured immediately before washout, capturing peak accumulation prior to dilution or biomass replacement"
Knowledge gaps & discussions (3)
KNOWLEDGE_GAP OPEN The final reactor community is resolved primarily at phylum level by 16S rRNA sequencing and by group-specific qPCR. Species- or MAG-level assignments for the dominant Euryarchaeota, Firmicutes, and Coprothermobacterota partners remain unresolved.
Genome-resolved metagenomics or isolates from the day-69 culture would determine which exact hydrogenotrophic, acetoclastic, and acetate-oxidizing taxa executed the inferred final-phase metabolism.
Attaches to: taxonomy
1 evidence item(s)
The microbial community structure was analysed at the phylum level
Confirms that the final amplicon composition was reported at phylum resolution.
HUMAN_MODEL_MISMATCH OPEN Long-term robustness under continuous, non-sterile industrial feeding is unvalidated because the proof-of-concept system used autoclaved digestate.
A non-sterile continuous-feeding trial would test whether the selected thermophilic consortium remains stable under industrially realistic operation rather than washout-managed autoclaved-sludge proof-of-concept conditions.
Attaches to: engineering_design, cultivation_setup
1 evidence item(s)
long-term stability under non-sterile conditions typical of industrial operation remains to be validated
Names the industrial robustness gap stated by the authors.
KNOWLEDGE_GAP OPEN Which taxon-specific VFA and methane routes were active beyond the bulk chemistry and DNA profiles?
The study follows one reactor through sequential temperature, gas and washout changes. Methane production is measured, but its organism-specific allocation and interspecies fluxes are inferred. Direct sludge qPCR/16S can include DNA from killed or inactive cells; bacterial plate recovery is a separate culturable fraction. The original taxonomy-resolution and industrial-stability discussions remain open. No new causal link between the two process nodes is introduced.
Attaches to: ecological_interactions#Thermophilic H2/CO2 Biomethanation, ecological_interactions#VFA dynamics and inferred interspecies turnover
1 evidence item(s)
These approaches reflect the total microbial DNA pool
External Resources
| Name | Repository | Resource ID |
|---|---|---|
|
Primary publication - thermophilic ex-situ biomethanation mixed culture
Open-access Frontiers in Microbiology study developing an autoclaved-sludge mixed microbial culture for high-throughput thermophilic ex-situ biomethanation. |
OTHER | PMID:42293522 |
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Environmental Factors
| Factor | Value | Unit |
|---|---|---|
| Thermophilic operating temperature | 50 | C |
|
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| H2/CO2 gas throughput | 500 | L/L/d |
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| Intermittent phase-4 washout | 25 | percent culture volume every 24 h |
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| Day-69 VFA concentration | 3.5 | g/L |
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Growth Media
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