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propionic acid fermentation

traitmech:000029 · CLASS · REVIEWED

A fermentation that produces propionate (with acetate and CO2) from sugars or lactate, typically via the Wood-Werkman (methylmalonyl-CoA) pathway. Characteristic of propionibacteria (e.g. Propionibacterium freudenreichii).

Trait evidence (2)

  • DOI:10.3390/molecules31020333

    Review of classical fermentations describes propionic acid fermentation (acetic acid, propionic acid, CO2) and propionibacteria as its agents, including the Wood-Werkman route.

  • DOI:10.3389/fmicb.2021.703525

    Review of fermentative energy conservation supports propionate formation as a redox-balancing, energy-conserving fermentation route.

Propionic acid fermentation produces propionate via the Wood-Werkman pathway

Evidence-backed causal sketch linking methylmalonyl-CoA-pathway catabolism of sugars or lactate to propionate, acetate, and CO2.

MECHANISTIC · Represents the Wood-Werkman reaction sequence and its biotin-dependent transcarboxylation step; the exemplar is explicitly one component of the three-subunit transcarboxylase, not the complete complex.

Propionic acid fermentation produces propionate via the Wood-Werkman pathway Interactive directed graph showing evidence-backed causal relationships for propionic acid fermentation.

Edge evidence

  • propionic acid fermentation participates in fermentation biolink:participates_in

    Propionic acid fermentation is a class of fermentation metabolism.

    • DOI:10.3389/fmicb.2021.703525 fermentation is defined as an anaerobic bacterial redox process of an organic substrate leading to different products Energy-conservation review supports propionate formation as a redox-balancing fermentation route.
  • propionic acid fermentation produces propionate METPO:2007800

    Propionate is the characteristic end product of the pathway.

    • DOI:10.3390/molecules31020333 substrates such as glucose, glycerol or lactic acid are converted into propionic acid Classical-fermentation review describes propionic acid fermentation via the Wood-Werkman pathway in propionibacteria.
  • propionic acid fermentation has major pathway Wood-Werkman cycle

    The Wood-Werkman methylmalonyl-CoA cycle is the predominant propionate-forming route.

    • DOI:10.3390/molecules31020333 In Propionibacterium spp., the predominant route is the Wood-Werkman pathway Wood-Werkman cycle described as the predominant propionate-forming route in Propionibacterium and Acidipropionibacterium.
  • pyruvate causally upstream of oxaloacetate

    Pyruvate is carboxylated to oxaloacetate in a biotin-dependent reaction.

    • DOI:10.3390/molecules31020333 pyruvate is converted to oxaloacetate in a biotin-dependent carboxyl transfer reaction Pyruvate is carboxylated to oxaloacetate by methylmalonyl-CoA carboxytransferase in a biotin-dependent reaction.
  • biotin cofactor for methylmalonyl-CoA carboxytransferase

    The transcarboxylation step is biotin-dependent.

    • DOI:10.3390/molecules31020333 biotin-dependent carboxyl transfer reaction catalyzed by methylmalonyl-CoA carboxytransferase The transcarboxylation converting pyruvate to oxaloacetate is explicitly described as biotin-dependent.
  • oxaloacetate causally upstream of malate

    Oxaloacetate is reduced to malate in the reductive branch.

    • DOI:10.3390/molecules31020333 Oxaloacetate is then reduced to malate Oxaloacetate is reduced to malate in the reductive branch leading toward succinate.
  • malate causally upstream of fumarate

    Malate is dehydrated to fumarate.

  • fumarate causally upstream of succinate

    Fumarate is reduced to succinate.

    • DOI:10.3390/molecules31020333 dehydrated to fumarate and reduced to succinate Fumarate is reduced to succinate en route to propionate formation.
  • succinyl-CoA causally upstream of methylmalonyl-CoA

    The pathway proceeds through succinyl-CoA and methylmalonyl-CoA intermediates.

    • DOI:10.3390/molecules31020333 Succinate is converted to succinyl-CoA by succinyl-CoA synthetase and rearranged via a vitamin B12-dependent methylmalonyl-CoA mutase to methylmalonyl-CoA The pathway proceeds through succinyl-CoA and methylmalonyl-CoA intermediates during propionate formation.
  • propionyl-CoA causally upstream of propionate

    Propionyl-CoA is converted to propionate by a CoA-transferase.

    • DOI:10.3390/molecules31020333 propionyl-CoA is converted to propionic acid with the release of CoA by a CoA-transferase Propionyl-CoA is finally converted to propionic acid or propionate by a CoA-transferase.
  • propionic acid fermentation has byproduct acetate

    The fermentation produces propionate with acetate as a co-product.

    • DOI:10.3390/molecules31020333 accompanied by acetic acid and CO2 formation The fermentation is defined as producing propionic acid with acetate as a co-product.
  • pyruvate contributes to Wood-Werkman cycle RO:0002326

    Pyruvate carboxylation initiates the Wood-Werkman cycle.

    • DOI:10.3390/molecules31020333 It starts from pyruvate, generated via glycolysis, which can follow two alternative routes: Carboxylation to oxaloacetate: this initiates the Wood–Werkman cycle and leads to propionic acid Verified against the public PMC full text.
  • succinate causally upstream of succinyl-CoA

    The propionate pathway converts succinate through succinyl-CoA.

    • DOI:10.1186/s12864-016-3367-x Succinate is then converted into succinyl-CoA, methyl malonyl CoA, propanoyl CoA and propionate by specific enzymes Verified against the open article full text.
  • methylmalonyl-CoA carboxytransferase catalyzes conversion of pyruvate

    Methylmalonyl-CoA carboxytransferase catalyzes the pyruvate-to-oxaloacetate entry reaction.

    • DOI:10.3390/molecules31020333 pyruvate is converted to oxaloacetate in a biotin-dependent carboxyl transfer reaction catalyzed by methylmalonyl-CoA carboxytransferase Verified against the public PMC full text.

Protein and taxon examples

Graph nodeProteinTaxonUniProt statusRole and evidence
methylmalonyl-CoA carboxytransferase UniProtKB:Q8GBW6
Methylmalonyl-CoA carboxyltransferase 12S subunit 		Propionibacterium freudenreichii subsp. shermanii
NCBITaxon:1752 		REVIEWED
retrieved 2026-08-23 · entry v97 · sequence v4

Forms the substrate-binding 12S component of the three-subunit transcarboxylase that couples methylmalonyl-CoA decarboxylation to pyruvate carboxylation.

  • DOI:10.1093/emboj/cdg244 TC 12S bound to its MMCoA substrate The primary structural study used the P. shermanii 12S component and resolved methylmalonyl-CoA binding; UniProtKB Q8GBW6 verifies the reviewed component identity and source taxon.

Provenance

Identifier source
TraitMech local identifier
Definition source
DOI:10.3390/molecules31020333

Parent traits (1)

Synonyms (1)

  • propionate fermentation RELATED_SYNONYM · DOI:10.3390/molecules31020333

kg-microbe context

Matched 1 kg-microbe node via parent_proxy.

  • METPO:1002005 [-0.758, -6.428, +3.551, +10.454, …]

512-dim DeepWalkSkipGramEnsmallen embedding from kg-microbe (2026-04-25).

Nearest neighbors in embedding space

Top-8 cosine-similar METPO traits from the 2026-04-25 deepwalk (512-D).

Deep research

Generated by just research-trait; source: research/traits/metabolism/propionic_acid_fermentation-deep-research-falcon.md

Unreviewed literature output — not curated TraitMech content Ontology identifiers suggested below have not been resolved against their ontologies, and some are known to be wrong. Check any CURIE against the source before using it. 
# Curation report: propionic acid fermentation

## Trait record and scope

- **Trait label:** propionic acid fermentation
- **Trait identifier:** `traitmech:000029`
- **Category / kind / status:** METABOLISM / CLASS / REVIEWED
- **Parent:** `METPO:1002005`
- **Synonym:** propionate fermentation

### Recommended scope

This trait should represent an organism’s experimentally demonstrable capacity for **net fermentative production of propionate from sugars or lactate**, canonically in dairy propionibacteria through the Wood–Werkman, or methylmalonyl-CoA, pathway. The classical overall lactate stoichiometry is:

**3 lactate → 2 propionate + acetate + CO₂ + H₂O.**

The pathway couples pyruvate reduction to oxidation elsewhere in metabolism, consumes glycolysis-derived NADH, conserves energy as ATP, and commonly produces acetate and CO₂ with propionate. Theoretical Wood–Werkman fermentation from glucose has been estimated at up to 0.7 g propionate/g glucose (1.71 mol/mol) with supplemented reducing equivalents; the commonly cited pathway-level product ratio is approximately 2:1 propionate:acetate and estimated energy yield is 4 ATP/glucose. These are model/theoretical values rather than universal assay thresholds. (bucher2021propionicacidbacteria pages 3-5, gonzalezgarcia2017microbialpropionicacid pages 8-10, gonzalezgarcia2017microbialpropionicacid pages 3-5)

The best-supported exemplar is *Propionibacterium freudenreichii*. Native propionibacteria are regarded as strong biological-production candidates because propionate is a major fermentation product and the Wood–Werkman route is energetically efficient, although slow growth, acid inhibition, coproduct formation, and downstream recovery remain barriers. (gonzalezgarcia2017microbialpropionicacid pages 1-3)

### Boundaries and nearby traits

1. **Propionate presence alone is insufficient.** Propionate may arise through the acrylate, succinate/sodium-pumping, or 1,2-propanediol pathways, through amino-acid catabolism, or through engineered aerobic biosynthesis. Those routes should not automatically instantiate this narrowly defined Wood–Werkman-centered trait. (gonzalezgarcia2017microbialpropionicacid pages 6-8, gonzalezgarcia2017microbialpropionicacid pages 1-3, gonzalezgarcia2017microbialpropionicacid pages 5-6)
2. **Net production must be distinguished from consumption.** Under oxygen exposure, *P. freudenreichii* can consume previously formed propionate and acetate. Thus detection of pathway enzymes does not prove net fermentation under every condition. (loivamaa2024aerobicadaptationand pages 6-9, dank2021propionibacteriumfreudenreichiithrives pages 3-4)
3. **Gut Bacteroidia are a boundary case.** They frequently use a succinate route and show species-specific bicarbonate dependence. Their phenotype may merit a broader “fermentative propionate production” parent or a separate mechanistic child rather than direct assignment to this canonical class. (doring2024propionateproductionby pages 1-2, doring2024propionateproductionby pages 4-5)
4. **Engineered aerobic propionate production is out of scope.** An engineered *Pseudomonas taiwanensis* strain accumulated 2.8 g/L propionate aerobically using introduced succinyl-CoA-catabolic genes and an acyl-CoA hydrolase. This is propionate biosynthesis, but not classical propionic acid fermentation. (neves2024expandingpseudomonastaiwanensis pages 1-2)
5. **Assay recommendation:** require substrate depletion plus net propionate accumulation under anoxic or explicitly fermentative conditions. Acetate and CO₂ strengthen identification but should not be mandatory because ratios vary with strain, medium, redox state, and cofactors. (bucher2021propionicacidbacteria pages 3-5, doring2024propionateproductionby pages 4-5)

## Candidate nodes

Ontology identifiers below are restricted to identifiers directly supported by the retrieved literature. Chemical and gene identifiers should remain **label-only until independently checked against current ChEBI, Rhea, KEGG, MetaCyc, UniProt, and NCBI Taxonomy releases**; this avoids inventing or misassigning CURIEs.

### Trait and pathway modules

| Candidate node | Type | Grounding recommendation |
|---|---|---|
| propionic acid fermentation | Trait class | `traitmech:000029` |
| metabolism parent | Trait class | `METPO:1002005` |
| Wood–Werkman cycle | Pathway/module | Label-only pending MetaCyc/KEGG verification |
| glycolysis | Pathway/module | Label-only pending pathway-database verification |
| fermentative redox balancing | Biological process | Label-only; pathway-level interpretation |
| ATP generation during fermentation | Biological process | Label-only; do not assign a reaction-level identifier without verification |

### Organisms and taxonomic exemplars

- *Propionibacterium freudenreichii*: canonical dairy propionibacterium and principal exemplar.
- *Acidipropionibacterium acidipropionici*: native producer used in current high-density bioprocess research.
- Other dairy propionibacteria, including *Acidipropionibacterium jensenii* and *A. thoenii*: plausible taxon-specific instances, not universal mechanistic proxies.
- *Bacteroides propionicifaciens* and *Bacteroides graminisolvens*: succinate-route boundary exemplars.
- *Clostridium propionicum*, *Megasphaera elsdenii*, and *Prevotella ruminicola*: acrylate-route boundary exemplars.
- *Veillonella*, *Propionigenium*, and *Selenomonas*: succinate/sodium-coupled route boundary taxa. (gonzalezgarcia2017microbialpropionicacid pages 6-8, gonzalezgarcia2017microbialpropionicacid pages 5-6)

### Chemicals and metabolic roles

**Inputs/electron donors:** glucose and other fermentable sugars; lactate; glycerol in process-specific cofermentations.

**Central intermediates:** pyruvate, oxaloacetate, malate, fumarate, succinate, succinyl-CoA, methylmalonyl-CoA, propionyl-CoA.

**Outputs:** propionate/propionic acid; acetate/acetic acid; carbon dioxide; water. Succinate and lactate may remain as strain- and process-dependent coproducts.

Showing the first 60 of 247 lines of findings; the linked file also carries the run's front matter and the prompt it was given — read the full report.

Canonical examples (2)

Organisms cited as exemplars of this trait. Taxon ids are NCBITaxon and link out to the NCBI record.

  • Propionibacterium freudenreichii NCBITaxon:1744 PMID:21620505 Canonical propionic-acid fermenter (Swiss-cheese eyes and flavour).
  • Propionibacterium freudenreichii subsp. shermanii NCBITaxon:1752 DOI:10.1093/emboj/cdg244 Source organism for structural and substrate-bound characterization of the methylmalonyl-CoA transcarboxylase 12S component.

Curation history

  1. · CURATE_PROTEIN_TAXON_EXAMPLE · codex

    Reviewed the graph as mechanistic and added DOI-backed, taxon-paired UniProtKB Q8GBW6 as the transcarboxylase 12S component exemplar.

  2. · PROPOSED_FROM_RESEARCH · claude

    Proposed candidate METABOLISM trait (propionic acid fermentation); product-specific sub-variant of the existing Fermentation class (METPO:1002005).

  3. · CURATED_CAUSAL_GRAPH · claude

    Added evidence-backed causal graph (propionic acid fermentation) with GO node grounding and METPO/biolink predicate groundings; promoted PROPOSED to REVIEWED.

  4. · GROUND_CAUSAL_NODES · claude

    Grounded 1 causal-node grounding field(s) via mappings/node_grounding.tsv (CHEBI:17272×1).

  5. · ENRICH_CAUSAL_GRAPH · claude

    Added 9 evidence-backed generic edges (12 new nodes) from the deep-research report.

  6. · GROUND_CAUSAL_NODES · claude

    Grounded 1 causal-node grounding field(s) via mappings/node_grounding.tsv (CHEBI:29806×1).

  7. · GROUND_CAUSAL_NODES · claude

    Grounded 3 causal-node grounding field(s) via mappings/node_grounding.tsv (CHEBI:15361×1, CHEBI:16452×1, CHEBI:15539×1).

  8. · GROUND_CAUSAL_NODES · claude

    Grounded 1 causal-node grounding field(s) via mappings/node_grounding.tsv (UniProtKB:A0A3S9JES8×1).

  9. · RETRACT_DEAD_UNIPROT_GROUNDINGS · claude

    Retracted 1 UniProtKB grounding(s) whose accessions are deleted from UniProt; nodes demoted to label-only pending re-grounding (docs/GROUNDING_POLICY.md)

  10. · GROUND_CAUSAL_NODES · claude

    Grounded 1 causal-node grounding field(s) via mappings/node_grounding.tsv (GO:0047154×1).

  11. · MIGRATE_MICROBE_DOMAIN_EDGES_PART2 · claude

    Re-grounded 1 causal edge(s) off microbe-domain METPO predicates onto their causal-graph counterparts (1 to produces), issue 301 part 2. The previous predicates are transitively rdfs:subPropertyOf METPO:2000001, whose rdfs:domain is METPO:1000525 (microbe), so a causal-graph subject entailed that the subject IS a microbe; CausalNodeTypeEnum has no organism member, so no such edge could ever satisfy the domain. Each replacement is a 1:1 mirror of its source predicate that changes only the domain, so the claim each edge makes is unchanged and directions are unchanged. The replacements are proposed in proposals/metpo_traitmech_v9 and are placeholder ids until METPO mints them.

  12. · CONNECT_CAUSAL_GRAPH_COMPONENTS · codex

    Resolved issue #183 graph fragmentation (4 components to 1) using 3 public-source, verbatim-snippet-backed connector(s). No paid research service was called.