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lactic acid fermentation

traitmech:000026 · CLASS · REVIEWED

A fermentation in which sugars are converted mainly to lactate, with ATP generated by substrate-level phosphorylation. Homolactic fermentation yields ~2 lactate per glucose via glycolysis; heterolactic fermentation also yields ethanol/acetate and CO2. Characteristic of lactic acid bacteria (e.g. Lactobacillus, Lactococcus).

Trait evidence (2)

  • DOI:10.3389/fmicb.2021.703525

    Review of energy conservation in anaerobic fermentations supports lactate as a fermentation end product generated with substrate-level phosphorylation.

  • DOI:10.3390/molecules31020333

    Review of classical food fermentations describes the lactic-acid pathway and lactic acid bacteria as its agents.

Lactic acid fermentation converts sugars to lactate

Evidence-backed causal sketch linking glycolysis-coupled lactate production to substrate-level ATP generation in lactic acid bacteria.

MECHANISTIC · Represents pyruvate reduction, NAD+ regeneration, ATP-producing glycolysis, and acidification effects; the protein exemplar supports the central LDH step in L. lactis IL1403.

Lactic acid fermentation converts sugars to lactate Interactive directed graph showing evidence-backed causal relationships for lactic acid fermentation.

Edge evidence

  • lactic acid fermentation participates in fermentation biolink:participates_in

    Lactic 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 lactate as a fermentation end product.
  • lactic acid fermentation produces lactate METPO:2007800

    Lactate is the characteristic end product of the pathway.

    • DOI:10.3390/molecules31020333 lactic fermentation channels carbohydrate metabolism toward lactate formation Classical-fermentation review describes the lactic-acid pathway.
  • glucose is fermented via EMP/glycolysis pathway

    Homofermentative LAB ferment glucose mainly via the EMP/glycolysis pathway.

    • DOI:10.3390/molecules31020333 Homolactic LAB metabolize hexoses (primarily glucose) via the EMP pathway homofermentative LAB rely mainly on glycolysis (EMP).
  • EMP/glycolysis pathway has output pyruvate RO:0002234

    Glycolysis yields pyruvate as the intermediate reduced to lactate.

    • DOI:10.3390/foods12152850 glucose acts as the carbon source to create pyruvate through the glycolysis process Glycolysis of glucose generates pyruvate, which lactate dehydrogenase reduces to lactate.
  • pyruvate is converted by lactate dehydrogenase

    Pyruvate is the substrate of lactate dehydrogenase.

    • DOI:10.3390/foods12152850 subsequently converted to lactic acid by lactate dehydrogenase Lactate dehydrogenase converts pyruvate to lactate.
  • lactate dehydrogenase produces lactate METPO:2007800

    Lactate dehydrogenase reduces pyruvate to lactate.

    • DOI:10.3390/foods12152850 Lactate dehydrogenase plays an important role in the production of lactic acid from pyruvate one mole of glucose produces two moles of lactic acid and two ATP molecules via LDH.
  • phosphoketolase pathway yields lactate biolink:produces

    Heterofermentative phosphoketolase route yields lactate among its products.

    • DOI:10.3390/molecules31020333 This route typically yields equimolar lactate, ethanol (or acetate) and CO2 products are lactate, carbon dioxide, and either ethanol or acetate (phosphoketolase route).
  • phosphoketolase pathway yields carbon dioxide biolink:produces

    Heterolactic phosphoketolase route co-produces CO2.

    • DOI:10.3390/molecules31020333 leading to the formation of lactate, ethanol or acetate, and CO2 heterolactic products are lactate, carbon dioxide, and ethanol or acetate.
  • phosphoketolase pathway yields ethanol biolink:produces

    Heterolactic phosphoketolase route co-produces ethanol (or acetate).

    • DOI:10.3390/molecules31020333 glucose is processed through the 6-phosphogluconate/phosphoketolase pathway, leading to the formation of lactate, ethanol or acetate heterolactic products include ethanol or acetate.
  • lactate causes decreased pH biolink:causes

    Accumulation of lactic acid acidifies the medium.

    • DOI:10.3390/molecules31020333 lactic fermentation channels carbohydrate metabolism toward lactate formation and rapid acidification of the environment acidification from lactic acid exerts antagonistic effects on microbes.
  • decreased pH inhibits pathogenic/spoilage microbe RO:0002212

    Lactate-driven acidification inhibits spoilage and pathogenic microbes (biopreservation).

    • DOI:10.3390/molecules31020333 lowering pH and inhibiting pathogenic and spoilage microorganisms higher lactic acid / lower pH increases inhibition of spoilage and pathogenic microbes.

Protein and taxon examples

Graph nodeProteinTaxonUniProt statusRole and evidence
lactate dehydrogenase UniProtKB:Q01462
L-lactate dehydrogenase 1 (ldh1) 		Lactococcus lactis subsp. lactis IL1403
NCBITaxon:272623 		REVIEWED
retrieved 2026-08-23 · entry v182 · sequence v3

Catalyzes reduction of pyruvate to L-lactate during homolactic fermentation in the canonical L. lactis strain.

  • DOI:10.1128/JB.183.13.3817-3824.2001 high lactate dehydrogenase activity The primary study measured LDH activity and homolactic physiology in L. lactis IL1403; UniProtKB Q01462 supplies the exact reviewed protein and strain pairing.

Provenance

Identifier source
TraitMech local identifier
Definition source
DOI:10.3389/fmicb.2021.703525

Parent traits (1)

Synonyms (1)

  • lactate fermentation RELATED_SYNONYM · DOI:10.3389/fmicb.2021.703525

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/lactic_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. 
# TraitMech curation report: lactic acid fermentation

## 1. Trait record and scope

- **Trait label:** lactic acid fermentation
- **Trait identifier:** `traitmech:000026`
- **Category / kind / status:** METABOLISM / CLASS / REVIEWED
- **Parent:** `METPO:1002005`
- **Synonym:** lactate fermentation

### Operational definition

This trait is the microbial capacity to conserve energy by fermentatively converting carbohydrate-derived pyruvate mainly to lactate. ATP is generated principally by substrate-level phosphorylation in glycolysis, while lactate dehydrogenase (LDH) reoxidizes NADH to NAD+, allowing glycolysis to continue. In the canonical homolactic route, one glucose gives approximately two pyruvate, two lactate, and net two ATP; reported experimental lactate yields are approximately 0.74–0.99 g per g substrate versus a theoretical value near 1 g/g. (gayathri2023roleofaerobic pages 4-6, gayathri2023roleofaerobic pages 7-8, bintsis2018lacticacidbacteria pages 1-3)

The class should include both:

1. **Homolactic fermentation:** lactate is the dominant carbon end product, commonly through the Embden–Meyerhof–Parnas pathway.
2. **Heterolactic fermentation:** the phosphoketolase pathway yields lactate together with CO2 and ethanol and/or acetate. Product allocation depends on redox balance and growth conditions. (bintsis2018lacticacidbacteria pages 1-3, bintsis2018lacticacidbacteria pages 3-7)

### Boundary cases

Do **not** equate the trait with any observation of lactate production. The following should normally be excluded or separately represented:

- **Aerobic glycolysis/Warburg metabolism:** lactate production in oxygenated eukaryotic cells is not necessarily microbial fermentation.
- **Malolactic fermentation:** malate is decarboxylated to lactate and CO2; this is an acid-modulating conversion, not sugar-to-lactate energy metabolism.
- **Lactate oxidation or assimilation:** lactate is the substrate rather than the fermentation product.
- **Chemical lactic-acid synthesis** and polymerization to polylactic acid.
- **Mixed-acid fermentation with only minor lactate:** curate as lactic acid fermentation only if lactate is a defining or major end product under the assayed condition.
- **Genotype-only predictions:** the presence of an `ldh` homolog is insufficient because LDHs can differ in stereospecificity, direction, cofactor use, and physiological role.

Fermentation mode is also condition-dependent. Carbon limitation, temperature, pH, oxygen, and NADH-reoxidation capacity can redirect nominally homofermentative organisms toward mixed products. Obligately heterofermentative examples include *Lactobacillus brevis*, *L. fermentum*, and *L. reuteri*, whereas *Lactiplantibacillus plantarum*, *Lactococcus lactis*, *L. casei*, and *L. rhamnosus* can exhibit facultative heterofermentative behavior. (bintsis2018lacticacidbacteria pages 1-3, bintsis2018lacticacidbacteria pages 3-7)

## 2. Candidate graph nodes

### Pathways and biological processes

- Lactic acid fermentation — `traitmech:000026`
- Glycolytic process / EMP pathway — `GO:0006096`
- Substrate-level phosphorylation — label-only pending identifier verification
- Homolactic fermentation — label-only candidate
- Heterolactic phosphoketolase pathway — label-only candidate
- NAD+ regeneration — label-only candidate
- Pyruvate-to-lactate fermentation — label-only candidate
- Acid-stress response — label-only candidate
- Intracellular-pH homeostasis — label-only candidate
- Lactate export — label-only candidate
- Mixed-acid fermentation — label-only boundary node

### Chemicals and cofactors

- Glucose — `CHEBI:17234`
- Pyruvate — `CHEBI:15361`
- Lactate, unspecified stereochemistry — `CHEBI:24996`
- L-lactate — `CHEBI:57945`
- D-lactate — `CHEBI:16004`
- NADH — `CHEBI:16908`
- NAD+ — `CHEBI:57540`
- ATP — `CHEBI:15422`
- Carbon dioxide — `CHEBI:16526`
- Ethanol — retain label-only here pending CURIE verification

Showing the first 60 of 248 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.

Curation history

  1. · PROPOSED_FROM_RESEARCH · claude

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

  2. · CURATE_PROTEIN_TAXON_EXAMPLE · codex

    Reviewed the graph as mechanistic and added DOI-backed, taxon-paired UniProtKB Q01462 as the L. lactis IL1403 lactate-dehydrogenase exemplar.

  3. · CURATED_CAUSAL_GRAPH · claude

    Added evidence-backed causal graph (lactic acid fermentation / lactate production) 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:24996×1).

  5. · ENRICH_CAUSAL_GRAPH · claude

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

  6. · GROUND_CAUSAL_PREDICATES · claude

    Grounded 7 causal-edge predicate_id field(s) via mappings/predicate_grounding.tsv (biolink:produces×3, METPO:2000202×2, biolink:causes×1, RO:0002212×1).

  7. · GROUND_CAUSAL_NODES · claude

    Grounded 3 causal-node grounding field(s) via mappings/node_grounding.tsv (CHEBI:17234×1, CHEBI:16526×1, CHEBI:16236×1).

  8. · GROUND_CAUSAL_NODES · claude

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

  9. · GROUND_CAUSAL_NODES · claude

    Grounded 1 causal-node grounding field(s) via mappings/node_grounding.tsv (UniProtKB:A0A073JRC3×1).

  10. · 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)

  11. · GROUND_CAUSAL_NODES · claude

    Grounded 1 causal-node grounding field(s) via mappings/node_grounding.tsv (GO:0004457×1).

  12. · MIGRATE_MICROBE_DOMAIN_EDGES · claude

    Re-grounded 1 causal edge(s) off microbe-domain METPO predicates (1 to has output), issue 301. 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. Edge directions are unchanged - this pass only relabels and re-grounds. RO:0002234 (has output) is used where the subject is an activity, since biolink gives it the domain 'biological process or activity'; the METPO replacements are proposed in proposals/metpo_traitmech_v8 and v9 and are placeholder ids until METPO mints them.

  13. · MIGRATE_MICROBE_DOMAIN_EDGES_PART2 · claude

    Re-grounded 2 causal edge(s) off microbe-domain METPO predicates onto their causal-graph counterparts (2 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.

  14. · REVIEW_EVIDENCE_REFERENCE_CHURN · codex

    Offline review for issue 520 retained 6 evidence-reference replacement(s) that PR 511 made on surviving causal edges outside its stated protein-taxon scope. The pre-tranche evidence entries had references but no snippets; the retained entries supply edge-specific snippets and explanatory notes. Reverting would discard that claim-level provenance, so the scope defect is resolved by documenting the decision instead. This audit changed no causal claim or evidence field. Reviewed replacements: DOI:10.3390/fermentation10030168 -> DOI:10.3390/molecules31020333 (6 edges).