identifier: traitmech:000026
label: lactic acid fermentation
definition: 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).
definition_source: DOI:10.3389/fmicb.2021.703525
trait_category: METABOLISM
term_kind: CLASS
mapping_status: REVIEWED
parent_traits:
- METPO:1002005
synonyms:
- synonym_text: lactate fermentation
  synonym_type: RELATED_SYNONYM
  source: DOI:10.3389/fmicb.2021.703525
evidence:
- reference: DOI:10.3389/fmicb.2021.703525
  notes: Review of energy conservation in anaerobic fermentations supports lactate
    as a fermentation end product generated with substrate-level phosphorylation.
- reference: DOI:10.3390/molecules31020333
  notes: Review of classical food fermentations describes the lactic-acid pathway
    and lactic acid bacteria as its agents.
canonical_examples:
- taxon_id: NCBITaxon:1358
  taxon_label: Lactococcus lactis
  note: "Canonical homolactic fermenter and dairy model organism."
  reference: PMID:17307855
causal_graphs:
- graph_id: lactic_acid_fermentation_lactate
  title: Lactic acid fermentation converts sugars to lactate
  description: Evidence-backed causal sketch linking glycolysis-coupled lactate production
    to substrate-level ATP generation in lactic acid bacteria.
  nodes:
  - node_id: lactic_acid_fermentation_trait
    label: lactic acid fermentation
    node_type: TRAIT
    grounding: traitmech:000026
    description: Fermentation producing lactate as the principal end product.
  - node_id: fermentation_process
    label: fermentation
    node_type: BIOLOGICAL_PROCESS
    grounding: GO:0006113
    description: ATP-yielding catabolism with organic terminal acceptors.
  - node_id: lactate
    label: lactate
    node_type: CHEMICAL
    description: Principal end product of homolactic fermentation.
    grounding: CHEBI:24996
  - node_id: glucose
    label: glucose
    node_type: CHEMICAL
    description: Hexose substrate fermented by lactic acid bacteria.
    grounding: CHEBI:17234
  - node_id: glycolysis_emp
    label: EMP/glycolysis pathway
    node_type: PATHWAY
    description: Embden-Meyerhof-Parnas glycolytic pathway used by homofermentative
      LAB.
  - node_id: pyruvate
    label: pyruvate
    node_type: CHEMICAL
    description: Glycolytic intermediate reduced to lactate.
    grounding: CHEBI:15361
  - node_id: lactate_dehydrogenase
    label: lactate dehydrogenase
    node_type: GENE_OR_PROTEIN
    description: Enzyme that reduces pyruvate to lactate (EC 1.1.1.27).
    grounding: UniProtKB:A0A073JRC3
  - node_id: phosphoketolase_pathway
    label: phosphoketolase pathway
    node_type: PATHWAY
    description: Pentose-phosphate/phosphoketolase route used by heterofermentative
      LAB.
  - node_id: carbon_dioxide
    label: carbon dioxide
    node_type: CHEMICAL
    description: Co-product of heterolactic fermentation.
    grounding: CHEBI:16526
  - node_id: ethanol
    label: ethanol
    node_type: CHEMICAL
    description: Co-product of heterolactic fermentation.
    grounding: CHEBI:16236
  - node_id: decreased_ph
    label: decreased pH
    node_type: QUALITY
    description: Acidification resulting from lactic acid accumulation.
  - node_id: pathogenic_microbe
    label: pathogenic/spoilage microbe
    node_type: BIOLOGICAL_PROCESS
    description: Spoilage and pathogenic microbes inhibited by acidification.
  edges:
  - subject: lactic_acid_fermentation_trait
    predicate: participates in
    object: fermentation_process
    description: Lactic acid fermentation is a class of fermentation metabolism.
    evidence:
    - reference: DOI:10.3389/fmicb.2021.703525
      notes: Energy-conservation review supports lactate as a fermentation end product.
    predicate_id: biolink:participates_in
  - subject: lactic_acid_fermentation_trait
    predicate: produces
    object: lactate
    description: Lactate is the characteristic end product of the pathway.
    evidence:
    - reference: DOI:10.3390/molecules31020333
      notes: Classical-fermentation review describes the lactic-acid pathway.
    predicate_id: METPO:2000202
  - subject: glucose
    predicate: is fermented via
    object: glycolysis_emp
    description: Homofermentative LAB ferment glucose mainly via the EMP/glycolysis
      pathway.
    evidence:
    - reference: DOI:10.3390/fermentation10030168
      notes: homofermentative LAB rely mainly on glycolysis (EMP).
  - subject: glycolysis_emp
    predicate: produces
    object: pyruvate
    description: Glycolysis yields pyruvate as the intermediate reduced to lactate.
    evidence:
    - reference: DOI:10.3390/foods12152850
      notes: Glycolysis of glucose generates pyruvate, which lactate dehydrogenase
        reduces to lactate.
    predicate_id: METPO:2000202
  - subject: pyruvate
    predicate: is converted by
    object: lactate_dehydrogenase
    description: Pyruvate is the substrate of lactate dehydrogenase.
    evidence:
    - reference: DOI:10.3390/foods12152850
      notes: Lactate dehydrogenase converts pyruvate to lactate.
  - subject: lactate_dehydrogenase
    predicate: produces
    object: lactate
    description: Lactate dehydrogenase reduces pyruvate to lactate.
    evidence:
    - reference: DOI:10.3390/foods12152850
      notes: one mole of glucose produces two moles of lactic acid and two ATP molecules
        via LDH.
    predicate_id: METPO:2000202
  - subject: phosphoketolase_pathway
    predicate: yields
    object: lactate
    description: Heterofermentative phosphoketolase route yields lactate among its
      products.
    evidence:
    - reference: DOI:10.3390/fermentation10030168
      notes: products are lactate, carbon dioxide, and either ethanol or acetate (phosphoketolase
        route).
    predicate_id: biolink:produces
  - subject: phosphoketolase_pathway
    predicate: yields
    object: carbon_dioxide
    description: Heterolactic phosphoketolase route co-produces CO2.
    evidence:
    - reference: DOI:10.3390/fermentation10030168
      notes: heterolactic products are lactate, carbon dioxide, and ethanol or acetate.
    predicate_id: biolink:produces
  - subject: phosphoketolase_pathway
    predicate: yields
    object: ethanol
    description: Heterolactic phosphoketolase route co-produces ethanol (or acetate).
    evidence:
    - reference: DOI:10.3390/fermentation10030168
      notes: heterolactic products include ethanol or acetate.
    predicate_id: biolink:produces
  - subject: lactate
    predicate: causes
    object: decreased_ph
    description: Accumulation of lactic acid acidifies the medium.
    evidence:
    - reference: DOI:10.3390/fermentation10030168
      notes: acidification from lactic acid exerts antagonistic effects on microbes.
    predicate_id: biolink:causes
  - subject: decreased_ph
    predicate: inhibits
    object: pathogenic_microbe
    description: Lactate-driven acidification inhibits spoilage and pathogenic microbes
      (biopreservation).
    evidence:
    - reference: DOI:10.3390/fermentation10030168
      notes: higher lactic acid / lower pH increases inhibition of spoilage and pathogenic
        microbes.
    predicate_id: RO:0002212
curation_history:
- timestamp: '2026-05-30T00:00:00Z'
  curator: claude
  action: PROPOSED_FROM_RESEARCH
  changes: Proposed candidate METABOLISM trait (lactic acid fermentation); product-specific
    sub-variant of the existing Fermentation class (METPO:1002005).
  llm_assisted: true
- timestamp: '2026-06-10T14:00:00Z'
  curator: claude
  action: CURATED_CAUSAL_GRAPH
  changes: Added evidence-backed causal graph (lactic acid fermentation / lactate
    production) with GO node grounding and METPO/biolink predicate groundings; promoted
    PROPOSED to REVIEWED.
  llm_assisted: true
- timestamp: '2026-06-14T06:55:38Z'
  curator: claude
  action: GROUND_CAUSAL_NODES
  changes: Grounded 1 causal-node grounding field(s) via mappings/node_grounding.tsv
    (CHEBI:24996×1).
  llm_assisted: true
- timestamp: '2026-06-23T00:00:00Z'
  curator: claude
  action: ENRICH_CAUSAL_GRAPH
  changes: Added 9 evidence-backed generic edges (9 new nodes) from the deep-research
    report.
  llm_assisted: true
- timestamp: '2026-06-24T17:21:12Z'
  curator: claude
  action: GROUND_CAUSAL_PREDICATES
  changes: 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).
  llm_assisted: true
- timestamp: '2026-06-24T17:21:18Z'
  curator: claude
  action: GROUND_CAUSAL_NODES
  changes: Grounded 3 causal-node grounding field(s) via mappings/node_grounding.tsv
    (CHEBI:17234×1, CHEBI:16526×1, CHEBI:16236×1).
  llm_assisted: true
- timestamp: '2026-06-24T17:23:32Z'
  curator: claude
  action: GROUND_CAUSAL_NODES
  changes: Grounded 1 causal-node grounding field(s) via mappings/node_grounding.tsv
    (CHEBI:15361×1).
  llm_assisted: true
- timestamp: '2026-06-26T07:15:18Z'
  curator: claude
  action: GROUND_CAUSAL_NODES
  changes: Grounded 1 causal-node grounding field(s) via mappings/node_grounding.tsv
    (UniProtKB:A0A073JRC3×1).
  llm_assisted: true