identifier: traitmech:000016
label: mercury tolerant
definition: A metal tolerance in which an organism grows in the presence of toxic
  inorganic or organic mercury compounds, typically via the mer operon, whose mercuric
  reductase (MerA) reduces reactive Hg(II) to volatile Hg(0).
definition_source: DOI:10.1016/S0168-6445(03)00046-9
trait_category: ENVIRONMENT
term_kind: CLASS
mapping_status: REVIEWED
parent_traits:
- traitmech:000012
synonyms:
- synonym_text: mercury resistant
  synonym_type: RELATED_SYNONYM
  source: DOI:10.1016/S0168-6445(03)00046-9
evidence:
- reference: DOI:10.1016/S0168-6445(03)00046-9
  snippet: Bacterial resistance to inorganic and organic mercury compounds (HgR) is
    one of the most widely observed phenotypes in eubacteria
  notes: Review supports mercury resistance as a widespread bacterial phenotype mediated
    by MerA, "that reduces reactive ionic Hg(II) to volatile, relatively inert, monoatomic
    Hg(0) vapor".
- reference: PMID:12829273
  snippet: CBA efflux pumps driven by proteins of the resistance-nodulation-cell division
    superfamily, P-type ATPases, cation diffusion facilitator and chromate proteins
  notes: Heavy-metal resistance review situates mercury detoxification within the
    broader prokaryotic metal-resistance machinery.
canonical_examples:
- taxon_id: NCBITaxon:119219
  taxon_label: Cupriavidus metallidurans
  note: "mer-operon mercury resistance"
  reference: PMID:21423734
- taxon_id: NCBITaxon:303
  taxon_label: Pseudomonas putida
  note: "mercury-resistant"
  reference: PMID:21751007
causal_graphs:
- graph_id: mercury_tolerance_mer_reduction
  title: Mercury tolerance via mer-operon MerA reductase
  description: Evidence-backed causal sketch linking mer-operon mercuric reductase
    to volatilization of Hg(II) into Hg(0).
  nodes:
  - node_id: mercury_tolerant_trait
    label: mercury tolerant
    node_type: TRAIT
    grounding: traitmech:000016
    description: Capacity to grow in the presence of toxic mercury compounds.
  - node_id: mercury_ii_ion
    label: mercury(2+) ion
    node_type: CHEMICAL
    grounding: CHEBI:25195
    description: Reactive ionic mercury accumulating intracellularly.
  - node_id: mer_operon
    label: mer operon (MerA reductase)
    node_type: GENE_OR_PROTEIN
    description: Mercuric reductase reducing Hg(II) to volatile Hg(0).
  - node_id: mercury_reduction
    label: mercury(II) reduction
    node_type: BIOLOGICAL_PROCESS
    description: Enzymatic reduction of Hg(II) to volatile elemental Hg(0).
  - node_id: mercury_zero
    label: mercury(0)
    node_type: CHEMICAL
    description: Volatile, relatively inert elemental mercury Hg(0).
    grounding: CHEBI:16170
  - node_id: merb_lyase
    label: MerB (organomercurial lyase)
    node_type: GENE_OR_PROTEIN
    description: Organomercury lyase cleaving C-Hg bonds of organomercurials to release
      Hg(II).
  - node_id: organomercurial
    label: organomercurial compound
    node_type: CHEMICAL
    description: Organic mercury compounds such as methylmercury.
  - node_id: merr_sensor
    label: MerR (Hg-responsive regulator)
    node_type: GENE_OR_PROTEIN
    description: Mercury-responsive transcription factor controlling mer operon induction.
  - node_id: mer_transcription
    label: mer operon transcription
    node_type: BIOLOGICAL_PROCESS
    description: Transcriptional activation of mer detoxification genes from the Pmer
      promoter.
  edges:
  - subject: mercury_ii_ion
    predicate: challenges
    object: mercury_tolerant_trait
    description: Reactive Hg(II) is the toxic challenge the trait counters.
    evidence:
    - reference: PMID:12829273
      notes: Mercury detoxification sits within the broader prokaryotic metal-resistance
        machinery.
    predicate_id: METPO:2007406
  - subject: mer_operon
    predicate: enables
    object: mercury_reduction
    description: MerA reduces Hg(II) to volatile, inert Hg(0) vapour.
    evidence:
    - reference: DOI:10.1016/S0168-6445(03)00046-9
      notes: MerA reduces reactive ionic Hg(II) to volatile, relatively inert, monoatomic
        Hg(0) vapor.
    predicate_id: RO:0002327
  - subject: mercury_reduction
    predicate: mitigates
    object: mercury_ii_ion
    description: Reduction to Hg(0) depletes the reactive Hg(II) pool.
    evidence:
    - reference: DOI:10.1016/S0168-6445(03)00046-9
      notes: Mercury reduction is the basis of mer-mediated resistance.
    predicate_id: METPO:2007407
  - subject: mer_operon
    predicate: produces
    object: mercury_zero
    description: MerA reduction of Hg(II) yields volatile elemental Hg(0).
    evidence:
    - reference: DOI:10.1186/s12866-024-03391-5
      notes: MerA reduces Hg2+ to volatile Hg0, relieving intracellular Hg(II) toxicity.
    predicate_id: METPO:2000202
  - subject: merb_lyase
    predicate: cleaves
    object: organomercurial
    description: MerB lyase cleaves C-Hg bonds of organomercurials to release Hg(II)
      for MerA reduction.
    evidence:
    - reference: DOI:10.21203/rs.3.rs-3854515/v1
      notes: MerB is an organomercury lyase that cleaves methylmercury to Hg2+ and
        methane.
  - subject: merb_lyase
    predicate: produces
    object: mercury_ii_ion
    description: Organomercurial cleavage yields Hg(II), the substrate for MerA reduction.
    evidence:
    - reference: DOI:10.21203/rs.3.rs-3854515/v1
      notes: C-Hg bond cleavage produces Hg(II) for subsequent MerA reduction.
    predicate_id: METPO:2000202
  - subject: merr_sensor
    predicate: senses
    object: mercury_ii_ion
    description: MerR senses Hg(II), acting as a mercury-responsive transcriptional
      regulator.
    evidence:
    - reference: DOI:10.21203/rs.3.rs-3854515/v1
      notes: MerR functions as a repressor/activator responsive to Hg2+.
  - subject: merr_sensor
    predicate: activates
    object: mer_transcription
    description: Hg(II)-bound MerR activates transcription of the mer detoxification
      genes from Pmer.
    evidence:
    - reference: DOI:10.3389/fbioe.2023.1178680
      notes: MerR-mediated activation of Pmer drives mer operon transcription when
        Hg(II) is present.
    predicate_id: RO:0002213
curation_history:
- timestamp: '2026-05-28T00:00:00Z'
  curator: claude
  action: PROPOSED_FROM_RESEARCH
  changes: Proposed candidate ENVIRONMENT trait (mercury tolerance) from literature
    research; metal-specific sub-variant of metal tolerant.
  llm_assisted: true
- timestamp: '2026-06-09T14:00:00Z'
  curator: claude
  action: CURATED_CAUSAL_GRAPH
  changes: Added evidence-backed causal graph (mer-operon Hg(II) reduction) with CHEBI
    node grounding and RO/METPO predicate groundings; promoted PROPOSED to REVIEWED.
  llm_assisted: true
- timestamp: '2026-06-23T00:00:00Z'
  curator: claude
  action: ENRICH_CAUSAL_GRAPH
  changes: Added 5 evidence-backed generic edges (5 new nodes) from the deep-research
    report.
  llm_assisted: true
- timestamp: '2026-06-24T17:21:10Z'
  curator: claude
  action: GROUND_CAUSAL_PREDICATES
  changes: Grounded 3 causal-edge predicate_id field(s) via mappings/predicate_grounding.tsv
    (METPO:2000202×2, RO:0002213×1).
  llm_assisted: true
- timestamp: '2026-06-24T17:23:30Z'
  curator: claude
  action: GROUND_CAUSAL_NODES
  changes: Grounded 1 causal-node grounding field(s) via mappings/node_grounding.tsv
    (CHEBI:16170×1).
  llm_assisted: true