identifier: traitmech:000035
label: anoxygenic photosynthesis
definition: A phototrophic metabolism that uses light energy with a single photosystem
  and bacteriochlorophyll, using electron donors other than water (e.g. H2S, H2, Fe(II),
  organics) and therefore not evolving oxygen. Characteristic of purple and green
  sulfur bacteria, Chloroflexi, and heliobacteria.
definition_source: DOI:10.1016/j.tim.2006.09.001
trait_category: METABOLISM
term_kind: CLASS
mapping_status: REVIEWED
parent_traits:
- traitmech:000038
synonyms:
- synonym_text: bacterial photosynthesis
  synonym_type: RELATED_SYNONYM
  source: DOI:10.1016/j.tim.2006.09.001
evidence:
- reference: DOI:10.1016/j.tim.2006.09.001
  notes: Bryant & Frigaard describe anoxygenic photosynthesis across five prokaryotic
    phyla using bacteriochlorophyll and a single photosystem without O2 evolution.
- reference: DOI:10.3389/fmicb.2024.1417714
  notes: Review of anoxygenic photosynthesis in green sulfur bacteria supports sulfide
    as electron donor and the absence of oxygen production.
canonical_examples:
- taxon_id: NCBITaxon:1063
  taxon_label: Cereibacter sphaeroides
  note: "Textbook purple-bacterial (Type II) anoxygenic phototroph (formerly Rhodobacter sphaeroides). Chlorobaculum tepidum is the green-sulfur (Type I) model."
  reference: DOI:10.1023/A:1006350405674
causal_graphs:
- graph_id: anoxygenic_photosynthesis_sulfide_donor
  title: Anoxygenic photosynthesis uses non-water electron donors
  description: Evidence-backed causal sketch linking a single bacteriochlorophyll
    photosystem and non-water electron donors (sulfide, H2, Fe(II), organics) to photosynthetic
    electron flow without O2 evolution.
  nodes:
  - node_id: anoxygenic_photosynthesis_trait
    label: anoxygenic photosynthesis
    node_type: TRAIT
    grounding: traitmech:000035
    description: Bacteriochlorophyll-based photosynthesis using non-water electron
      donors.
  - node_id: sulfide
    label: sulfide
    node_type: CHEMICAL
    grounding: CHEBI:15138
    description: Reduced sulfur electron donor (representative anoxygenic donor).
  - node_id: photosynthetic_etc
    label: photosynthetic electron transport
    node_type: PATHWAY
    grounding: GO:0009767
    description: Single-photosystem electron transport powering anoxygenic photosynthesis.
  - node_id: bacteriochlorophyll
    label: bacteriochlorophyll
    node_type: CHEMICAL
    description: Light-harvesting pigment of anoxygenic phototrophs.
    grounding: CHEBI:38201
  - node_id: light_energy
    label: light energy
    node_type: ENVIRONMENTAL_FACTOR
    description: Light input driving photochemistry in anoxygenic photosynthesis.
  - node_id: type_i_reaction_center
    label: Type I reaction center
    node_type: GENE_OR_PROTEIN
    description: Homodimeric Type I reaction-center photosystem of anoxygenic phototrophs.
  - node_id: elemental_sulfur
    label: elemental sulfur (S0)
    node_type: CHEMICAL
    description: Oxidized sulfur product from sulfide oxidation during anoxygenic
      photosynthesis.
  edges:
  - subject: sulfide
    predicate: feeds electrons into
    object: photosynthetic_etc
    description: Sulfide and other non-water donors feed electrons into the single
      photosystem.
    evidence:
    - reference: DOI:10.3389/fmicb.2024.1417714
      notes: Review of green sulfur bacteria supports sulfide as electron donor and
        the absence of oxygen production.
    predicate_id: METPO:2007402
  - subject: photosynthetic_etc
    predicate: enables
    object: anoxygenic_photosynthesis_trait
    description: Bacteriochlorophyll-based electron flow realizes anoxygenic photosynthesis.
    evidence:
    - reference: DOI:10.1016/j.tim.2006.09.001
      notes: Bryant & Frigaard describe anoxygenic photosynthesis across five prokaryotic
        phyla using bacteriochlorophyll and a single photosystem.
    predicate_id: RO:0002327
  - subject: bacteriochlorophyll
    predicate: absorbs
    object: light_energy
    description: Bacteriochlorophyll harvests light energy to drive single-photosystem
      photochemistry.
    evidence:
    - reference: DOI:10.1016/j.tim.2006.09.001
      notes: 'Bryant & Frigaard: anoxygenic photosynthesis uses bacteriochlorophyll
        and a single photosystem to capture light energy.'
  - subject: light_energy
    predicate: powers
    object: photosynthetic_etc
    description: Absorbed light energy drives photosynthetic electron transport through
      the single photosystem.
    evidence:
    - reference: DOI:10.1016/j.tim.2006.09.001
      notes: Light energy captured by bacteriochlorophyll powers single-photosystem
        electron flow in anoxygenic phototrophs.
  - subject: type_i_reaction_center
    predicate: enables
    object: anoxygenic_photosynthesis_trait
    description: A homodimeric Type I reaction-center photosystem mediates anoxygenic
      photosynthesis across diverse phyla.
    evidence:
    - reference: DOI:10.3390/biom14030311
      notes: 'Niederman: diverse homodimeric Type I reaction-center photosystems underpin
        anoxygenic phototrophic bacteria; complemented by Tsuji et al. DOI:10.1038/s41586-024-07180-y
        showing Chloroflexota use a Type I RC.'
    predicate_id: RO:0002327
  - subject: type_i_reaction_center
    predicate: part of
    object: photosynthetic_etc
    description: The Type I reaction center is the photochemical core of the single-photosystem
      electron transport chain.
    evidence:
    - reference: DOI:10.1038/s41586-024-07180-y
      notes: 'Tsuji et al.: an anoxygenic phototroph of the Chloroflexota uses a Type
        I reaction centre for photosynthetic electron transport.'
    predicate_id: biolink:part_of
  - subject: sulfide
    predicate: oxidized to
    object: elemental_sulfur
    description: Sulfide donated to the photosystem is oxidized to elemental sulfur
      (S0) during anoxygenic photosynthesis.
    evidence:
    - reference: DOI:10.3389/fmicb.2024.1417714
      notes: 'Kushkevych et al.: H2S serves as electron donor and is oxidized to S0
        in green/purple sulfur bacteria anoxygenic photosynthesis.'
    predicate_id: METPO:2007405
curation_history:
- timestamp: '2026-05-30T00:00:00Z'
  curator: claude
  action: PROPOSED_FROM_RESEARCH
  changes: Proposed candidate METABOLISM trait (anoxygenic photosynthesis) from literature
    research to fill the phototrophy gap.
  llm_assisted: true
- timestamp: '2026-06-10T14:00:00Z'
  curator: claude
  action: CURATED_CAUSAL_GRAPH
  changes: Added evidence-backed causal graph (sulfide-driven anoxygenic photosynthesis)
    with CHEBI/GO node groundings 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 (4 new nodes) from the deep-research
    report.
  llm_assisted: true
- timestamp: '2026-06-24T17:21:12Z'
  curator: claude
  action: GROUND_CAUSAL_PREDICATES
  changes: Grounded 3 causal-edge predicate_id field(s) via mappings/predicate_grounding.tsv
    (RO:0002327×1, biolink:part_of×1, METPO:2007405×1).
  llm_assisted: true
- timestamp: '2026-06-24T17:21:18Z'
  curator: claude
  action: GROUND_CAUSAL_NODES
  changes: Grounded 1 causal-node grounding field(s) via mappings/node_grounding.tsv
    (CHEBI:38201×1).
  llm_assisted: true