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photosynthesis

traitmech:000038 · CLASS · REVIEWED

A phototrophic metabolism that uses light energy and chlorophyll- or bacteriochlorophyll-based photochemical reaction centers to drive electron flow, fixing CO2 and/or generating reducing power. Subdivided into oxygenic and anoxygenic photosynthesis.

Trait evidence (2)

  • DOI:10.1016/j.tim.2006.09.001

    Bryant & Frigaard treat prokaryotic photosynthesis (reaction-center based) as encompassing both oxygenic and anoxygenic forms across five phyla.

  • DOI:10.1146/annurev-earth-060313-054810

    Fischer et al., "Evolution of Oxygenic Photosynthesis", supports reaction-center photosynthesis as the chlorophyll-based, CO2-fixing branch of phototrophy distinct from rhodopsin-based light capture.

Chlorophyll-based photosynthesis drives electron flow and CO2 fixation

Evidence-backed causal sketch linking chlorophyll-based reaction centers to electron flow that powers CO2 fixation.

MECHANISTIC · The graph spans oxygenic and anoxygenic chlorophyll-based photosynthesis. The Synechocystis PsbA2 example supports the oxygenic photosystem II branch only; anoxygenic reaction centers use different protein families.

Chlorophyll-based photosynthesis drives electron flow and CO2 fixation Interactive directed graph showing evidence-backed causal relationships for photosynthesis.

Edge evidence

  • photosynthesis confers photosynthesis METPO:2007700

    Reaction-center photochemistry underlies the photosynthetic trait.

  • photosynthesis contributes to carbon fixation RO:0002326

    Photosynthetic electron flow powers autotrophic CO2 fixation.

  • light energy enables light harvesting / excitation transfer RO:0002327

    Light energy drives pigment absorption and excitation transfer to reaction-center antennae.

  • light harvesting / excitation transfer initiates reaction-center charge separation

    Transferred excitation energy drives primary charge separation at the reaction-center special pair.

    • DOI:10.3390/biom14030311 Light-driven charge separation in reaction-center photosystems initiates downstream electron flow (generic to Type I/II RCs).
  • reaction-center charge separation powers photosynthetic electron transport

    Reaction-center charge separation drives photosynthetic electron transport (linear or cyclic).

    • DOI:10.3390/biom14030311 Light-driven charge separation powers electron transfer pathways; generalization for reaction-center photosystems.
  • photosynthetic electron transport generates transmembrane electrochemical proton gradient biolink:produces

    Photosynthetic electron transport establishes a transmembrane electrochemical proton gradient.

    • DOI:10.3390/biom14030311 Electron transfer creates a transmembrane electrochemical proton gradient (energy-conservation edge).
  • transmembrane electrochemical proton gradient drives ATP synthesis

    The proton motive force is used to drive chemiosmotic ATP synthesis.

  • photosynthesis has output reducing power (NAD(P)H) RO:0002234

    Light-dependent reactions generate ATP and NAD(P)H reducing power.

    • DOI:10.5287/ora-8jgz2nrvd Light-dependent reactions generate ATP and NAD(P)H; broad linkage across chlorophyll-based photosynthetic systems.
  • reducing power (NAD(P)H) used in carbon fixation

    NADPH reducing power supplies electrons for autotrophic CO2 fixation.

  • photosystem II initiates reaction-center charge separation

    Photosystem II initiates oxygenic electron transfer through light-induced reaction-center charge separation.

    • DOI:10.1073/pnas.1520211113 PSII reactions are initiated by light-induced charge separation between a chlorophyll dimer and a pheophytin electron acceptor. The primary spectroelectrochemical study supports the generic PSII charge-separation edge; the PsbA2 accession separately grounds a Synechocystis complex component.
  • photosynthetic electron transport contributes to reducing power (NAD(P)H) RO:0002326

    Photosynthetic electron-transfer reactions contribute the NADPH reducing power used by downstream carbon fixation.

    • DOI:10.1111/1751-7915.14519 NADPH and ATP are produced from a proton gradient formed coincident with the electron transfer reactions and fuel downstream processes, including carbon fixation Verified against the public PMC full text; the passage describes the oxygenic branch represented by the existing PSII node.

Protein and taxon examples

Graph nodeProteinTaxonUniProt statusRole and evidence
photosystem II UniProtKB:P16033
Photosystem II protein D1 2 (psbA2) 		Synechocystis sp. PCC 6803
NCBITaxon:1111708 		REVIEWED
retrieved 2026-08-24 · entry v186 · sequence v1

D1 reaction-center component of photosystem II; this accession is not presented as the complete water-oxidizing complex.

  • DOI:10.1074/jbc.M806116200 the PsbA (D1) subunit of photosystem II (PSII) A primary Synechocystis PCC 6803 study identifies PsbA/D1 as a PSII subunit and studies its biogenesis; UniProtKB P16033 verifies the reviewed PsbA2 protein and strain taxon.

Provenance

Identifier source
TraitMech local identifier
Definition source
DOI:10.1016/j.tim.2006.09.001

Parent traits (1)

Children (2)

Cross-references

  • GO:0015979

kg-microbe context

Matched 1 kg-microbe node via parent_proxy.

  • METPO:1000060 [-1.052, -1.766, -1.194, +0.291, …]

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/photosynthesis-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: microbial photosynthesis (`traitmech:000038`)

## Executive scope

**Recommended interpretation.** `traitmech:000038` should represent the cellular capacity for **chlorophyll- or bacteriochlorophyll-based reaction-center photochemistry**: antenna pigments absorb light, excitation reaches a type I or type II reaction center, charge separation initiates electron transport, and membrane bioenergetics produces reducing power and/or ATP. It encompasses **oxygenic photosynthesis** and **anoxygenic photosynthesis**, including photoautotrophic and photoheterotrophic implementations. Type I and type II reaction centers occur in multiple bacterial lineages, whereas cyanobacteria couple heterodimeric PSI and PSII for oxygenic photosynthesis. (martin2018aphysiologicalperspective pages 2-3)

**Important separation of modules.** Photosynthesis supplies photochemical energy and electrons, but it does not necessarily imply CO2 fixation. Aerobic anoxygenic phototrophs can be photoheterotrophs, while carbon-fixing phototrophs use lineage-dependent pathways, including the Calvin–Benson–Bassham (CBB) or reverse TCA cycles. Green sulfur bacteria, for example, assimilate CO2 through reverse TCA, whereas oxygenic phototrophs commonly use CBB. (tomasch2024aphotoheterotrophicbacterium pages 1-2, kushkevych2024anoxygenicphotosynthesiswith pages 1-2, li2021exogenouselectricityflowing pages 1-6)

### Boundary cases

Include:

- Cyanobacterial oxygenic photosynthesis using PSII and PSI.
- Anoxygenic reaction-center phototrophy driven by bacteriochlorophyll.
- Cyclic anoxygenic electron transport that generates proton motive force and ATP even when carbon fixation is absent.
- Photoheterotrophic reaction-center activity.

Exclude or model separately:

- **Rhodopsin-based phototrophy**, because it uses retinal proton/ion pumps rather than chlorophyll reaction centers and charge-separated electron-transfer chains.
- Chlorophyll or bacteriochlorophyll biosynthesis alone; pigment production is neither sufficient evidence of an assembled functional reaction center nor of photosynthetic growth.
- CO2 fixation alone, which can be chemolithoautotrophic.
- Phototaxis, fluorescence, light sensing, or photoprotection without reaction-center electron transport.
- Artificial illumination and exogenous-electron inputs as defining components of the natural trait; these are experimental modifiers.

A practical positive assay should demonstrate at least one of: light-dependent reaction-center charge separation/electron transport, oxygen evolution, photophosphorylation, light-dependent growth dependent on a reaction center, or a functional reaction-center spectroscopic signature. Genomic photosynthesis-gene clusters are useful predictions but should remain genotype-level evidence until function is shown.

## Candidate graph architecture

A single linear graph would incorrectly imply that all phototrophs use PSII, water, oxygen evolution, PSI, and CBB. The YAML should therefore have a conserved upstream core followed by explicit **oxygenic** and **anoxygenic** branches:

1. light → antenna excitation → reaction-center excitation → charge separation;
2. oxygenic branch: PSII/water → quinone → cytochrome b6f → PSI → ferredoxin/NADPH, coupled to proton motive force and ATP synthesis;
3. anoxygenic branch: external donor and/or cyclic flow → type I or II reaction center → quinone/cytochrome or ferredoxin pathways → proton motive force/reducing power;
4. optional downstream carbon-fixation modules, linked conditionally rather than made definitional.

## Candidate nodes

### Trait and processes

- photosynthesis — `traitmech:000038`
- parent trait — `traitmech:000037`
- photosynthesis — `GO:0015979`
- light reaction of photosynthesis — `GO:0019684`
- photosynthetic electron transport chain — label candidate; verify the desired GO child term for each branch
- photosynthetic electron transport in photosystem II — `GO:0009772`
- photosynthetic electron transport in photosystem I — `GO:0009773`
- carbon fixation — `GO:0015977`
- Calvin–Benson–Bassham cycle — label candidate
- reverse tricarboxylic-acid cycle — label candidate
- cyclic photosynthetic electron transport — label candidate
- oxygenic photosynthesis; anoxygenic photosynthesis — retain as branch labels unless project-approved ontology terms are confirmed

### Complexes, proteins, and cofactors

- photosystem II; photosystem I
- PSII oxygen-evolving complex / Mn4CaO5 cluster
- P680; D1 protein/PsbA; D2/PsbD; redox-active TyrZ (D1-Y161)
- QA and QB plastoquinone sites
- cytochrome b6f complex

Showing the first 60 of 239 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 (3)

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

    Minted intermediate axis class (photosynthesis) under phototrophy to parent the oxygenic- and anoxygenic-photosynthesis traits.

  2. · CURATED_CAUSAL_GRAPH · claude

    Added evidence-backed causal graph (reaction-center photosynthesis / CO2 fixation) with GO node groundings and RO predicate groundings; promoted PROPOSED to REVIEWED.

  3. · ENRICH_CAUSAL_GRAPH · claude

    Added 7 evidence-backed generic edges (7 new nodes) from the deep-research report.

  4. · GROUND_CAUSAL_PREDICATES · claude

    Grounded 3 causal-edge predicate_id field(s) via mappings/predicate_grounding.tsv (RO:0002327×1, biolink:produces×1, METPO:2000202×1).

  5. · GROUND_CAUSAL_NODES · claude

    Grounded 1 causal-node grounding field(s) via mappings/node_grounding.tsv (GO:0006754×1).

  6. · MIGRATE_ENABLES_TRAIT_EDGES · claude

    Migrated 1 causal edge(s) off enables/RO:0002327 with a TRAIT object (1 to confers), issue 302. RO:0002327 has range 'biological process or activity', which a trait (a disposition) cannot satisfy, so the previous form entailed trait is-a BiologicalProcessOrActivity. The replacements are proposed in proposals/metpo_traitmech_v8 and are placeholder ids until METPO mints them.

  7. · 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.

  8. · NORMALISE_NODE_TYPE · claude

    Normalised causal-node type(s) so one node_id means one thing corpus-wide (issue 356): reducing_power: CHEMICAL -> CAPACITY. The schema's OWN example of CAPACITY: 'an electron-donating pool, ATP charge, or other reservoir-of-X notion ... Examples include reducing power (NADH/NADPH pool)'. The lone CHEMICAL occurrence (metabolism/photosynthesis.yaml) describes 'NADPH/NAD(P)H reducing equivalents', i.e. the pool, not a single species -- which is the very distinction CAPACITY exists to draw, and the one docs/CURATION_PLAYBOOK.md records as the reservoir sense that must NOT be retyped to TRAIT (#352).

  9. · CURATE_PROTEIN_TAXON_EXAMPLE · codex

    Added a DOI-backed Synechocystis PCC 6803 PsbA2 component example, a GO-grounded photosystem II node, a primary-source PSII charge-separation edge, and scope notes separating oxygenic from anoxygenic branches.

  10. · ADD_EXACT_ONTOLOGY_MATCH · codex

    Ontology exact-match review (2026-08-25): approved exact xref(s): GO:0015979. Evidence is predicate-scoped in the versioned ontology snapshots; OAK cross-checked direct data, and OLS4 spot-checked release deltas and disputed hits.

  11. · CONNECT_CAUSAL_GRAPH_COMPONENTS · codex

    Resolved issue #183 graph fragmentation (2 components to 1) using 1 public-source, verbatim-snippet-backed connector(s). No paid research service was called.