dissimilatory sulfate reduction

Deep research

Generated by just research-trait; source: research/traits/metabolism/dissimilatory_sulfate_reduction-deep-research-falcon.md

# Curation report: dissimilatory sulfate reduction

**Trait:** `traitmech:000105`  
**Category:** METABOLISM · **Kind:** CLASS · **Status:** REVIEWED  
**Parent:** `METPO:1000802`  
**Synonym:** sulfate respiration

## 1. Scope summary

Dissimilatory sulfate reduction is an anaerobic respiratory metabolism in which sulfate, sulfur oxidation state +VI, is used as the terminal electron acceptor and is reduced through APS and sulfite to predominantly sulfide, oxidation state −II. Electrons come from oxidation of organic substrates or H₂, and the pathway supports energy conservation rather than sulfur incorporation into biomass. In oxygen-depleted marine sediments, sulfate reduction accounts for more than half of organic-matter remineralization; a recent global synthesis estimates that one-third of the 260 Tmol organic carbon reaching the seabed annually is mineralized through sulfate reduction. Approximately 90% of the resulting sulfide is reoxidized, consuming about 25% of global sedimentary oxygen; in coastal sediments, sulfate reduction accounts for about 50% of organic-carbon mineralization. (sim2023whatcontrolsthe pages 1-2, diao2023globaldiversityand pages 1-2)

The canonical sequence is sulfate uptake → Sat-mediated activation to APS → AprAB-mediated APS reduction to sulfite → DsrAB/DsrC-mediated sulfite reduction → DsrMKJOP-dependent terminal reduction and sulfide release. QmoABC and DsrMKJOP deliver electrons to the APS- and sulfite-reduction modules, respectively. (klier2024evolutionaryhistoryand pages 1-2, sim2023whatcontrolsthe pages 1-2)

### Inclusion criteria

Curate the trait when there is physiological evidence for sulfate-dependent anaerobic growth or sulfate consumption with sulfide formation, or strong genomic evidence for both:

1. a sulfate-to-sulfite module—typically `sat`, `aprAB`, and `qmoABC`; and
2. a reductive Dsr module—`dsrAB`, `dsrC`, and usually `dsrMKJOP`, with pathway-direction evidence.

### Boundary cases

- **Sulfite respiration:** organisms that reduce supplied sulfite but cannot use sulfate lack the upstream sulfate-activation capability. `dsrAB` alone therefore supports dissimilatory **sulfite** reduction, not necessarily `traitmech:000105`. (klier2024evolutionaryhistoryand pages 1-2, neukirchen2023stepwisepathwayfor pages 2-3)
- **Assimilatory sulfate reduction:** sulfate is reduced for cysteine/methionine biosynthesis and sulfur is retained in biomass. Presence of Sat/Apr-like proteins is not by itself diagnostic; these proteins can have assimilatory functions. (neukirchen2023stepwisepathwayfor pages 8-9)
- **Dsr-mediated sulfur oxidation:** oxidative Dsr systems can share Sat, AprAB, QmoABC, DsrC, DsrAB, and DsrMKJOP with reducers. Direction must therefore be inferred from gene context, DsrAB type, `dsrD`, `dsrL` type, `dsrEFH`, physiology, and expression—not from `dsrAB` alone. Four phyla contain organisms with genomic potential for both directions. (diao2023globaldiversityand pages 1-2)
- **Sulfur disproportionation:** simultaneous production of sulfate and sulfide from elemental sulfur, sulfite, or thiosulfate is a separate trait. Dsr proteins of known disproportionators can be phylogenetically indistinguishable from reductive Dsr proteins, and the mechanism is incompletely resolved; genome content alone cannot reliably distinguish disproportionators from sulfate reducers. (neukirchen2023stepwisepathwayfor pages 8-9)
- **Alternative zero-valent sulfur output:** a 2023 study reported sulfate-to-zero-valent-sulfur conversion by sulfate-reducing microorganisms. This is an important branch or boundary phenotype, but it should not replace sulfide as the canonical product without organism- and condition-specific evidence.
- **Oxygen exposure:** the metabolism is anaerobic, but possession of the trait does not imply obligate intolerance of oxygen. Sulfate reducers can survive oxic transitions, and some can switch to oxygen respiration.

## 2. Candidate nodes

### Trait and process nodes

- dissimilatory sulfate reduction — `traitmech:000105`
- sulfate respiration — synonym of the target trait
- anaerobic respiration — GO grounding candidate; verify exact GO CURIE before YAML insertion
- sulfate transport — GO grounding candidate
- APS reduction
- dissimilatory sulfite reduction
- electron transport / energy conservation
- sulfur isotope fractionation
- sulfide biomineralization / metal-sulfide precipitation

### Chemicals and metabolites

Use ChEBI records after identifier validation during ingestion:

- sulfate (`SO4²⁻`)
- ATP
- adenosine 5′-phosphosulfate, APS
- pyrophosphate
- sulfite (`SO3²⁻`)
- sulfide / hydrogen sulfide / hydrosulfide—represent protonation states explicitly if the graph schema permits
- DsrC trisulfide
- reduced and oxidized menaquinone
- electron donors: H₂, lactate, acetate, glycerol, and other organic substrates
- elemental or zero-valent sulfur, S(0)—branch product/alternative acceptor, not canonical endpoint
- iron(II)/iron(III), pyrite, and metal sulfides—downstream environmental nodes

Modern seawater contains about 28 mM sulfate, whereas many freshwater environments contain approximately 10–300 μM; sulfate limitation changes pathway flux and isotopic expression. (sim2023whatcontrolsthe pages 3-5, diao2023globaldiversityand pages 1-2)

Showing the first 60 of 206 lines of findings; the linked file also carries the run's front matter and the prompt it was given — read the full report.