lithotrophic

Deep research

Generated by just research-trait; source: research/traits/physiology/lithotrophic-deep-research-falcon.md

# Curation report: lithotrophic

## Trait record and scope

- **Trait label:** lithotrophic
- **Trait identifier:** **“METPO:1000649”**
- **Category / kind / status:** PHYSIOLOGY / CLASS / REVIEWED
- **Parent:** METPO:1000631
- **Synonyms:** TT_lithotroph; lithotroph
- **Operational definition:** a trophic type in which an organism uses inorganic compounds as electron donors for energy generation.

### Interpretation for TraitMech

Lithotrophy classifies the **source of reducing electrons**, not the carbon source, terminal electron acceptor, or primary energy source. A lithotroph oxidizes an inorganic donor—commonly H₂, NH₃/NH₄⁺, NO₂⁻, H₂S/HS⁻, S⁰, S₂O₃²⁻, Fe(II), CO, or an inorganic mineral/electrode—and transfers the electrons into an energy-conserving system. The recurrent mechanistic pattern is:

**inorganic donor → donor-specific oxidoreductase/conduit → electron carriers and respiratory or photosynthetic chain → electrochemical ion gradient → ATP synthesis**, often with reverse electron transport or electron bifurcation supplying low-potential reductant for biosynthesis.

Lithotrophy does **not** imply autotrophy. A lithoautotroph fixes inorganic carbon, whereas a lithoheterotroph uses an inorganic electron donor but obtains biomass carbon from organic compounds. Similarly, chemolithotrophs derive energy from chemical oxidation, while photolithotrophs combine inorganic electron donors with light-driven energy conversion. Organisms may switch among lithotrophic, organotrophic, autotrophic, heterotrophic, and mixotrophic modes; therefore, the trait should be curated from demonstrated physiology rather than inferred solely from taxonomy.

Extracellular electron uptake (EEU) is a boundary case. It qualifies when an insoluble inorganic mineral or electrode is experimentally shown to supply electrons that support energy metabolism or growth. EEU includes direct outer-membrane conduits and indirect redox shuttles, but it is not a universal mechanism of lithotrophy. (gupta2020extracellularelectronuptake pages 1-2)

## Recommended graph design

The existing 19-node/12-edge graph should be retained as a **generic core**, with donor-specific branches represented as alternative modules rather than a single universal pathway. This avoids implying that every lithotroph carries hydrogenase, Sox, AMO, NXR, Cyc2, or the same carbon-fixation pathway.

| donor/module | initiating catalyst or conduit | downstream energy-conservation module | representative acceptor/carbon-fixation coupling | evidence strength/limitations |
|---|---|---|---|---|
| H2 lithotrophy | [NiFe]-hydrogenase; membrane-bound/extracellular uptake hydrogenase in some taxa (colman2024themicrobialecology pages 21-24) | electrons relayed to quinones/ubiquinone, then cytochrome complexes/terminal oxidases or ferrireductase; proton translocation generates PMF; ATP and NADH generation supported (colman2024themicrobialecology pages 21-24, gupta2020extracellularelectronuptake pages 5-6) | O2 or Fe(III) can serve as acceptors in documented systems; H2-supported autotrophy occurs in serpentinites and SRB/acetogen systems; carbon fixation may couple via Wood–Ljungdahl or other autotrophic routes depending on taxon (colman2024themicrobialecology pages 11-14, gupta2020extracellularelectronuptake pages 5-6) | Strong for H2 as inorganic donor and hydrogenase–quinone–PMF coupling; specific chain architecture is taxon-specific and partly inferred from omics/models outside a few systems (colman2024themicrobialecology pages 21-24, gupta2020extracellularelectronuptake pages 5-6) |
| Reduced sulfur oxidation | Sox pathway components (soxXA, soxYZ, soxB, soxCD); S4I components tsdA and tetH; rDsr/incomplete Sox in some lineages (twible2024phandthiosulfate pages 1-2) | sulfur oxidation feeds respiratory electron transport; pathway choice correlates with acidity generation vs limited acidity generation under different pH regimes (twible2024phandthiosulfate pages 1-2) | Commonly coupled to O2 or NO3- reduction in sulfur oxidizers; sulfur oxidizers often fix CO2 via CBB cycle in reviewed examples (gupta2020extracellularelectronuptake pages 8-9, twible2024phandthiosulfate pages 1-2) | Strong for sulfur donors supporting lithotrophy; exact initiating enzyme differs among sulfur species and taxa; SQR-specific evidence was not directly retrieved here, so curate Sox/S4I/rDsr conservatively and leave SQR as candidate-only (twible2024phandthiosulfate pages 1-2, gupta2020extracellularelectronuptake pages 8-9) |
| Ammonia oxidation | AMO (ammonia monooxygenase); downstream oxidation of hydroxylamine and possibly nitric oxide remains mechanistically unresolved in AOA compared with canonical bacterial models (wright2023nitrificationandbeyond pages 5-7) | ammonia oxidation supplies reductant for respiratory energy conservation and autotrophy; detailed electron-transfer steps vary across AOA/AOB and are incompletely resolved in AOA (wright2023nitrificationandbeyond pages 5-7) | AOA are chemolithoautotrophs fixing carbon via the 3-hydroxypropionate/4-hydroxybutyrate pathway; experimentally confirmed energy-yielding substrates include ammonia, urea, cyanate, hydroxylamine, and hydrazine (wright2023nitrificationandbeyond pages 5-7) | Strong that ammonia oxidation is lithotrophic; weak/moderate for universal mechanistic edges beyond AMO because archaeal downstream pathway details remain uncertain and differ from bacterial textbook schemes (wright2023nitrificationandbeyond pages 5-7) |
| Nitrite oxidation | nitrite oxidoreductase (NXR/NOR) (supported in retrieved nitrite-oxidizer summaries) | nitrite oxidation transfers electrons into electron transport and can require reverse electron transport for reducing power (supported in retrieved nitrite-oxidizer summaries) | nitrite-oxidizing bacteria are chemolithoautotrophs; carbon fixation can proceed via reductive TCA in Nitrospina/Nitrospira examples from retrieved searches, but these details were not in gathered-context IDs and should be added cautiously | Moderate: nitrite oxidation is a clear lithotrophic module, but direct citation support in gathered context IDs is limited; avoid over-curating transporter/topology details without stronger in-context evidence |
| Fe(II) oxidation | outer membrane cytochrome c conduit Cyc2 in iron oxidizers; Fe(II)-derived electrons transferred toward periplasmic/interior carriers (gupta2020extracellularelectronuptake pages 3-3) | reviewed examples support electron transfer through cytochrome networks and reverse electron transfer in some Fe-oxidizing/autotrophic systems; PMF generation is part of the broader EEU/Fe oxidation framing (gupta2020extracellularelectronuptake pages 8-9, gupta2020extracellularelectronuptake pages 9-10) | Fe(II) oxidation supports chemolithotrophic carbon assimilation in iron oxidizers; representative donors include FeS, FeCO3, FeS2, Fe3O4, and green rust in reviewed EEU context (gupta2020extracellularelectronuptake pages 3-3) | Moderate: Fe(II) as donor and Cyc2 as conduit are well supported, but specific downstream chain components are lineage-specific and much evidence is comparative/review-based rather than direct biochemistry in the gathered set (gupta2020extracellularelectronuptake pages 3-3, gupta2020extracellularelectronuptake pages 8-9) |
| Extracellular electron uptake (electrode/mineral/cell-derived electrons) | multiheme c-type cytochromes; outer membrane conduits; periplasmic cytochromes such as tetraheme c3 in SRB examples (gupta2020extracellularelectronuptake pages 1-2, gupta2020extracellularelectronuptake pages 5-6) | electrons routed to inner-membrane quinone-interacting complexes (for example Qrc/Tmc, QmoABC, DsrMKJOP in SRB examples), generating transmembrane proton gradients and supporting ATP synthesis/reverse electron flow (gupta2020extracellularelectronuptake pages 5-6) | documented in autotrophs including sulfur oxidizers, iron oxidizers, SRB, acetogens, and phototroph-linked systems; can support CO2 fixation where reducing power is generated (gupta2020extracellularelectronuptake pages 1-2, gupta2020extracellularelectronuptake pages 9-10) | Moderate and assay-specific: EEU is relevant as a lithotrophic-like edge when insoluble inorganic donors/electrodes serve as electron sources, but mechanisms are not universal and many examples are model-system specific (gupta2020extracellularelectronuptake pages 1-2, gupta2020extracellularelectronuptake pages 5-6) |
| Shared respiratory core across lithotrophs | donor-specific oxidoreductase/conduit feeds quinone pool and cytochrome carriers (colman2024themicrobialecology pages 21-24, gupta2020extracellularelectronuptake pages 5-6) | quinone/cytochrome electron transport drives ion-gradient formation (PMF); ATP synthesis and often reverse electron flow/NADH generation follow (gupta2020extracellularelectronuptake pages 5-6) | coupled variably to O2, NO3-, Fe(III), and carbon fixation modules depending on taxon and environment (colman2024themicrobialecology pages 11-14, gupta2020extracellularelectronuptake pages 8-9) | Strong as a high-level conserved motif, but not every lithotroph uses the same quinone, cytochromes, or carbon-fixation pathway; curate as an abstract module, not a single universal gene set (gupta2020extracellularelectronuptake pages 5-6, colman2024themicrobialecology pages 21-24) |


*Table: This table summarizes evidence-backed donor modules and shared bioenergetic architecture relevant to curating the lithotrophic trait. It highlights where evidence is strong enough for core TraitMech edges and where mechanisms remain taxon-specific or uncertain.*

## Candidate nodes grouped by type

### 1. Trait and process nodes

| Candidate node | Suggested grounding | Curation role |
|---|---|---|
| lithotrophic | **METPO:1000649** | Target trait |
| oxidation–reduction process | GO:0055114 | Broad process; use only if allowed by schema |
| electron transport chain | GO:0022900 | Shared energy-conservation module |
| respiratory electron transport chain | GO:0022904 | Chemolithotrophic branch |
| proton motive force / proton electrochemical gradient | Label; GO:0015988 may be considered for energy coupled proton transport | Intermediate energetic state |
| ATP synthesis coupled proton transport | GO:0015986 | Conserved energetic output |
| carbon fixation | GO:0015977 | Optional downstream process; not part of the defining trait |
| reverse electron transport | Label-only candidate | Generates low-potential reductant in several lithotrophs |
| extracellular electron uptake | Label-only candidate | Assay-specific extension |

### 2. Inorganic electron donors and products

Recommended chemical nodes include molecular hydrogen (**CHEBI:18276**), ammonia (**CHEBI:16134**), ammonium (**CHEBI:28938**), nitrite (**CHEBI:16301**), nitrate (**CHEBI:17632**), hydrogen sulfide (**CHEBI:16136**), thiosulfate (**CHEBI:26977**), elemental sulfur (label; validate the intended CHEBI form), ferrous iron/Fe(II) (**CHEBI:29033**), ferric iron/Fe(III) (**CHEBI:29034**), carbon monoxide (**CHEBI:17245**), carbon dioxide (**CHEBI:16526**), oxygen (**CHEBI:15379**), and electron (**CHEBI:10545**). Exact protonation states should match assay pH and source wording.

Additional sulfur nodes—HS⁻, sulfite, sulfate, tetrathionate, and polysulfides—should be added only to the relevant sulfur-oxidation subgraph. Mineral donors such as FeS, FeCO₃, FeS₂, Fe₃O₄, and green rust are documented in the EEU/iron-lithotrophy literature, but mineral phase and oxidation state must be represented precisely. (gupta2020extracellularelectronuptake pages 3-3)

Showing the first 60 of 212 lines of findings; the linked file also carries the run's front matter and the prompt it was given — read the full report.