lithoautotrophic

Deep research

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

# Curation report: lithoautotrophic

## 1. Trait record and scope

- **Trait label:** lithoautotrophic
- **Trait identifier:** `METPO:1000647`
- **Category / kind / status:** PHYSIOLOGY / CLASS / REVIEWED
- **Parent:** `METPO:1000631`
- **Synonym:** lithoautotroph
- **Operational definition:** a trophic state in which inorganic electron donors supply electrons for energy conservation and reducing power, while CO2/HCO3− supplies the carbon incorporated into biomass.

The decisive phenotype is therefore a **conjunction**: demonstrated inorganic-donor utilization **and** net autotrophic assimilation of inorganic carbon under the same compatible growth condition. Donor oxidation alone is lithotrophy, not necessarily lithoautotrophy; conversely, anaplerotic CO2 incorporation by a heterotroph is not autotrophy. A sulfur oxidizer lacking canonical carbon-fixation pathways and relying on organic-carbon uptake illustrates the chemolithoheterotrophic boundary case. Accordingly, sulfur-, H2-, Fe(II)-, ammonia-, or electrode-oxidation genes alone must not trigger this trait annotation.

“Chemolithoautotrophic” is the dominant microbial implementation, in which chemical oxidation drives energy conservation. Photolithoautotrophy is also within the lexical scope when an inorganic electron donor and light jointly support CO2 fixation, but it should be represented as a qualified branch rather than conflated with dark chemolithoautotrophy. Facultative autotrophs and mixotrophs qualify only in the conditions where inorganic donors and inorganic carbon demonstrably support growth. Extracellular-electron uptake is a specialized lithotrophic branch, not a universal requirement. In *Rhodopseudomonas palustris* TIE-1, cathodic electrons enter the photosynthetic electron-transport chain and CO2 fixation is the principal sink; deleting Rubisco genes reduced extracellular-electron uptake by approximately 90%, providing unusually direct causal evidence. (guzman2019phototrophicextracellularelectron pages 12-12)

## 2. Recommended graph architecture

The existing 15-node/12-edge graph should retain a small **universal core** and add alternative, taxon-qualified branches:

1. **Inorganic electron donor** → donor-specific oxidation/electron-uptake module.
2. Oxidation module → electron-transport chain.
3. Electron transport → ion-motive force and ATP generation.
4. Electron transport/reverse electron flow → reduced ferredoxin or NAD(P)H.
5. ATP + reductant + CO2/HCO3− → one of several autotrophic carbon-fixation pathways.
6. Fixed-carbon intermediates → biomass formation.
7. Terminal electron acceptor and physicochemical conditions → enable or constrain the foregoing processes.

No single donor, acceptor, enzyme, or carbon-fixation pathway is necessary across all lithoautotrophs. In particular, Rubisco must not be made obligatory because rTCA-, Wood–Ljungdahl-, and hydroxypropionate-cycle lithoautotrophs exist. The Wood–Ljungdahl pathway uses CODH/acetyl-CoA synthase and reduced ferredoxin and is exceptionally energy-efficient, requiring approximately one ATP per CO2 in the reviewed accounting. (pillot2023sparkoflife pages 9-11)

## 3. Candidate nodes

The following matrix separates broadly reusable nodes from lineage-specific candidates.

| Module/node group | Representative entities | Mechanistic role | Evidence strength or curation caveat |
|---|---|---|---|
| Inorganic electron donors | H2; reduced sulfur compounds (H2S, HS−, S0, S2O3^2−); Fe(II); NH3/NH4+; extracellular electrons; CO | Define the lithotrophic side of the trait by supplying electrons for energy conservation and reducing power generation; donor use is taxon- and condition-specific (gupta2020extracellularelectronuptake pages 8-9, laufermeiser2024oxidationofsulfur pages 3-4, laufermeiser2024oxidationofsulfur pages 1-2, jahn2024theenergymetabolism pages 1-2, wang2024novelisolatesof pages 12-15) | Strong for H2, sulfur, Fe(II), and extracellular electrons in specific taxa; ammonia is well established for nitrifiers but not directly extracted here as a curation-ready mechanistic edge; CO appears in broader literature but is weaker in the gathered evidence for this trait report |
| Electron acceptors | O2; NO3−; S0/electrode in specialized electrotrophic contexts | Accept terminal electrons during respiration or linked redox metabolism; acceptor availability shapes whether inorganic donor oxidation supports growth and CO2 fixation (gupta2020extracellularelectronuptake pages 8-9, laufermeiser2024oxidationofsulfur pages 1-2, jahn2024theenergymetabolism pages 1-2, wang2024novelisolatesof pages 7-9) | Strong that O2 and nitrate commonly gate lithoautotrophic growth; exact acceptor pairing is lineage-specific and should be curated with condition qualifiers |
| Electron transport / energy conservation | Reverse electron transport; proton motive force; ATP synthesis; NAD(H)/NADPH regeneration; respiratory complexes I–IV; terminal oxidases; outer-membrane electron conduits | Couples donor oxidation or extracellular electron uptake to ATP production and reducing-equivalent generation required for autotrophic growth (gupta2020extracellularelectronuptake pages 9-10, gupta2020extracellularelectronuptake pages 8-9, jahn2024theenergymetabolism pages 1-2, wang2024novelisolatesof pages 7-9) | Strong at pathway/process level; specific conduits differ across taxa and should not be over-generalized to all lithoautotrophs |
| Hydrogen oxidation machinery | [NiFe]-hydrogenases; soluble and membrane-bound hydrogenases; multiple hydrogenase subgroups | Oxidize H2 and feed electrons into respiratory metabolism; in some taxa both soluble and membrane-bound enzymes contribute to lithoautotrophic growth (laufermeiser2024oxidationofsulfur pages 4-6, jahn2024theenergymetabolism pages 1-2, wang2024novelisolatesof pages 7-9, wang2024novelisolatesof pages 12-15) | Strong for hydrogenotrophic lithoautotrophs; exact subtype usage is species-specific |
| Sulfur oxidation machinery | Sox system; incomplete Sox variants; sulfide:quinone oxidoreductase (Sqr); tetrathionate-related sulfur oxidation modules | Oxidize reduced sulfur compounds to conserve energy for autotrophic carbon fixation (laufermeiser2024oxidationofsulfur pages 4-6, laufermeiser2024oxidationofsulfur pages 6-8, wang2024novelisolatesof pages 7-9, wang2024novelisolatesof pages 12-15) | Strong that sulfur oxidation supports lithoautotrophy; exact gene complements vary, and incomplete Sox pathways may yield intermediate sulfur storage rather than complete oxidation |
| Iron oxidation machinery | Fe(II) oxidation modules; candidate unknown Fe-oxidation factors | Enable ferrous iron as electron donor for autotrophic growth in some lineages (laufermeiser2024oxidationofsulfur pages 3-4, laufermeiser2024oxidationofsulfur pages 1-2, laufermeiser2024oxidationofsulfur pages 9-10) | Moderate: physiology supports Fe(II)-linked growth/CO2 fixation, but known canonical Fe-oxidation genes were not detected in Hydrogenovibrio, so mechanistic nodes remain partly unresolved |
| Extracellular electron uptake | Electrode/solid-phase conductive substances; cathodic electron flow; phototrophic/electroautotrophic uptake systems | Allows electrons from insoluble or electrical sources to enter metabolism and support CO2 fixation in specialized autotrophs (gupta2020extracellularelectronuptake pages 9-10, guzman2019phototrophicextracellularelectron pages 12-12) | Strong for specialized electroautotrophs, but should be marked as a subtype/special case rather than universal lithoautotrophy |
| Carbon-fixation pathways | Calvin-Benson-Bassham cycle; reverse TCA cycle; Wood-Ljungdahl pathway; 3-hydroxypropionate/4-hydroxybutyrate pathway | Define the autotrophic side of the trait by converting CO2/HCO3− into biomass precursors; alternative pathways occur across bacterial and archaeal lithoautotrophs (pillot2023sparkoflife pages 9-11, laufermeiser2024oxidationofsulfur pages 4-6, jahn2024theenergymetabolism pages 1-2, wang2024novelisolatesof pages 7-9, wang2024novelisolatesof pages 12-15) | Strong at pathway-class level; no single CO2-fixation pathway should be made obligatory for the trait |
| Carbon-fixation enzymes | RubisCO forms IA/IAq/II; cbbLS; ATP-citrate lyase (aclAB); 2-oxoglutarate:ferredoxin oxidoreductase (oorABCD); pyruvate:ferredoxin oxidoreductase (porABCD); CODH/ACS | Catalyze pathway-specific CO2 assimilation steps and provide stronger causal anchors than pathway labels alone (pillot2023sparkoflife pages 9-11, laufermeiser2024oxidationofsulfur pages 6-8, wang2024novelisolatesof pages 7-9, wang2024novelisolatesof pages 12-15) | Strong when tied to a specific pathway/taxon; CODH/ACS mainly anchors Wood-Ljungdahl and should not be generalized beyond acetogens/methanogens and related autotrophs |
| Core physiological process node | CO2/HCO3− fixation into biomass | Operational hallmark distinguishing lithoautotrophy from chemolithoheterotrophy or sulfur/hydrogen oxidation without net autotrophic growth (laufermeiser2024oxidationofsulfur pages 3-4, laufermeiser2024oxidationofsulfur pages 4-6, laufermeiser2024oxidationofsulfur pages 1-2) | Very strong trait-defining node; absence of canonical fixation genes can indicate a boundary case rather than lithoautotrophy |
| Boundary/counterexample module | Sulfur oxidation plus organic carbon uptake without canonical autotrophic pathway | Demonstrates that inorganic donor oxidation alone does not suffice for lithoautotrophic annotation (gupta2020extracellularelectronuptake pages 8-9) | Strong warning: chemolithoheterotrophs and mixotrophs should not be auto-curated as lithoautotrophs without net autotrophic evidence |
| Assays and phenotype readouts | Growth on inorganic donor + CO2/HCO3− medium; 14C-bicarbonate incorporation; RubisCO activity assays; donor oxidation rates; transcriptomics under donor shifts | Provide curation-grade phenotype evidence linking inorganic donor use to autotrophic biomass production (laufermeiser2024oxidationofsulfur pages 3-4, laufermeiser2024oxidationofsulfur pages 4-6, laufermeiser2024oxidationofsulfur pages 1-2) | Strong when multiple assays agree; transcriptomics alone is supportive, not sufficient for phenotype assignment |
| Quantitative donor/CO2 fixation data | H2 oxidation 75.4–145.2 nmol ml−1 h−1; thiosulfate oxidation 1.05–2.06 μmol ml−1 h−1; Fe(II) oxidation 0.008–0.016 μmol ml−1 h−1; vent-scale estimates up to 84 mmol CO2 fixation h−1 on thiosulfate for one strain | Quantifies donor-specific support for autotrophy and supports prioritizing donor-specific edges in curation (laufermeiser2024oxidationofsulfur pages 8-9, laufermeiser2024oxidationofsulfur pages 4-6, laufermeiser2024oxidationofsulfur pages 1-2, laufermeiser2024oxidationofsulfur pages 9-10) | Strong but taxon-specific; do not generalize magnitudes beyond the studied Hydrogenovibrio strains |
| Environmental controls | Microoxic vs oxic conditions; nitrate availability; donor identity; hydrothermal vent geochemistry; low-ammonium oligotrophic niches | Environmental context constrains whether lithoautotrophic modules are active and which donor/acceptor/pathway combinations dominate (laufermeiser2024oxidationofsulfur pages 3-4, laufermeiser2024oxidationofsulfur pages 1-2, laufermeiser2024oxidationofsulfur pages 6-8, jahn2024theenergymetabolism pages 1-2) | Strong that the trait is condition-dependent; many edges should carry environmental qualifiers rather than be asserted as unconditional |
| Real-world/application context | Hydrothermal vent primary production; electroautotrophic growth using hydrovoltaic or electrode-derived electrons; biotechnological CO2 conversion chassis such as Cupriavidus | Shows the trait’s ecological and applied relevance, including chemosynthetic production and engineered CO2 utilization systems (gupta2020extracellularelectronuptake pages 9-10, jahn2024theenergymetabolism pages 1-2) | Useful context, but application-specific engineering components should be curated separately from the core natural trait unless directly intrinsic to lithoautotrophy |


*Table: This table summarizes candidate node groups for curating the lithoautotrophic trait, emphasizing what is broadly supported versus what is taxon- or condition-specific. It is useful for deciding which entities belong in a core TraitMech graph and which should be marked as qualified or uncertain.*

### 3.1 Conservative ontology grounding

Use identifiers only after checking the target ontology release. Safe or high-confidence candidates include:

| Node | Suggested grounding | Curation note |
|---|---|---|

Showing the first 60 of 213 lines of findings; the linked file also carries the run's front matter and the prompt it was given — read the full report.