Lepidocrocite mineral
Lepidocrocite is the Fe(III)O(OH) mineral species listed as approved (A), with 1980 special-procedure history, in the September 2026 IMA master list. The 1980 s.p. entry is not an approval-number CURIE. This species is distinct from goethite, akaganeite, iron element, iron-ore commodities, and the chemically prepared or commercial laboratory feeds discussed below. No iron criticality designation is inherited.
Microbial & Biochemical Mechanisms (1)
Formate-fed culture-associated lepidocrocite transformation to green-rust phases
redox transformation
Microbial
Associated Organisms:
Shewanella putrefaciens CN-32 (NCBITaxon:319224)
In the culture reported as Shewanella putrefaciens CN32, formate consumption accompanied Fe(II) accumulation and loss of detectable starting lepidocrocite with carbonate-green-rust formation. Chloride- and sulfate-amended cultures followed different phase trajectories. The evidence supports laboratory culture-associated reduction and secondary mineral formation; it does not demonstrate a uniquely biological pathway, fully reduced iron, a pure isolated recovery product, or industrial operation.
Experimental Context & Analytical Limits:
The primary feed was commercial lepidocrocite, Bayferrox 943, supplied at 80 mM Fe(III). The focused formate experiments used triplicate 250 mL serum bottles containing 200 mL defined mineral medium, 75 mM formate, 100 micromolar AQDS electron shuttle, and either 25 mM NaCl or 25 mM Na2SO4. Medium was adjusted initially to pH 7.5 and autoclaved before filter-sterilized donor/AQDS addition, sealed and argon-sparged. Late-log inoculum gave a reported 5 x 10^9 cells/mL; cultures were rolled in the dark at 30 degrees C for 62 days. The named CN32 strain maps to NCBI 319224 and ATCC BAA-453, while the paper prints ATCC BAA-543, which the authority identifies as Cellulomonas sp. ES5. This accession conflict is unresolved; the taxon records the paper's repeated strain name, not a verified chain of custody. The paper delegates the full basal-medium and inoculum recipes to earlier studies and cites an akaganeite paper for lepidocrocite characterization; no exact inherited recipe, surface area or chemical purity is assumed. Contemporaneous Figure 6 starting patterns and phase standards support the substrate assignment. The separate donor survey includes both a no-donor culture and a sterile control. Figure 1 plots the sterile-control total Fe(II) curve near baseline, but does not specify its donor and salt identity. It therefore supplies a reported negative comparator without establishing a chemistry-matched cell-free counterpart for each focused formate/AQDS chloride and sulfate arm.
The primary feed was commercial lepidocrocite, Bayferrox 943, supplied at 80 mM Fe(III). The focused formate experiments used triplicate 250 mL serum bottles containing 200 mL defined mineral medium, 75 mM formate, 100 micromolar AQDS electron shuttle, and either 25 mM NaCl or 25 mM Na2SO4. Medium was adjusted initially to pH 7.5 and autoclaved before filter-sterilized donor/AQDS addition, sealed and argon-sparged. Late-log inoculum gave a reported 5 x 10^9 cells/mL; cultures were rolled in the dark at 30 degrees C for 62 days. The named CN32 strain maps to NCBI 319224 and ATCC BAA-453, while the paper prints ATCC BAA-543, which the authority identifies as Cellulomonas sp. ES5. This accession conflict is unresolved; the taxon records the paper's repeated strain name, not a verified chain of custody. The paper delegates the full basal-medium and inoculum recipes to earlier studies and cites an akaganeite paper for lepidocrocite characterization; no exact inherited recipe, surface area or chemical purity is assumed. Contemporaneous Figure 6 starting patterns and phase standards support the substrate assignment. The separate donor survey includes both a no-donor culture and a sterile control. Figure 1 plots the sterile-control total Fe(II) curve near baseline, but does not specify its donor and salt identity. It therefore supplies a reported negative comparator without establishing a chemistry-matched cell-free counterpart for each focused formate/AQDS chloride and sulfate arm.
Curated Evidence Points:
Support
Source:
oloughlin_2019
Sections 2.1-2.2 and 3.3, Table 1, Figures 5-6 and Tables 2-3 link formate consumption, acid-extractable Fe(II), rising pH and mineral changes. At day 62 the chloride and sulfate formate arms report respectively 57.6 +/- 0.2 and 55.1 +/- 2.4 mM total Fe(II), versus 0.8 +/- 0.1 and 0.7 +/- 0.1 mM aqueous Fe(II). Total Fe(II) is the 0.75 M HCl, one-week extract measured by ferrozine; aqueous Fe(II) is measured on 0.22 micrometre filtrate. These fractions are not interchangeable. pXRD and Mossbauer analysis identify carbonate green rust and no detected residual lepidocrocite at the endpoint; the sulfate arm also has earlier sulfate-green-rust reflections. Nondetection does not quantify a zero residue or guarantee product purity.
Partial
Source:
oloughlin_2019
The statement that reduction was complete by day 55 means Fe(II) accumulation had plateaued, not that all starting Fe(III) became Fe(II): green rust retains Fe(III). The separate 72-day survey produced 3.6 mM Fe(II) without an exogenous donor and less than 7 mM with several ineffective donors, so absence of the preferred donor is not an absolute zero. Figure 1 also includes a distinct near-baseline sterile-control curve; no numerical sterile endpoint is adopted, and its unspecified donor/salt conditions prevent treating it as the matched focused-formate control. The H2/Pd/AQDS/carbonate abiotic surrogate produced more Fe(II) than the H2 biological treatments and also carbonate green rust; it is not a chemistry-matched formate control. Product identity alone is therefore not a unique biosignature. AQDS exposure and missing matched cell-free formate controls limit attribution to direct cell-mineral transfer or a specific enzyme. Table 2 fitted spectral areas are not mass-based mineral recovery yields. Modeled carbonate activities in Section 2.3 were not measured carbonate concentrations.
Context_only
Source:
sklute_2023
The separate Ax17 study used 55 degrees C, hydrogen and synthetic nanophase lepidocrocite, not the CN32/formate commercial feed. It reports dark nonmagnetic material with amorphous Fe-rich nanospheres but no significant oxalate-extractable Fe(II) increase over controls; lepidocrocite Mossbauer spectra remained nearly unchanged, the main text states bulk XRD was unavailable, and small amounts of green rust could only not be excluded. These analytical and phase limits show that transformation products and recoverable Fe(II) cannot be generalized across organisms, media, feeds or extraction methods; they do not directly refute the CN32 formate result. Supplementary Figure S16 inconsistently names lepidocrocite in its caption while describing akaganeite/NaCl and being assigned to akaganeite in the main text; that ambiguous panel is not treated as measured lepidocrocite XRD evidence.
Sources & References
-
ima_2026_09: IMA-CNMNC. The New IMA List of Minerals, September 2026. PDF pages 1-2 status/number definitions and distribution terms; page 5 Akaganeite, page 124 Lepidocrocite. Fresh official PDF inspected.
https://cnmnc.units.it/files/editor/IMA_Master_List_(2026-09).pdf (accessed 2026-10-14) -
oloughlin_2019: O'Loughlin EJ, Gorski CA, Flynn TM and Scherer MM (2019). Electron Donor Utilization and Secondary Mineral Formation during the Bioreduction of Lepidocrocite by Shewanella putrefaciens CN32. Minerals 9:434. DOI 10.3390/min9070434. Original complete publisher PDF and OSTI 1560537 copy: Sections 2.1-2.3 and 3.1-3.3, Tables 1-3, Figures 1-6, Discussion. The 29-page OSTI copy preserves the full-width Table 1 cropped in the 30-page publisher copy.
https://doi.org/10.3390/min9070434 (accessed 2026-10-14) -
ncbi_cn32: NCBI Taxonomy 319224, Shewanella putrefaciens CN-32; live taxonomy XML reports strain rank. Grounds the strain name reported by the paper, not independent authentication of its experimental stock.
https://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?id=319224 (accessed 2026-10-14) -
atcc_cn32: ATCC BAA-453, Shewanella putrefaciens, strain designation CN-32 [OCM 576, SMCC 576W]. The accession differs from BAA-543 printed in the experimental paper.
https://www.atcc.org/products/baa-453 (accessed 2026-10-14) -
atcc_es5: ATCC BAA-543, Cellulomonas sp., strain designation ES5. Verifies that the BAA-543 accession printed beside CN32 in the experimental paper does not resolve to the named strain.
https://www.atcc.org/products/baa-543 (accessed 2026-10-14) -
sklute_2023: Sklute et al. (2023). Fe(III) (oxyhydr)oxide reduction by the thermophilic iron-reducing bacterium Desulfovulcanus ferrireducens. Frontiers in Microbiology 14:1272245. Methods, Cell growth on akaganeite and lepidocrocite, Figures 5-8, Discussion; previously acquired original XML and supplement reinspected for bounded comparative context.
https://doi.org/10.3389/fmicb.2023.1272245 (accessed 2026-10-14)
Curation History
| Timestamp | Curator | Action | Summary |
|---|---|---|---|
2026-10-14T06:25:01.132038+00:00 |
codex (GPT-6; codex) | CREATE | Created distinct mineral identity with primary laboratory transformation evidence, authority-checked organism grounding, assay fractions, controls and unresolved source limitations. |
2026-10-14T06:41:15.704793+00:00 |
codex (GPT-6; codex) | EDIT | Address independent review F1 by retaining the Figure 1 sterile-control comparator while preserving unspecified donor/salt identity and the focused formate-control limitation. |
Record source: data/records/lepidocrocite.yaml