Akaganeite mineral
Akaganeite is a distinct iron oxyhydroxide mineral species, listed with formula (Fe(III),Ni(II))8(OH,O)16Cl1.25·nH2O, renamed status (Rn), and IMA number 1962-004 in the September 2026 IMA master list. The experimental abbreviation beta-FeOOH identifies the synthetic phase assignment used by the study; it does not establish the ideal IMA composition or nickel content of that preparation. This record is separate from iron element, other iron oxyhydroxide species, iron-ore commodities, and mixed waste feeds. No constituent criticality designation is inherited.
Identifiers & Classification
| System | Identifier | Label |
|---|---|---|
| IMA |
IMA:1962-004
|
Akaganeite |
Microbial & Biochemical Mechanisms (1)
Condition-dependent akaganeite reduction by Geobacter sulfurreducens PCA
redox transformation
Microbial
Associated Organisms:
Geobacter sulfurreducens PCA (NCBITaxon:243231)
Living wild-type Geobacter sulfurreducens PCA cultures increased acid-extractable Fe(II) from freshly prepared XRD-assigned akaganeite. Comparisons with delta-imcH and delta-cbcL mutants associate the timing and extent of reduction with those electron-transfer systems, with strong dependence on starting pH and autoclaving. The study supports conditional microbial Fe(III) reduction, not elemental iron production, a purified mineral product, or direct measurement of akaganeite redox potential.
Experimental Context & Analytical Limits:
The synthetic substrate was prepared by slowly titrating 0.4 M FeCl3 with 25% NaOH over 90 minutes to pH 7, holding for one hour, washing with water, and using it within 24 hours. Powder XRD assigned the product to akaganeite. Mineral incubations used 1 mL mineral suspension plus 9 mL modified NB basal medium, acetate as electron/carbon donor, no added fumarate, nitrilotriacetate-free trace minerals, and N2:CO2 (80:20). The basal recipe specifies 20 mM acetate; phosphate was increased to 0.69 g/L NaH2PO4·H2O before autoclaving. Separate comparisons used pH 6.8 or 6.3, with fresh medium or 20 minutes autoclaving at 121 degrees C. Each received 100 microlitres of stationary-phase cells grown on acetate/fumarate from separate colony picks. Figure 2 reports triplicate culture means and standard deviations, representative of at least duplicate incubations, over approximately 14-15 days. Samples were extracted in 0.5 N HCl for at least 24 hours at 23-25 degrees C before the ferrozine assay; that temperature is for extraction, while the mineral-culture incubation temperature is not stated in the inspected Methods. Acid-extractable Fe(II) is not a dissolved-only fraction. Initial akaganeite Fe loading is not independently quantified here; the nearby approximately 20 mM Methods statement follows the goethite preparation and is not transferred to this assay.
The synthetic substrate was prepared by slowly titrating 0.4 M FeCl3 with 25% NaOH over 90 minutes to pH 7, holding for one hour, washing with water, and using it within 24 hours. Powder XRD assigned the product to akaganeite. Mineral incubations used 1 mL mineral suspension plus 9 mL modified NB basal medium, acetate as electron/carbon donor, no added fumarate, nitrilotriacetate-free trace minerals, and N2:CO2 (80:20). The basal recipe specifies 20 mM acetate; phosphate was increased to 0.69 g/L NaH2PO4·H2O before autoclaving. Separate comparisons used pH 6.8 or 6.3, with fresh medium or 20 minutes autoclaving at 121 degrees C. Each received 100 microlitres of stationary-phase cells grown on acetate/fumarate from separate colony picks. Figure 2 reports triplicate culture means and standard deviations, representative of at least duplicate incubations, over approximately 14-15 days. Samples were extracted in 0.5 N HCl for at least 24 hours at 23-25 degrees C before the ferrozine assay; that temperature is for extraction, while the mineral-culture incubation temperature is not stated in the inspected Methods. Acid-extractable Fe(II) is not a dissolved-only fraction. Initial akaganeite Fe loading is not independently quantified here; the nearby approximately 20 mM Methods statement follows the goethite preparation and is not transferred to this assay.
Curated Evidence Points:
Support
Source:
levar_2017
Methods and Results, Evidence that the electron transfer pathway changes even in the absence of XRD pattern changes, plus Figure 2 show wild-type reduction at pH 6.8 and no observable reduction in the reported 14-day cell-free controls. Delta-cbcL starts reducing but stalls below wild type; fresh-medium delta-imcH has a roughly seven-day lag before approaching the wild-type endpoint. Autoclaving at pH 6.8 shortens that lag. At pH 6.3, delta-imcH reduction is strongly suppressed and autoclaving does not restore it. Table 1 fumarate-growth comparisons help exclude a gross pH-dependent growth defect. These are condition-specific phenotypes, not universal knockout inability.
Partial
Source:
levar_2017
The discussion explicitly states that mineral redox potentials cannot be directly measured in these experiments; quantitative voltage measurements in Figure 1 concern soluble Fe(III)-citrate, not akaganeite. Similar powder XRD before/after autoclaving does not exclude changes in aggregation, short-range order or surface properties. Direct ImcH/CbcL electron movement from the quinone pool is not demonstrated, and complementation is cited from earlier studies rather than performed as a Figure 2 control. The record therefore retains pathway association and inferred redox interpretation without treating a particular mineral voltage, direct protein mechanism, complete feed conversion, isolated recovery or industrial deployment as demonstrated.
Context_only
Source:
sklute_2023
A separate 55 degrees C hydrogen-fed Ax17 experiment on synthetic nanophase akaganeite gave a dark nonmagnetic product with amorphous iron-rich nanospheres; oxalate-extractable Fe(II) was not significantly different from controls, while temperature-dependent Mossbauer analysis detected new ferric and ferrous components with nonunique phase fits. Heated abiotic controls also changed. That different organism, medium and analytical extraction is not a direct replication or refutation of PCA reduction, and cautions against assuming a universal crystalline recovery product or equating an extraction null with no transformation.
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) -
levar_2017: Levar CE, Hoffman CL, Dunshee AJ, Toner BM and Bond DR (2017). Redox potential as a master variable controlling pathways of metal reduction by Geobacter sulfurreducens. ISME Journal 11:741-752. DOI 10.1038/ismej.2016.146. Complete 12-page original and Europe PMC XML: Methods pp742-744, Table 1, Results pp745-749, Figure 2.
https://doi.org/10.1038/ismej.2016.146 (accessed 2026-10-14) -
ncbi_pca: NCBI Taxonomy 243231, Geobacter sulfurreducens PCA; live taxonomy XML reports strain rank. This identifier does not separately identify the engineered deletion mutants.
https://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?id=243231 (accessed 2026-10-14) -
atcc_pca: ATCC 51573, Geobacter sulfurreducens, strain designation PCA. Independently resolves the wild-type collection number printed as ATCCZ51573 in Levar et al. Table 1.
https://www.atcc.org/products/51573 (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. |
Record source: data/records/akaganeite.yaml