Uraninite mineral
Uraninite is the UO2 mineral species listed with grandfathered status G and original-description year 1845 in the September 2026 IMA compilation. It is distinct from elemental uranium, uranyl salts, biomass-bound U(IV) complexes and uranium-bearing ores. The observation below concerns laboratory-formed nanocrystalline UO2 identified as uraninite, not a natural ore feed. No criticality designation is inherited from uranium.
Microbial & Biochemical Mechanisms (1)
Cytochrome-associated formation of nanocrystalline uraninite by MR-1
redox transformation
Microbial
Associated Organisms:
Shewanella oneidensis MR-1 (NCBITaxon:211586)
Living resting MR-1 cells reduce dissolved U(VI) and form U-bearing nanoparticles with diffraction consistent with uraninite. A cytochrome-maturation-deficient comparator fails to show comparable U(VI) reduction, while MtrC and OmcA deletion comparators retain slower activity. MtrC contributes to extracellular reduction and particle localization; it is not demonstrated to be the sole reductase. Extracellular polymeric material is associated with many particles, but its complete composition and causal function remain unresolved. This is a laboratory transformation observation, not a recovered-product yield or industrial deployment.
Experimental Context & Analytical Limits:
Marshall et al. used washed cells from a 16 h, 30 degrees C tryptic-soy-broth-minus-dextrose culture. Resting-cell assays used 250 micromolar U(VI) added as uranyl acetate, 10 mM sodium lactate, 30 mM sodium bicarbonate buffer initially pH 7.0 and a final density of 2 x 10^8 cells/mL. The anoxic N2/CO2 80:20 assay was incubated at 30 degrees C with 25 rpm shaking; kinetic measurements extended to 48 h, and standard localization samples were collected at 24 h. Soluble U(VI) in less-than-0.2-micrometre filtrates was measured by kinetic phosphorescence. TEM, selected-area diffraction and elemental analysis provided separate evidence about particles. Figure 1 shows means from representative experiments without a stated replicate count or uncertainty bars. No matched no-cell or killed-cell reduction time course is reported in that figure. The CcmC-deficient strain is a genetic comparator, not an abiotic blank. Heme and immune localization used a separate 100 micromolar U(VI) condition; other EPS characterization used fumarate in place of uranium. These preparations are not pooled as one quantitatively equivalent assay.
Marshall et al. used washed cells from a 16 h, 30 degrees C tryptic-soy-broth-minus-dextrose culture. Resting-cell assays used 250 micromolar U(VI) added as uranyl acetate, 10 mM sodium lactate, 30 mM sodium bicarbonate buffer initially pH 7.0 and a final density of 2 x 10^8 cells/mL. The anoxic N2/CO2 80:20 assay was incubated at 30 degrees C with 25 rpm shaking; kinetic measurements extended to 48 h, and standard localization samples were collected at 24 h. Soluble U(VI) in less-than-0.2-micrometre filtrates was measured by kinetic phosphorescence. TEM, selected-area diffraction and elemental analysis provided separate evidence about particles. Figure 1 shows means from representative experiments without a stated replicate count or uncertainty bars. No matched no-cell or killed-cell reduction time course is reported in that figure. The CcmC-deficient strain is a genetic comparator, not an abiotic blank. Heme and immune localization used a separate 100 micromolar U(VI) condition; other EPS characterization used fumarate in place of uranium. These preparations are not pooled as one quantitatively equivalent assay.
Curated Evidence Points:
Support
Source:
marshall2006
Figure 1 and Results show falling aqueous U(VI) in wild-type and slower MtrC/OmcA deletion cultures, with little change in the CcmC-deficient comparator. Figure 2I and Figure S4 combine lattice imaging, selected-area diffraction and U elemental signals, supporting nanocrystalline UO2 rather than inferring a mineral solely from solution loss. Reported 1-5 nm particles occur extracellularly and in the periplasm, with altered localization in the MtrC deletion comparators. Table S1 identifies the MR-1 derivatives and Figure S1 tests protein loss; these comparators do not prove that one cytochrome is the exclusive pathway.
Partial
Source:
marshall2006
Results and Figure S2 show electron transfer from purified reduced MtrC to uranyl citrate in a separate cell-free assay; OmcA shows no detectable corresponding activity under those conditions despite its whole-cell deletion phenotype. This ligand and preparation differ from the carbonate-buffered cellular experiment. Figures 3-6 support EPS association, not a demonstrated long-term immobilization benefit. The authors report partial particle oxidation during heme staining and leave EPS genesis and environmental stability unresolved. Figure 1 still shows residual aqueous U(VI) at 24 h despite the narrative describing complete reduction within 24 h; no exact complete-conversion endpoint or mineral yield is adopted here.
Partial
Source:
bernier_latmani2010
The separate MR-1 medium comparison limits extrapolation from U(VI) reduction to uraninite formation. Table 1, Figures 1-2 and SI Figures SI-1/SI-2 compare hydrogen-amended bicarbonate/ PIPES medium with fresh or spent Widdel low-phosphate medium. Sample A in the simple medium has diffraction-identified uraninite, whereas WLP samples are dominated by biomass-bound non-uraninite U(IV) interpretations. Figure 2B nevertheless allows a small amount of very small uraninite from broad diffraction rings, so the prose saying no uraninite is not treated as absolute phase absence. Main Table 2 and SI-1 allow P or C neighbors in the EXAFS fits; exclusive phosphate coordination is unproven. The main methods' generic 500 micromolar addition conflicts with Table 1's 400 or 100 micromolar WLP entries. This is contextual evidence for medium-dependent products, not a matched replication of the 2006 lactate assay or a refutation of its observed particles.
Context_only
Source:
ncbi_mr1
NCBI resolves 211586 at strain rank as Shewanella oneidensis MR-1. This identifies the wild-type strain; the experimental deletion derivatives are described by the primary paper and are not assigned invented separate taxonomy identifiers.
Sources & References
-
ima_2026_09: IMA-CNMNC. The New IMA List of Minerals, September 2026. Uraninite row on PDF page 224; column definitions and terms on pages 1-2. Retained original rechecked on the access date.
https://cnmnc.units.it/files/editor/IMA_Master_List_(2026-09).pdf (accessed 2026-10-11) -
marshall2006: Marshall et al. (2006). c-Type Cytochrome-Dependent Formation of U(IV) Nanoparticles by Shewanella oneidensis. PLOS Biology, e268. DOI 10.1371/journal.pbio.0040268. Methods, Results, Figures 1-6; original Figures S1-S6, Protocol S1 and Tables S1-S3.
https://doi.org/10.1371/journal.pbio.0040268 (accessed 2026-10-11) -
bernier_latmani2010: Bernier-Latmani et al. (2010). Non-uraninite Products of Microbial U(VI) Reduction. Environmental Science & Technology 44, 9456-9462. DOI 10.1021/es101675a. Methods, Tables 1-2, Figures 1-2; Supporting Information section SI-1, Tables SI-1/SI-2, Figures SI-1/SI-2 and sample B in Figure SI-4.
https://doi.org/10.1021/es101675a (accessed 2026-10-11) -
ncbi_mr1: NCBI Taxonomy 211586, Shewanella oneidensis MR-1, strain node.
https://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?id=211586 (accessed 2026-10-11)
Curation History
| Timestamp | Curator | Action | Summary |
|---|---|---|---|
2026-10-11T21:07:17Z |
codex (GPT-6; codex) | CREATE | Added uraninite identity and phase-supported MR-1 nanoparticle formation, retaining mutant and ligand limits, medium-dependent alternative products and source contradictions without assigning complete conversion or recovery. |
Record source: data/records/uraninite.yaml