Titanium element Critical Material
The element Ti, distinct from titanium dioxide phases, titanium-bearing mineral species, alloy formulations and the titanium-metal commodity. The United States 2025 Titanium designation is mapped to this element; it does not designate every titanium compound or establish microbial recovery of metallic titanium. The curated experiment concerns alteration of an oxide film on commercially pure titanium laboratory specimens.
Identifiers & Classification
| System | Identifier | Label |
|---|---|---|
| CHEBI |
CHEBI:33341
|
titanium atom |
Criticality Designations
| Jurisdiction | List Name | Edition / Document | Classification | Source |
|---|---|---|---|---|
| United States | Department of the Interior Final List of Critical Minerals | 2025 final list, published 7 November 2025 | critical |
us_2025
|
Microbial & Biochemical Mechanisms (1)
Shewanella-associated reduction of the titanium oxide passive film
redox transformation
Microbial
Associated Organisms:
Shewanella algae (NCBITaxon:38313)
Shewanella algae biofilms were associated with oxygen depletion near the titanium surface, a thinner oxide film, increased lower-valence titanium spectral components and enhanced corrosion relative to uninoculated controls. Riboflavin addition and overproduction support an electron-shuttle contribution. Reduction of the pre-existing oxide film and subsequent corrosion of underlying Ti are distinct processes; these experiments do not demonstrate recovery of a titanium product.
Experimental Context & Analytical Limits:
The reported strain is S. algae MCC 1A11468 from the Marine Culture Collection of China; the linked taxonomy ID resolves the species only. Commercially pure Ti cylinders were 10 mm in diameter and 3 mm high, with a 0.785 cm2 exposed electrochemical surface, ground to 1000 grit, ethanol-cleaned, water-rinsed and UV-sterilized for 30 min. The culture medium was 2216E at initial pH 7.2 +/- 0.2; Figure S1 shows changing pH rather than a constant-pH experiment. Main film and electrochemical comparisons run to 21 days in bulk aerobic medium. The separate Figure 5 mechanistic incubations were anaerobic, using lactate as donor and simulated seawater deoxygenated with filtered nitrogen for at least 30 min. The inspected main article and full supplement do not specify incubation temperature, starting cell density, lactate concentration or riboflavin amendment concentration. The RF construct overexpressed S. oneidensis MR-1 riboflavin genes in S. algae; it is not a second organism independently tested here. These are laboratory coupon experiments, not an industrial extraction or recovery process.
The reported strain is S. algae MCC 1A11468 from the Marine Culture Collection of China; the linked taxonomy ID resolves the species only. Commercially pure Ti cylinders were 10 mm in diameter and 3 mm high, with a 0.785 cm2 exposed electrochemical surface, ground to 1000 grit, ethanol-cleaned, water-rinsed and UV-sterilized for 30 min. The culture medium was 2216E at initial pH 7.2 +/- 0.2; Figure S1 shows changing pH rather than a constant-pH experiment. Main film and electrochemical comparisons run to 21 days in bulk aerobic medium. The separate Figure 5 mechanistic incubations were anaerobic, using lactate as donor and simulated seawater deoxygenated with filtered nitrogen for at least 30 min. The inspected main article and full supplement do not specify incubation temperature, starting cell density, lactate concentration or riboflavin amendment concentration. The RF construct overexpressed S. oneidensis MR-1 riboflavin genes in S. algae; it is not a second organism independently tested here. These are laboratory coupon experiments, not an industrial extraction or recovery process.
Curated Evidence Points:
Support
Source:
li_2026
Figure 1 and its Results report passive-film thickness of 8.0 +/- 0.7 nm in the abiotic control and 5.9 +/- 0.5 nm beneath biofilms after 21 days. Figure 1f samples ten image locations; these are not ten independent culture replicates. FIB-TEM, TOF-SIMS and XPS comparisons jointly support film alteration. Figure 2 reports a roughly sixfold higher corrosion current density after 21 days, derived by cathodic Tafel extrapolation, with mean and SD of three independent replicates. This fitted electrochemical outcome is not a measured dissolved-Ti yield.
Support
Source:
li_2026
Figure 5d-e compares wild type, riboflavin-overproducing RF and riboflavin-amended wild type. Greater extracellular riboflavin accompanies higher corrosion currents despite broadly similar biofilm biomass. The authors report no riboflavin effect in the abiotic medium, although the two plotted control means are not identical. Figure S7 is an abiotic reduced-riboflavin fluorescence assay with TiO2, while Figure 5a-c is a DFT calculation. These different observations support the shuttle model without proving that every Ti transformation requires living cells.
Partial
Source:
li_2026
Supplementary pages 12-13 acknowledge XPS fitting, charging and sputtering-induced reduction uncertainties; matching analytical settings support comparisons but do not eliminate artifacts. Figure 5g reuses the abiotic XPS data from Figure S2 rather than documenting a separate matched anaerobic control, and labels its abiotic TiO2 fraction 80.6%, whereas Figure 1h gives 84.2% at 3 nm. This unresolved difference prevents treating these spectral fractions as exact conversion yields. Supplementary methods describe CRISPRi of mtrA/mtrB/mtrC, but the inspected article and supplement present no corresponding repression outcome; a demonstrated requirement for MtrCAB is not curated.
Sources & References
-
chebi_titanium: ChEBI:33341 - titanium atom; formula Ti and net charge 0
https://www.ebi.ac.uk/chebi/CHEBI:33341 (accessed 2026-10-11) -
us_2025: US Department of the Interior, Geological Survey. Final 2025 List of Critical Minerals, 7 November 2025, Federal Register 90:50494-50497, document 2025-19813; Titanium row on page 50497.
https://www.govinfo.gov/content/pkg/FR-2025-11-07/html/2025-19813.htm (accessed 2026-10-11) -
li_2026: Li et al. (2026). Microbially reduced flavins destabilize the TiO2 passive film of titanium under bulk aerobic conditions. National Science Review 13(16):nwag426. DOI 10.1093/nsr/nwag426; Figures 1-6, Methods and Supplementary Materials, especially Figures S1, S2, S7, S9 and pages 12-14.
https://doi.org/10.1093/nsr/nwag426 (accessed 2026-10-11) -
ncbi_shewanella_algae: NCBI Taxonomy 38313 - Shewanella algae; species, not the experimental strain
https://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?id=38313&mode=Info (accessed 2026-10-11)
Curation History
| Timestamp | Curator | Action | Summary |
|---|---|---|---|
2026-10-11T07:24:26Z |
Codex (GPT-6; Codex) | CREATE | Created titanium identity and dated US criticality with controlled laboratory passive-film transformation evidence, distinct assay arms and preserved protocol, spectral and causal limits. |
Record source: data/records/titanium.yaml