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Silicon element Critical Material

The element Si, distinct from dissolved silicic acid, biogenic silica, crystalline silica minerals and the silicon-metal commodity. The United States 2025 list's Silicon material designation is mapped to this element; it does not designate every silicate or imply that diatom silica formation recovers semiconductor-grade or metallic silicon.

Identifiers & Classification

System Identifier Label
CHEBI CHEBI:27573 silicon 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)

Conditional SIT contribution to diatom silicic-acid uptake and silica incorporation

biomineralization Microbial

Associated Organisms: Thalassiosira pseudonana CCMP1335 (NCBITaxon:296543)

Living Thalassiosira pseudonana CCMP1335 cultures depleted silicic acid from medium and incorporated a fluorescent silica tracer into their frustules. Joint SIT1/SIT2 knockdown delayed solution depletion and reduced the silica-associated fluorescence at low silicic-acid supply. This supports a conditional contribution to silicon utilization and cell-wall biosilicification, without establishing an exclusive transporter, a directly demonstrated sensing pathway, or metal recovery.

Experimental Context & Analytical Limits:
Laboratory stock cultures grew in NEPC medium containing 100 micromolar Si(OH)4, on an orbital shaker at 18 degrees C under continuous light of 100 microeinsteins/m2/s. Exponentially growing cells were harvested and deprived of silicic acid before replenishment. Silica-incorporation Methods specify 24 h deprivation; Figures 7-8 describe overnight starvation. Sodium silicate supplied a nominal 20 micromolar Si(OH)4 concentration for the selected assays. Silicomolybdate colorimetry of centrifuged supernatant measured disappearance, normalized per cell; this is a net-depletion proxy for uptake. PDMPO at 100 ng/mL, added five minutes before silicate, provided a flow-cytometric proxy for newly incorporated silica. A subset of clones was compared at 200 micromolar supply in a separate incorporation assay. Measured assay pH and an abiotic medium-depletion blank are not specified in the inspected main methods. No isolated silica mass, crystallographic phase, Si(0) product or industrial deployment is established here.
Curated Evidence Points:
Figure 7 compares wild type with RNAi clones R-13, R-14 and R-22 and antisense clones A-2, A-7 and A-8. Results report that wild type depleted the supplied silicic acid by 2 h, whereas the RNAi clones required an additional hour; antisense clones showed a similar delay. Figure 8A-B shows lower PDMPO fluorescence in the knockdowns at 20 micromolar supply. These are different assays and do not equate net solution depletion with the amount of solid silica.
Figure 8C tests wild type, R-13, A-2 and A-7 at 200 micromolar supply. The authors report no incorporation difference in this comparison; the plotted trajectories are not numerically identical. Figures 7-8 state standard deviations with n=3 but do not identify independent culture versus technical replication. The captions provide no inferential statistical test for the high-supply null statement. This limits claims that SIT knockdown universally suppresses silicification or that passive diffusion was directly demonstrated by this assay.
Vector design and Figure 6 establish knockdown rather than gene deletion. Sequence similarity prevented separate SIT1 and SIT2 perturbations; the immunoblot antiserum recognized all three SITs. No rescue experiment is described in the inspected main article. A sensing role is the authors' hypothesis, with an upstream sensor retained as an alternative. Supplementary construct/alignment files could not be acquired through the checked legitimate routes, so their sequences and supplementary predictions were not verified.

Sources & References

  1. chebi_silicon: ChEBI:27573 - silicon atom; formula Si and net charge 0
    https://www.ebi.ac.uk/chebi/CHEBI:27573 (accessed 2026-10-11)
  2. 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; Silicon row on page 50497.
    https://www.govinfo.gov/content/pkg/FR-2025-11-07/html/2025-19813.htm (accessed 2026-10-11)
  3. shrestha_2015: Shrestha and Hildebrand (2015). Evidence for a Regulatory Role of Diatom Silicon Transporters in Cellular Silicon Responses. Eukaryotic Cell 14:29-40. DOI 10.1128/EC.00209-14; PMC4279021. Culture conditions, silicon uptake and silica incorporation methods; Results and Figures 6-8; Discussion.
    https://doi.org/10.1128/EC.00209-14 (accessed 2026-10-11)
  4. ncbi_ccmp1335: NCBI Taxonomy 296543 - Thalassiosira pseudonana CCMP1335; strain-specific entry displayed as no rank in the Taxonomy Browser.
    https://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?id=296543&mode=Info (accessed 2026-10-11)

Curation History

Timestamp Curator Action Summary
2026-10-11T06:50:31Z Codex (GPT-6; Codex) CREATE Created silicon identity and dated US criticality with primary diatom uptake and silica-incorporation evidence, preserving conditional joint knockdown effects and assay, causal and supplementary-access limits.

Record source: data/records/silicon.yaml