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Hydroxylapatite mineral

Hydroxylapatite is the hydroxyl-dominant apatite mineral species Ca5(PO4)3(OH), commonly called hydroxyapatite in experimental literature. The September 2026 IMA list gives renamed status and 2010 s.p.; this is a nomenclatural special procedure, not a new-mineral accession. It is distinct from fluorapatite, chlorapatite, generic apatite, mixed phosphate rock and elemental phosphorus or calcium. This record concerns source-assigned nanocrystalline hydroxyapatite in a laboratory biofilm model, without assuming a measured pure end-member composition, criticality designation or industrial recovery.

Microbial & Biochemical Mechanisms (1)

Biofilm-associated nanocrystalline calcium-phosphate precipitation

biomineralization Microbial

Associated Organisms: Escherichia coli str. K-12 substr. W3110 (NCBITaxon:316407)

E. coli W3110 biofilms grown with calcium chloride and beta-glycerophosphate contained diffraction features assigned to hydroxyapatite. Enzyme additions, inhibitor experiments and fixed-biofilm comparisons support a possible phosphatase contribution but do not establish that living cells or a uniquely identified PhoA pathway are necessary.

Experimental Context & Analytical Limits:
Zorzetto et al. used E. coli K-12 W3110 bearing constitutive mCherry plasmid pMP7604. A single colony was grown overnight in LB at 37 degrees C and 250 rpm; nine 5-microlitre droplets of approximately OD600 5.0 suspension were placed on 15-cm plates and incubated at 28 degrees C for 5, 7 or 10 days. The salt-free LB base contained 1.8% w/v agar, 1% tryptone and 0.5% yeast extract. Mineralizing arms added 10 mM sodium beta-glycerophosphate with either 1 or 10 mM CaCl2 (P-Ca 10:1 or 10:10); precursor stocks were 0.22-micrometre filtered and added after base autoclaving. Calcein 4 micromolar was used where required. No culture-pH trajectory is supplied. Except stereomicroscopy samples, the Methods specify fixation with 4% paraformaldehyde in phosphate-buffered saline followed by PBS rinsing. Most diffraction samples were then lyophilized and ground; Figure 4B additionally examines hydrated, non-lyophilized samples. These are laboratory agar/biofilm composites, not isolated mineral product or treated natural ore.
Curated Evidence Points:
Results and Figure 3 compare biofilm WAXS against reference hydroxyapatite powder: stronger characteristic reflections develop in P-Ca 10:10 over 5-10 days; the lower-calcium 10:1 arm is reported to show mineral reflections by day 10. Figure 4B supports an apatite-like signal in hydrated samples, reducing reliance on lyophilization alone. Diffraction supports the source phase assignment, but no OH/F/Cl occupancy measurement or quantitative phase-purity refinement of the biofilm is reported. Generic calcium staining alone is not treated as phase identification.
Figures S5-S6 compare salt-free control biofilms, supplemented agar sampled away from biofilms, near-biofilm residue and single-precursor arms. Phosphate-only supplementation showed no comparable mineral reflections; calcium-only biofilms showed weak features, with yeast-extract P proposed as an alternative phosphate source. These controls and main Figure 4B constrain preparation artifacts but do not provide a phosphate-source tracer or a fixation-free complete mass balance. Salt-free means no added NaCl in the LB base, not chemically ion-free medium.
Figure 4A shows delayed/weaker mineral reflections with 20 mM L-glutathione in the agar; its preculture also received 5 mM inhibitor. Residual reflections remained at later times. This is not a phoA deletion/complementation test or proof of an exclusive enzyme mechanism. The paper describes an essential and sufficient role more strongly than the controls establish.
Figure S7 shows inhibitor-treated biofilm diameters resembling the salt-free control and larger than the mineralizing P-Ca 10:10 arm without inhibitor at later times. Therefore the general statement that inhibitor treatment did not alter growth cannot be used as evidence of identical biofilm development across the actual mineralizing comparison. Diameter is not viable-cell number or metabolic rate.
Purified E. coli ALP was applied as 100 microlitres at 20 U/mL in 0.1 M glycine/NaOH buffer, pH 10.4, with 1 mM MgCl2 and 1 mM ZnCl2 onto P-Ca 10:10 agar overnight at 28 degrees C (Figure 4B). Mineral-associated signals support precipitation in this enzyme-containing preparation. No matched buffer-only or inactive-enzyme agar arm is shown, so alkalinity, added ions and enzyme action are not independently partitioned.
Figure S9 used five-day salt-free biofilms fixed in 4% PFA/PBS, pooled and resuspended in water, then deposited on new agar for 10 days at 28 degrees C; source-assigned hydroxyapatite appeared on P-Ca 10:10. Table S10 separately compares medium, overnight culture, purified enzyme, fixed biofilm and filtered/sonicated culture material after 3 days in liquid media at 28 degrees C, 120 rpm. Fixed material retained measured phosphatase-assay signal and could mineralize; living-cell necessity is therefore not inferred. Residual phosphate from fixation and assay-specific handling remain possible contributors, and no quantitative recovery fraction is supplied.
Figures 1-2 locate mineral-associated signals in a heterogeneous biofilm and its surroundings. Scherrer sizes are diffraction-based estimates rather than direct particle dimensions; Table S3 local segmented volumes are not whole-biofilm mineral yield. This record adopts neither fitted crystal-size values nor segmented population percentages, and does not infer cell death, cooperative behavior or industrial material performance from these images.
Context_only Source: ncbi_w3110
NCBI 316407 supplies the W3110 taxon label. It does not establish plasmid carriage, exact laboratory-stock authentication or the mineralization phenotype independently of the experiment.

Sources & References

  1. ima_2026_09: IMA-CNMNC. The New IMA List of Minerals, September 2026. Definitions pp 1-2 and Hydroxylapatite row p99, Rn, 2010 s.p. Official list reopened and retained original row visually inspected on 14 October 2026.
    https://cnmnc.units.it/files/editor/IMA_Master_List_(2026-09).pdf (accessed 2026-10-14)
  2. hydroxylapatite_handbook: Handbook of Mineralogy. Hydroxylapatite. Complete one-page entry; OH-dominant species identity, not composition analysis of the experimental biofilm.
    https://www.handbookofmineralogy.org/pdfs/hydroxylapatite.pdf (accessed 2026-10-14)
  3. zorzetto_2023: Zorzetto, Laura; Scoppola, Ernesto; Raguin, Emeline; Blank, Kerstin G.; Fratzl, Peter; Bidan, Cecile M. (2023). Induced Mineralization of Hydroxyapatite in Escherichia coli Biofilms and the Potential Role of Bacterial Alkaline Phosphatase. Chemistry of Materials 35(7):2762-2772. DOI 10.1021/acs.chemmater.2c02969. Complete 11-page publisher original retained by Max Planck; main Figures 1-4 inspected.
    https://doi.org/10.1021/acs.chemmater.2c02969 (accessed 2026-10-14)
  4. zorzetto_2023_si: Zorzetto et al. 2023 supporting information, DOI 10.1021/acs.chemmater.2c02969.s001; ACS Figshare article 22461879, file 39913176, cm2c02969_si_001.pdf. Complete 10-page PDF read and claim-bearing Figures S1,S5-S9 and Tables S3,S10 visually inspected. Separate 180 MB reconstruction video S2 was not acquired; no quantitative segmentation claim is adopted.
    https://doi.org/10.1021/acs.chemmater.2c02969.s001 (accessed 2026-10-14)
  5. ncbi_w3110: NCBI Taxonomy 316407, Escherichia coli str. K-12 substr. W3110, no-rank taxon under E. coli. Official XML checked 14 October 2026; name provenance does not authenticate the transformed stock used in the experiment.
    https://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?id=316407 (accessed 2026-10-14)

Curation History

Timestamp Curator Action Summary
2026-10-14T11:27:13.959985+00:00 codex (GPT-6; codex) CREATE Created hydroxylapatite mineral record with primary experimental evidence, exact phase and assay boundaries, controls and unresolved causal limits.

Record source: data/records/hydroxylapatite.yaml