coccolith vesicle

cellstructuremech:coccolith_vesicle · Membrane organelle · Membrane bounded organelle · Proposed

A membrane-bounded intracellular compartment of coccolithophores that encloses a developing calcite coccolith. Its bounding membrane surrounds the site of coccolith mineralization and can change shape as the crystals grow. [DOI:10.1021/jacs.6c02151]

Calcidiscus leptoporus, Figure 2. A: schematic cell organization, not to scale. B: cryo-SEM of a cell containing an intracellular coccolith. C-D: cryo-FIB-SEM sections, with the vesicle membrane highlighted in white. E: five reconstructed coccolith stages, showing the enclosing membrane on each right half. Arrows distinguish close and more variable membrane-crystal spacing; the panels are not a time-lapse of one cell. SEM · *Calcidiscus leptoporus* (`NCBITaxon:127549`) · Emanuel M. Avrahami, Dmitry Karpov, Lior Aram, Nadav Elad, Razi Safadi, Irit Rosenhek-Goldian, Xiao-Meng Sui, Diede de Haan, Neta Varsano, Sidney R. Cohen, et al.; CC BY 4.0, via PubMed Central · CC_BY_4_0 · source: PMC PMC13067266.1 fig2 · `DOI:10.1021/jacs.6c02151`

UniProt location names: UniProt Consortium, CC BY 4.0. Reference label and route sources.

Components

Component	Type	Part of / acts on	Grounding	Genes	Stoichiometry	Essential	Role
membrane	Other	part of	`GO:0016020`			UNKNOWN	Bounds the vesicle lumen around the developing coccolith. `DOI:10.1021/jacs.6c02151` Figures 2 and 3 resolve the membrane around intracellular coccoliths; the molecular inventory and assembly essentiality are not established.

Canonical examples

NCBITaxon:127549 Calcidiscus leptoporus — Strain RCC1130. Supplementary Methods identify the culture; cryo-SEM, cryo-FIB-SEM and cryo-electron tomography show the vesicle and its relationship to developing coccolith crystals. External coccoliths were removed before plunge freezing for FIB imaging; Figure 2B instead uses high-pressure freezing and freeze fracture. [DOI:10.1021/jacs.6c02151]
NCBITaxon:2903 Emiliania huxleyi — Strain AWI1516. Cryo-FIB-SEM resolves intracellular coccoliths in the coccolith-vesicle/reticular-body system separately from a calcium-rich storage compartment. The label follows the verified NCBI taxon, which retains Gephyrocapsa huxleyi as a synonym. [DOI:10.1038/ncomms11228]

Functions

intracellular coccolith formation — Provides the membrane-bounded environment in which coccolith calcite crystals develop. This site-of-formation claim does not specify the molecular mechanism that sets crystal shape.
- DOI:10.1021/jacs.6c02151 Results and Figures 2-3 image membrane-enclosed coccoliths at different developmental stages in Calcidiscus leptoporus.
- DOI:10.1038/ncomms11228 Figures 3-4 distinguish the calcite-forming compartment from the separate calcium-rich storage compartment in Emiliania huxleyi.

Discussions

CURATION_TODO (RESOLVED): Keep the coccolith-forming vesicle distinct from its mineral product and neighboring calcium store. Similarity in calcium content or close membrane apposition does not make these entities equivalent.
CURATION_TODO (RESOLVED): Do not assign unidentified luminal particles to a full ATPase complex or import cargo scaffolds as vesicle-building proteins. Ultrastructural resemblance is insufficient to choose a protein family or infer transport activity.
CURATION_TODO (OPEN): Resolve molecular transport, membrane shaping, developmental dynamics and occurrence across additional species and life-cycle phases. Near-native snapshots and elemental maps establish morphology but do not independently prove a general causal mechanism.

Evidence

DOI:10.1021/jacs.6c02151 Avrahami et al. (2026), Journal of the American Chemical Society. Primary Results, Discussion, Conclusions, figure captions and supplementary culture/imaging Methods read. Membrane-crystal proximity varies with position and stage; mechanistic compartmentalization remains an interpretation of structural and elemental observations.
DOI:10.1038/ncomms11228 Sviben et al. (2016), Nature Communications. Primary microscopy Results, Discussion and culture Methods read. The calcium/phosphorus-rich storage compartment is distinct from the coccolith-vesicle/reticular-body system; apposition does not establish continuity or an identified transfer mechanism.
GO:0043231 Verified broad intracellular membrane-bounded organelle parent, not an exact coccolith-vesicle identity.

Curation history

2026-10-03T17:53:43Z codex · CREATED_RECORD — Scaffolded by scripts/new_record.py
2026-10-03T17:54:47Z codex · EXPANDED_RECORD — Added evidence-backed morphology, two verified species examples, membrane constituent and calcification-site function; documented compartment, protein and causal boundaries; added inspected CC BY 4.0 Figure 2 with verified ALI licence and checksums.

Source: data/structures/membrane_organelle/coccolith_vesicle.yaml