toxicyst
A ciliate offensive extrusome that stores toxic discharge material and ejects on prey contact to immobilize prey during raptorial feeding. [DOI:10.1186/s12915-024-01904-2]
Components
| Component | Type | Part of / acts on | Grounding | Genes | Stoichiometry | Essential | Role |
|---|---|---|---|---|---|---|---|
| toxicyst membrane | Lipid | part of | Reviewed label only (reviewed name; no accession asserted) | ESSENTIAL | Membrane envelope that bounds the resting toxicyst and can fuse with the plasma membrane during toxicyst discharge.
| ||
| toxicyst toxic discharge material | Small molecule | part of | Reviewed label only (reviewed name; no accession asserted) | UNKNOWN | Toxic material released by the toxicyst discharge and implicated in chemical offense against prey ciliates.
|
Taxonomic distribution
NCBITaxon:197905Haptoria — COMMON: Raptorial haptorian ciliates carry oral toxicysts, and long type I toxicysts are described as consistently present across Haptoria. [DOI:10.1186/s12915-024-01904-2]NCBITaxon:60000Coleps hirtus — COMMON: Coleps hirtus cells carry toxicysts that cluster mainly in and around the oral aperture and assist carnivorous feeding. [DOI:10.1111/jeu.12106]
Canonical examples
NCBITaxon:60000Coleps hirtus — Freshwater ciliate in which toxicyst discharge material was isolated from living cells and tested for cytotoxic effects against other ciliates. [DOI:10.1111/jeu.12106]
Functions
- prey immobilization — Toxicysts rapidly discharge during ciliate predation and release toxic material that helps immobilize prey.
DOI:10.1111/jeu.12106Buonanno et al. 2014 tested the cytotoxic effects of Coleps hirtus toxicyst discharge and connected it to effective predatory behavior.DOI:10.1186/s12915-024-01904-2Chen et al. 2024 observed raptorial haptorian ciliates using toxicysts near the oral apparatus during predation.
Mechanism graphs
Toxicysts discharge toxic material during predation (FUNCTION)
A ciliate toxicyst is enclosed by a membrane, discharges during predatory prey contact, and releases toxic cargo that supports prey immobilization.
| Subject | Predicate | Object | Evidence |
|---|---|---|---|
| toxicyst membrane | bounds | toxicyst |
|
| prey contact | triggers | toxicyst discharge |
|
| toxicyst discharge | releases | toxicyst toxic discharge material |
|
| toxicyst toxic discharge material | supports | prey immobilization |
|
Discussions
- CURATION_TODO (OPEN): Resolve exact small-molecule and biosynthetic boundaries for toxicyst toxic discharge material. Coleps discharge contains several free fatty acids and a minor amount of phytanic acid, while haptorian genomes are enriched for candidate toxin-related PKS and L-amino acid oxidase genes; this first record therefore leaves the toxic material aggregated until exact secreted molecules are localized to toxicysts.
- INTERPRETATION (RESOLVED): Do not curate haptorian PKS or L-amino acid oxidase expansions as mature toxicyst components without direct toxicyst localization. Chen et al. 2024 identified PKS and L-amino acid oxidase genes as duplicated candidate toxin genes in Haptoria, but those genes were not resolved as mature structural cargo or membrane constituents of the toxicyst organelle.
Evidence
DOI:10.1186/s12915-024-01904-2Chen et al. 2024, Genomic insights into the cellular specialization of predation in raptorial protists, BMC Biology.DOI:10.1111/jeu.12106Buonanno et al. 2014, Chemical offense by means of toxicysts in the freshwater ciliate, Coleps hirtus, Journal of Eukaryotic Microbiology.
Curation history
2026-10-03T07:46:18Zcodex · CREATED_RECORD — Scaffolded by scripts/new_record.py2026-10-03T07:47:23Zcodex · EXPANDED_RECORD — Added toxicyst membrane and toxic discharge-material components, Haptoria and Coleps hirtus taxonomic scope, Coleps hirtus as a canonical example, predatory discharge evidence, a nonmechanistic toxicyst discharge graph, and curation discussions for unresolved toxin chemistry and candidate PKS/LAAO boundary handling.2026-10-03T08:04:23Zcodex · ADDRESS_REVIEW — Resolved PR #1973 review issue #1974 by removing an uncoupled Didinium nasutum Ca2+-triggered discharge citation from the record-level evidence list.