In biology, Kappa organism or Kappa particle refers to inheritable cytoplasmic symbionts, occurring in some strains of the ciliate Paramecium. Paramecium strains possessing the particles are known as "killer paramecia". They liberate a substance also known as paramecin[1][2] into the culture medium that is lethal to Paramecium that do not contain kappa particles. Kappa particles are found in genotypes of Paramecium aurelia syngen 2 that carry the dominant gene K.[3][4]
Kappa particles are Feulgen-positive and stain with Giemsa after acid hydrolysis. The length of the particles is 0.2–0.5μ.[5]
While there was initial confusion over the status of kappa particles as viruses, bacteria, organelles,[6] or mere nucleoprotein,[7] the particles are intracellular bacterial symbionts called Caedibacter taeniospiralis.[8] Caedibacter taeniospiralis contains cytoplasmic protein inclusions called R bodieswhich act as a toxin delivery system.
https://en.wikipedia.org/wiki/Kappa_organism
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