In biology,Kappa organism orKappa particle refers to inheritablecytoplasmicsymbionts, occurring in some strains of theciliateParamecium.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 toParamecium that do not contain kappa particles. Kappa particles are found ingenotypes ofParamecium aurelia syngen 2 that carry the dominantgene K.[3][4]
Kappa particles areFeulgen-positive and stain withGiemsa 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 asviruses,bacteria,organelles,[6] or merenucleoprotein,[7] the particles are intracellular bacterial symbionts calledCaedibacter taeniospiralis.[8]Caedibacter taeniospiralis contains cytoplasmic protein inclusions calledR bodies which act as a toxin delivery system.
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