In biology, Kappa organism or Kappa particle refers to inheritable cytoplasmic symbionts, occurring in some strains of Paramecium. Paramecium stains possessing the particles (“Killers”) liberate into the culture medium a substance lethal to Paramecium not containing kappa particles.
Kappa particles are Feulgen-positive, stain with Giemsa after acid hydrolysis. The length of the particles is 0.2–0.5μ.[1]
The particles are considered to be intracellular symbionts, occupying a position between viruses, bacteria, and organelles,[2] mere nucleoprotein[3] or, by another sources bacterium Caenobacter taenospiralis.