Kappa organism

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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 bodies which act as a toxin delivery system.


  1. ^ Sonneborn, T. M. (1950). "Paramecium in modern biology". BIOS. 21 (1): 31–43.
  2. ^ Takayanagi, Tan; Hayashi, Shinji (1964). "Cytological and Cytogenetical Studies on Paramecium polycaryum. V. Lethal Interactions in Certain Stocks". Journal of Eukaryotic Microbiology. 11 (1): 128–132. doi:10.1111/j.1550-7408.1964.tb01733.x. PMID 14119554.
  3. ^ Lawrence E. (1999). Henderson's Dictionary of biological terms. London: Longman Group Ltd. ISBN 0-582-22708-9.
  4. ^ Rieger R. Michaelis A.; Green M. M. (1976). Glossary of genetics and cytogenetics: Classical and molecular. Heidelberg - New York: Springer-Verlag. ISBN 0-387-07668-9.
  5. ^ Brown, C. H. (1950). "Elimination of Kappa Particles from 'Killer' Strains of Paramecium aurelia by Treatment with Chloromycetin". Nature. 166 (4221): 527. Bibcode:1950Natur.166..527B. doi:10.1038/166527A0. PMID 14780133.
  6. ^ Kappa Particles in mediLexicon
  7. ^ Kappa Particles in McGraw-Hill Science & Technology Dictionary
  8. ^ Pond, F. R.; Gibson, I.; Lalucat, J.; Quackenbush, R. L. (1989-03-01). "R-body-producing bacteria". Microbiological Reviews. 53 (1): 25–67. doi:10.1128/mr.53.1.25-67.1989. ISSN 0146-0749. PMC 372716. PMID 2651865.

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