Kappa particles are cytoplasmic bacterial endosymbionts that live in some strains of Paramecium infusoria and are able to be inherited from the mother cell to the daughter cells.
Ciliates infected with kappa particles belong to special “killer strains” (killer lines). For example, Paramecium aurelia has killer lines causing the death of members of other strains of the same species. The cytoplasm of paramecium killers contains kappa particles, the bacteria Caedibacter (they can also be cultivated in artificial media outside the cells of the infusoria). Usually, kappa particles are not transmitted during conjugation , since this results in an exchange of nuclei , and not cytoplasm. However, when conjugation is delayed, when the cytoplasm can be transmitted, the kappa particles can pass into sensitive partners. In this case, "infected" ciliates themselves become "killers." It was found that the preservation of kappa particles in the cytoplasm depends on the dominant state of the three nuclear genes . Kappa particles are released into the medium by killer strains and, when absorbed by sensitive ciliates, cause their death.
Kappa particles positively stained according to Feulgen , also stained according to Romanovsky-Giemsa after acid hydrolysis . The particle length is 0.2–0.5 µm [1] .
There has been much controversy about the nature of kappa particles. In size, shape, method of reproduction (division), the absence of a nucleus, they are similar to bacteria. However, they do not have a cell wall and some enzymes. From viruses, they differ primarily larger size. For a long time they were considered special organelles - plasmagens and even nucleoproteins. It is now proven that kappa particles are endosymbiotic bacteria [2] of the genus Caedibacter .
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Kappa Particle Types
There are two types of kappa particles: those containing refractive bodies ( R-bodies ) and the B-particles that look bright because of this (“shiny”) and the dark N-particles that do not have these little bodies. During conjugation with the transition, the cytoplasm "infects" and turns the partner into a "killer" precisely the N-particles capable of division. B-particles are subsequently formed from them. [2] Some of their killer strains are excreted into the external environment, and they are swallowed by sensitive strains. B-particles contain protein tapes - R-bodies , which, turning around sharply, pierce the membrane of the victim's digestive vacuole and facilitate delivery of the deadly toxin to its cytoplasm.
Inheritance
Kappa particles provide immunity from threats from other parameciums, as well as competitive advantage for existence [3] . They are genetically independent and, when dividing the ciliates, are unevenly distributed among the daughter cells, so that if the host multiplies ahead of the kappa particles, some descendants may lose their symbionts without having the ability to recover them and lose the properties of the "killers." The presence of kappa particles in paramecium is determined by the inheritance of the K and k genes. HK homozygotes contain more symbionts than Kk heterozygotes. As for animals with the genetic constitution kk, they do not contain these bacteria at all.
When conjugating homozygous killer and sensitive ciliates without transferring cytoplasm, both paramecia turn into heterozygotes, however, one of the animals still remains sensitive, since it has not acquired kappa particles. Thus, the phenotype of an individual depends not only on its genotype, but also on the presence of a symbiont in the cytoplasm.
Notes
- ↑ Brown, CH (1950). Elimination of Kappa Particles from 'Killer' Strains of Paramecium aurelia by Chloromycetin. Nature 166 (4221): 527. doi: 10.1038 / 166527A0
- ↑ 1 2 I. V. Drozdova. Amazing biology. 2006., M. Publishing house NTS ENAS
- ↑ JR Preer, Jr, LB Preer, and A Jurand. Kappa and other endosymbionts in Paramecium aurelia. Bacteriol Rev. 1974 Jun; 38 (2): 113–163. PMCID: PMC413848
Literature
- S.G. Inge-Vechtomov. Genetics with the basics of selection. - St. Petersburg: NL Publishing House, 2010. - p. 289. - 718 p. - ISBN 978-5-94869-105-3 .