Transplantation of Killer Endosymbionts in Paramecium

Abstract

SEVERAL syngens or breeding groups of Paramecium aurelia contain endosymbionts which may result in the development of the killer trait¹. The symbionts are of different morphological types and it has been suggested that these are non-randomly distributed between syngens². Experiments involving crosses between paramecia with and without symbionts showed that each endosymbiont required a specific nuclear gene for its maintenance. A single gene controlled the presence or absence of endosymbionts as shown by segregation in the F₂ generation. The pattern of loss of symbionts in some of those F₂ clones varies, generally extending over a number of asexual fissions which for different endosymbionts can be from two to over sixty. Infection experiments also demonstrate the requirement for a specific gene. Infection of endosymbionts from homogenates or purified preparations occurs via the medium but only into particular cells possessing a specific gene^1,3. Finally, some endosymbionts growing in vitro retain their infectivity into certain paramecia (author's laboratory).