Bacterial Endosymbiosis in Paramecium aurelia: Bacteriophage-like Inclusions in a Kappa Symbiont

SUMMARY: The bacterial endosymbiont kappa of stock A35 of Paramecium aurelia (syngen 2) carries virus-like inclusions after it has developed a refractile or R body which is necessary for kappa to exert the killing effect.

In exponentially growing Paramecium, the proportion of symbionts bearing R bodies and virus-like inclusions is very low. On starvation, R bodies and virus-like inclusions reappear, and the proportion builds up to between one-quarter and one-half of the total number of symbionts in a cell. Thus the development of R bodies, virus-like inclusions and killing action is influenced by the environment of the host Paramecium cell.