Strategies of the macronuclear endocytobionts of Paramecium during the sexual process of the host

Paramecia infected with endonucleobiotic bacteria were traditionally thought to loose the capacity to undergo the sexual process as a result of the infection. On the other hand, successful conjugation with newly generated macronuclei should lead to a loss of bacteria from the macronuclear compartment. Certain types of the nucleobiosis between Paramecium and bacteria namely P. caudatum-Holospora obtusa, P. caudatum-Nonospora macronucleata, P. duboscqui-Caedibacter macronucleorum and P. biaurelia-H. caryophila were studied with regard to the strategies of these bacteria during the host's conjugation. The enumerated bacteria were found to be able to survive during the host's conjugation in two different ways: modification (mainly) of this sexual process or prevention of its completion. As a result of the modifications of the nuclear reorganization, the infected exconjugant's progeny maintained the old macronucleus (macronuclear regeneration). For the first time it was demonstrated that intranuclear bacteria (N. macronucleata) induce the fusion of old nuclear fragments and new macronuclear anlagen with the forming macronuclear heterokaryon. Only for H. caryophila an alternative way - infection of the new macronuclear anlagen by a few of the bacteria from the old macronuclear fragments - was shown.