Release of the endonucleobiotic bacterium Holospora elegans from its host cell Paramecium caudatum

The endonucleobiotic bacterium Holospora elegans inhabits the micronucleus of Paramecium caudatum. In this paper the release of the infectious form (IF) of H. elegans from its host is described. During the anaphase of the micronuclear division most of the IFs remain within the connecting piece which, therefore, may become enormously distended. In the course of the cytokinesis of the host cell the connecting piece is usually positioned in one half of the dividing cell. Long time observations with the LM combined with EM studies revealed that the connecting piece bursts shortly after cytokinesis and thus releases the IFs into the cytoplasm. The IFs are initially not surrounded by host membranes, but thirty min later all of them are enclosed by one or two host membranes. The IF containing vesicles were never observed to accumulate acridine orange or neutral red and are, therefore, supposed not to become acidified. The release of the IFs by exocytosis via the cytoproct starts about 30 min after cytokinesis and is usually finished another 30 min later. The bacterial fine structure remains unchanged during the course of release.