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Eur J Protistol. 1989 Feb 24;24(2):101-9. doi: 10.1016/S0932-4739(89)80037-9. Epub 2011 Nov 2.

Route of infection of the bacteria Holospora elegans and Holospora obtusa into the nuclei of Paramecium caudatum.

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Zoologisches Institut der Universität Münster, Münster, FRG.


The route of infection of two endonucleobiotic bacteria in Paramecium caudatum was investigated with the electron microscope. The bacterium Holospora elegans specifically infects the micronucleus, whereas Holospora obtusa infects the macronucleus. The infectious forms of both bacteria are ingested by the prospective host cell into a phagosome. The bacteria leave the phagosome without destroying its membrane. During their transport to the nuclei the bacteria remain surrounded by host membranes forming a transport vesicle. The outer membrane of the bacteria and the vesicle membrane become connected by fibrillar material. Eventually, the transport vesicles are encircled in addition by flat vesicles, which sometimes appear to be part of the endoplasmic reticulum. Later, membranes surrounding the bacterium in the host cytoplasm fuse with the membranes of the nuclear envelope and the bacterium is sluiced into the nucleus. As an alternative mode the infecting bacteria leave their transport-vesicles before invading the nucleus and seem to penetrate the nuclear envelope directly. Inside the nucleus chromatin granules immediately adhere to the bacterial surface. Later a dense layer of chromatin is formed around the endonucleobiotic bacterium.

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