Endosymbiosis of Chlorella species to the ciliate Paramecium bursaria alters the distribution of the host’s trichocysts beneath the host cell cortex
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Each symbiotic Chlorella of the ciliate Paramecium bursaria is enclosed in a perialgal vacuole membrane derived from the host digestive vacuole membrane. Alga-free paramecia and symbiotic algae can grow independently. Mixing them experimentally can cause reinfection. Earlier, we reported that the symbiotic algae appear to push the host trichocysts aside to become fixed beneath the host cell cortex during the algal reinfection process. Indirect immunofluorescence microscopy with a monoclonal antibody against the trichocysts demonstrates that the trichocysts change their locality to form algal attachment sites and decrease their density beneath the host cell cortex through algal reinfection. Transmission electron microscopy to detect acid phosphatase activity showed that some trichocysts near the host cell cortex are digested by the host lysosomal fusion during algal reinfection. Removal of algae from the host cell using cycloheximide recovers the trichocyst's arrangement and number near the host cell cortex. These results indicate that symbiotic algae compete for their attachment sites with preexisting trichocysts and that the algae have the ability to ensure algal attachment sites beneath the host cell cortex.
KeywordsAcid phosphatase activity Cell cortex Endosymbiosis Monoclonal antibody Perialgal vacuole membrane Trichocysts
We thank Mr. Yoji Morifuku, the Center for Instrumental Analysis, Yamaguchi University, for his kind technical assistance in the use of the TEM CCD camera. This work was supported by a Japan Society for the Promotion of Science (JSPS) Research Fellowship for Young Scientists granted to Y. Kodama, and by a Narishige Zoological Science Award granted to M. Fujishima.
Conflicts of interest
The authors declare that they have no conflicts of interest.
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