The ciliate Paramecium bursaria harbors several hundred symbiotic Chlorella spp. cells in the cytoplasm. Algal re-endosymbiosis can be artificially induced using alga-removed P. bursaria. During algal re-endosymbiosis, algae ingested into the host digestive vacuoles (DVs) avoid digestion by the host lysosomal enzymes and then escape into the cytoplasm by budding off of the DV membrane. The budded alga-enclosing DV membrane then differentiates into the symbiosome or perialgal vacuole (PV) membrane and is localized beneath the host cell cortex. In this study, we determined whether the PV membrane has the ability to recognize the symbiotic alga singly by eliminating other small microspheres in the same DV. To clarify the accuracy of the budding process, we mixed fluorescent-labeled microspheres of diameter 0.20 µm with isolated symbiotic algae during algal re-endosymbiosis. No fluorescence was observed from the PV membrane, as expected, and the budding DVs that enclosed both undigested and digested algae. Additionally, the algal re-endosymbiosis rate was significantly reduced in the presence of microspheres. These observations showed that the host P. bursaria allowed budding of the algae singly from the membranes of DVs without microspheres and this process required close contact between the DV membrane and the algal cell wall.

纤毛虫草履虫含有数百种共生的小球藻。细胞质中的细胞。可以使用去除藻类的P. bursaria人工诱导藻类再共生. 在藻类重新内共生过程中，摄入宿主消化液泡 (DV) 的藻类避免被宿主溶酶体酶消化，然后通过 DV 膜出芽逃逸到细胞质中。发芽的藻类包围 DV 膜然后分化成共生体或 perialgal 液泡 (PV) 膜，并位于宿主细胞皮层下方。在这项研究中，我们通过消除同一 DV 中的其他小微球来确定 PV 膜是否具有单独识别共生藻类的能力。为了阐明出芽过程的准确性，我们在藻类再内共生过程中将直径为 0.20 µm 的荧光标记微球与分离的共生藻类混合。正如预期的那样，从 PV 膜上没有观察到荧光，并且在包围未消化和消化的藻类的萌芽 DVs 中没有观察到荧光。此外，在微球的存在下，藻类再内共生率显着降低。这些观察表明，宿主P. bursaria允许藻类在没有微球的情况下单独从 DV 的膜出芽，这个过程需要 DV 膜和藻类细胞壁之间的紧密接触。