Life Cycle Analysis of Endosymbiotic Algae in an Endosymbiotic Situation with Paramecium bursaria Using Capillary Flow Cytometry

Along with algae as producers in ecosystems and industrial applications, some microalgae existing in special ecological niches through endosymbiosis with other organisms represent fascinating examples of biological evolution. Although reproducing endosymbiosis experimentally is difficult in many situations, endosymbiosis of several ongoing types is possible. Endosymbiosis in Paramecium bursaria is a particularly excellent model. Although many studies of P. bursaria have specifically examined infection processes such as the host recognition of symbionts, coordination of host-symbiont division, which has been explored for eukaryotic organelles, is worth pursuing. Evaluating the cell (life) cycle of algae is crucially important for algal applications. Flow cytometry (FCM) has been used to study cell cycles of several eukaryotic cells including microalgae. Microscopy, however, has been used mainly to study endosymbiosis, as with P. bursaria, because of their larger size than suitable cells for FCM with hydrodynamic focusing. Vast amounts of time have been expended for microscopic analysis. This review presents an approach using capillary FCM to elucidate the endosymbiosis of P. bursaria. Results reveal that endosymbiotic algae of P. bursaria finely adjust their cell cycle schedule with their comfortable host and show that a coincident endosymbiont–host life cycle is virtually assured in their endosymbiosis.