Flow cytometric studies of the host-regulated cell cycle in algae symbiotic with green paramecium

Abstract

Paramecium bursaria (green paramecium) possesses endosymbiotically growing chlorella-like green algae. An aposymbiotic cell line of P. bursaria (MBw-1) was prepared from the green MB-1 strain with the herbicide paraquat. The SA-2 clone of symbiotic algae was employed to reinfect MBw-1 cells and thus a regreened cell line (MBr-1) was obtained. The regreened paramecia were used to study the impact of the host's growth status on the life cycle of the symbiotic algae. Firstly, the relationship between the timing of algal propagation and the host cell division was investigated by counting the algal cells in single host cells during and after the host cell division and also in the stationary phase. Secondly, the changes in the endogenous chlorophyll level, DNA content, and cell size in the symbiotic algae were monitored by flow cytometry and fluorescence microscopy. The number of algae was shown to be doubled prior to or during the host cell division and the algal population in the two daughter cells is maintained at constant level until the host cell cycle reenters the cytokinesis, suggesting that algal propagation and cell cycle are dependent on the host's cell cycle. During the host's stationary growth, unicellular algal vegetatives with low chlorophyll content were dominant. In contrast, complexes of algal cells called sporangia (containing 1-4 autospores) were present in the logarithmically growing hosts, indicating that algal cell division leading to the formation of sporangia with multiple autospores is active in the dividing paramecia.

The Chlorella variabilis NC64A Genome Reveals Adaptation to Photosymbiosis, Coevolution with Viruses, and Cryptic Sex

“…These genes are also found in most of the other sequenced chlorophyte algal species (see Supplemental Table 6 online). Chlorella species, including symbionts of P. bursaria, have been observed only in the haploid phase (Pickett-Heaps, 1975;Gerashchenko et al, 2001;Kadono et al, 2004), but the presence of meiosis genes suggests that NC64A also has a diploid phase and that its sexual reproductive cycle might have been overlooked, like the cryptic sex recently identified in Ostreococcus species (Grimsley et al, 2010). In addition, we found 19 NC64A homologs of the Chlamydomonas gametolysin proteins that promote the disassembly of the gametic cell walls and allow gamete fusion as well as an NC64A ortholog (id:137637) to the Chlamydomonas GCS1 protein essential for cell fusion (Goodenough et al, 2007).…”

Green Paramecia as an Evolutionary Winner of Oxidative Symbiosis: A Hypothesis and Supportive Data

“…During co-habitation, ESA cells are protected from the severe environmental changes and the algae benefit nitrogenous nutrition from the host organism which feeds various microbes (Kosaka, 1994;Kadono et al, 2004a). A recent study has shown that the algal cell cycle in P. bursaria is highly governed by the cell cycle of the host cells (Kadono et al, 2004b). However, the mechanism required for establishment and maintenance of this plant-protozoan 0939Ð5075/2004/0700Ð0538 $ 06.00 " 2004 Verlag der Zeitschrift für Naturforschung, Tübingen · http://www.znaturforsch.com · D symbiosis is not fully understood, and a reasonable explanation in the evolutionary view has not been provided to date.…”

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

“…Endosymbiotic algae of P. bursaria, unlike organelles such as chloroplasts, are expected to be able to self-manage their cell cycle pace even if they remain in the host Paramecium. From several single-cell analyses of P. bursaria, these studies using microscopy have clarified that a host cell of P. bursaria strictly modulates the number of endosymbiotic algae [15,51] (Figure 3). This study using capillary FCM also captures the feature of the cell-cycle cooperative dynamics between the host Paramecium and the endosymbiotic algae (Figures 7 and 8).…”