2006 Fiscal Year Final Research Report Summary
Mechanism of establishing an exclusive symbiosis in Paramecium bursaria
| Project/Area Number |
16570053
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Morphology/Structure
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| Research Institution | Kobe University |
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Principal Investigator |
SUZAKI Toshinobu Kobe University, Faculty of Science, Associate Professor, 理学部, 助教授 (00187692)
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| Co-Investigator(Kenkyū-buntansha) |
ISHIDA Masaki Nara University of Education, School of Science Education, Associate Professor, 教育学部, 助教授 (80291053)
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| Project Period (FY) |
2004 – 2006
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| Keywords | Protozoa / Paramecium / Symbiosis / Chlorella / Paramecium bursaria |
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| Research Abstract |
A bacteria-free monoxenic culture of Paramecium bursaria was established. Chlorogonium elongatum was used as a sole food source and a large number of easily-maintained P. bursaria was obtained. Additional enhancement of the growth of P bursaria was achieved by supplementing the culture medium with soybean lecithin. By Percoll density gradient centrifugation, symbiotic Chlorella cells were isolated from P. bursaria with their surrounding peri-algal vacuole (PV) membranes. Integrity of PV and purity of Chlorella cells with PV membrane were monitored by transmission electron microscopy, which showed that > 80% of the isolated Chlorella cells retained the PV membrane without notable contamination with other cytoplasmic components. Free-floating Chlorella emerged in the medium of a bacteria-free monoxenic culture of P bursaria. Light microscopy showed that P. bursaria released exocytotically its intact symbiotic Chlorella cells from its cytoproct. Possible contribution of outflow of symbiotic Chlorella cells to the regulation of the symbiotic algal population density in the host P. bursaria cell was suggested. It was also found that Yarrowia lipolytica (yeast) is able to infect aposymbiotic P. bursaria (ciliate). Electron microscopy showed that in the host cell, yeast cells are enclosed in membrane vacuoles (peri-symbiotic vacuole). When yeast-infected host cells were fed to grow at full strength, many of them fell in incomplete cell divisions, resulting in formation of chained cells and clumps of cells (monster cells), which appeared to be due to hyphal and pseudohyphal yeast cells filling the host's cytoplasm.
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