Behavior of U(VI) in a simple prey (Yeast) - predator (Paramecium) food chain

捕食者(ゾウリムシ)-被捕食者(酵母)からなる単純化した食物連鎖におけるU(VI)の挙動

香西 直文   ; 大貫 敏彦; 江夏 昌志; 佐藤 隆博; 神谷 富裕; 江坂 文孝  

Kozai, Naofumi; Onuki, Toshihiko; Koka, Masashi; Sato, Takahiro; Kamiya, Tomihiro; Esaka, Fumitaka

放射性核種の環境中での移行における原生動物の役割を明らかにするために、Uを吸着させた酵母を用いてゾウリムシの培養を行い、その間のUの挙動を検討した。原生動物の中でその性質が最も知られている単細胞動物であるゾウリムシをモデル生物に選んだ。U溶液に酵母を接触させると、酵母細胞表面にUリン酸塩が生成した。この酵母を用いてミドリゾウリムシ(P. bursaria)を培養した。培養の間、酵母から培養液に溶出したUは、酵母に吸着していたUの3%に過ぎなかった。培養が進むと、膜状の沈殿物が生成した。この沈殿物は、酵母の未消化細胞及び消化残渣とそれらの間隙を充填する緻密な有機物から成る。この膜状の沈殿物には、酵母細胞に生成したUリン酸塩と大きさ形状がよく似たUリン酸塩が多数観察された。これらの結果は、本研究における単純な食物連鎖系において酵母のウラン固定効果が失われないことを示唆する。

To reveal the role of protozoa in migration of radionuclides in the environment, this study investigated behavior of U(VI) during culture of Paramecium sp. (P. bursaria) in media containing yeast on which U was sorbed. Paramecium was chosen as model protozoa because it is the most well known unicellular protozoa. After the contact of yeast cells with a U (VI) solution, U phosphates formed on yeast cells. P. bursaria cells were cultured with those yeast cells in an inorganic salt solution containing no phosphate. Only 3% of the presorbed U was dissolved from yeast cells into the liquid phases during the culture of Paramecium. As culture time advances, membranous precipitates formed. These membranous precipitates contained undigested and digested yeast cells and dense membranous organic substance filling gaps between those cells. In the membranous precipitates many particles of U phosphates which size and morphology are similar to those observed in the yeast cells were observed. These results suggest that the U immobilization effect of yeast cells was preserved in the prey-predator system