1996 Fiscal Year Final Research Report Summary
Fate of Toxic Cyclic Heptapeptides, the Microcystins, from Blooms of Microcystis in a lake ecosystem
| Project/Area Number |
06640829
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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 |
生態
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| Research Institution | NATIONAL INSTITTE FOR ENVIRONMENTAL STUDIES |
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Principal Investigator |
WATANABE Makoto M National Institute for Environmental Studies, Environmental Biology Division, Laboratory Chief, 生物圏環境部, 室長 (10132870)
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| Co-Investigator(Kenkyū-buntansha) |
YASUNO Masayuki Shiga Profectural University, Faculty of Environmental Science, Professor, 環境科学部, 教授 (10109902)
KAYA Kunimitsu National Institute for Environmental Studies, Environmental Chemistry Division,, 化学環境部, 室長 (40124341)
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| Project Period (FY) |
1994 – 1996
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| Keywords | Toxic Microcystis / Microcystins / Bosmina fatalis / Mixotrophic chrysomonad / Poterioochromanas malhamensis / L-lysine / Moina macrocopa / Pana grylio |
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| Research Abstract |
The objective of the present study is to know the fate of toxic cyclic heptapeptides, the microcystins, from blooms of Microcystis in a lake ecosystem based on the field and laboratory surveys.
Microcystims were detected in all samples of Microcystis with quantities varying seasonally and spatially (151.8-632.8mug・g dry wt^<-1> in Lake Inba and 74.0-609.5mug・g dry wt^<-1> in Lake Kasumigaura and composed of microcystion-LR,-RR,and -YR.Considerable amounts of microcystin (0.1-0.33mug・L^<-1>) were detected in filtered lake water in both lakes. Large amounts of microcystings (6.3-270mug・g dry wt^<-1> only in herbivorous cladoceran Bonsmina fatalis in both lakes.
A mixotrophic chrysomonad, Poterioochromonas malhamensis ingests and digests toxic Microcystis cells. The detail of grazing processes of a Microcystis cell by P.malhamensis are as follows : A Microcystis cell is attached to the tip long flagellum of P.malhamensis, transported to the flagellar base by contorting movement of long flag
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ellum, and engulfed by a feeding cup. Aferthen, the Microcysis cell grazed by P.malhamensis is transported to a single membrane-bound food vacuole and digested there. Almost all of the microcystinns are excluded from the chrysomonad cells immediately after release into the food vacuole. Microstins may be released into lake water not only by bacterial decompositio of toxic cyanobacterial cells bt also during grazing and digestion by mixotrophic chrysomonads.
Cells of toxic Microcystis viridivs (10^5 cells・mL^<-1>) are completely killed within 48 h by L-lysine at a concentration 1.0 mug・mL^<-1> (1 ppm), whereas lysine is non-toxic to Anabaena species at the same concentration. The concentrations of free amino acids in Lake Kasumigaura range from 0.1 to 1.2 ppm, suggesting that decomposition of Microcystis cells and release of microcystins into lake water may be due to frce amio acids toxic to Microcystis.
A herbivoros cladoceran, Moina macrocopa is killed by toxic Microcystis. The responsible toxin is not microcystion but a compound closely related to microcystin metabolism. Tadpoles ofediblc frog, Rana grylio are not affected by toxic Microcystis blooms and their toxins. They showed a great ability to grow from tadpole to frog on a diet of toxic Microcystis and possess high feeding capability for Microcystis spp. , resulting in decline fo toxic Microcystis cell density. Less
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