| Co-Investigator(Kenkyū-buntansha) |
YAMAGUCHI Mineo Fukuyama University, Natl. Res. Inst. Fish Environ. Inland Sea HAB Div., Head of Harmful Phytoplankton Sec., 赤潮環境部, 赤潮生物研究室長
MIWA Yasuhiko Fukuyama University, Fac. Life Science and Biotechnology Dept. Marine Biotechnology, Associate Professor, 生命科学部, 助教授 (00219833)
MITSUTANI Atsushi Fukuyama University, Fac. Life Science and Biotechnology Dept. Marine Biotechnology, Associate Professor, 生命科学部, 助教授 (80309632)
KITAGUCHI Hirotaka Fukuyama University, Fac. Life Science and Biotechnology Dept. Marine Biotechnology, Research Associate, 生命工学部, 教授 (10320037)
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| Research Abstract |
Blooms of harmful dinoflagellate, Heterocapsa circularisquama, have caused mass mortality of bivalves such as oysters. So, there is a demand for preventing blooms of this species. This project was carried out based on the concept of applying bacteria that can kill microalgae (algicidal bacteria) to regulate harmful algal blooms of H. circularisquama.
First, we determined the frequency of H. circularisquama-killing bacteria (HKB) in seawater and sediment of Etajima Bay, in the Seto Inland Sea of Japan. At the same time, HKB were screened. Although the frequency of HKB was low during the sampling period, strain EHK-1, which had a strong algicidal activity against H. circularisquama, was isolated. Strain EHK-1 was a hovel marine bacterium belonging to the gamma-subgroup of proteobacteria. This bacterium lysed both the vegetative cells and temporary cysts of H. circularisquama within 48 hours. The algicidal mechanism of strain EHK-1 was investigated. As a result, it was elucidated that strain EHK-1 killed H. circularisquama by heat stable algicidal compounds.
Then, we promoted the development of techniques to use algicidal bacteria as bioremediator. One of the problems is the high bacterial cell density required for algicidal effect to be expressed. So, we determined immobilization of algicidal bacteria in gel matrix. Strain EHK-1 entrapped in agar gel indicated algicidal activity and survived at least 2 weeks. These results inferred that immobilization should be a favorable tool for applying algicidal bacteria in natural seawater.
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