Molecular Ecology for Prevention of Heterocapsa Blooms

有害的甲藻，环壳异囊藻的大量繁殖导致牡蛎等双壳类的大量死亡。因此，需要防止该物种的开花。本项目是基于应用杀藻细菌（溶藻细菌）调控赤潮的概念而开展的。首先测定了H.日本濑户内海江田岛湾的海水和沉积物中的环孢壳杀灭细菌（HKB）。同时对HKB进行筛查。虽然HKB的出现频率较低，但EHK-1菌株对H. circuliarumquama，被隔离。菌株EHK-1是一株小型海洋细菌，属于变形菌纲γ亚群。该菌能溶解H.在48小时内完成。研究了菌株EHK-1的溶藻机理。结果表明，菌株EHK-1对H.通过热稳定溶藻化合物对环藻进行降解，促进了溶藻细菌作为生物修复体技术的发展。问题之一是要表现出杀藻效果所需的高细菌细胞密度。因此，我们确定了溶藻细菌在凝胶基质中的固定化。菌株EHK-1在琼脂凝胶中具有杀藻活性，存活至少2周。这些结果表明，固定化溶藻细菌是一种在天然海水中应用的有利工具。

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.