Studies on diversity and origins of parasitic dinoflagellates.

日本对寄生甲藻的研究很少。因此，本研究的目的是：1)了解日本近海寄生甲藻的物种多样性；2)在分子系统发育分析的基础上，了解它们的起源及其与其他甲藻的亲缘关系。综上所述，共鉴定出日本各地寄生甲藻8种，隶属5属。这些细菌包括：Blastoddium、Ooddium、阿米巴菲亚、Synddium和Dubosquella。我们借助光学显微镜和透射电子显微镜研究了每一个物种。并利用单细胞聚合酶链式反应技术对这些物种的SSU rDNA序列进行了分析。我们的分子树表明Blastoddium和Ooddium起源于典型的甲藻，而阿米巴夫里亚和Syndiniuim则属于海洋纤毛虫第二群。寄生纤毛虫的海洋原生生物被鉴定为杜氏原生纤毛虫。我们发现该微生物属于海洋蜂窝状类群I(MAG-I)。后一个分支被认为是仅由微浮游级组分形成的环境克隆序列的组合，没有发现真正属于这个分支的生物(虽然最近发现放射虫的寄生虫属于这个分支，但它们的形态还没有被研究过。Dolven et al.2007)。因此，我们的发现是对这一神秘支系成员的第一次生物鉴定。海洋中几乎任何地方都可以检测到MAG-I的环境克隆序列，MAG-I的成员主要由放射虫或纤毛虫的寄生虫组成，这表明海洋环境中充满了这些寄生虫的(活动细胞)。我们的研究表明了寄生在海洋生态中的重要性。

Little studies on parasitic dinoflagellates have been undertaken in Japan. The aims of this research are, therefore, 1)to understand species diversity of parasitic dinoflagellates around the Japanese coastal waters and 2)to understand their origins and their phylogenetic affinities with other dinoflagellates based on molecular phylogenetic analyses. In summary, we were able to recognize 8 species of parasitic dinoflagellates from various localities of Japan, belonging to 5 genera. These include, Blastodinium, Oodinium, Amoebophrya, Syndinium and Duboscquella. We have investigated each species with the aid of light and transmission electron microscopes. Also we have analyzed SSU rDNA sequences of these species using single cell PCR technique. Our molecular trees suggested that Blastodinium and Oodinium had originated from typical dinoflagellates, while Amoebophrya and Syndiniuim belong to the clade named Marine Alveoalte Group II. The marine protist parasitizing tintinnid ciliate, Favella ehrenbergii was identified as Duboscquella aspida. We found that this organism was included in the clade named, Marine Alveolate Group I (MAG-I). The latter clade has been recognized as assemblage of only environmental clone sequences originated from picoplanktonic size fractions and no actual organisms belonging to this clade have been identified (Although parasites of radiolarians have been found to belong this clade recently, their morphology has not been investigated. Dolven et al. 2007). Our finding, therefore, is the first organismal identification of the member of this enigmatic clade. The facts that environmental clone sequences of MAG-I have been detected almost anywhere in the ocean and members of the MAG-I mainly consists of parasites of radiolarians or ciliates suggest that the oceanic environments are full of (motile cells of) these parasites. Our research suggested importance of parasitism in the marine ocean ecology.