Stentiford Grant D, Bateman Kelly S, Small Hamish J, Pond Michelle, Ungfors Anette
European Union Reference Laboratory for Crustacean Diseases, Centre for Environment, Fisheries and Aquaculture Science (Cefas), Barrack Road, Weymouth, Dorset, DT4 8UB, United Kingdom.
Aquat Biosyst. 2012 Sep 7;8(1):24. doi: 10.1186/2046-9063-8-24.
Parasitic dinoflagellates of the genus Hematodinium are significant pathogens affecting the global decapod crustacean fishery. Despite this, considerable knowledge gaps exist regarding the life history of the pathogen in vivo, and the role of free living life stages in transmission to naïve hosts.
In this study, we describe a novel disease in European brown shrimp (Crangon crangon) caused by infection with a parasitic dinoflagellate of the genus Hematodinium. This is the second example host within the Infraorder Caridea (shrimp) and significantly, the first description within the superfamily Crangonoidea. Based upon analysis of the rRNA gene (SSU) and spacers (ITS1), the parasite in C. crangon is the same as that previously described infecting Nephrops norvegicus and Cancer pagurus from European seas, and to the parasite infecting several other commercially important crab species in the Northern Hemisphere. The parasite is however distinct from the type species, H. perezi, found infecting type hosts (Carcinus maenas and Liocarcinus depurator) from nearby sites within Europe. Despite these similarities, the current study has also described for the first time, a bacteria-like endosymbiont within dinospore stages of the parasite infecting shrimp. The endosymbionts were either contained individually within electron lucent vacuoles within the parasite cell cytoplasm, or remained in direct contact with the parasite cytoplasm or in some cases, the nucleoplasm. In all of these cases, no apparent detrimental effects of colonization were observed within the parasite cell.
The presence of bacteria-like endosymbionts within dinospore life stages presumes that the relationship between the dinoflagellate and the bacteria is extended beyond the period of liberation of spores from the infected host shrimp. In this context, a potential role of endosymbiosis in the survival of free-living stages of the parasite is possible. The finding offers a further intriguing insight into the life history of this enigmatic pathogen of marine crustacean hosts and highlights a potential for mixotrophy in the parasitic dinoflagellates contained within the genus Hematodinium.
血卵涡鞭虫属的寄生性双鞭毛虫是影响全球十足目甲壳类渔业的重要病原体。尽管如此，关于该病原体在宿主体内的生活史以及自由生活阶段在传播至新宿主过程中的作用，仍存在相当多的知识空白。
在本研究中，我们描述了一种由血卵涡鞭虫属的寄生性双鞭毛虫感染欧洲褐虾（Crangon crangon）所引发的新型疾病。这是真虾下目（虾类）中的第二个已知宿主实例，并且重要的是，这是蟹虾总科内的首次描述。基于对核糖体RNA基因（小亚基，SSU）和间隔区（ITS1）的分析，欧洲褐虾体内的寄生虫与先前描述的感染欧洲海域挪威龙虾和黄道蟹的寄生虫相同，也与感染北半球其他几种重要商业蟹类的寄生虫相同。然而，该寄生虫与模式种佩氏血卵涡鞭虫不同，后者感染来自欧洲附近地区的模式宿主（滨蟹和瘦叶梭子蟹）。尽管存在这些相似之处，本研究还首次描述了感染虾的寄生虫动孢子阶段内类似细菌的内共生体。这些内共生体要么单独存在于寄生虫细胞质内的电子透明液泡中，要么与寄生虫细胞质直接接触，在某些情况下还与核质直接接触。在所有这些情况下，未观察到内共生体在寄生虫细胞内产生明显的有害影响。
动孢子生活阶段存在类似细菌的内共生体，这意味着双鞭毛虫与细菌之间的关系在孢子从受感染宿主虾中释放后仍会延续。在这种情况下，内共生可能在寄生虫自由生活阶段的生存中发挥潜在作用。这一发现为这种神秘海洋甲壳类宿主病原体的生活史提供了进一步有趣的见解，并突出了血卵涡鞭虫属寄生性双鞭毛虫中混合营养的可能性。
