Sokolnikova Yulia, Magarlamov Timur, Stenkova Anna, Kumeiko Vadim
School of Natural Science, Far Eastern Federal University, Vladivostok 690950, Russian Federation.
School of Biomedicine, Far Eastern Federal University, Vladivostok 690950, Russian Federation; A.V. Zhirmunsky Institute of Marine Biology, Far Eastern Branch of Russian Academy of Sciences, Vladivostok 690059, Russian Federation.
J Invertebr Pathol. 2016 Oct;140:25-34. doi: 10.1016/j.jip.2016.07.012. Epub 2016 Jul 25.
Animals with deformed shells and microalgal invasion have been identified in the natural population of the horse mussel species Modiolus kurilensis of Peter the Great Bay in the Sea of Japan. The haemolymph is initially infested with algae, followed by the rectum, siphons, mantles and gonads located in the posterior body areas. Mantles, which are primarily exposed to light, are major depots for algae. The microscopic analysis of algal cells has revealed the absence of flagella and pyrenoids, the presence of single chloroplast, and reproduction by autosporulation, with dispores prevailing over tetraspores. These results, together with the nearly complete sequence analysis of small subunit (SSU) 18S rDNA (1728bp), have confirmed that these cells are Coccomyxa parasitica. A newly developed method of isolating microalgae from mollusk tissues has facilitated the continuous pure - probably axenic - culture of C. parasitica, thereby providing a description of the time course of each life stage. Histological analyses have revealed significant haemocyte infiltration into the mantles, gonads, kidneys and digestive gland tissues infested with microalgae and the gill tissues, in which the intruder was not identified. Algal encapsulation with major focal areas of fibrosis and amorphic necrosis has been revealed in these infested organs. The spaces between the gonad follicles and digestive gland tubules were significantly widened as these areas were filled with a mass of algae and phagocytic haemocytes, showing acini with a thickened basement membrane. The mantles and kidneys of Modiolus displayed significant morphological deviations of different cells in epithelial, connective and muscle tissues, resulting in the dysfunction of the infested organs. Therefore, C. parasitica, which reproduces in the culture, regardless of the host, is a facultative parasite, causing major pathological alterations, such as anomalous histomorphological patterns and infested organ dysfunctions.
在日本海彼得大帝湾的紫贻贝自然种群中，已发现有贝壳变形和微藻入侵的动物。血淋巴最初受到藻类感染，随后是位于身体后部区域的直肠、虹吸管、外套膜和性腺。主要暴露于光下的外套膜是藻类的主要储存部位。对藻类细胞的显微镜分析显示，其没有鞭毛和蛋白核，有单个叶绿体，通过自体孢子生殖进行繁殖，二分孢子比四分孢子占优势。这些结果，连同小亚基（SSU）18S rDNA（1728bp）的近乎完整序列分析，证实这些细胞是寄生球菌。一种新开发的从软体动物组织中分离微藻的方法，促进了寄生球菌的连续纯培养——可能是无菌培养，从而描述了每个生命阶段的时间进程。组织学分析显示，在受微藻感染的外套膜、性腺、肾脏和消化腺组织以及未发现入侵者的鳃组织中，有大量血细胞浸润。在这些受感染的器官中，已发现藻类被包裹，伴有主要的纤维化和无定形坏死病灶。性腺滤泡和消化腺小管之间的间隙明显增宽，因为这些区域充满了大量藻类和吞噬性血细胞，显示出腺泡基底膜增厚。紫贻贝的外套膜和肾脏在上皮、结缔和肌肉组织中显示出不同细胞的明显形态偏差，导致受感染器官功能障碍。因此，无论宿主如何，在培养物中繁殖的寄生球菌是一种兼性寄生虫，会引起主要的病理改变，如异常的组织形态学模式和受感染器官功能障碍。
