Fard M Reza Saghari, Jørgensen Anders, Sterud Erik, Bleiss Wilfrid, Poynton Sarah L
Department of Inland Fisheries, Leibniz-Institute of Freshwater Ecology and Inland Fisheries, Mülggelseedamm 310, 12587 Berlin, Germany.
Dis Aquat Organ. 2007 Mar 29;75(1):37-50. doi: 10.3354/dao075037.
Diplomonad flagellates infect a wide range of fish hosts in aquaculture and in the wild in North America, Asia and Europe. Intestinal diplomonad infection in juvenile farmed trout can be associated with morbidity and mortality, and in Germany, diplomonads in trout are commonly reported, and yet are poorly characterised. We therefore undertook a comprehensive study of diplomonads from German rainbow trout Oncorhynchus mykiss, using scanning and transmission electron microscopy, and sequencing of the small subunit (ssu) rRNA gene. The diplomonad was identified as Spironucleus salmonis, formerly reported from Germany as Hexamita salmonis. Our new surface morphology studies showed that the cell surface was unadorned and a caudal projection was present. Transmission electron microscopy facilitated new observations of functional morphology, including vacuoles discharging from the body surface, and multi-lobed apices of the nuclei. We suggest the lobes form, via hydrostatic pressure on the nucleoplasm, in response to the beat of the anterior-medial flagella. The lobes serve to intertwine the nuclei, providing stability in the region of the cell exposed to internal mechanical stress. The ssu rRNA gene sequence clearly distinguished S. salmonis from S. barkhanus, S. salmonicida, and S. vortens from fish, and can be used for identification purposes. A 1405 bp sequence of the ssu rRNA gene from S. salmonis was obtained and included in a phylogenetic analysis of a selection of closely related diplomonads, showing that S. salmonis was recovered as sister taxon to S. vortens.
双滴虫鞭毛虫感染北美、亚洲和欧洲水产养殖及野生环境中的多种鱼类宿主。养殖虹鳟幼鱼的肠道双滴虫感染可能与发病和死亡有关，在德国，虹鳟体内的双滴虫常有报道，但特征描述不足。因此，我们对来自德国虹鳟（Oncorhynchus mykiss）的双滴虫进行了全面研究，采用扫描电子显微镜和透射电子显微镜观察，并对小亚基（ssu）rRNA基因进行测序。该双滴虫被鉴定为鲑居尾孢虫（Spironucleus salmonis），此前在德国被报道为鲑六鞭虫（Hexamita salmonis）。我们新的表面形态学研究表明，细胞表面无装饰且存在尾突。透射电子显微镜有助于对功能形态进行新的观察，包括从体表排出的液泡以及细胞核的多叶顶端。我们认为这些叶状结构是通过核质上的静水压力形成的，以响应前内侧鞭毛的摆动。这些叶状结构使细胞核相互缠绕，在细胞受到内部机械应力的区域提供稳定性。ssu rRNA基因序列能清晰区分鲑居尾孢虫与巴氏尾孢虫（S. barkhanus）、鲑杀尾孢虫（S. salmonicida）以及鱼类的涡状尾孢虫（S. vortens），可用于鉴定。我们获得了鲑居尾孢虫ssu rRNA基因的1405 bp序列，并将其纳入对一些密切相关双滴虫的系统发育分析中，结果表明鲑居尾孢虫是涡状尾孢虫的姐妹分类群。
