Jørgensen Anders, Sterud Erik
National Veterinary Institute, P.O. Box 8156 Dep., 0033 Oslo, Norway.
J Eukaryot Microbiol. 2006 Nov-Dec;53(6):531-41. doi: 10.1111/j.1550-7408.2006.00144.x.
There are two genotypes of the diplomonad Spironucleus barkhanus. Based on sequence data from the small subunit ribosomal RNA gene the conspecificity of these two genotypes has been questioned. Therefore, we have sampled Spironucleus from 27 fish, representing 14 populations, five species, and four genera. Partial nucleotide sequences from the three genes; small subunit ribosomal DNA, glutamate dehydrogenase 1 and alpha-tubulin were compared. The pathogenic isolates of S. barkhanus, which causes systemic spironucleosis in Atlantic salmon, Chinook salmon, and Arctic charr, all farmed in sea water, were genetically very different from the commensal isolate found in wild freshwater populations of Arctic charr and grayling. The genetic distances between the genotypes were of the same magnitude as those separating species of Giardia. Based on these genetic and ecological data, the pathogenic genotype from farmed salmonids is described as a new species, Spironucleus salmonicida n. sp. Scanning and transmission electron microscopy showed no specific morphological or ultrastructural features distinguishing S. salmonicida n. sp. from S. barkhanus. The present study clearly demonstrates the value of applying genetics in identification of Spironucleus species. Phylogenetic analyses that included the isolates of S. salmonicida n. sp. did not change the phylogenetic relationship within the genus Spironucleus.
双滴虫类的巴氏螺旋体有两种基因型。基于小亚基核糖体RNA基因的序列数据，这两种基因型的同种特异性受到了质疑。因此，我们从27条鱼中采集了螺旋体样本，这些鱼代表了14个种群、5个物种和4个属。比较了三个基因的部分核苷酸序列，即小亚基核糖体DNA、谷氨酸脱氢酶1和α-微管蛋白。巴氏螺旋体的致病分离株会在海水养殖的大西洋鲑、奇努克鲑和北极红点鲑中引发全身性螺旋体病，在遗传上与北极红点鲑和河鲈野生淡水种群中发现的共生分离株有很大差异。这些基因型之间的遗传距离与区分贾第虫物种的遗传距离处于同一量级。基于这些遗传和生态数据，养殖鲑科鱼类中的致病基因型被描述为一个新物种，即鲑螺旋体（Spironucleus salmonicida n. sp.）。扫描电子显微镜和透射电子显微镜观察显示，没有特定的形态学或超微结构特征能够区分鲑螺旋体与巴氏螺旋体。本研究清楚地证明了应用遗传学鉴定螺旋体物种的价值。包含鲑螺旋体分离株的系统发育分析并未改变螺旋体属内的系统发育关系。
