Sanil N K, Suja G, Lijo J, Vijayan K K
Central Marine Fisheries Research Institute, Kerala, India.
Dis Aquat Organ. 2012 Apr 26;98(3):209-20. doi: 10.3354/dao02440.
Protozoan parasites of the genus Perkinsus are considered important pathogens responsible for mass mortalities in many wild and farmed bivalve populations. The present study was initiated to screen populations of the Indian edible oyster Crassostrea madrasensis, a promising candidate for aquaculture along the Indian coasts, for the presence of Perkinsus spp. The study reports the presence of P. beihaiensis for the first time in C. madrasensis populations from the Indian subcontinent and south Asia. Samples collected from the east and west coasts of India were subjected to Ray's fluid thioglycollate medium (RFTM) culture and histology which indicated the presence of Perkinsus spp. PCR screening of the tissues using specific primers amplified the product specific to the genus Perkinsus. The taxonomic affinities of the parasites were determined by sequencing both internal transcribed spacer (ITS) and actin genes followed by basic local alignment search tool (BLAST) analysis. Analysis based on the ITS sequences showed 98 to 100% identity to Perkinsus spp. (P. beihaiensis and Brazilian Perkinsus sp.). The pairwise genetic distance values and phylogenetic analysis confirmed that 2 of the present samples belonged to the P. beihaiensis clade while the other 4 showed close affinities with the Brazilian Perkinsus sp. clade. The genetic divergence data, close affinity with the Brazilian Perkinsus sp., and co-existence with P. beihaiensis in the same host species in the same habitat show that the remaining 4 samples exhibit some degree of variation from P. beihaiensis. As expected, the sequencing of actin genes did not show any divergence among the samples studied. They probably could be intraspecific variants of P. beihaiensis having a separate lineage in the process of evolution.
帕金虫属的原生动物寄生虫被认为是导致许多野生和养殖双壳贝类种群大量死亡的重要病原体。本研究旨在筛查印度可食用牡蛎——马氏珠母贝（Crassostrea madrasensis）种群中是否存在帕金虫属物种，马氏珠母贝是印度沿海水产养殖的一个有潜力的候选品种。该研究首次报道了在来自印度次大陆和南亚的马氏珠母贝种群中存在北海帕金虫（P. beihaiensis）。从印度东、西海岸采集的样本进行了雷氏硫乙醇酸盐培养基（RFTM）培养和组织学检查，结果表明存在帕金虫属物种。使用特异性引物对组织进行PCR筛查，扩增出了帕金虫属特异性产物。通过对内部转录间隔区（ITS）和肌动蛋白基因进行测序，随后进行基本局部比对搜索工具（BLAST）分析，确定了寄生虫的分类亲缘关系。基于ITS序列的分析显示，与帕金虫属物种（北海帕金虫和巴西帕金虫）的同一性为98%至100%。成对遗传距离值和系统发育分析证实，目前的2个样本属于北海帕金虫分支，而其他4个样本与巴西帕金虫分支显示出密切的亲缘关系。遗传分化数据、与巴西帕金虫的密切亲缘关系以及在同一栖息地的同一宿主物种中与北海帕金虫共存，表明其余4个样本与北海帕金虫存在一定程度的差异。正如预期的那样，肌动蛋白基因测序在所研究的样本中未显示出任何差异。它们可能是北海帕金虫的种内变体，在进化过程中具有独立的谱系。
