Chi Hongshu, Taik Patricia, Foley Emily J, Racicot Alycia C, Gray Hilary M, Guzzetta Katherine E, Lin Hsin-Yun, Song Yen-Ling, Tung Che-Huang, Zenke Kosuke, Yoshinaga Tomoyoshi, Cheng Chao-Yin, Chang Wei-Jen, Gong Hui
Biotechnology Institute, Fujian Academy of Agricultural Sciences, Fuzhou, Fujian 350003, China.
Department of Biology, Hamilton College, Clinton, NY 13323, USA.
Mol Phylogenet Evol. 2017 Jul;112:47-52. doi: 10.1016/j.ympev.2017.04.015. Epub 2017 Apr 18.
The ciliate protozoan Cryptocaryon irritans parasitizes marine fish and causes lethal white spot disease. Sporadic infections as well as large-scale outbreaks have been reported globally and the parasite's broad host range poses particular threat to the aquaculture and ornamental fish markets. In order to better understand C. irritans' population structure, we sequenced and compared mitochondrial cox-1, SSU rRNA, and ITS-1 sequences from 8 new isolates of C. irritans collected in China, Japan, and Taiwan. We detected two SSU rRNA haplotypes, which differ at three positions, separating the isolates into two main groups (I and II). Cox-1 sequences also support the division into two groups, and the cox-1 divergence between these two groups is unexpectedly high (9.28% for 1582 nucleotide positions). The divergence is much greater than that detected in Ichthyophthirius multifiliis, the ciliate protozoan causing freshwater white spot disease in fish, where intraspecies divergence on cox-1 sequence is only 1.95%. ITS-1 sequences derived from these eight isolates and from all other C. irritans isolates (deposited in the GenBank) not only support the two groups, but further suggest the presence of a third group with even greater sequence divergence. Finally, a small Ka/Ks ratio estimated from cox-1 sequences suggests that this gene in C. irritans remains under strong purifying selection. Taken together, the C. irritans species may consists of many subspecies and/or syngens. Further work is needed to determine if there is reproductive isolation between the groups we have defined.
纤毛虫原生动物刺激隐核虫寄生于海水鱼类，引发致死性白点病。全球范围内均有零星感染以及大规模暴发的报道，该寄生虫广泛的宿主范围对水产养殖和观赏鱼市场构成了特殊威胁。为了更好地了解刺激隐核虫的种群结构，我们对从中国、日本和台湾收集的8株新的刺激隐核虫分离株的线粒体细胞色素c氧化酶亚基1（cox-1）、小亚基核糖体RNA（SSU rRNA）和内转录间隔区1（ITS-1）序列进行了测序和比较。我们检测到两种SSU rRNA单倍型，它们在三个位置存在差异，将分离株分为两个主要组（I和II）。Cox-1序列也支持分为两组，并且这两组之间的cox-1差异出乎意料地高（1582个核苷酸位置的差异为9.28%）。这种差异远大于在多子小瓜虫中检测到的差异，多子小瓜虫是导致鱼类淡水白点病的纤毛虫原生动物，其cox-1序列的种内差异仅为1.95%。来自这8个分离株以及所有其他刺激隐核虫分离株（保存在GenBank中）的ITS-1序列不仅支持这两个组，而且进一步表明存在第三个差异更大的组。最后，根据cox-1序列估计的较小的Ka/Ks比值表明，刺激隐核虫中的该基因仍处于强烈的纯化选择之下。综上所述，刺激隐核虫物种可能由许多亚种和/或同宗群组成。需要进一步的工作来确定我们定义的组之间是否存在生殖隔离。
