Kasai Akihiro, Setsuda Aogu, Sato Hiroshi
Laboratory of Parasitology, Joint Faculty of Veterinary Medicine, Yamaguchi University, 1677-1 Yoshida, Yamaguchi, 753-8515, Japan.
United Graduate School of Veterinary Science, Yamaguchi University, 1677-1 Yoshida, Yamaguchi, 753-8515, Japan.
Parasitol Res. 2017 Feb;116(2):647-659. doi: 10.1007/s00436-016-5329-2. Epub 2016 Dec 7.
Molecular genetic characterization using the ribosomal RNA (rDNA) gene accrues a wealth of knowledge regarding the true nature of species diversity of Kudoa Meglitsch, 1947 (Myxozoa: Myxosporea: Multivalvulida) and the biogeographical relationships of isolates from different host fish and sea areas. In the present study, we characterized morphologically and genetically three Kudoa spp. with four shell valves and polar capsules (SV/PC), forming pseudocysts in the myofiber of trunk muscles of Cheilodactylus zonatus or Acanthogobius hasta in the natural seawater around Japan. Myxospores from C. zonatus fished in the western Pacific Ocean off Kochi, Japan, were unequal quadrangular pyramids with one large and three smaller SV/PC, morphologically closest to Kudoa whippsi recorded in various pomacentrid and apogonid fish from the Australian Coral Sea. The 18S and 28S rDNA nucleotide sequences of the Japanese isolate were highly similar to some Australian K. whippsi isolates, but also displayed less similarity to other K. whippsi isolates from the same sea mainly due to instability of nucleotides at certain base positions and/or segments of different isolates. All the K. whippsi isolates including the present Japanese isolate, however, were distinct from Kudoa gunterae, K. whippsi's closest kudoid species in morphology, molecular phylogeny, and biogeography. Our detection of K. whippsi from C. zonatus in the natural seawater around Japan is a new host and geographical record. Kudoid myxospores from A. hasta from the Sea of Ariake, a deep bay of the western part of Japan, exhibited two morphotypes, one resembling K. whippsi and the other Kudoa quadricornis with distinct posteriolateral SV projections. However, rDNA nucleotide sequencing revealed that these two Kudoa spp. were distinct from any known congeners; thus, Kudoa akihitoi n. sp. and Kudoa empressmichikoae n. sp. were erected. The morphological differentiation of K. akihitoi n. sp. from multiple Kudoa spp. with scalene stellate myxospores containing one large and three smaller SV/PC was difficult, whereas K. empressmichikoae n. sp. with spherical spore bodies extending small posteriolateral SV projections was distinct from known congeners with similar but elongated spore bodies and PC, i.e., K. quadricornis and Kudoa paraquadricornis, found in the trunk muscle of carangid fish from the Australian Coral Sea.
利用核糖体RNA（rDNA）基因进行分子遗传特征分析，积累了大量有关1947年库道虫属（粘孢子虫纲：多壳目）物种多样性的真实性质以及来自不同宿主鱼类和海域的分离株生物地理关系的知识。在本研究中，我们对三种具有四个壳瓣和极囊（SV/PC）的库道虫属物种进行了形态学和遗传学特征分析，这些物种在日本周围天然海水中的斑鳍唇指䱵或矛尾虾虎鱼的躯干肌肉肌纤维中形成假囊肿。从日本高知以西的西太平洋捕捞的斑鳍唇指䱵的粘孢子虫为不等四边形锥体，有一个大的和三个较小的SV/PC，形态上最接近在澳大利亚珊瑚海的各种雀鲷科和天竺鲷科鱼类中记录的惠氏库道虫。日本分离株的18S和28S rDNA核苷酸序列与一些澳大利亚惠氏库道虫分离株高度相似，但与来自同一海域的其他惠氏库道虫分离株的相似性也较低，这主要是由于不同分离株在某些碱基位置和/或片段的核苷酸不稳定。然而，包括本日本分离株在内的所有惠氏库道虫分离株在形态、分子系统发育和生物地理学上均与贡氏库道虫不同，贡氏库道虫是惠氏库道虫在形态上最接近的库道虫属物种。我们在日本周围天然海水中从斑鳍唇指䱵中检测到惠氏库道虫是一个新的宿主和地理记录。来自日本西部深湾有明海的矛尾虾虎鱼的库道虫属粘孢子虫表现出两种形态类型，一种类似于惠氏库道虫，另一种是具有明显后外侧SV突起的四角库道虫。然而，rDNA核苷酸测序显示这两种库道虫属物种与任何已知的同属物种都不同；因此，新种秋筱宫库道虫和雅子皇后库道虫被建立。秋筱宫库道虫与多种具有不等边星状粘孢子虫且含有一个大的和三个较小的SV/PC的库道虫属物种在形态上难以区分，而雅子皇后库道虫具有球形孢子体并延伸出小的后外侧SV突起，与已知的具有相似但细长的孢子体和极囊的同属物种不同，即在澳大利亚珊瑚海的鲹科鱼类躯干肌肉中发现的四角库道虫和拟四角库道虫。
