Seto Kensuke, Kagami Maiko, Degawa Yousuke
Sugadaira Montane Research Center, University of Tsukuba, 1278-294, Sugadaira-Kogen, Ueda, Nagano, 386-2204, Japan.
Faculty of Science, Toho University, 2-2-1, Miyama, Funabashi, Chiba, 274-8510, Japan.
J Eukaryot Microbiol. 2017 May;64(3):383-393. doi: 10.1111/jeu.12373. Epub 2016 Nov 14.
Chytrids are true fungi that reproduce with posteriorly uniflagellate zoospores. In the last decade, environmental DNA surveys revealed a large number of uncultured chytrids as well as undescribed order-level novel clades in Chytridiomycota. Although many species have been morphologically described, only some DNA sequence data of parasitic chytrids are available from the database. We herein discuss five cultures of parasitic chytrids on diatoms Aulacoseira spp. and Asterionella formosa. In order to identify the chytrids examined, thallus morphologies were observed using light microscopy. We also conducted a phylogenetic analysis using 18S, 5.8S, and 28S rDNA sequences to obtain their phylogenetic positions. Based on their morphological characteristics, two cultures parasitic on As. formosa were identified as Rhizophydium planktonicum and Zygorhizidium planktonicum. The other three cultures infecting Aulacoseira spp. (two on Aulacoseira ambigua and the other on Aulacoseira granulata) were regarded as Zygorhizidium aff. melosirae. The results of the molecular phylogenetic analysis revealed that R. planktonicum belonged to the known order Chytridiales, while the two species of Zygorhizidium were placed in a novel clade that was previously reported as an undescribed clade composed of only the environmental sequences of uncultured chytrids.
壶菌是真正的真菌，通过具后端单鞭毛的游动孢子进行繁殖。在过去十年中，环境DNA调查揭示了大量未培养的壶菌以及壶菌门中未描述的目级新分支。尽管许多物种已在形态上进行了描述，但数据库中仅可获得一些寄生壶菌的DNA序列数据。我们在此讨论了寄生于硅藻Aulacoseira spp.和美丽星杆藻（Asterionella formosa）上的五种寄生壶菌培养物。为了鉴定所研究的壶菌，使用光学显微镜观察了菌体形态。我们还利用18S、5.8S和28S核糖体DNA序列进行了系统发育分析，以确定它们的系统发育位置。根据其形态特征，寄生于美丽星杆藻上的两种培养物被鉴定为浮游根壶菌（Rhizophydium planktonicum）和浮游合根壶菌（Zygorhizidium planktonicum）。另外三种感染Aulacoseira spp.的培养物（两种寄生于模糊小环藻（Aulacoseira ambigua），另一种寄生于颗粒直链藻（Aulacoseira granulata））被视为近美丽星杆藻合根壶菌（Zygorhizidium aff. melosirae）。分子系统发育分析结果表明，浮游根壶菌属于已知的壶菌目，而合根壶菌的两个物种则被置于一个新分支中，该分支此前被报道为一个仅由未培养壶菌的环境序列组成的未描述分支。
