ABSTRACT: Zoosporic fungi play an important role in aquatic environments, but their diversity, especially that of parasitic fungi of phytoplankton, has still not been fully revealed. We conducted monthly analyses of the community structure of zoosporic fungi at a pelagic site in Lake Biwa, Japan, from May to December 2016. Metabarcoding analysis, targeted to a large subunit region of ribosomal DNA in the nano-size fraction of particles (2-20 µm), was carried out on the samples. We also counted large phytoplankton and chytrid sporangia attached to the hosts. We detected 3 zoosporic fungal phyla (Blastocladiomycota, Chytridiomycota and Cryptomycota) within 107 operational taxonomic units (OTUs), in which Chytridiomycota was the most diverse and abundant phylum. Few fungal OTUs overlapped between months, and specific communities were detected in each month. These results showed that diverse zoosporic fungi with high temporal variability inhabited the lake. Five large phytoplankton species were found to be infected by chytrids: Staurastrum dorsidentiferum, S. rotula, Closterium aciculare, Asterionella formosa and Aulacoseira granulata. Some chytrids were detected by metabarcoding analysis: Zygophlyctis asterionellae infecting A. formosa, Staurastromyces oculus infecting S. dorsidentiferum and Pendulichytrium sphaericum infecting A. granulata. One OTU detected in association with infected C. aciculare by microscopic counting might have been an obligate parasitic chytrid of C. aciculare. The results indicated that a combination of metabarcoding and microscopic analysis revealed more information on zoosporic fungi, including those that are parasitic.

中文翻译：

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日本琵琶湖游动孢子真菌群落结构的时间变化

摘要：游动真菌在水生环境中发挥着重要作用，但其多样性，尤其是浮游植物寄生真菌的多样性尚未完全揭示。2016 年 5 月至 12 月，我们对日本琵琶湖一个远洋地点的游动孢子真菌群落结构进行了每月分析。 Metabarcoding 分析，针对纳米级颗粒 (2- 20 µm)，在样品上进行。我们还计算了附着在宿主上的大型浮游植物和壶菌孢子囊。我们在 107 个操作分类单元 (OTU) 内检测到 3 个游动孢子真菌门（芽生菌门、壶菌门和隐菌门），其中壶菌门是最多样化和最丰富的门。几个月之间很少有真菌 OTU 重叠，每个月都会检测到特定的社区。这些结果表明，湖泊中栖息着具有高度时间变异性的各种游动孢子真菌。发现五种大型浮游植物物种被壶菌感染：Staurastrum dorsidentiferum，S. rotula，新月aciculare，星杆聚丰和Aulacoseira granulata。一些壶菌通过metabarcoding分析检测：Zygophlyctis asterionellae感染A.台塑，Staurastromyces Oculus公司感染S. dorsidentiferum和Pendulichytrium sphaericum感染A. granulata。通过显微镜计数检测到的与感染的C. aciculare相关的一个 OTU可能是C. aciculare的专性寄生壶菌. 结果表明，元条形码和显微分析的结合揭示了更多关于游动孢子真菌的信息，包括那些寄生的真菌。