Studies on freshwater Perkinsea are scarce compared to their marine counterparts; they are therefore not well ecologically characterized. In this study, we investigated the diversity, distribution and ecological role of Perkinsea in freshwater ecosystems. Our approach included (1) the phylogenetic analyses of near full-length SSU and LSU sequences of freshwater Perkinsea, (2) a meta-analysis of public Perkinsea 18S ribosomal RNA gene sequences available from the freshwater environments (25 lakes, 4 rivers), (3) microscopic observations of Perkinsea associated with planktonic communities and (4) single amplified genome analysis. Whereas Perkinsea appear to be rare in river ecosystems (85 reads), they are found in almost all of the lakes studied. However, their diversity does vary considerably between lakes (from 0 to 2 463 Operational Taxonomic Units (OTUs)). Phylogenetic analysis showed that the Parvilucifera/Dinovorax/Snorkelia and Perkinsus/Xcellia/Gadixcellia clades resulted from an initial speciation event. This second clade is further split into well-supported, monophyletic groups, including a clade dominated by freshwater representatives, which is further structured into three distinct subclades: freshwater clade 1, freshwater clade 2 and a freshwater and brackish clade. The Perkinsea Single Amplified Genome (SAG) as well as most of the abundant Operational Taxonomic Units (OTUs) fall into freshwater clade 2. The tyramide signal amplification-fluorescent in situ hybridization method showed an internal association between Perkinsea and the colonial phytoplankton Sphaerocystis. The Single Amplified Genome (SAG) annotation contained 698 genes and gene ontology terms could be assigned to 486 protein-coding genes. Although the number of genes appears to be low (10.6% of the entire gene set assessed by BUSCO), the analysis of the proteome revealed some putative secreted virulence factors. This study showed a large distribution of Perkinsea across lake ecosystems and potential parasitic association with phytoplankton. However, further investigations are needed for a better knowledge on the role of these microorganisms in freshwater ecosystems.

中文翻译：

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淡水珀金西：多样性，生态学和基因组信息

与海洋同行相比，对珀金西淡水的研究很少。因此，它们的生态特性不好。在这项研究中，我们调查了珀金西在淡水生态系统中的多样性，分布和生态作用。我们的方法包括（1）对淡水Perkinsea的近全长SSU和LSU序列进行系统发育分析，（2）对从淡水环境（25个湖泊，4条河流）可获得的公共Perkinsea 18S核糖体RNA基因序列进行荟萃分析， （3）珀金西与浮游生物群落相关的显微镜观察，以及（4）单扩增基因组分析。珀金西在河流生态系统中似乎很少见（85次读取），但几乎在所有研究的湖泊中都发现了它们。然而，湖泊之间的多样性差异很大（从0到2463个操作生物分类单位（OTU））。系统发育分析表明Parvilucifera / Dinovorax / Snorkelia和Perkinsus / Xcellia / Gadixcellia进化枝来自最初的物种形成事件。第二个进化枝进一步分为支撑良好的一类种群，包括以淡水代表为主的进化枝，进一步分为三个不同的子进化枝：淡水进化枝1，淡水进化枝2和淡水和咸味进化枝。所述Perkinsea单扩增的基因组（SAG）以及最丰富的操作分类单元（的OTU）的落入进化枝淡水2.酪胺信号扩增的荧光原位杂交法表明Perkinsea和殖民浮游植物之间的内部关联Sphaerocystis。单扩增基因组（SAG）注释包含698个基因，并且可以将基因本体术语分配给486个蛋白质编码基因。尽管基因数量似乎很少（由BUSCO评估，占整个基因组的10.6％），但是对蛋白质组的分析显示出某些推测的分泌毒力因子。这项研究表明，珀金西岛在整个湖泊生态系统中分布广泛，并且可能与浮游植物产生寄生关系。但是，需要进一步的研究以更好地了解这些微生物在淡水生态系统中的作用。