Leibniz Institute of Freshwater Ecology and Inland Fisheries (IGB), Berlin, Germany; Swiss Federal Institute of Aquatic Science and Technology (Eawag), Dübendorf, Switzerland.
Institut de Biologia Evolutiva (CSIC-Universitat Pompeu Fabra), Barcelona, Catalonia, Spain.
Mol Phylogenet Evol. 2020 Oct;151:106891. doi: 10.1016/j.ympev.2020.106891. Epub 2020 Jun 18.
Caullerya mesnili is a common and virulent parasite of the water flea, Daphnia. It was classified within the Haplosporidia (Rhizaria) for over a century. However, a recent molecular phylogeny based on the 18S rRNA gene suggested it belonged to the Ichthyosporea, a class of protists closely related to animals within the Opisthokonta clade. The exact phylogenetic position of C. mesnili remained uncertain because it appeared in the 18S rRNA tree with a very long branch and separated from all other taxa, suggesting that its position could be artifactual. A better understanding of its phylogenetic position has been constrained by a lack of molecular markers and the difficulty of obtaining a suitable quantity and quality of DNA from in vitro cultures, as this intracellular parasite cannot be cultured without its host. We isolated and collected spores of C. mesnili and sequenced genomic libraries. Phylogenetic analyses of a newly generated multi-protein data set (22 proteins, 4998 amino acids) and of sequences from the 18S rRNA gene both placed C. mesnili within the Ichthyophonida sub-clade of Ichthyosporea, as sister-taxon to Abeoforma whisleri and Pirum gemmata. Our study highlights the utility of metagenomic approaches for obtaining genomic information from intracellular parasites and for more accurate phylogenetic placement in evolutionary studies.
Mesnilia caulleryi 是水蚤（Daphnia）的一种常见且具有强感染力的寄生虫。它在一个多世纪以来被归类于裂体动物门（Rhizaria）的 Haplosporidia。然而，最近基于 18S rRNA 基因的分子系统发育分析表明，它属于 Ichthyosporea，这是一类与后生动物动物界（Opisthokonta）中的干群密切相关的原生动物。由于 Mesnilia caulleryi 在 18S rRNA 树中具有非常长的分支，与所有其他分类群分离，表明其位置可能是人为的，因此其确切的系统发育位置仍然不确定。由于缺乏分子标记以及从体外培养物中获得适量和高质量 DNA 的困难，对其系统发育位置的更好理解受到限制，因为这种细胞内寄生虫在没有宿主的情况下无法培养。我们分离并收集了 Mesnilia caulleryi 的孢子并对基因组文库进行了测序。新生成的多蛋白数据集（22 种蛋白质，4998 个氨基酸）和 18S rRNA 基因序列的系统发育分析均将 Mesnilia caulleryi 置于 Ichthyophonida 亚目中，作为 Abeoforma whisleri 和 Pirum gemmata 的姐妹分类群。我们的研究强调了宏基因组学方法在从细胞内寄生虫中获取基因组信息以及在进化研究中进行更准确的系统发育定位方面的应用。
