Telonemia are one of the oldest identified marine protists that for most part of their history have been recognized as a distinct incertae sedis lineage. Today, their evolutionary proximity to the SAR supergroup (Stramenopiles, Alveolates, and Rhizaria) is firmly established. However, their ecological distribution and importance as a natural predatory flagellate, especially in freshwater food webs, still remains unclear. To unravel the distribution and diversity of the phylum Telonemia in freshwater habitats, we examined over a thousand freshwater metagenomes from all over the world. In addition, to directly quantify absolute abundances, we analysed 407 samples from 97 lakes and reservoirs using Catalyzed Reporter Deposition-Fluorescence in situ Hybridization (CARD-FISH). We recovered Telonemia 18S rRNA gene sequences from hundreds of metagenomic samples from a wide variety of habitats, indicating a global distribution of this phylum. However, even after this extensive sampling, our phylogenetic analysis did not reveal any new major clades, suggesting current molecular surveys are near to capturing the full diversity within this group. We observed excellent concordance between CARD-FISH analyses and estimates of abundances from metagenomes. Both approaches suggest that Telonemia are largely absent from shallow lakes and prefer to inhabit the colder hypolimnion of lakes and reservoirs in the Northern Hemisphere, where they frequently bloom, reaching 10–20% of the total heterotrophic flagellate population, making them important predatory flagellates in the freshwater food web.

中文翻译：

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Telonemia 原生生物的全球淡水分布


Telonemia 是已发现的最古老的海洋原生生物之一，在其历史的大部分时间里，它被认为是一个独特的 incertae sedis 谱系。今天，它们在进化上与 SAR 超群（Stramenopiles、Alveolates 和 Rhizaria）的接近性已经牢固确立。然而，它们的生态分布和作为天然捕食性鞭毛虫的重要性，尤其是在淡水食物网中，仍不清楚。为了揭示 Telonemia 门在淡水栖息地中的分布和多样性，我们检查了来自世界各地的 1000 多个淡水宏基因组。此外，为了直接量化绝对丰度，我们使用催化报告基因沉积-荧光原位杂交 （CARD-FISH） 分析了来自 97 个湖泊和水库的 407 个样品。我们从来自各种栖息地的数百个宏基因组样本中回收了 Telonemia 18S rRNA 基因序列，表明该门的全球分布。然而，即使在如此广泛的采样之后，我们的系统发育分析也没有发现任何新的主要分支，这表明目前的分子调查接近捕捉到该组内的全部多样性。我们观察到 CARD-FISH 分析与宏基因组丰度估计之间极好的一致性。这两种方法都表明，Telonemia 在浅水湖中基本上不存在，并且更喜欢栖息在北半球较冷的湖泊和水库的低层环境中，它们经常在那里开花，达到异养鞭毛虫总数的 10-20%，使它们成为淡水食物网中重要的捕食性鞭毛虫。