Phylogenetic diversity in freshwater‐dwelling Isochrysidales haptophytes with implications for alkenone production
Phylogenetic diversity in freshwater‐dwelling Isochrysidales haptophytes with implications for alkenone production
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DOI：
10.1111/gbi.12330
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发表时间：
2019-02
期刊：
影响因子：
3.7
通讯作者：
N. Richter;W. Longo;S. George;A. Shipunova;Y. Huang;L. Amaral-Zettler
中科院分区：
文献类型：
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作者：
N. Richter;W. Longo;S. George;A. Shipunova;Y. Huang;L. Amaral-Zettler
等鞭金藻目的成员在附着植物谱系中是独特的，因为它们是烯酮的唯一生产者，长链酮通常用于古温度重建。根据分子生态学数据，产生烯酮的附着植物主要分为三大类：第一类发现于淡水湖泊，第二类通常出现在半咸水和沿海海洋环境中，第三类包括开放的海洋物种。每个组都有不同的烯酮分布;然而，目前只有第二和第三组Isochryphilales有培养的代表。未培养的第I组等鞭金藻目的地球化学特征是存在于水柱和沉积物样品中的三不饱和烯酮异构体（C37：3b Me，C38：3b Et，C38：3b Me，C39：3b Et），但它们的遗传多样性，形态和环境控制在很大程度上是未知的。使用小亚基（SSU）核糖体RNA（rRNA）标记基因扩增子高通量测序的环境水柱和沉积物样品，我们表明，第一组是单系的高系统发育多样性，并包含一个良好的支持分支分离先前描述的“EV”分支从“格陵兰”分支。我们推断第一个部分大亚基（LSU）rRNA基因组I序列同源性，这揭示了嵌入组I中的其他支持良好的进化枝。相对于第二组，第一组揭示了更高水平的遗传多样性，尽管保存的烯酮签名和更密切的进化关系与第三组。在第I组中，三不饱和烯酮异构体的存在似乎是保守的，而第II组的情况并非如此。这表明不同的环境对I组和II组的影响，并可能揭示了进化的限制烯酮的生物合成。
Members of the order Isochrysidales are unique among haptophyte lineages in being the exclusive producers of alkenones, long‐chain ketones that are commonly used for paleotemperature reconstructions. Alkenone‐producing haptophytes are divided into three major groups based largely on molecular ecological data: Group I is found in freshwater lakes, Group II commonly occurs in brackish and coastal marine environments, and Group III consists of open ocean species. Each group has distinct alkenone distributions; however, only Groups II and III Isochrysidales currently have cultured representatives. The uncultured Group I Isochrysidales are distinguished geochemically by the presence of tri‐unsaturated alkenone isomers (C37:3b Me, C38:3b Et, C38:3b Me, C39:3b Et) present in water column and sediment samples, yet their genetic diversity, morphology, and environmental controls are largely unknown. Using small‐subunit (SSU) ribosomal RNA (rRNA) marker gene amplicon high‐throughput sequencing of environmental water column and sediment samples, we show that Group I is monophyletic with high phylogenetic diversity and contains a well‐supported clade separating the previously described “EV” clade from the “Greenland” clade. We infer the first partial large‐subunit (LSU) rRNA gene Group I sequence phylogeny, which uncovered additional well‐supported clades embedded within Group I. Relative to Group II, Group I revealed higher levels of genetic diversity despite conservation of alkenone signatures and a closer evolutionary relationship with Group III. In Group I, the presence of the tri‐unsaturated alkenone isomers appears to be conserved, which is not the case for Group II. This suggests differing environmental influences on Group I and II and perhaps uncovers evolutionary constraints on alkenone biosynthesis.