ABSTRACT

East African Great Lakes are old and unique natural resources heavily utilized by their bordering countries. In those lakes, ecosystem functioning is dominated by pelagic processes, where microorganisms are key components; however, protistan diversity is barely known. We investigated the community composition of small eukaryotes (<10 µm) in surface waters of four African Lakes (Kivu, Edward, Albert and Victoria) by sequencing the 18S rRNA gene. Moreover, in the meromictic Lake Kivu, two stations were vertically studied. We found high protistan diversity distributed in 779 operational taxonomic units (OTUs), spanning in 11 high-rank lineages, being Alveolata (31%), Opisthokonta (20%) and Stramenopiles (17%) the most represented supergroups. Surface protistan assemblages were associated with conductivity and productivity gradients, whereas depth had a strong effect on protistan community in Kivu, with higher contribution of heterotrophic organisms. Approximately 40% of OTUs had low similarity (<90%) with reported sequences in public databases; these were mostly coming from deep anoxic waters of Kivu, suggesting a high extent of novel diversity. We also detected several taxa so far considered exclusive of marine ecosystems. Our results unveiled a complex and largely undescribed protistan community, in which several lineages have adapted to different niches after crossing the salinity boundary.

中文翻译：

---

四个热带东非大湖的微生物真核生物组合和潜在的新多样性

摘要

东非五大湖是其邻国大量利用的古老而独特的自然资源。在这些湖泊中，生态系统功能由远洋过程主导，其中微生物是关键组成部分；然而，原生生物的多样性鲜为人知。我们通过对 18S rRNA 基因进行测序，研究了四个非洲湖泊（基伍、爱德华、阿尔伯特和维多利亚）地表水中小型真核生物（<10 µm）的群落组成。此外，在 meromictic 基伍湖，垂直研究了两个站点。我们发现高度的原生生物多样性分布在 779 个操作分类单元 (OTU) 中，跨越 11 个高级谱系，其中 Alveolata (31%)、Opisthokonta (20%) 和 Stramenopiles (17%) 是最具代表性的超群。表面原生生物组合与电导率和生产力梯度有关，而深度对基伍的原生生物群落有很强的影响，异养生物的贡献更大。大约 40% 的 OTU 与公共数据库中报告的序列具有低相似性（<90%）；这些主要来自基伍深部缺氧水域，表明高度新颖的多样性。我们还发现了几种迄今为止被认为不属于海洋生态系统的分类群。我们的研究结果揭示了一个复杂且很大程度上未描述的原生生物群落，其中几个谱系在跨越盐度边界后适应了不同的生态位。暗示高度新颖的多样性。我们还发现了几种迄今为止被认为不属于海洋生态系统的分类群。我们的研究结果揭示了一个复杂且很大程度上未描述的原生生物群落，其中几个谱系在跨越盐度边界后适应了不同的生态位。暗示高度新颖的多样性。我们还发现了几种迄今为止被认为不属于海洋生态系统的分类群。我们的研究结果揭示了一个复杂且很大程度上未描述的原生生物群落，其中几个谱系在跨越盐度边界后适应了不同的生态位。