The study of microbial diversity over time and space is fundamental to the understanding of their ecology and evolution. The underlying processes driving these patterns are not fully resolved but can be studied using population genetic approaches. Here we investigated the population genetic structure of Gonyostomum semen, a bloom-forming phytoplankton species, across two continents. The species appears to be expanding in Europe, whereas similar trends are not observed in the United States. Our aim was to investigate if populations of G. semen in Europe and in the United States are genetically differentiated, if there is population genetic structure within the continents, and what the potential drivers of differentiation are. To this end, we used a novel method based on Single Amplified Genomes (SAGs) combined with RADseq (SAG-RAD), that allows de novo genotyping of natural single cell isolates without the need for culturing. We amplified over 900 single-cell genomes from 25 lake populations across Europe and the United States and identified two distinct population clusters, one in Europe and another in the United States. Low genetic diversity in European populations supports the hypothesized recent expansion of G. semen on this continent. Geographic population structure within each continent was associated with differences in environmental variables which may have led to ecological divergence of population clusters. Overall, our results show that SAG-RAD can be used to analyze microalgal population structure and differentiation based on single-cell isolates from natural, uncultured samples.

中文翻译：

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形成水华的浮游植物物种的单细胞基因组学揭示了各大洲的种群遗传结构

研究微生物随时间和空间的多样性对于理解其生态和进化至关重要。驱动这些模式的潜在过程尚未完全解决，但可以使用群体遗传方法进行研究。在这里，我们研究了跨两大洲的沟口藻（一种形成水华的浮游植物物种）的种群遗传结构。该物种似乎在欧洲正在扩张，而在美国却没有观察到类似的趋势。我们的目的是调查欧洲和美国的 G. 精液种群是否存在遗传分化，各大洲内是否存在种群遗传结构，以及分化的潜在驱动因素是什么。为此，我们使用了一种基于单扩增基因组 (SAG) 与 RADseq (SAG-RAD) 相结合的新方法，无需培养即可对天然单细胞分离株进行从头基因分型。我们扩增了来自欧洲和美国 25 个湖泊种群的 900 多个单细胞基因组，并确定了两个不同的种群集群，一个在欧洲，另一个在美国。欧洲人群遗传多样性较低，支持了最近 G. 精液在该大陆扩张的假设。每个大陆内的地理人口结构与环境变量的差异相关，这可能导致人口集群的生态分化。总的来说，我们的结果表明，SAG-RAD 可用于基于来自天然、未培养样品的单细胞分离物来分析微藻种群结构和分化。