The Laurentian Great Lakes are a vast, interconnected freshwater system spanning strong physicochemical gradients, thus constituting a powerful natural laboratory for addressing fundamental questions about microbial ecology and evolution. We present a comparative analysis of pelagic microbial communities across all five Laurentian Great Lakes, focusing on Bacterial and Archaeal picoplankton characterized via 16S rRNA amplicon sequencing. We collected samples throughout the water column from the major basins of each lake in spring and summer over 2 years. Two oligotypes, classified as LD12 (Alphaproteobacteria) and acI-B1 (Actinobacteria), were among the most abundant in every sample. At the same time, microbial communities showed distinct patterns with depth during summer stratification. Deep hypolimnion samples were frequently dominated by a Chloroflexi oligotype that reached up to 19% relative abundance. Stratified surface communities differed between the colder, less productive upper lakes (Superior, Michigan, Huron) and warmer, more productive lower lakes (Erie, Ontario), in part due to an Actinobacteria oligotype (acI-C2) that averaged 7.7% of sequences in the lower lakes but <0.2% in the upper lakes. Together, our findings suggest that both hydrologic connectivity and local selective pressures shape microbial communities in the Great Lakes and establish a framework for future investigations.

中文翻译：

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劳伦大湖的微生物群落反映了连通性和当地的生物地球化学。

劳伦山脉五大湖是一个广阔的，相互联系的淡水系统，跨越了很强的物理化学梯度，因此构成了一个强大的天然实验室，用于解决有关微生物生态学和进化的基本问题。我们提出了对所有五个劳伦大湖中上层微生物群落的比较分析，重点是通过16S rRNA扩增子测序表征的细菌和古细菌微微浮游生物。在2年的春季和夏季，我们从每个湖泊的主要盆地收集了整个水柱中的样本。每个样品中最丰富的有两种寡聚体，分别归类为LD12（丙酸杆菌）和acI-B1（放线菌）。同时，在夏季分层过程中，微生物群落表现出不同的深度模式。深层次品样品通常以相对丰度高达19％的Chloroflexi寡聚型为主导。在较冷，生产力较低的上层湖泊（Superior，密歇根州，休伦市）与较温暖，生产力较高的下层湖泊（伊利，安大略省）之间，分层的地表群落有所不同，部分原因是放线菌的寡聚型（acI-C2）平均序列的7.7％在下游湖泊中，但<0.2％在上游湖泊中。总之，我们的发现表明，水文连通性和局部选择压力共同影响了大湖地区的微生物群落，并为今后的研究建立了框架。部分原因是放线菌的寡核苷酸型（acI-C2）在下游湖泊中平均7.7％的序列，但在上游湖泊中<0.2％。总之，我们的发现表明，水文连通性和局部选择压力共同影响了大湖地区的微生物群落，并为今后的研究建立了框架。部分原因是放线菌的寡核苷酸型（acI-C2）在下游湖泊中平均占7.7％，而在上游湖泊中<0.2％。总之，我们的发现表明，水文连通性和局部选择压力共同塑造了大湖地区的微生物群落，并为今后的调查建立了框架。