Research Department for Limnology, University of Innsbruck, Mondseestrasse 9, A-5310 Mondsee, Austria.
Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences, Uppsala SE-75651, Sweden.
Genome Biol Evol. 2021 Mar 1;13(3). doi: 10.1093/gbe/evab019.
Allopatric divergence is one of the principal mechanisms for speciation of macro-organisms. Microbes by comparison are assumed to disperse more freely and to be less limited by dispersal barriers. However, thermophilic prokaryotes restricted to geothermal springs have shown clear signals of geographic isolation, but robust studies on this topic for microbes with less strict habitat requirements are scarce. Furthermore, it has only recently been recognized that homologous recombination among conspecific individuals provides species coherence in a wide range of prokaryotes. Recombination barriers thus may define prokaryotic species boundaries, yet, the extent to which geographic distance between populations gives rise to such barriers is an open question. Here, we investigated gene flow and population structure in a widespread species of pelagic freshwater bacteria, Polynucleobacter paneuropaeus. Through comparative genomics of 113 conspecific strains isolated from freshwater lakes and ponds located across a North-South range of more than 3,000 km, we were able to reconstruct past gene flow events. The species turned out to be highly recombinogenic as indicated by significant signs of gene transfer and extensive genome mosaicism. Although genomic differences increased with spatial distance on a regional scale (<170 km), such correlations were mostly absent on larger scales up to 3,400 km. We conclude that allopatric divergence in European P. paneuropaeus is minor, and that effective gene flow across the sampled geographic range in combination with a high recombination efficacy maintains species coherence.
异域分歧是宏观生物物种形成的主要机制之一。相比之下，微生物被认为具有更自由的扩散能力，并且受到扩散障碍的限制较小。然而，仅限于温泉的嗜热原核生物已经显示出明显的地理隔离信号，但对于栖息地要求不那么严格的微生物，关于这个主题的有力研究却很少。此外，最近才认识到同种个体之间的同源重组为广泛的原核生物提供了物种一致性。因此，重组障碍可能定义了原核生物的物种边界，但种群之间的地理距离在多大程度上产生了这种障碍是一个悬而未决的问题。在这里，我们研究了广泛分布于淡水浮游细菌 Polynucleobacter paneuropaeus 的基因流动和种群结构。通过对从位于 3000 多公里南北跨度的淡水湖泊和池塘中分离出的 113 株同种菌株进行比较基因组学分析，我们能够重建过去的基因流动事件。该物种表现出高度的重组能力，这表明存在显著的基因转移和广泛的基因组镶嵌现象。尽管在区域尺度上（<170 公里），基因组差异随空间距离的增加而增加，但在更大的尺度上（高达 3400 公里），这种相关性大多不存在。我们得出结论，欧洲 P. paneuropaeus 的异域分歧很小，有效的基因流动与高重组效率相结合，维持了物种的一致性。
