University of Oslo, Microbial Evolution Research Group, Department of Biology, Oslo, Norway.
Appl Environ Microbiol. 2013 Jan;79(2):508-15. doi: 10.1128/AEM.02417-12. Epub 2012 Nov 2.
Several Planktothrix strains, each producing a distinct oligopeptide profile, have been shown to coexist within Lake Steinsfjorden (Norway). Using nonribosomal peptide synthetase (NRPS) genes as markers, it has been shown that the Planktothrix community comprises distinct genetic variants displaying differences in bloom dynamics, suggesting a Planktothrix subpopulation structure. Here, we investigate the Planktothrix variants inhabiting four lakes in southeast of Norway utilizing both NRPS and non-NRPS genes. Phylogenetic analyses showed similar topologies for both NRPS and non-NRPS genes, and the lakes appear to have similar structuring of Planktothrix genetic variants. The structure of distinct variants was also supported by very low genetic diversity within variants compared to the between-variant diversity. Incongruent topologies and split decomposition revealed recombination events between Planktothrix variants. In several strains the gene variants seem to be a result of recombination. Both NRPS and non-NRPS genes are dominated by purifying selection; however, sites subjected to positive selection were also detected. The presence of similar and well-separated Planktothrix variants with low internal genetic diversity indicates gene flow within Planktothrix populations. Further, the low genetic diversity found between lakes (similar range as within lakes) indicates gene flow also between Planktothrix populations and suggests recent, or recurrent, dispersals. Our data also indicate that recombination has resulted in new genetic variants. Stability within variants and the development of new variants are likely to be influenced by selection patterns and within-variant homologous recombination.
已证实，几种束丝藻（Planktothrix）菌株在 Steinsfjorden 湖（挪威）中共存，它们各自产生独特的寡肽图谱。利用非核糖体肽合成酶（NRPS）基因作为标记，表明束丝藻群落由具有不同生物发光动态的不同遗传变体组成，这表明束丝藻存在亚种群结构。在这里，我们利用 NRPS 和非-NRPS 基因研究了挪威东南部的四个湖泊中的束丝藻变体。系统发育分析表明，NRPS 和非-NRPS 基因具有相似的拓扑结构，并且这些湖泊似乎具有相似的束丝藻遗传变体结构。与变体之间的多样性相比，变体之间非常低的遗传多样性也支持了不同变体的结构。不一致的拓扑结构和分裂分解表明束丝藻变体之间存在重组事件。在几种菌株中，基因变体似乎是重组的结果。NRPS 和非-NRPS 基因都受到纯化选择的主导；然而，也检测到了受正选择作用的位点。存在相似且分离良好的、具有低内部遗传多样性的束丝藻变体表明束丝藻种群内存在基因流。此外，在湖泊之间发现的低遗传多样性（与湖泊内的相似范围）表明束丝藻种群之间也存在基因流，并暗示最近或反复发生了扩散。我们的数据还表明，重组导致了新的遗传变体的产生。变体内部的稳定性和新变体的发展可能受到选择模式和变体内部同源重组的影响。
