Horizontal gene transfer is a significant driver of evolutionary dynamics across microbial populations. Although the benefits of the acquisition of new genetic material are often quite clear, experiments across systems have demonstrated that gene transfer events can cause significant phenotypic changes and entail fitness costs in a way that is dependent on the genomic and environmental context. Here, we test for the generality of one previously identified cost, sensitization of cells to the antibiotic nalidixic acid after acquisition of an ∼1-Mb megaplasmid, across Pseudomonas strains and species. Overall, we find that the presence of this megaplasmid sensitizes many different Pseudomonas strains to nalidixic acid but that this same horizontal gene transfer event increases resistance of Pseudomonas putida KT2440 to nalidixic acid across assays as well as to ciprofloxacin under competitive conditions. These phenotypic results are not easily explained away as secondary consequences of overall fitness effects and appear to occur independently of another cost associated with this megaplasmid, sensitization to higher temperatures. Lastly, we draw parallels between these reported results and the phenomenon of sign epistasis for de novo mutations and explore how context dependence of effects of plasmid acquisition could impact overall evolutionary dynamics and the evolution of antimicrobial resistance.

中文翻译：

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基因组背景控制假单胞菌获得大质粒时对萘啶酸的反作用

水平基因转移是微生物种群进化动力学的重要驱动因素。尽管获得新遗传材料的好处通常很明显，但跨系统的实验表明，基因转移事件会导致显着的表型变化，并以依赖于基因组和环境背景的方式带来适应成本。在这里，我们测试了一种先前确定的成本的普遍性，即在获得~1-Mb 大质粒后，细胞对抗生素萘啶酸的敏感性，跨越假单胞菌菌株和物种。总的来说，我们发现这种大质粒的存在使许多不同的假单胞菌敏感菌株对萘啶酸的影响，但这种相同的水平基因转移事件增加了恶臭假单胞菌KT2440 对萘啶酸的抗性，以及在竞争条件下对环丙沙星的抗性。这些表型结果不容易被解释为整体健康效应的次要后果，并且似乎独立于与这种大质粒相关的另一个成本，即对更高温度的敏感性。最后，我们将这些报告的结果与de novo突变的符号上位现象进行了比较，并探讨了质粒获取效应的上下文依赖性如何影响整体进化动力学和抗菌素耐药性的进化。