Bacteriophages limit the existence conditions for conjugative plasmids.
Bacteriophages limit the existence conditions for conjugative plasmids.
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DOI：
10.1128/mbio.00586-15
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发表时间：
2015-06-02
期刊：
影响因子：
6.4
通讯作者：
Brockhurst MA
中科院分区：
文献类型：
--
作者：
Harrison E;Wood AJ;Dytham C;Pitchford JW;Truman J;Spiers A;Paterson S;Brockhurst MA
噬菌体是细菌死亡的主要原因，并对自然细菌种群施加了强烈的选择，但它们对接合质粒动态的影响很少被测试。我们结合实验进化、数学建模和基于个体的模拟来解释噬菌体对细菌的生态和种群遗传学效应是如何相互作用来确定接合质粒的动态及其持久性的。预测了噬菌体对细菌的生态效应，以限制接合质粒的存在条件，防止在弱选择下对质粒附属性状的持久性。实验表明，在质粒无益处的环境中，噬菌体可以加速质粒的消亡，但也揭示了在这些条件下噬菌体对质粒动力学的更复杂的影响，特别是，在固定状态下，质粒暂时保持在固定状态，然后迅速丢失。我们推测，噬菌体的群体遗传效应，特别是对噬菌体抗性突变的选择，可能导致了这种情况。进一步的数学建模和基于个体的模拟支持了我们的假设，表明接合质粒可能搭乘细菌染色体中噬菌体抗性突变的便车。接合质粒是DNA的感染性环，能够在细菌细胞之间和物种之间传递DNA。由于质粒通常携带额外的基因，使细菌能够生活在原本不适宜居住的环境中，因此它们的动态对于理解细菌的适应性进化是至关重要的。通常研究的是孤立的质粒-细菌相互作用，但在自然细菌群落中，噬菌体，即感染细菌的病毒，是无处不在的。利用实验、数学模型和计算机模拟，我们证明了噬菌体通过其对细菌的生态和进化作用来驱动质粒动力学，并最终限制了允许质粒存在的条件。这些结果促进了我们对细菌适应的理解，并表明噬菌体可以用来筛选携带不良特征的质粒，如抗生素耐药性。
Bacteriophages are a major cause of bacterial mortality and impose strong selection on natural bacterial populations, yet their effects on the dynamics of conjugative plasmids have rarely been tested. We combined experimental evolution, mathematical modeling, and individual-based simulations to explain how the ecological and population genetics effects of bacteriophages upon bacteria interact to determine the dynamics of conjugative plasmids and their persistence. The ecological effects of bacteriophages on bacteria are predicted to limit the existence conditions for conjugative plasmids, preventing persistence under weak selection for plasmid accessory traits. Experiments showed that phages drove faster extinction of plasmids in environments where the plasmid conferred no benefit, but they also revealed more complex effects of phages on plasmid dynamics under these conditions, specifically, the temporary maintenance of plasmids at fixation followed by rapid loss. We hypothesized that the population genetic effects of bacteriophages, specifically, selection for phage resistance mutations, may have caused this. Further mathematical modeling and individual-based simulations supported our hypothesis, showing that conjugative plasmids may hitchhike with phage resistance mutations in the bacterial chromosome. Conjugative plasmids are infectious loops of DNA capable of transmitting DNA between bacterial cells and between species. Because plasmids often carry extra genes that allow bacteria to live in otherwise-inhospitable environments, their dynamics are central to understanding bacterial adaptive evolution. The plasmid-bacterium interaction has typically been studied in isolation, but in natural bacterial communities, bacteriophages, viruses that infect bacteria, are ubiquitous. Using experiments, mathematical models, and computer simulations we show that bacteriophages drive plasmid dynamics through their ecological and evolutionary effects on bacteria and ultimately limit the conditions allowing plasmid existence. These results advance our understanding of bacterial adaptation and show that bacteriophages could be used to select against plasmids carrying undesirable traits, such as antibiotic resistance.