Genomic evolution of bacterial populations under coselection by antibiotics and phage
Genomic evolution of bacterial populations under coselection by antibiotics and phage
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DOI：
10.1111/mec.13950
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发表时间：
2017-04-01
影响因子：
4.9
通讯作者：
Becks, Lutz
中科院分区：
文献类型：
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作者：
Cairns, Johannes;Frickel, Jens;Becks, Lutz
细菌生活在动态系统中，选择压力会迅速改变，迫使它们适应当前的环境。特别是，在许多环境中，人为来源的噬菌体和抗生素是主要的细菌应激源。我们之前观察到，与单独暴露于噬菌体的群体相比，暴露于裂解噬菌体SBW25 phi 2和非抑制浓度的抗生素链霉素（共选择）的荧光假单胞菌SBW25群体获得了更高水平的噬菌体抗性。此外，噬菌体在共选择下灭绝，而在噬菌体单独存在的环境中仍然存在。此外，表型测试表明，这些观察结果可能与共选择下突变率的增加有关。在这项研究中，我们通过从实验结束时分离的全基因组测序克隆检查了这些表型背后的遗传原因。我们能够确定可能导致链霉素耐药、噬菌体耐药和超变（突变）表型的遗传因素。这构成了基因组证据，支持噬菌体的存在不影响抗生素耐药性的观察，但抗生素的存在影响了噬菌体的耐药性。我们之前假设突变体与共选择下噬菌体抗性水平升高之间存在关联。然而，我们关于其机制的证据是不确定的，因为尽管噬菌体突变体只在共选择下发现，但缺乏额外的基因组证据，并且在共选择下非突变体中也观察到噬菌体抗性。更一般地说，我们的研究为单变量和多变量选择（这里是两个压力源）之间的进化以及自然群落中超变异的潜在作用提供了新的见解。
Bacteria live in dynamic systems where selection pressures can alter rapidly, forcing adaptation to the prevailing conditions. In particular, bacteriophages and antibiotics of anthropogenic origin are major bacterial stressors in many environments. We previously observed that populations of the bacterium Pseudomonas fluorescens SBW25 exposed to the lytic bacteriophage SBW25 phi 2 and a noninhibitive concentration of the antibiotic streptomycin (coselection) achieved higher levels of phage resistance compared to populations exposed to the phage alone. In addition, the phage became extinct under coselection while remaining present in the phage alone environment. Further, phenotypic tests indicated that these observations might be associated with increased mutation rate under coselection. In this study, we examined the genetic causes behind these phenotypes by whole-genome sequencing clones isolated from the end of the experiments. We were able to identify genetic factors likely responsible for streptomycin resistance, phage resistance and hypermutable (mutator) phenotypes. This constitutes genomic evidence in support of the observation that while the presence of phage did not affect antibiotic resistance, the presence of antibiotic affected phage resistance. We had previously hypothesized an association between mutators and elevated levels of phage resistance under coselection. However, our evidence regarding the mechanism was inconclusive, as although with phage mutators were only found under coselection, additional genomic evidence was lacking and phage resistance was also observed in nonmutators under coselection. More generally, our study provides novel insights into evolution between univariate and multivariate selection (here two stressors), as well as the potential role of hypermutability in natural communities.