Plasmids are extrachromosomal genetic elements commonly found in prokaryotic (and sometime eukaryotic) cells. Small plasmids are often considered cryptic and their effect on the host is elusive, while large plasmids may encode functions that are essential for the host lifestyle and attain a secondary chromosome status. Plasmids are thus an important source of raw material for microbial genome evolution outside the mainstream of bacterial chromosomes. The discovery of plasmid‐mediated antibiotic resistance led to extensive research on the contribution of plasmids to the environmental dimensions of antibiotic resistance and the evolution of plasmid‐host interactions following the acquisition of plasmids encoding for antibiotic resistance. Recent experimental studies revealed the importance of intracellular plasmid diversity for plasmid‐host interactions. Here we describe the evolutionary forces at play during plasmid evolution in a top‐down approach: this includes the effect of processes at the level of the host population and the consideration of plasmids as Darwinian individuals within the host cell.

中文翻译：

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染色体外遗传元素的达尔文个性需要群体遗传学修补

质粒是在原核（有时是真核）细胞中常见的染色体外遗传元件。小质粒通常被认为是神秘的，它们对宿主的影响难以捉摸，而大质粒可能编码对宿主生活方式至关重要的功能，并获得二级染色体状态。因此，质粒是细菌染色体主流之外微生物基因组进化的重要原材料来源。质粒介导的抗生素耐药性的发现导致了对质粒对抗生素耐药性环境维度的贡献以及获得编码抗生素耐药性的质粒后质粒-宿主相互作用演变的广泛研究。最近的实验研究揭示了细胞内质粒多样性对质粒-宿主相互作用的重要性。在这里，我们以自上而下的方法描述了在质粒进化过程中发挥作用的进化力量：这包括宿主群体水平上的过程的影响以及将质粒视为宿主细胞内的达尔文个体。