摘要
      质粒可以通过接合在细胞之间转移，从而通过水平基因转移驱动细菌进化。然而，我们忽略了许多质粒转移的分子机制，因为它们缺乏结合所需的所有蛋白质编码基因。我们通过在大肠杆菌和金黄色葡萄球菌中鉴定数百个具有结合转移来源的质粒和染色体，解决了这个难题。这些质粒（pOriT）劫持了偶联或可移动元件的松弛酶，但不是两者都劫持。pOriT和其他质粒之间的功能依赖性解释了它们的共存：pOriT在具有许多质粒的细胞中丰富，而结合质粒在其他质粒中最常见。我们系统地描述了与接合和替代转移机制有关的质粒迁移率，现在可以提出其中约90%的假定转移机制。在大多数情况下，质粒的迁移似乎涉及结合。有趣的是，迁移机制是质粒编码的附属性状的重要决定因素，因为pOriTs具有最高密度的抗微生物抗性基因，而缺乏假定转移机制的质粒具有最低密度。我们阐明了质粒之间的进化关系，并表明许多pOriT可能是由其他类型质粒中的基因缺失引起的。这些结果表明，大多数质粒可以通过接合转移。
Abstract
Plasmids can be transferred between cells by conjugation, thereby driving bacterial evolution by horizontal gene transfer. Yet, we ignore the molecular mechanisms of transfer for many plasmids because they lack all protein-coding genes required for conjugation. We solved this conundrum by identifying hundreds of plasmids and chromosomes with conjugative origins of transfer in Escherichia coli and Staphylococcus aureus. These plasmids (pOriT) hijack the relaxases of conjugative or mobilizable elements, but not both. The functional dependencies between pOriT and other plasmids explain their co-occurrence: pOriT are abundant in cells with many plasmids, whereas conjugative plasmids are the most common in the others. We systematically characterized plasmid mobility in relation to conjugation and alternative mechanisms of transfer and can now propose a putative mechanism of transfer for ∼90% of them. In most cases, plasmid mobility seems to involve conjugation. Interestingly, the mechanisms of mobility are important determinants of plasmid-encoded accessory traits, since pOriTs have the highest densities of antimicrobial resistance genes, whereas plasmids lacking putative mechanisms of transfer have the lowest. We illuminate the evolutionary relationships between plasmids and suggest that many pOriT may have arisen by gene deletions in other types of plasmids. These results suggest that most plasmids can be transferred by conjugation.

https://academic.oup.com/nar/article/51/7/3001/6849495?login=false