Data from: Positive selection inhibits gene mobilization and transfer in soil bacterial communities

Horizontal gene transfer (HGT) between bacterial lineages is a fundamental evolutionary process that accelerates adaptation. Sequence analyses show that conjugative plasmids are principal agents of HGT in natural communities. However, we lack understanding of how the ecology of bacterial communities and their environments affect the dynamics of plasmid-mediated gene mobilization and transfer. Here we show, in simple experimental soil bacterial communities containing a conjugative mercury resistance plasmid, the repeated, independent mobilization of transposon-borne genes from chromosome to plasmid, plasmid to chromosome and, in the absence of mercury selection, interspecific gene transfers from the chromosome of one species to the other via the plasmid. By reducing conjugation, positive selection for plasmid-encoded traits, like mercury resistance, can consequently inhibit HGT. Our results suggest that interspecific plasmid-mediated gene mobilization is most likely to occur in environments where plasmids are infectious, parasitic elements rather than those where plasmids are positively selected, beneficial elements.细菌谱系间的水平基因转移（Horizontal Gene Transfer, HGT）是一类加速生物适应性演化的核心进化过程。序列分析研究表明，接合型质粒是自然群落中水平基因转移的主要介导因子。然而，学界目前仍未完全明晰细菌群落的生态特征及其栖息环境如何调控质粒介导的基因动员与转移动态。本研究在含接合型抗汞质粒的简化实验土壤细菌群落中证实：转座子携带的基因可通过质粒在染色体与质粒之间反复独立地发生转移——既包含从染色体向质粒的转移，也包含从质粒向染色体的转移；在无汞选择压力的条件下，还可通过质粒实现不同物种间的染色体基因跨种转移。对质粒编码性状（如抗汞特性）的正向选择，可通过降低接合效率进而抑制水平基因转移过程。本研究结果显示，质粒介导的跨种基因动员事件更易发生在将质粒视作侵染性寄生因子的环境中，而非将质粒视为受正向选择的有益遗传元件的环境。