Source-sink plasmid transfer dynamics maintain gene mobility in soil bacterial communities

Horizontal gene transfer is a fundamental process in bacterial evolution that can accelerate adaptation via the sharing of genes between lineages. Conjugative plasmids are the principal genetic elements mediating the horizontal transfer of genes, both within and between bacterial species. In some species, plasmids are unstable and likely to be lost through purifying selection, but when alternative hosts are available, interspecific plasmid transfer could counteract this and maintain access to plasmid-borne genes. To investigate the evolutionary importance of alternative hosts to plasmid population dynamics in an ecologically relevant environment, we established simple soil microcosm communities comprising two species of common soil bacteria, Pseudomonas fluorescens and Pseudomonas putida, and a mercury resistance (HgR) plasmid, pQBR57, both with and without positive selection [i.e., addition of Hg(II)]. In single-species populations, plasmid stability varied between species: although pQ...

水平基因转移是细菌演化中的核心过程，可通过不同谱系间的基因共享加速物种适应。接合性质粒（Conjugative plasmids）是介导细菌种内及种间基因水平转移的主要遗传元件。在部分细菌物种中，质粒并不稳定，易通过纯化选择（purifying selection）丢失；但当存在可供选择的宿主时，种间质粒转移可抵消这一过程，维持对质粒携带基因的获取。为探究在符合生态学场景的环境中，可供选择的宿主对质粒种群动态的演化重要性，我们构建了简易土壤微宇宙（soil microcosm）群落，包含两种常见土壤细菌——荧光假单胞菌（Pseudomonas fluorescens）与恶臭假单胞菌（Pseudomonas putida），以及汞抗性（HgR）质粒pQBR57，并设置了施加与不施加正选择压力（即添加Hg(II)）的两组实验。在单物种种群中，质粒稳定性因物种而异：尽管pQ……