Source-sink plasmid transfer dynamics maintain gene mobility in soil bacterial communities
Source-sink plasmid transfer dynamics maintain gene mobility in soil bacterial communities
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DOI：
10.1073/pnas.1600974113
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发表时间：
2016-07-19
影响因子：
11.1
通讯作者：
Brockhurst, Michael A.
中科院分区：
文献类型：
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作者：
Hall, James P. J.;Wood, A. Jamie;Brockhurst, Michael A.
水平基因转移是细菌进化的一个基本过程，它可以通过在谱系之间共享基因来加速适应。共轭质粒是介导细菌物种内部和物种之间基因水平转移的主要遗传因子。在一些物种中，质粒是不稳定的，很可能在净化选择中丢失，但当有替代宿主时，种间质粒转移可以抵消这一点，并保持对质粒携带基因的获取。为了研究在生态相关环境中替代宿主对质粒种群动态的进化重要性，我们建立了简单的土壤微观群落，包括两种常见的土壤细菌，荧光假单胞菌和腐殖假单胞菌，以及抗汞质粒pQBR57，在有和没有正选择的情况下[即添加Hg(II)]。在单物种种群中，质粒的稳定性因物种而异：尽管pQBR57在荧光假单胞菌中有或没有阳性选择都存活了下来，但在腐殖质假单胞菌中，pQBR57丢失或被捕获到染色体上的不可转移的Hg-R所取代。一个简单的数学模型表明，这些差异可能是由于pQBR57在p.p putida中较低的种内结合率。相比之下，在两种群落中，模型和实验都表明，来自荧光假单胞菌的种间结合使pQBR57通过源库转移动力学在恶臭假单胞菌中持续存在。此外，在共培养中，pQBR57被不可转移的染色体Hg-R取代的速度减慢。种间转移允许质粒在宿主物种中存活，而宿主物种无法在单一栽培中维持质粒，从而促进了整个群落对质粒携带的辅助基因库的利用，从而增强了未来的可进化性。
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 (Hg-R) plasmid, pQBR57, both with and without positive selection [i.e., addition of Hg(II)]. In single-species populations, plasmid stability varied between species: although pQBR57 survived both with and without positive selection in P. fluorescens, it was lost or replaced by nontransferable Hg-R captured to the chromosome in P. putida. A simple mathematical model suggests these differences were likely due to pQBR57's lower intraspecific conjugation rate in P. putida. By contrast, in two-species communities, both models and experiments show that interspecific conjugation from P. fluorescens allowed pQBR57 to persist in P. putida via source-sink transfer dynamics. Moreover, the replacement of pQBR57 by nontransferable chromosomal Hg-R in P. putida was slowed in coculture. Interspecific transfer allows plasmid survival in host species unable to sustain the plasmid in monoculture, promoting community-wide access to the plasmid-borne accessory gene pool and thus potentiating future evolvability.