Replication and Active Partition of Integrative and Conjugative Elements (ICEs) of the SXT/R391 Family: The Line between ICEs and Conjugative Plasmids Is Getting Thinner.
Replication and Active Partition of Integrative and Conjugative Elements (ICEs) of the SXT/R391 Family: The Line between ICEs and Conjugative Plasmids Is Getting Thinner.
复制标题
DOI：
10.1371/journal.pgen.1005298
复制
发表时间：
2015-06
期刊：
影响因子：
4.5
通讯作者：
Burrus V
中科院分区：
文献类型：
--
作者：
Carraro N;Poulin D;Burrus V
SXT/R391家族的整合和共轭元件（ICEs）在致病性γ变形菌（如霍乱弧菌）中传播多药耐药。SXT/R391 ice是一种可移动的遗传元件，它们驻留在宿主的染色体上，并最终通过偶联自转移到其他细菌中。SXT/R391 ice的共轭转移涉及一种短暂的染色体外环状质粒样形式，被认为是单链DNA通过交配孔转运到受体细胞的底物。这种质粒样的形式被认为是非复制的，因此预计是高度不稳定的。我们在这里报道，在细胞分裂过程中，罗维登夏的ICE R391不受损失的影响。我们研究了影响R391稳定性的遗传决定因素。首先，我们发现hiab样毒素/抗毒素系统改善了R391的稳定性，因为它的缺失导致R391的损失增加了10倍。由于hipAB不是SXT/R391 ice的保守特征，我们寻求替代和保守的稳定机制。我们发现共轭性本身并不能稳定R391，因为删除traG，消除共轭转移，并不影响损失的频率。然而，松弛编码基因的缺失或转移起源（oriT）都会导致R391损失的急剧增加，并导致其质粒样形式的拷贝数减少。这一观察结果表明，由TraI在oriT上启动的复制不仅对共轭转移至关重要，而且对SXT/R391 ice的稳定也至关重要。最后，我们发现了srpMRC，这是一个保守的位点，编码与质粒R1 II型（肌动蛋白型atp酶）parMRC分配系统有远亲关系的两个蛋白质。R391和质粒稳定实验表明，srpMRC具有活性，有助于减少R391的损失。虽然分区系统通常稳定低拷贝质粒，但srpMRC是第一个被报道稳定ice家族的。整合和共轭元件（ICEs）是一类可移动的遗传元件，其特点是能够整合到宿主细胞的染色体上并通过共轭转移。一些研究最多的ice属于SXT/R391家族，该家族是多种致病性γ变形菌间多药耐药传播的主要驱动因素。将SXT/R391 ice转移到新宿主首先需要将其作为一个圆形分子从染色体上切除，如果细胞分裂，它可能会丢失。硅分析揭示了R391携带的几个假定的稳定系统，R391是最初从Providencia rettgeri中分离出来的SXT/R391 ICEs家族的原型成员。我们发现，除了整合到染色体上的稳定性外，SXT/R391 ice的稳定性还取决于毒素/抗毒素系统和质粒样特征，包括细胞内复制和活性分裂。因此，尽管人们早就知道ice和共轭质粒使用相似的策略在细菌种群之间转移，但我们的工作揭示了它们在宿主细胞中维持机制的额外不可预见的相似性。
Integrative and Conjugative Elements (ICEs) of the SXT/R391 family disseminate multidrug resistance among pathogenic Gammaproteobacteria such as Vibrio cholerae. SXT/R391 ICEs are mobile genetic elements that reside in the chromosome of their host and eventually self-transfer to other bacteria by conjugation. Conjugative transfer of SXT/R391 ICEs involves a transient extrachromosomal circular plasmid-like form that is thought to be the substrate for single-stranded DNA translocation to the recipient cell through the mating pore. This plasmid-like form is thought to be non-replicative and is consequently expected to be highly unstable. We report here that the ICE R391 of Providencia rettgeri is impervious to loss upon cell division. We have investigated the genetic determinants contributing to R391 stability. First, we found that a hipAB-like toxin/antitoxin system improves R391 stability as its deletion resulted in a tenfold increase of R391 loss. Because hipAB is not a conserved feature of SXT/R391 ICEs, we sought for alternative and conserved stabilization mechanisms. We found that conjugation itself does not stabilize R391 as deletion of traG, which abolishes conjugative transfer, did not influence the frequency of loss. However, deletion of either the relaxase-encoding gene traI or the origin of transfer (oriT) led to a dramatic increase of R391 loss correlated with a copy number decrease of its plasmid-like form. This observation suggests that replication initiated at oriT by TraI is essential not only for conjugative transfer but also for stabilization of SXT/R391 ICEs. Finally, we uncovered srpMRC, a conserved locus coding for two proteins distantly related to the type II (actin-type ATPase) parMRC partitioning system of plasmid R1. R391 and plasmid stabilization assays demonstrate that srpMRC is active and contributes to reducing R391 loss. While partitioning systems usually stabilizes low-copy plasmids, srpMRC is the first to be reported that stabilizes a family of ICEs. Integrative and conjugative elements (ICEs) constitute a class of mobile genetic elements defined by their ability to integrate into the chromosome of their host cell and to transfer by conjugation. Some of the most studied ICEs belong to the SXT/R391 family, which are major drivers of multidrug resistance dissemination among various pathogenic Gammaproteobacteria. Transfer of SXT/R391 ICEs to a new host first requires its excision from the chromosome as a circular molecule, which may be lost if the cell divides. In silico analyses revealed several putative stabilization systems carried by R391, a prototypical member of the SXT/R391 ICEs family originally isolated from Providencia rettgeri. We discovered that, besides stabilization by integration into the chromosome, stability of SXT/R391 ICEs also depends on toxin/antitoxin systems and plasmid-like features including intracellular replication and active partition. Thus, although it has been known for a long time that ICEs and conjugative plasmids use similar strategies to transfer between bacterial populations, our work reveals additional unforeseen similarities in their mechanisms of maintenance in the host cell.
登录
查看更多内容
影响因子：
3.5
作者：
CHEREPANOV, PP;WACKERNAGEL, W
通讯作者：
WACKERNAGEL, W
影响因子：
64.8
作者：
Beaber, JW;Hochhut, B;Waldor, MK
通讯作者：
Waldor, MK
影响因子：
5.2
作者：
Carraro N;Sauvé M;Matteau D;Lauzon G;Rodrigue S;Burrus V
通讯作者：
Burrus V
影响因子：
6.4
作者：
Baek JH;Rajagopala SV;Chattoraj DK
通讯作者：
Chattoraj DK
影响因子：
3.2
作者：
Beaber, JW;Hochhut, B;Waldor, MK
通讯作者：
Waldor, MK