Multidrug-Resistant Organism Repository and Surveillance Network, Walter Reed Army Institute of Research, Silver Spring, Maryland, USA.
Multidrug-Resistant Organism Repository and Surveillance Network, Walter Reed Army Institute of Research, Silver Spring, Maryland, USA
mBio. 2018 Feb 13;9(1):e02381-17. doi: 10.1128/mBio.02381-17.
The origin and mobilization of the ~2,609-bp DNA segment containing the mobile colistin resistance gene continue to be sources of uncertainty, but recent evidence suggests that the gene originated in species. Moreover can be mobilized as an IS-flanked composite transposon (Tn), but many sequences have been identified without IS or with just a single copy (single ended). To further clarify the origins and mobilization of , we employed the Geneious R8 software suite to comprehensively analyze the genetic environment of every complete structure deposited in GenBank as of this writing (September 2017) both with and without associated IS ( = 273). This revealed that the 2,609-bp structure was likely mobilized from a close relative of a novel species of containing a chromosomal region sharing >96% nucleotide identity with the canonical sequence. This chromosomal region is bounded by AT and CG dinucleotides, which have been described on the inside ends (IE) of all intact Tn described to date and represent the ancestral 2-bp target site duplications (TSDs) generated by IS transposition. We further demonstrate that all structures with just one IS copy or with no IS copies were formed by deletion of IS from the ancestral Tn, likely by a process related to the "copy-out-paste-in" transposition mechanism. Finally, we show that only the rare examples of single-ended structures that have retained a portion of the excised downstream IS including the entire inverted right repeat might be capable of mobilization. A comprehensive analysis of all intact sequences in GenBank was used to identify a region on the chromosome of a novel species with remarkable homology to the canonical structure and that likely represents the origin of this important gene. These data also demonstrate that all structures lacking one or both flanking IS were formed from ancestral composite transposons that subsequently lost the insertion sequences by a process of abortive transposition. This observation conclusively shows that mobilization of occurs as part of a composite transposon and that structures lacking the downstream IS are not capable of mobilization.
这段 DNA 片段长约 2609 个碱基，包含可移动的粘菌素耐药基因，其起源和转移一直存在不确定性，但最近的证据表明，该基因起源于 种。此外，它可以作为带有 IS 的复合转座子（Tn）进行转移，但已经发现许多序列没有 IS 或只有一个拷贝（单端）。为了进一步阐明 的起源和转移，我们使用 Geneious R8 软件套件，对截至 2017 年 9 月 GenBank 中所有已存入的完整 结构的遗传环境进行了全面分析，无论是否与 IS 相关（=273）。这表明，2609 个碱基的 结构可能是从一种新型 种的近缘种中转移而来的，该种的染色体区域与典型序列具有 >96%的核苷酸同一性。这个染色体区域由 AT 和 CG 二核苷酸组成，在迄今为止描述的所有完整 Tn 的内端（IE）都有描述，代表由 IS 转位产生的原始 2 个碱基靶序列重复（TSD）。我们进一步证明，所有只有一个 IS 拷贝或没有 IS 拷贝的 结构都是通过从原始 Tn 中缺失 IS 形成的，这很可能是通过与“复制-粘贴”转位机制有关的过程。最后，我们表明，只有那些罕见的单端结构，保留了一部分切除的下游 IS，包括整个反向重复，才可能具有转移能力。对 GenBank 中所有完整 序列的全面分析，鉴定出一个新型 种染色体上的一个区域，与典型 结构具有显著同源性，这可能代表该重要基因的起源。这些数据还表明，所有缺乏一个或两个侧翼 IS 的 结构都是由原始复合转座子形成的，这些转座子随后通过失败的转位过程失去了插入序列。这一观察结果明确表明， 的转移是作为复合转座子的一部分发生的，缺乏下游 IS 的结构不能进行转移。
