Ummels Roy, Abdallah Abdallah M, Kuiper Vincent, Aâjoud Anouar, Sparrius Marion, Naeem Raeece, Spaink Herman P, van Soolingen Dick, Pain Arnab, Bitter Wilbert
Department of Medical Microbiology and Infection Control, VU University Medical Center, Amsterdam, The Netherlands.
Pathogen Genomics Group, Biological and Environmental Sciences and Engineering (BESE) Division, King Abdullah University of Science and Technology, Thuwal, Saudi Arabia.
mBio. 2014 Sep 23;5(5):e01744-14. doi: 10.1128/mBio.01744-14.
Conjugative plasmids have been identified in a wide variety of different bacteria, ranging from proteobacteria to firmicutes, and conjugation is one of the most efficient routes for horizontal gene transfer. The most widespread mechanism of plasmid conjugation relies on different variants of the type IV secretion pathway. Here, we describe the identification of a novel type of conjugative plasmid that seems to be unique for mycobacteria. Interestingly, while this plasmid is efficiently exchanged between different species of slow-growing mycobacteria, including Mycobacterium tuberculosis, it could not be transferred to any of the fast-growing mycobacteria tested. Genetic analysis of the conjugative plasmid showed the presence of a locus containing homologues of three type IV secretion system components and a relaxase. In addition, a new type VII secretion locus was present. Using transposon insertion mutagenesis, we show that in fact both these secretion systems are essential for conjugation, indicating that this plasmid represents a new class of conjugative plasmids requiring two secretion machineries. This plasmid could form a useful new tool to exchange or introduce DNA in slow-growing mycobacteria.
Conjugative plasmids play an important role in horizontal gene transfer between different bacteria and, as such, in their adaptation and evolution. This effect is most obvious in the spread of antibiotic resistance genes. Thus far, conjugation of natural plasmids has been described only rarely for mycobacterial species. In fact, it is generally accepted that M. tuberculosis does not show any recent sign of horizontal gene transfer. In this study, we describe the identification of a new widespread conjugative plasmid that can also be efficiently transferred to M. tuberculosis. This plasmid therefore poses both a threat and an opportunity. The threat is that, through the acquisition of antibiotic resistance markers, this plasmid could start a rapid spread of antibiotic resistance genes between pathogenic mycobacteria. The opportunity is that we could use this plasmid to generate new tools for the efficient introduction of foreign DNA in slow-growing mycobacteria.
接合质粒已在从变形菌到厚壁菌等多种不同细菌中被鉴定出来，而接合作用是水平基因转移最有效的途径之一。质粒接合最普遍的机制依赖于IV型分泌途径的不同变体。在此，我们描述了一种新型接合质粒的鉴定，这种质粒似乎是分枝杆菌所特有的。有趣的是，虽然这种质粒能在包括结核分枝杆菌在内的不同种缓慢生长分枝杆菌之间高效交换，但它无法转移到所测试的任何一种快速生长分枝杆菌中。对接合质粒的遗传分析表明，存在一个位点，其中包含三种IV型分泌系统组分和一种松弛酶的同源物。此外，还存在一个新型VII型分泌位点。利用转座子插入诱变，我们表明事实上这两种分泌系统对于接合作用都是必不可少的，这表明这种质粒代表了一类需要两种分泌机制的新型接合质粒。这种质粒可成为在缓慢生长分枝杆菌中交换或引入DNA的有用新工具。
接合质粒在不同细菌之间的水平基因转移中发挥着重要作用，因此在它们的适应和进化中也起着重要作用。这种作用在抗生素抗性基因的传播中最为明显。到目前为止，仅很少描述过分枝杆菌物种天然质粒的接合作用。事实上，人们普遍认为结核分枝杆菌没有显示出任何近期水平基因转移的迹象。在本研究中，我们描述了一种新的广泛存在的接合质粒的鉴定，这种质粒也能有效地转移到结核分枝杆菌中。因此，这种质粒既构成威胁也带来机遇。威胁在于，通过获得抗生素抗性标记，这种质粒可能会在致病性分枝杆菌之间引发抗生素抗性基因的快速传播。机遇在于，我们可以利用这种质粒生成新工具，以便在缓慢生长分枝杆菌中高效引入外源DNA。
