Neisseria gonorrhoeae secretes chromosomal DNA via a novel type IV secretion system
Neisseria gonorrhoeae secretes chromosomal DNA via a novel type IV secretion system
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DOI：
10.1111/j.1365-2958.2005.04521.x
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发表时间：
2005-03-01
影响因子：
3.6
通讯作者：
Dillard, JP
中科院分区：
文献类型：
--
作者：
Hamilton, HL;Domínguez, NM;Dillard, JP
人们对细菌自然转化的 DNA 捐赠过程知之甚少，并被认为涉及细菌细胞死亡。最近，我们在淋病奈瑟菌中发现，淋球菌遗传岛 (GGI) 中三个基因的突变降低了菌株在转化中充当供体以及将 DNA 释放到培养物中的能力。为了更好地表征 GGI 和 DNA 捐赠过程，对 57 kb 遗传岛进行了克隆、测序和插入突变。 DNA测序表明，GGI具有水平获得的基因组岛的特征，并编码IV型分泌系统蛋白的同源物。发现 GGI 掺入染色体复制末端附近的 diff 位点，该序列是位点特异性重组酶 XerCD 的靶向序列。使用携带一小部分 GGI 和相关 diff 位点的质粒，我们证明该模型岛可以整合到不携带 GGI 的菌株的 diff 位点，并自发地从该位点切除。此外，我们还能够通过用缺乏 GGI 的菌株的 DNA 进行转化来删除整个 57 kb 区域。因此，GGI可能是通过位点特异性重组获得并整合到淋球菌染色体中的，并且可能通过位点特异性重组或自然转化而丢失。我们对六个假定的 IV 型分泌系统基因进行了突变，并分析了这些菌株分泌 DNA 的能力。其中五个突变大大减少或完全消除了 DNA 分泌。我们的数据表明淋病奈瑟菌通过特定过程分泌 DNA。捐赠的 DNA 可用于自然转化，促进抗原变异和抗生素耐药性的传播，并且可以调节宿主免疫反应。
The process of DNA donation for natural transformation of bacteria is poorly understood and has been assumed to involve bacterial cell death. Recently in Neisseria gonorrhoeae we found that mutations in three genes in the gonococcal genetic island (GGI) reduced the ability of a strain to act as a donor in transformation and to release DNA into the culture. To better characterize the GGI and the process of DNA donation, the 57 kb genetic island was cloned, sequenced and subjected to insertional mutagenesis. DNA sequencing revealed that the GGI has characteristics of a horizontally acquired genomic island and encodes homologues of type IV secretion system proteins. The GGI was found to be incorporated near the chromosomal replication terminus at the dif site, a sequence targeted by the site-specific recombinase XerCD. Using a plasmid carrying a small region of the GGI and the associated dif site, we demonstrated that this model island could be integrated at the dif site in strains not carrying the GGI and was spontaneously excised from that site. Also, we were able to delete the entire 57 kb region by transformation with DNA from a strain lacking the GGI. Thus the GGI was likely acquired and integrated into the gonococcal chromosome by site-specific recombination and may be lost by site-specific recombination or natural transformation. We made mutations in six putative type IV secretion system genes and assayed these strains for the ability to secrete DNA. Five of the mutations greatly reduced or completely eliminated DNA secretion. Our data indicate that N. gonorrhoeae secretes DNA via a specific process. Donated DNA may be used in natural transformation, contributing to antigenic variation and the spread of antibiotic resistance, and it may modulate the host immune response.