The opportunistic pathogen Stenotrophomonas maltophilia utilizes a type IV secretion system for interbacterial killing
The opportunistic pathogen Stenotrophomonas maltophilia utilizes a type IV secretion system for interbacterial killing
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DOI：
10.1371/journal.ppat.1007651
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发表时间：
2019-09-01
期刊：
影响因子：
6.7
通讯作者：
Farah, Chuck Shaker
中科院分区：
文献类型：
--
作者：
Bayer-Santos, Ethel;Cenens, William;Farah, Chuck Shaker
细菌IV型分泌系统（T4 SS）是一个高度多样化但进化上相关的大分子转运蛋白家族，其可以将蛋白质和DNA分泌到细胞外介质或靶细胞中。最近的研究表明，植物病原体柑橘黄单胞菌携带的T4 SS亚型将毒素转移到靶细胞中。在这里，我们表明来自多重耐药机会病原体嗜麦芽窄食单胞菌的类似T4 SS擅长杀死竞争对手细菌物种。依赖T4 SS的S. maltophilia和X.通过延时荧光显微镜观察Citri。利用生物信息学方法对S. maltophilia K279 a基因组中含有X. Citri T4 SS效应子（XVIPCD）鉴定了12种推定的效应子及其同源免疫蛋白。我们选择了一个假定的S。因此，本发明的目的在于进一步表征具有未知功能的嗜麦芽窄食单胞菌效应子（Smlt 3024），并证实其确实以T4 SS依赖性方式分泌。Smlt 3024在E. coli或其通过T4 SS接触依赖性递送至E.大肠杆菌X.柑橘导致生长速率降低，这可以通过在靶细胞中表达其同源抑制剂Smlt 3025来抵消。此外，还对X. citri能恢复S. maltophilia Delta virD 4，表明来自一个物种的效应子可以被来自另一个物种的T4 SS识别转移。有趣的是，Smlt 3024与大的Ca 2+结合RTX蛋白的N-末端结构域同源，Smlt 3025的晶体结构揭示了与脑膜炎奈瑟氏菌的铁调节蛋白FrpD相似的拓扑结构，其已被证明与RTX蛋白FrpC相互作用。这项工作扩展了我们目前对细菌杀伤T4 SS功能的认识，并增加了已知参与T4 SS介导的细菌间竞争的效应子，这可能有助于建立S。微生物之间的竞争决定了哪些物种将在特定的栖息地占主导地位或被根除。细菌使用一系列机制来杀死或阻止竞争对手的繁殖。我们发现，机会致病菌，嗜麦芽窄食单胞菌，窝藏IV型分泌系统（T4 SS），作为一种武器杀死竞争对手的细菌物种。我们鉴定了一系列新的由S.嗜麦芽窄食单胞菌及其同源免疫蛋白。对一株S.功能未知的嗜麦芽窄食单胞菌效应子（Smlt 3024）显示其降低E. coli细胞。其同源免疫蛋白Smlt 3025呈现与脑膜炎奈瑟氏菌的FrpD脂蛋白相似的结构。Smlt 3024在柑橘黄单胞菌中表达，并能在E.大肠杆菌细胞，突出T4 SSs毒素的可互换特性和分泌系统功能的保守性。我们证明X. citri和S.嗜麦芽窄食单胞菌可以以T4 SS依赖性的方式相互杀死，这很可能是由于它们的效应物-免疫蛋白对队列的差异。这项工作扩展了我们目前对杀菌T4 SS功能的了解，以及这些系统在与其他物种相遇时发射的细菌武器库。
Bacterial type IV secretion systems (T4SS) are a highly diversified but evolutionarily related family of macromolecule transporters that can secrete proteins and DNA into the extracellular medium or into target cells. It was recently shown that a subtype of T4SS harboured by the plant pathogen Xanthomonas citri transfers toxins into target cells. Here, we show that a similar T4SS from the multi-drug-resistant opportunistic pathogen Stenotrophomonas maltophilia is proficient in killing competitor bacterial species. T4SS-dependent duelling between S. maltophilia and X. citri was observed by time-lapse fluorescence microscopy. A bioinformatic search of the S. maltophilia K279a genome for proteins containing a C-terminal domain conserved in X. citri T4SS effectors (XVIPCD) identified twelve putative effectors and their cognate immunity proteins. We selected a putative S. maltophilia effector with unknown function (Smlt3024) for further characterization and confirmed that it is indeed secreted in a T4SS-dependent manner. Expression of Smlt3024 in the periplasm of E. coli or its contact-dependent delivery via T4SS into E. coli by X. citri resulted in reduced growth rates, which could be counteracted by expression of its cognate inhibitor Smlt3025 in the target cell. Furthermore, expression of the VirD4 coupling protein of X. citri can restore the function of S. maltophilia Delta virD4, demonstrating that effectors from one species can be recognized for transfer by T4SSs from another species. Interestingly, Smlt3024 is homologous to the N-terminal domain of large Ca2+-binding RTX proteins and the crystal structure of Smlt3025 revealed a topology similar to the iron-regulated protein FrpD from Neisseria meningitidis which has been shown to interact with the RTX protein FrpC. This work expands our current knowledge about the function of bacteria-killing T4SSs and increases the panel of effectors known to be involved in T4SS-mediated interbacterial competition, which possibly contribute to the establishment of S. maltophilia in clinical and environmental settings.Author summary Competition between microorganisms determines which species will dominate or be eradicated from a specific habitat. Bacteria use a series of mechanisms to kill or prevent multiplication of competitors. We show that an opportunistic pathogen, Stenotrophomonas maltophilia, harbours a type IV secretion system (T4SS) that works as a weapon to kill competitor bacterial species. We identified a series of new putative toxic T4SS effectors secreted by S. maltophilia and their cognate immunity proteins. Characterization of one S. maltophilia effector with unknown function (Smlt3024) shows that it reduces growth rate of E. coli cells. Its cognate immunity protein, Smlt3025, presents a structure similar to the FrpD lipoprotein from Neisseria meningitidis. Smlt3024 expressed in the plant pathogen Xanthomonas citri can be translocated into E. coli cells, highlighting the interchangeable characteristic of T4SSs toxins and the conservation of secretion system function. We show that X. citri and S. maltophilia can kill each other in a T4SS-dependent manner, most likely due to differences in their cohorts of effector-immunity protein pairs. This work expands our current knowledge about the function of bacteria-killing T4SSs and the bacterial arsenal fired by these systems during encounters with other species.