Tanner Jennifer R, Li Laam, Faucher Sébastien P, Brassinga Ann Karen C
Department of Microbiology, Faculty of Science, University of Manitoba, Winnipeg, MB, R3T 2N2, Canada.
Faculty of Agricultural and Environmental Sciences, Department of Natural Resource Sciences, McGill University, Ste-Anne-de-Bellevue, QC, H9X 3V9, Canada.
Mol Microbiol. 2016 Jun;100(6):1017-38. doi: 10.1111/mmi.13365. Epub 2016 Apr 20.
The bacterium Legionella pneumophila is capable of intracellular replication within freshwater protozoa as well as human macrophages, the latter of which results in the serious pneumonia Legionnaires' disease. A primary factor involved in these host cell interactions is the Dot/Icm Type IV secretion system responsible for translocating effector proteins needed to establish and maintain the bacterial replicative niche. Several regulatory factors have been identified to control the expression of the Dot/Icm system and effectors, one of which is the CpxRA two-component system, suggesting essentiality for virulence. In this study, we generated cpxR, cpxA and cpxRA in-frame null mutant strains to further delineate the role of the CpxRA system in bacterial survival and virulence. We found that cpxR is essential for intracellular replication within Acanthamoeba castellanii, but not in U937-derived macrophages. Transcriptome analysis revealed that CpxRA regulates a large number of virulence-associated proteins including Dot/Icm effectors as well as Type II secreted substrates. Furthermore, the cpxR and cpxRA mutant strains were more sodium resistant than the parental strain Lp02, and cpxRA expression reaches maximal levels during postexponential phase. Taken together, our findings suggest the CpxRA system is a key contributor to L. pneumophila virulence in protozoa via virulence factor regulation.
嗜肺军团菌能够在淡水原生动物以及人类巨噬细胞内进行细胞内复制，后者会导致严重的肺炎——军团病。参与这些宿主细胞相互作用的一个主要因素是Dot/Icm IV型分泌系统，该系统负责转运建立和维持细菌复制龛所需的效应蛋白。已鉴定出几种调控因子来控制Dot/Icm系统和效应蛋白的表达，其中之一是CpxRA双组分系统，这表明其对毒力至关重要。在本研究中，我们构建了cpxR、cpxA和cpxRA的框内缺失突变株，以进一步阐明CpxRA系统在细菌存活和毒力中的作用。我们发现cpxR对于嗜肺军团菌在卡氏棘阿米巴内的细胞内复制至关重要，但在U937衍生的巨噬细胞中并非如此。转录组分析表明，CpxRA调控大量与毒力相关的蛋白质，包括Dot/Icm效应蛋白以及II型分泌底物。此外，cpxR和cpxRA突变株比亲本菌株Lp02更耐钠，并且cpxRA表达在指数后期达到最高水平。综上所述，我们的研究结果表明，CpxRA系统通过调控毒力因子，是嗜肺军团菌在原生动物中毒力的关键贡献者。
