The Type VI Secretion System Encoded in Salmonella Pathogenicity Island 19 Is Required for Salmonella enterica Serotype Gallinarum Survival within Infected Macrophages
The Type VI Secretion System Encoded in Salmonella Pathogenicity Island 19 Is Required for Salmonella enterica Serotype Gallinarum Survival within Infected Macrophages
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DOI：
10.1128/iai.01165-12
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发表时间：
2013-04-01
影响因子：
3.1
通讯作者：
Contreras, Ines
中科院分区：
文献类型：
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作者：
Blondel, Carlos J.;Jimenez, Juan C.;Contreras, Ines
鸡血清型肠炎沙门氏菌是禽伤寒的病原体，禽伤寒是一种以高发病率和死亡率为特征的疾病，对家禽生产造成重大经济损失。我们报道了沙门氏菌致病性岛19 （SPI-19）中含有一个VI型分泌系统（T6SS），该系统是雏鸡有效定植所必需的。在本研究中，我们旨在表征SPI-19 T6SS的功能，并研究之前在体内观察到的表型背后的机制。表达分析表明，SPI-19 T6SS核心成分在体外细菌生长条件下得以表达和产生。然而，结构/分泌成分Hcp1、Hcp2和VgrG向培养基的分泌无法确定，这表明这些蛋白的t6ss依赖性分泌需要额外的信号。体外细菌竞争试验未能证明SPI-19 T6SS在细菌间杀伤中的作用。相比之下，小鼠和禽类巨噬细胞（分别为RAW264.7和HD11）的细胞培养实验显示，沙门氏菌摄取后不久就产生了绿色荧光蛋白标记的VgrG。此外，用SPI-19缺失突变体或编码特定T6SS核心成分基因（clpV和vgrG）的菌株感染RAW264.7和HD11巨噬细胞，发现SPI-19 T6SS有助于鸡链球菌在摄取后20小时在巨噬细胞内存活。SPI-19 T6SS功能与沙门氏菌诱导的感染巨噬细胞的细胞毒性或细胞死亡无关，这与其他T6SS的描述不同。我们的数据表明，SPI-19 T6SS对应于沙门氏菌在宿主细胞内生存的一种新工具。
Salmonella enterica serotype Gallinarum is the causative agent of fowl typhoid, a disease characterized by high morbidity and mortality that causes major economic losses in poultry production. We have reported that S. Gallinarum harbors a type VI secretion system (T6SS) encoded in Salmonella pathogenicity island 19 (SPI-19) that is required for efficient colonization of chicks. In the present study, we aimed to characterize the SPI-19 T6SS functionality and to investigate the mechanisms behind the phenotypes previously observed in vivo. Expression analyses revealed that SPI-19 T6SS core components are expressed and produced under in vitro bacterial growth conditions. However, secretion of the structural/secreted components Hcp1, Hcp2, and VgrG to the culture medium could not be determined, suggesting that additional signals are required for T6SS-dependent secretion of these proteins. In vitro bacterial competition assays failed to demonstrate a role for SPI-19 T6SS in interbacterial killing. In contrast, cell culture experiments with murine and avian macrophages (RAW264.7 and HD11, respectively) revealed production of a green fluorescent protein-tagged version of VgrG soon after Salmonella uptake. Furthermore, infection of RAW264.7 and HD11 macrophages with deletion mutants of SPI-19 or strains with genes encoding specific T6SS core components (clpV and vgrG) revealed that SPI-19 T6SS contributes to S. Gallinarum survival within macrophages at 20 h postuptake. SPI-19 T6SS function was not linked to Salmonella-induced cytotoxicity or cell death of infected macrophages, as has been described for other T6SS. Our data indicate that SPI-19 T6SS corresponds to a novel tool used by Salmonella to survive within host cells.