Garmendia Junkal, Beuzón Carmen R, Ruiz-Albert Javier, Holden David W
Department of Infectious Diseases, Centre for Molecular Microbiology and Infection, Imperial College London, Armstrong Road, London SW7 2AZ, UK.
Microbiology (Reading). 2003 Sep;149(Pt 9):2385-2396. doi: 10.1099/mic.0.26397-0.
The type III secretion system (TTSS) encoded by Salmonella typhimurium pathogenicity island 2 (SPI-2) is expressed after bacterial entry into host cells. The SPI-2 TTSS secretes the translocon components SseBCD, which translocate across the vacuolar membrane a number of effector proteins whose action is required for intracellular bacterial replication. Several of these effectors, including SifA and SifB, are encoded outside SPI-2. The two-component regulatory system SsrA-SsrB, encoded within SPI-2, controls the expression of components of the SPI-2 TTSS apparatus as well as its translocated effectors. The expression of SsrA-B is in turn regulated by the OmpR-EnvZ two-component system, by direct binding of OmpR to the ssrAB promoter. Several environmental signals have been shown to induce in vitro expression of genes regulated by the SsrA-B or OmpR-EnvZ systems. In this work, immunoblotting and flow cytometry were used to analyse the roles of SsrA-B and OmpR-EnvZ in coupling different environmental signals to changes in expression of a SPI-2 TTSS translocon component (SseB) and two effector genes (sifA and sifB). Using single and double mutant strains the relative contribution of each regulatory system to the response generated by low osmolarity, acidic pH or the absence of Ca2+ was determined. SsrA-B was found to be essential for the induction of SPI-2 gene expression in response to each of these individual signals. OmpR-EnvZ was found to play a minor role in sensing these signals and to require a functional SsrA-B system to mediate their effect on SPI-2 TTSS gene expression.
鼠伤寒沙门氏菌致病岛2（SPI-2）编码的III型分泌系统（TTSS）在细菌进入宿主细胞后表达。SPI-2 TTSS分泌转位孔蛋白组分SseBCD，其将多种效应蛋白转运穿过液泡膜，这些效应蛋白的作用是细胞内细菌复制所必需的。其中一些效应蛋白，包括SifA和SifB，是在SPI-2之外编码的。SPI-2内编码的双组分调节系统SsrA-SsrB控制SPI-2 TTSS装置组分及其转运效应蛋白的表达。SsrA-B的表达反过来又受OmpR-EnvZ双组分系统调控，通过OmpR直接结合到ssrAB启动子上。已表明几种环境信号可在体外诱导受SsrA-B或OmpR-EnvZ系统调控的基因表达。在这项研究中，采用免疫印迹和流式细胞术分析SsrA-B和OmpR-EnvZ在将不同环境信号与SPI-2 TTSS转位孔蛋白组分（SseB）和两个效应基因（sifA和sifB）表达变化偶联中的作用。使用单突变和双突变菌株确定了每个调节系统对低渗透压、酸性pH或缺乏Ca2+所产生应答的相对贡献。发现SsrA-B对于响应这些单个信号诱导SPI-2基因表达至关重要。发现OmpR-EnvZ在感知这些信号中起次要作用，并且需要功能性SsrA-B系统来介导它们对SPI-2 TTSS基因表达的影响。
