Löber Stefanie, Jäckel Daniela, Kaiser Nina, Hensel Michael
Institut für Klinische Mikrobiologie, Immunologie und Hygiene, FAU Erlangen-Nürnberg, Wasserturmstrasse 3-5, D-91054 Erlangen, Germany.
Int J Med Microbiol. 2006 Nov;296(7):435-47. doi: 10.1016/j.ijmm.2006.05.001. Epub 2006 Aug 14.
The function of a type III secretion system (T3SS) encoded by Salmonella pathogenicity island 2 (SPI2) is essential for the intracellular lifestyle of Salmonella enterica serovar Typhimurium. Expression of SPI2 genes is induced within the Salmonella-containing vacuole (SCV) inside host cells and is controlled by the SsrAB two-component system. However, the nature of the signals leading to expression of SPI2 genes is controversial. Here we report that expression of SPI2 genes can be induced independently by two different environmental stimuli. Exposure of bacteria to slightly acidic pH was sufficient to induce a rapid up-regulation of SPI2 genes. In contrast, limitation of inorganic phosphate (P(i)) in the growth media led to activation of SPI2 genes in the late exponential growth phase and was independent of the media pH. Limitation of P(i) induced an over-expression of sensor protein SsrB. Response to both environmental stimuli required a functional SsrAB system. In vivo analyses indicated that limitation of P(i) is also encountered by intracellular Salmonella. Our observations allow the integration of previous disparate reports on the induction of SPI2 genes.
由沙门氏菌致病岛2（SPI2）编码的III型分泌系统（T3SS）的功能对于肠炎沙门氏菌鼠伤寒血清型在细胞内的生存方式至关重要。SPI2基因的表达在宿主细胞内的含沙门氏菌液泡（SCV）中被诱导，并受SsrAB双组分系统控制。然而，导致SPI2基因表达的信号性质存在争议。在此我们报告，SPI2基因的表达可由两种不同的环境刺激独立诱导。将细菌暴露于微酸性pH足以诱导SPI2基因的快速上调。相反，生长培养基中无机磷酸盐（P(i)）的限制导致SPI2基因在指数生长后期被激活，且与培养基pH无关。P(i)的限制诱导了传感器蛋白SsrB的过度表达。对这两种环境刺激的反应都需要一个功能性的SsrAB系统。体内分析表明，细胞内的沙门氏菌也会遇到P(i)的限制。我们的观察结果使之前关于SPI2基因诱导的不同报道得以整合。
