Miao Edward A, Freeman Jeremy A, Miller Samuel I
Department of Microbiology, Health Sciences Building, University of Washington, Seattle, WA 98195, USA.
J Bacteriol. 2002 Mar;184(5):1493-7. doi: 10.1128/JB.184.5.1493-1497.2002.
The Salmonella pathogenicity island 2 (SPI-2) type III secretion system is expressed by intracellular bacteria and translocates effector proteins across the vacuolar membrane. Signals sensed by Salmonella enterica serovar Typhimurium in the intracellular compartment activate SPI-2 gene expression through the two-component regulatory system SsrAB. The effects of environmental and genetic signals on expression of the SsrAB-regulated gene sspH2 were examined. SsrAB-dependent activation of sspH2 was detected in the presence of both low and moderate concentrations of magnesium or calcium and at acidic and neutral pHs. The levels of expression were comparable to those detected in bacteria recovered from cultured macrophages. The induction in media at alkaline pHs (pH 7.5 and 8.0) was greatly reduced compared to the induction observed at pH 7.0 or at a lower pH, suggesting that alkaline pH represses SsrAB activation. In addition, the PhoPQ two-component system, which is also activated intracellularly, was not required for activation of SsrAB.
沙门氏菌致病岛2（SPI-2）III型分泌系统由胞内细菌表达，并将效应蛋白转运穿过液泡膜。鼠伤寒沙门氏菌在胞内区室中感知到的信号通过双组分调控系统SsrAB激活SPI-2基因表达。研究了环境和遗传信号对SsrAB调控基因sspH2表达的影响。在低浓度和中等浓度的镁或钙存在下以及在酸性和中性pH条件下，均检测到sspH2的SsrAB依赖性激活。表达水平与从培养的巨噬细胞中回收的细菌中检测到的水平相当。与在pH 7.0或更低pH下观察到的诱导相比，在碱性pH（pH 7.5和8.0）培养基中的诱导大大降低，这表明碱性pH抑制SsrAB激活。此外，同样在胞内被激活的PhoPQ双组分系统对于SsrAB的激活不是必需的。
