Department of Population Medicine and Diagnostic Sciences, Cornell University, Ithaca, New York, United States of America.
PLoS One. 2012;7(3):e34220. doi: 10.1371/journal.pone.0034220. Epub 2012 Mar 27.
Salmonella pathogenicity island 1 (SPI1), comprising a type III section system that translocates effector proteins into host cells, is essential for the enteric pathogen Salmonella to penetrate the intestinal epithelium and subsequently to cause disease. Using random transposon mutagenesis, we found that a Tn10 disruption in the flagellar fliDST operon induced SPI1 expression when the strain was grown under conditions designed to repress SPI1, by mimicking the environment of the large intestine through the use of the intestinal fatty acid butyrate. Our genetic studies showed that only fliT within this operon was required for this effect, and that exogenous over-expression of fliT alone significantly reduced the expression of SPI1 genes, including the invasion regulator hilA and the sipBCDA operon, encoding type III section system effector proteins, and Salmonella invasion of cultured epithelial cells. fliT has been known to inhibit the flagellar machinery through repression of the flagellar master regulator flhDC. We found that the repressive effect of fliT on invasion genes was completely abolished in the absence of flhDC or fliZ, the latter previously shown to induce SPI1, indicating that this regulatory pathway is required for invasion control by fliT. Although this flhDC-fliZ pathway was necessary for fliT to negatively control invasion genes, fliZ was not essential for the repressive effect of fliT on motility, placing fliT high in the regulatory cascade for both invasion and motility.
沙门氏菌致病岛 1（SPI1）由一个 III 型分泌系统组成，该系统将效应蛋白易位到宿主细胞中，对于肠道病原体沙门氏菌穿透肠上皮并随后引起疾病是必不可少的。使用随机转座子突变，我们发现当菌株在设计用于抑制 SPI1 的条件下生长时，Tn10 在鞭毛 fliDST 操纵子中的破坏会诱导 SPI1 的表达，通过使用肠道脂肪酸丁酸模拟大肠环境。我们的遗传研究表明，该操纵子中只有 fliT 是产生这种效应所必需的，并且单独过表达 fliT 就可以显著降低 SPI1 基因的表达，包括侵袭调节因子 hilA 和 sipBCDA 操纵子，编码 III 型分泌系统效应蛋白，以及沙门氏菌对培养上皮细胞的侵袭。 fliT 已被证明通过抑制鞭毛主调节因子 flhDC 来抑制鞭毛机制。我们发现，在没有 flhDC 或 fliZ 的情况下，fliT 对侵袭基因的抑制作用完全被消除，后者先前被证明能诱导 SPI1，表明这种调控途径是 fliT 控制侵袭所必需的。尽管这种 flhDC-fliZ 途径是 fliT 负调控侵袭基因所必需的，但 fliZ 对于 fliT 对运动性的抑制作用并不是必需的，这使得 fliT 在侵袭和运动性的调控级联中处于高位。
