Tiaden André, Spirig Thomas, Weber Stefan S, Brüggemann Holger, Bosshard Rachel, Buchrieser Carmen, Hilbi Hubert
Institute of Microbiology, ETH Zürich, Wolfgang-Pauli-Strasse 10, 8093 Zürich, Switzerland.
Cell Microbiol. 2007 Dec;9(12):2903-20. doi: 10.1111/j.1462-5822.2007.01005.x. Epub 2007 Jul 5.
Legionella pneumophila is an opportunistic human pathogen that replicates within environmental amoebae including Acanthamoeba castellanii and Dictyostelium discoideum. The Icm/Dot type IV secretion system promotes phagocytosis and intracellular replication of L. pneumophila in an endoplasmic reticulum-derived 'Legionella-containing vacuole' (LCV). L. pneumophila adopts a biphasic life cycle consisting of a replicative growth phase and a transmissive (stationary) phase, the latter of which is characterized by the preferential expression of genes required for motility and virulence. A bioinformatic analysis of the L. pneumophila genome revealed a gene cluster homologous to the Vibrio cholerae cqsAS genes, encoding a putative quorum sensing autoinducer synthase (lqsA) and a sensor kinase (lqsS), which flank a novel response regulator (lqsR). We report here that an L. pneumophila lqsR deletion mutant grew in broth with the same rate as wild-type bacteria, but entered the replicative growth phase earlier. Overexpression of lqsR led to an elongated morphology of the bacteria. The lqsR mutant strain was found to be more salt-resistant and impaired for intracellular growth in A. castellanii, D. discoideum and macrophages, formation of the ER-derived LCV and toxicity. Moreover, L. pneumophila lacking LqsR, as well as strains lacking the stationary sigma factor RpoS or the two-component response regulator LetA, were phagocytosed less efficiently by A. castellanii, D. discoideum or macrophages. The expression of lqsR was dependent on RpoS and, to a lesser extent, also on LetA. DNA microarray experiments revealed that lqsR regulates the expression of genes involved in virulence, motility and cell division, consistent with a role for LqsR in the transition from the replicative to the transmissive (virulent) phase. Our findings indicate that LqsR is a novel pleiotropic regulator involved in RpoS- and LetA-controlled interactions of L. pneumophila with phagocytes.
嗜肺军团菌是一种机会性人类病原体，可在包括卡氏棘阿米巴和盘基网柄菌在内的环境变形虫内复制。Icm/Dot IV型分泌系统促进嗜肺军团菌在内质网衍生的“含军团菌液泡”（LCV）中的吞噬作用和细胞内复制。嗜肺军团菌采用双相生命周期，包括复制生长阶段和传播（静止）阶段，后者的特征是运动性和毒力所需基因的优先表达。对嗜肺军团菌基因组的生物信息学分析揭示了一个与霍乱弧菌cqsAS基因同源的基因簇，编码一种假定的群体感应自诱导物合酶（lqsA）和一种传感器激酶（lqsS），它们位于一个新的反应调节因子（lqsR）两侧。我们在此报告，嗜肺军团菌lqsR缺失突变体在肉汤中的生长速度与野生型细菌相同，但更早进入复制生长阶段。lqsR的过表达导致细菌形态拉长。发现lqsR突变株更耐盐，并且在卡氏棘阿米巴、盘基网柄菌和巨噬细胞中的细胞内生长、内质网衍生的LCV形成和毒性受损。此外，缺乏LqsR的嗜肺军团菌以及缺乏静止sigma因子RpoS或双组分反应调节因子LetA的菌株，被卡氏棘阿米巴、盘基网柄菌或巨噬细胞吞噬的效率较低。lqsR的表达依赖于RpoS，在较小程度上也依赖于LetA。DNA微阵列实验表明，lqsR调节参与毒力、运动性和细胞分裂的基因的表达，这与LqsR在从复制阶段向传播（有毒）阶段转变中的作用一致。我们的研究结果表明，LqsR是一种新型多效调节因子，参与RpoS和LetA控制的嗜肺军团菌与吞噬细胞的相互作用。
