Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, MI, USA.
Mol Microbiol. 2010 Apr;76(1):200-19. doi: 10.1111/j.1365-2958.2010.07094.x. Epub 2010 Feb 28.
To transit between hosts, intracellular Legionella pneumophila transform into a motile, infectious, transmissive state. Here we exploit the pathogen's life cycle to examine how guanosine tetraphosphate (ppGpp) and DksA cooperate to govern bacterial differentiation. Transcriptional profiling revealed that during transmission alarmone accumulation increases the mRNA for flagellar and Type IV-secretion components, secreted host effectors and regulators, and decreases transcripts for translation, membrane modification and ATP synthesis machinery. DksA is critical for differentiation, since mutants are defective for stationary phase survival, flagellar gene activation, lysosome avoidance and macrophage cytotoxicity. The roles of ppGpp and DksA depend on the context. For macrophage transmission, ppGpp is essential, whereas DksA is dispensable, indicating that ppGpp can act autonomously. In broth, DksA promotes differentiation when ppGpp levels increase, or during fatty acid stress, as judged by flaA expression and evasion of degradation by macrophages. For flagella morphogenesis, DksA is required for basal fliA (sigma(28)) promoter activity. When alarmone levels increase, DksA cooperates with ppGpp to generate a pulse of Class II rod RNA or to amplify the Class III sigma factor and Class IV flagellin RNAs. Thus, DksA responds to the level of ppGpp and other stress signals to co-ordinate L. pneumophila differentiation.
为了在宿主间转移，细胞内的嗜肺军团菌会转化为可移动、有感染力、可传播的状态。在这里，我们利用病原体的生命周期来研究鸟苷四磷酸（ppGpp）和 DksA 如何合作来控制细菌分化。转录谱分析显示，在传播过程中，警报素的积累增加了鞭毛和 IV 型分泌成分、分泌的宿主效应子和调节剂的 mRNA，减少了翻译、膜修饰和 ATP 合成机制的转录物。DksA 对分化至关重要，因为突变体在静止期存活、鞭毛基因激活、溶酶体逃避和巨噬细胞细胞毒性方面存在缺陷。ppGpp 和 DksA 的作用取决于具体情况。对于巨噬细胞的传播，ppGpp 是必不可少的，而 DksA 是可有可无的，这表明 ppGpp 可以自主发挥作用。在肉汤中，当 ppGpp 水平增加或脂肪酸应激时，DksA 促进分化，这可以通过 flaA 表达和逃避巨噬细胞降解来判断。对于鞭毛形态发生，DksA 是基本的 fliA（sigma(28)）启动子活性所必需的。当警报素水平增加时，DksA 与 ppGpp 合作产生 II 类棒状 RNA 脉冲，或放大 III 类 sigma 因子和 IV 类鞭毛蛋白 RNA。因此，DksA 响应 ppGpp 水平和其他应激信号来协调嗜肺军团菌的分化。
