The response of WT, ∆rip1, and ∆sigL strains of Mycobacterium tuberculosis to dipyridyl treatment. The response of WT, ∆rip1, and ∆sigL strains of Mycobacterium tuberculosis to dipyridyl treatment

Mycobacterium tuberculosis is exposed to a variety of stresses during a chronic infection, as the immune system simultaneously produces bactericidal compounds and starves the pathogen for essential nutrients. The intramembrane protease, Rip1, plays an important role in the adaptation to these stresses, at least partially by the cleavage of membrane bound transcriptional regulators. Although Rip1 is known to be critical for surviving copper intoxication and nitric oxide exposure, these stresses do not fully account the regulatory protein’s essentiality during infection. In this work, we demonstrate that Rip1 is also necessary for growth in low iron and zinc conditions, similar to those imposed by the immune system. Using a newly generated library of sigma factor mutants, we show that the known regulatory target of Rip1, SigL, shares this defect. Transcriptional profiling under iron limiting conditions supported the coordinated activity of Rip1 and SigL and demonstrated that the loss of these proteins produces an exaggerated iron starvation response. These observations demonstrate that Rip1 coordinates several aspects of metal homeostasis and suggest that a Rip1- and SigL-dependent pathway is involved in the adaptation to the iron deficient environments encountered during infection. Overall design: Gene expression profiling of Mycobacterium tuberculosis WT H37Rv and knockout mutants in response to dipryidyl treatment

结核分枝杆菌（Mycobacterium tuberculosis）在慢性感染过程中会面临多种应激压力：宿主免疫系统会同时产生杀菌性化合物，并剥夺该病原体生长所需的必需营养物质。膜内蛋白酶（intramembrane protease）Rip1在适应这类应激过程中发挥关键作用，其功能至少部分通过剪切膜结合型转录调节因子实现。尽管已知Rip1对抵抗铜中毒和一氧化氮暴露至关重要，但上述应激因素无法完全解释该调节蛋白在感染过程中的必要性。本研究证实，Rip1同样是结核分枝杆菌在低铁、低锌条件下生长所必需的，这类环境与免疫系统施加的营养限制条件相似。利用新构建的σ因子（sigma factor）突变体文库，我们发现Rip1的已知调控靶点SigL同样存在该生长缺陷。铁限制条件下的转录谱分析证实了Rip1与SigL的协同调控活性，并表明缺失这两种蛋白会引发过度增强的铁饥饿应答。上述观察结果表明，Rip1可调控金属稳态的多个环节，并提示依赖Rip1和SigL的信号通路参与适应感染过程中遭遇的缺铁环境。整体实验设计：对结核分枝杆菌野生型H37Rv及其敲除突变体进行基因表达谱分析，处理条件为二吡啶基（dipryidyl）处理。