An intracellular phosphorus-starvation signal activates the PhoB/PhoR two-component system in Salmonella enterica. An intracellular phosphorus-starvation signal activates the PhoB/PhoR two-component system in Salmonella enterica

Bacteria acquire P primarily as inorganic orthophosphate (Pi, PO43-). Once internalized, Pi is rapidly assimilated into biomass during the synthesis of ATP. Because Pi is essential, but excessive ATP is toxic, the acquisition of environmental Pi is tightly regulated. In the bacterium Salmonella enterica (Salmonella), growth in Pi-limiting environments activates the membrane sensor histidine kinase PhoR, leading to the phosphorylation of its cognate transcriptional regulator PhoB and subsequent transcription of genes involved in adaptations to low Pi. Pi limitation is thought to promote PhoR kinase activity by altering the conformation of a membrane signaling complex comprised by PhoR, the multicomponent Pi transporter system PstSACB and the regulatory protein PhoU. The identity of the low Pi signal and how it controls PhoR activity remain unknown. Here we characterize the PhoB-dependent and independent transcriptional changes elicited by Salmonella in response to P starvation, and identify PhoB-independent genes that are required for the utilization of several organic-P sources. We use this knowledge to identify the cellular compartment where the PhoR signaling complex senses the low Pi signal. We demonstrate that the PhoB and PhoR signal transduction proteins can be maintained in an inactive state even when Salmonella is grown in media lacking Pi. Our results establish that PhoR activity is controlled by by an intracellular signal resulting from P insufficiency. Overall design: Comparative gene expression profiling analysis of RNA-seq data for Salmonella enterica 14028s and its ΔphoB::Kn derivative during growth in medium containing phosphate (Pi) or lacking a phosphorus source (P)

细菌主要通过摄取无机正磷酸盐（inorganic orthophosphate, Pi, PO4³⁻）来获取磷（P）。Pi被胞内摄取后，会在ATP合成过程中迅速同化为生物量。由于Pi是生命必需物质，但过量ATP具有毒性，因此环境Pi的摄取过程受到严格调控。在肠炎沙门氏菌（Salmonella enterica, Salmonella）中，Pi限制环境下的生长会激活膜传感器组氨酸激酶PhoR（membrane sensor histidine kinase PhoR），进而使其同源转录调控因子PhoB（cognate transcriptional regulator PhoB）发生磷酸化，并启动参与低Pi适应的相关基因的转录。现有研究认为，Pi限制可通过改变由PhoR、多组分Pi转运系统PstSACB（multicomponent Pi transporter system PstSACB）以及调控蛋白PhoU（regulatory protein PhoU）组成的膜信号复合物的构象，来增强PhoR的激酶活性。低Pi信号的本质及其调控PhoR活性的分子机制，目前仍未明确。本研究对沙门氏菌响应磷（P）饥饿时的PhoB依赖型与非依赖型转录变化进行了系统表征，并鉴定出参与多种有机磷源利用所必需的PhoB非依赖型基因。基于上述发现，本研究确定了PhoR信号复合物感知低Pi信号的细胞区域。本研究证实，即便在不含Pi的培养基中培养沙门氏菌，PhoB与PhoR信号转导蛋白仍可维持非激活状态。本研究结果表明，PhoR的活性受磷不足所产生的细胞内信号调控。实验整体设计：对在含磷酸盐（Pi）或不含磷源（P）的培养基中生长的肠炎沙门氏菌14028s及其ΔphoB::Kn缺失突变株进行RNA-seq比较基因表达谱分析。