Chekabab Samuel Mohammed, Jubelin Grégory, Dozois Charles M, Harel Josée
Research Group on Infectious Diseases of Swine, Montreal University, Faculty of Veterinary Medicine, Saint-Hyacinthe, Québec, Canada.
Unité de Microbiologie (UR454) INRA Clermont-Ferrand-Theix, St-Genes-Champanelle, France.
PLoS One. 2014 Apr 7;9(4):e94285. doi: 10.1371/journal.pone.0094285. eCollection 2014.
Enterohemorrhagic Escherichia coli (EHEC), an emerging food- and water-borne hazard, is highly pathogenic to humans. In the environment, EHEC must survive phosphate (Pi) limitation. The response to such Pi starvation is an induction of the Pho regulon including the Pst system that senses Pi variation. The interplay between the virulence of EHEC, Pho-Pst system and environmental Pi remains unknown. To understand the effects of Pi deprivation on the molecular mechanisms involved in EHEC survival and virulence under Pho regulon control, we undertook transcriptome profiling of the EDL933 wild-type strain grown under high Pi and low Pi conditions and its isogenic ΔphoB mutant grown in low Pi conditions. The differentially expressed genes included 1067 Pi-dependent genes and 603 PhoB-dependent genes. Of these 131 genes were both Pi and PhoB-dependent. Differentially expressed genes that were selected included those involved in Pi homeostasis, cellular metabolism, acid stress, oxidative stress and RpoS-dependent stress responses. Differentially expressed virulence systems included the locus of enterocyte effacement (LEE) encoding the type-3 secretion system (T3SS) and its effectors, as well as BP-933W prophage encoded Shiga toxin 2 genes. Moreover, PhoB directly regulated LEE and stx2 gene expression through binding to specific Pho boxes. However, in Pi-rich medium, constitutive activation of the Pho regulon decreased LEE gene expression and reduced adherence to HeLa cells. Together, these findings reveal that EHEC has evolved a sophisticated response to Pi limitation involving multiple biochemical strategies that contribute to its ability to respond to variations in environmental Pi and to coordinating the virulence response.
肠出血性大肠杆菌（EHEC）是一种新出现的通过食物和水传播的危害，对人类具有高度致病性。在环境中，EHEC必须在磷酸盐（Pi）限制条件下存活。对这种Pi饥饿的反应是诱导包括感知Pi变化的Pst系统在内的Pho调节子。EHEC的毒力、Pho-Pst系统与环境Pi之间的相互作用尚不清楚。为了了解Pi剥夺对Pho调节子控制下EHEC存活和毒力相关分子机制的影响，我们对在高Pi和低Pi条件下生长的EDL933野生型菌株以及在低Pi条件下生长的其同基因ΔphoB突变体进行了转录组分析。差异表达基因包括1067个Pi依赖性基因和603个PhoB依赖性基因。其中131个基因同时依赖Pi和PhoB。选择的差异表达基因包括参与Pi稳态、细胞代谢、酸应激、氧化应激和RpoS依赖性应激反应的基因。差异表达的毒力系统包括编码3型分泌系统（T3SS）及其效应子的肠上皮细胞损伤位点（LEE），以及噬菌体BP-933W编码的志贺毒素2基因。此外，PhoB通过与特定的Pho框结合直接调节LEE和stx2基因的表达。然而，在富含Pi的培养基中，Pho调节子的组成型激活降低了LEE基因的表达并减少了对HeLa细胞的粘附。总之，这些发现表明EHEC已经进化出对Pi限制的复杂反应，涉及多种生化策略，这有助于其对环境Pi变化做出反应并协调毒力反应的能力。
