title: RpoS integrates CRP, Fis, and PhoP signaling pathways to control Salmonella Typhi hlyE expression.
abstract: BACKGROUND
  SPI-18 is a pathogenicity island found in some Salmonella enterica serovars, including S. Typhi. SPI-18 harbors two ORFs organized into an operon, hlyE and taiA genes, both implicated in virulence. Regarding the hlyE regulation in S. Typhi, it has been reported that RpoS participates as transcriptional up-regulator under low pH and high osmolarity. In addition, CRP down-regulates hlyE expression during exponential growth. Previously, it has been suggested that there is another factor related to catabolite repression, different from CRP, involved in the down-regulation of hlyE. Moreover, PhoP-dependent hlyE up-regulation has been reported in bacteria cultured simultaneously under low pH and low concentration of Mg2+. Nevertheless, the relative contribution of each environmental signal is not completely clear. In this work we aimed to better understand the regulation of hlyE in S. Typhi and the integration of different environmental signals through global regulators.
  
  
  RESULTS
  We found that Fis participates as a CRP-independent glucose-dependent down-regulator of hlyE. Also, Fis and CRP seem to exert the repression over hlyE through down-regulating rpoS. Moreover, PhoP up-regulates hlyE expression via rpoS under low pH and low Mg2+ conditions.
  
  
  CONCLUSIONS
  All these results together show that, at least under the tested conditions, RpoS is the central regulator in the hlyE regulatory network, integrating multiple environmental signals and global regulators.
authors.forename: Matías R
authors.initials: MR
authors.lastname: Jofré
authors.forename: Leonardo M
authors.initials: LM
authors.lastname: Rodríguez
authors.forename: Nicolás A
authors.initials: NA
authors.lastname: Villagra
authors.forename: Alejandro A
authors.initials: AA
authors.lastname: Hidalgo
authors.forename: Guido C
authors.initials: GC
authors.lastname: Mora
authors.affiliation: Facultad de Ciencias Biológicas, Universidad Andres Bello, Santiago, Chile. jfuentes@unab.cl.
authors.forename: Juan A
authors.initials: JA
authors.lastname: Fuentes
mesh_terms: D001426:Bacterial Proteins / Q000378:metabolism*; D002373:Cyclic AMP Receptor Protein / Q000378:metabolism*; D035021:Factor For Inversion Stimulation Protein / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial; D006460:Hemolysin Proteins / Q000096:biosynthesis*; D012485:Salmonella typhi / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D012808:Sigma Factor / Q000378:metabolism*; D015398:Signal Transduction
chemical_list: D001426:Bacterial Proteins; D002373:Cyclic AMP Receptor Protein; D035021:Factor For Inversion Stimulation Protein; D006460:Hemolysin Proteins; C531350:HlyE protein, Salmonella enterica; D012808:Sigma Factor; C069567:sigma factor KatF protein, Bacteria; C061064:PhoP protein, Bacteria