title: RpoS- and Crp-dependent transcriptional control of Salmonella Typhi taiA and hlyE genes: role of environmental conditions.
abstract: A novel pathogenicity island, SPI-18, carries the taiA-hlyE operon, encoding virulence factors in Salmonella Typhi. To determine the effects of certain environmental conditions on the expression of these genes, beta-galactosidase assays, RT-PCR reactions, western blot analyses and measurement of hemolytic activity were performed. The conditions studied are those likely found by S. Typhi during infection in the human host. We found RpoS-dependent transcriptional upregulation in low pH and high osmolarity for both genes. Our results show that oxygen depletion apparently did not affect transcription of the taiA-hlyE operon. On the other hand, the transcriptional regulator Crp, previously described as an activator of hlyE transcription in Escherichia coli, is involved in transcriptional repression of hlyE in S. Typhi. Moreover, addition of glucose to the growth medium results in decreasing the hlyE mRNA, suggesting that there is another factor related to catabolite repression different from Crp and involved in downregulation of hlyE in S. Typhi.
authors.affiliation: Laboratorio de Microbiología, Facultad de Ciencias Biológicas y Facultad de Medicina, Universidad Andres Bello, República 217, Santiago de Chile, Chile. juan.fuentesa@uandresbello.edu
authors.forename: Juan A
authors.initials: JA
authors.lastname: Fuentes
authors.forename: Matías R
authors.initials: MR
authors.lastname: Jofré
authors.forename: Nicolás A
authors.initials: NA
authors.lastname: Villagra
authors.forename: Guido C
authors.initials: GC
authors.lastname: Mora
mesh_terms: D001426:Bacterial Proteins / Q000378:metabolism*; D002373:Cyclic AMP Receptor Protein / Q000378:metabolism*; D004777:Environment; D015964:Gene Expression Regulation, Bacterial; D044404:Genomic Islands; D006460:Hemolysin Proteins / Q000235:genetics* / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D009994:Osmolar Concentration; D012485:Salmonella typhi / Q000235:genetics*; D012808:Sigma Factor / Q000378:metabolism*; D037521:Virulence Factors / Q000235:genetics*
chemical_list: D001426:Bacterial Proteins; D002373:Cyclic AMP Receptor Protein; D006460:Hemolysin Proteins; C531350:HlyE protein, Salmonella enterica; D012808:Sigma Factor; D037521:Virulence Factors; C069567:sigma factor KatF protein, Bacteria