Molecular characterization of the Mg2+-responsive PhoP-PhoQ regulon in Salmonella enterica.

SERGIO LEJONA; ANDRÉS AGUIRRE; MARÍA LAURA CABEZA; ELEONORA GARCÍA VÉSCOVI; FERNANDO C. SONCINI

JOURNAL OF BACTERIOLOGY

American Society for Microbiology

Año: 2003 vol. 185 p. 6287 - 6294

0021-9193

The PhoP/PhoQ two-component system controls the extracellular magnesium deprivation response in Salmonella enterica.  In addition, several virulence-associated genes that are mainly required for intramacrophage survival during the infection process are under control of its transcriptional regulation.  Despite shared Mg2+ modulation of the expression of the PhoP-activated genes, no consensus sequence common to all of them could be detected in their promoter regions.  We have investigated the transcriptional regulation and the interaction of the response regulator PhoP with the promoter region of the PhoP-activated loci phoPQ, mgtA, slyB, pmrD, pcgL, phoN, pagC, and mgtCB.  A direct repeat of the heptanucleotide sequence (G/T)GTTTA(A/T) was identified as the conserved motif recognized by PhoP to directly control the gene expression of the first five loci, among which the first four are ancestral to enterobacteria.  On the other hand, no direct interaction of the response regulator with the promoters of phoN, pagC, and mgtCB was apparent by both in vitro and in vivo assays.  These loci are Salmonella specific and were probably acquired by horizontal DNA-transfer.  Besides, sequence analysis of pag promoters revealed the presence of a conserved PhoP-box in 6 out of the 12 genes analyzed.  Our results strongly suggest that the expression of a set of Mg2+-controlled genes is driven by PhoP via unknown intermediate regulatory mechanisms that could also involve ancillary factors.