PhoP-Induced Genes within Salmonella Pathogenicity Island 1

ANDRÉS AGUIRRE; MARÍA LAURA CABEZA; SILVANA V. SPINELLI; MICHAEL MCCLELLAND,; ELEONORA GARCÍA VÉSCOVI; FERNANDO C. SONCINI

JOURNAL OF BACTERIOLOGY

American Society for Microbiology

Año: 2006 vol. 188 p. 6889 - 6898

0021-9193

The invasive pathogen Salmonella enterica has evolved a sophisticated device that allows it to enter nonphagocytichost cells. This process requires the expression of Salmonella pathogenicity island 1 (SPI-1), which encodes aspecialized type III protein secretion system (TTSS). This TTSS delivers a set of effectors that produce a markedrearrangement of the host cytoskeleton, generating a profuse membrane ruffling at the site of interaction, drivingbacterial entry. It has been shown that the PhoP/PhoQ two-component system represses the expression of the SPI-1machinery by down-regulating the transcription of its master regulator, HilA. In this work, we reveal the presenceof a PhoP-activated operon within SPI-1. This operon is composed of the orgB and orgC genes, which encode aprotein that interacts with the InvC ATPase and a putative effector protein of the TTSS, respectively. UnderPhoP-inducing conditions, expression of this operon is directly activated by the phosphorylated form of the responseregulator, which recognizes a PhoP box located at the35 region relative to the transcription start site. Additionally,under invasion-inducing conditions, orgBC expression is driven both by the prgH promoter, induced by the SPI-1 masterregulator HilA, and by the directly controlled PhoP/PhoQ promoter. Together, these results indicate that in contrast tothe rest of the genes encompassed in the SPI-1 locus, orgBC is expressed during and after Salmonella entry into its hostcell, and they suggest a role for the products of this operon after host cell internalization.