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 non-phagocytic host cells. This process requires the expression of the Salmonella pathogenicity island 1 (SPI-1), wich encodes a specialized type III protein secretion system (TTSS). This TTSS delivers a set of effectors that produce a marked rearrangement of the host-cell cytoskeleton, generating a profuse membrane ruffling at the site of interaction, driving bacterial entry. It has been shown that the PhoP/PhoQ two-component system represses the expression of the SPI-1 machinery by down-regulating the transcription of its master regulator HilA. In this work, we reveal the presence of a PhoP-activated operon within SPI-1. This operon, is composed of the orgB and orgC genes, which encode a protein that interacts with the InvC ATPase, and a putative effector protein of this TTSS, respectively. In PhoP-inducing conditions, expression of this operon is directly activated by the phosphorylated form of the response regulator, which recognizes a PhoP-box located at the -35 region relative to the transcription start site. Additionally, in invasion-inducing conditions orgBC expression is driven both by the prgH promoter, induced by the SPI-1 master regulator HilA, and by the PhoP/PhoQ directly-controlled promoter. Together these results indicate that, in contrast to the rest of the genes encompassed in the SPI-1 locus, orgBC is expressed during and after Salmonella entry into its host cell, and suggest a role of the products of this operon after the host-cell internalization.