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Journal of Bacteriology, October 2006, p. 6889-6898, Vol. 188, No. 19
0021-9193/06/$08.00+0     doi:10.1128/JB.00804-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

PhoP-Induced Genes within Salmonella Pathogenicity Island 1

Andrés Aguirre,1 María Laura Cabeza,1 Silvana V. Spinelli,1 Michael McClelland,2 Eleonora García Véscovi,1 and Fernando C. Soncini1*

Instituto de Biología Molecular y Celular de Rosario, Consejo Nacional de Investigaciones Científicas y Técnicas, Departamento de Microbiología, Facultad de Ciencias Bioquímicas y Farmacéuticas, Universidad Nacional de Rosario, Suipacha 531, S2002LRK Rosario, Argentina,1 Sidney Kimmel Cancer Center, 10835 Altman Row, San Diego, California 921212

Received 6 June 2006/ Accepted 14 July 2006

The invasive pathogen Salmonella enterica has evolved a sophisticated device that allows it to enter nonphagocytic host cells. This process requires the expression of Salmonella pathogenicity island 1 (SPI-1), which encodes a specialized type III protein secretion system (TTSS). This TTSS delivers a set of effectors that produce a marked rearrangement of the host 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 the TTSS, respectively. Under 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, under invasion-inducing conditions, orgBC expression is driven both by the prgH promoter, induced by the SPI-1 master regulator HilA, and by the directly controlled PhoP/PhoQ 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 they suggest a role for the products of this operon after host cell internalization.

* Corresponding author. Mailing address: Instituto de Biología Molecular y Celular de Rosario (IBR-CONICET), Facultad de Ciencias Bioquímicas y Farmacéuticas (UNR), Departamento de Microbiología, Suipacha 531, S2002LRK Rosario, Argentina. Phone: 54-341-4356369. Fax: 54-341-4390465. E-mail: fsoncini{at}fbioyf.unr.edu.ar.

Journal of Bacteriology, October 2006, p. 6889-6898, Vol. 188, No. 19
0021-9193/06/$08.00+0     doi:10.1128/JB.00804-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.



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