title: The PhoP/PhoQ two-component system stabilizes the alternative sigma factor RpoS in Salmonella enterica.
abstract: The sigma factor RpoS regulates the expression of many stress response genes and is required for virulence in several bacterial species. We now report that RpoS accumulates when Salmonella enterica serovar Typhimurium is growing logarithmically in media with low Mg(2+) concentrations. This process requires the two-component regulatory system PhoP/PhoQ, which is specifically activated in low Mg(2+). We show that PhoP controls RpoS protein turnover by serving as a transcriptional activator of the iraP (yaiB) gene, which encodes a product that enhances RpoS stability by interacting with RssB, the protein that normally delivers RpoS to the ClpXP protease for degradation. Mutation of the phoP gene rendered Salmonella as sensitive to hydrogen peroxide as an rpoS mutant after growth in low Mg(2+). In Escherichia coli, low Mg(2+) leads to only modest RpoS stabilization, and iraP is not regulated by PhoP/PhoQ. These findings add the sigma factor RpoS to the regulatory proteins and two-component systems that are elevated in a PhoP/PhoQ-dependent fashion when Salmonella face low Mg(2+) environments. Our data also exemplify the critical differences in regulatory circuits that exist between the closely related enteric bacteria Salmonella and E. coli.
authors.affiliation: Department of Molecular Microbiology and Howard Hughes Medical Institute, Washington University School of Medicine, St. Louis, MO 63110, USA.
authors.forename: Xuanlin
authors.initials: X
authors.lastname: Tu
authors.forename: Tammy
authors.initials: T
authors.lastname: Latifi
authors.forename: Alexandre
authors.initials: A
authors.lastname: Bougdour
authors.forename: Susan
authors.initials: S
authors.lastname: Gottesman
authors.forename: Eduardo A
authors.initials: EA
authors.lastname: Groisman
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D015964:Gene Expression Regulation, Bacterial; D008954:Models, Biological; D008969:Molecular Sequence Data; D019779:Salmonella enterica / Q000145:classification / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D012689:Sequence Homology, Nucleic Acid; D012808:Sigma Factor / Q000235:genetics* / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; C079792:PhoQ protein, Bacteria; D012808:Sigma Factor; C061064:PhoP protein, Bacteria