title: Analysis of the Salmonella regulatory network suggests involvement of SsrB and H-NS in σ(E)-regulated SPI-2 gene expression.
abstract: The extracytoplasmic functioning sigma factor σ(E) is known to play an essential role for Salmonella enterica serovar Typhimurium to survive and proliferate in macrophages and mice. However, its regulatory network is not well-characterized, especially during infection. Here we used microarray to identify genes regulated by σ(E) in Salmonella grown in three conditions: a nutrient-rich condition and two others that mimic early and late intracellular infection. We found that in each condition σ(E) regulated different sets of genes, and notably, several global regulators. When comparing nutrient-rich and infection-like conditions, large changes were observed in the expression of genes involved in Salmonella pathogenesis island (SPI)-1 type-three secretion system (TTSS), SPI-2 TTSS, protein synthesis, and stress responses. In total, the expression of 58% of Salmonella genes was affected by σ(E) in at least one of the three conditions. An important finding is that σ(E) up-regulates SPI-2 genes, which are essential for Salmonella intracellular survival, by up-regulating SPI-2 activator ssrB expression at the early stage of infection and down-regulating SPI-2 repressor hns expression at a later stage. Moreover, σ(E) is capable of countering the silencing of H-NS, releasing the expression of SPI-2 genes. This connection between σ(E) and SPI-2 genes, combined with the global regulatory effect of σ(E), may account for the lethality of rpoE-deficient Salmonella in murine infection.
authors.affiliation: Department of Molecular Microbiology and Immunology, Oregon Health and Science University Portland, OR, USA.
authors.forename: Jie
authors.initials: J
authors.lastname: Li
authors.affiliation: Biological Sciences Division, Pacific Northwest National Laboratory Richland, WA, USA.
authors.forename: Christopher C
authors.initials: CC
authors.lastname: Overall
authors.affiliation: Biological Sciences Division, Pacific Northwest National Laboratory Richland, WA, USA.
authors.forename: Ernesto S
authors.initials: ES
authors.lastname: Nakayasu
authors.affiliation: Department of Molecular Microbiology and Immunology, Oregon Health and Science University Portland, OR, USA.
authors.forename: Afshan S
authors.initials: AS
authors.lastname: Kidwai
authors.affiliation: Department of Infectious Diseases, J. Craig Venter Institute Rockville, MD, USA.
authors.forename: Marcus B
authors.initials: MB
authors.lastname: Jones
authors.affiliation: Department of Molecular Microbiology and Immunology, Oregon Health and Science University Portland, OR, USA.
authors.forename: Rudd C
authors.initials: RC
authors.lastname: Johnson
authors.affiliation: Department of Molecular Microbiology and Immunology, Oregon Health and Science University Portland, OR, USA.
authors.forename: Nhu T
authors.initials: NT
authors.lastname: Nguyen
authors.affiliation: Biological Sciences Division, Pacific Northwest National Laboratory Richland, WA, USA.
authors.forename: Jason E
authors.initials: JE
authors.lastname: McDermott
authors.affiliation: Biological Sciences Division, Pacific Northwest National Laboratory Richland, WA, USA.
authors.forename: Charles
authors.initials: C
authors.lastname: Ansong
authors.affiliation: Department of Molecular Microbiology and Immunology, Oregon Health and Science University Portland, OR, USA.
authors.forename: Fred
authors.initials: F
authors.lastname: Heffron
authors.affiliation: Department of Molecular Microbiology and Immunology, Oregon Health and Science University Portland, OR, USA.
authors.forename: Eric D
authors.initials: ED
authors.lastname: Cambronne
authors.affiliation: Biological Sciences Division, Pacific Northwest National Laboratory Richland, WA, USA.
authors.forename: Joshua N
authors.initials: JN
authors.lastname: Adkins
keywords: ChIP-seq; H-NS; RpoE; SPI-2; Salmonella; microarray; regulation