title: Regulation of Salmonella pathogenicity island 2 genes by independent environmental signals.
abstract: The function of a type III secretion system (T3SS) encoded by Salmonella pathogenicity island 2 (SPI2) is essential for the intracellular lifestyle of Salmonella enterica serovar Typhimurium. Expression of SPI2 genes is induced within the Salmonella-containing vacuole (SCV) inside host cells and is controlled by the SsrAB two-component system. However, the nature of the signals leading to expression of SPI2 genes is controversial. Here we report that expression of SPI2 genes can be induced independently by two different environmental stimuli. Exposure of bacteria to slightly acidic pH was sufficient to induce a rapid up-regulation of SPI2 genes. In contrast, limitation of inorganic phosphate (P(i)) in the growth media led to activation of SPI2 genes in the late exponential growth phase and was independent of the media pH. Limitation of P(i) induced an over-expression of sensor protein SsrB. Response to both environmental stimuli required a functional SsrAB system. In vivo analyses indicated that limitation of P(i) is also encountered by intracellular Salmonella. Our observations allow the integration of previous disparate reports on the induction of SPI2 genes.
authors.affiliation: Institut für Klinische Mikrobiologie, Immunologie und Hygiene, FAU Erlangen-Nürnberg, Wasserturmstrasse 3-5, D-91054 Erlangen, Germany.
authors.forename: Stefanie
authors.initials: S
authors.lastname: Löber
authors.forename: Daniela
authors.initials: D
authors.lastname: Jäckel
authors.forename: Nina
authors.initials: N
authors.lastname: Kaiser
authors.forename: Michael
authors.initials: M
authors.lastname: Hensel
mesh_terms: D000222:Adaptation, Physiological; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001426:Bacterial Proteins / Q000096:biosynthesis* / Q000235:genetics / Q000502:physiology; D015153:Blotting, Western; D004591:Electrophoresis, Polyacrylamide Gel; D017353:Gene Deletion; D015964:Gene Expression Regulation, Bacterial; D044404:Genomic Islands / Q000235:genetics*; D049452:Green Fluorescent Proteins / Q000096:biosynthesis / Q000235:genetics; D006863:Hydrogen-Ion Concentration; D008156:Luciferases / Q000096:biosynthesis / Q000235:genetics; D016254:Mutagenesis, Insertional; D010710:Phosphates / Q000502:physiology; D012329:RNA, Bacterial / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology; D018085:Regulon; D012486:Salmonella typhimurium / Q000235:genetics* / Q000472:pathogenicity / Q000502:physiology*; D015398:Signal Transduction; D014157:Transcription Factors / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D010710:Phosphates; D012329:RNA, Bacterial; C119761:SsrB protein, Salmonella typhimurium; D014157:Transcription Factors; C485184:enhanced green fluorescent protein; C096222:tmRNA; D049452:Green Fluorescent Proteins; D008156:Luciferases