title: Genome expression analysis of nonproliferating intracellular Salmonella enterica serovar Typhimurium unravels an acid pH-dependent PhoP-PhoQ response essential for dormancy.
abstract: Genome-wide expression analyses have provided clues on how Salmonella proliferates inside cultured macrophages and epithelial cells. However, in vivo studies show that Salmonella does not replicate massively within host cells, leaving the underlying mechanisms of such growth control largely undefined. In vitro infection models based on fibroblasts or dendritic cells reveal limited proliferation of the pathogen, but it is presently unknown whether these phenomena reflect events occurring in vivo. Fibroblasts are distinctive, since they represent a nonphagocytic cell type in which S. enterica serovar Typhimurium actively attenuates intracellular growth. Here, we show in the mouse model that S. Typhimurium restrains intracellular growth within nonphagocytic cells positioned in the intestinal lamina propria. This response requires a functional PhoP-PhoQ system and is reproduced in primary fibroblasts isolated from the mouse intestine. The fibroblast infection model was exploited to generate transcriptome data, which revealed that ∼2% (98 genes) of the S. Typhimurium genome is differentially expressed in nongrowing intracellular bacteria. Changes include metabolic reprogramming to microaerophilic conditions, induction of virulence plasmid genes, upregulation of the pathogenicity islands SPI-1 and SPI-2, and shutdown of flagella production and chemotaxis. Comparison of relative protein levels of several PhoP-PhoQ-regulated functions (PagN, PagP, and VirK) in nongrowing intracellular bacteria and extracellular bacteria exposed to diverse PhoP-PhoQ-inducing signals denoted a regulation responding to acidic pH. These data demonstrate that S. Typhimurium restrains intracellular growth in vivo and support a model in which dormant intracellular bacteria could sense vacuolar acidification to stimulate the PhoP-PhoQ system for preventing intracellular overgrowth.
authors.affiliation: Departamento de Biotecnología Microbiana, Centro Nacional de Biotecnología-Consejo Superior de Investigaciones Científicas, Madrid, Spain.
authors.forename: Cristina
authors.initials: C
authors.lastname: Núñez-Hernández
authors.forename: Alberto
authors.initials: A
authors.lastname: Tierrez
authors.forename: Alvaro D
authors.initials: AD
authors.lastname: Ortega
authors.forename: M Graciela
authors.initials: MG
authors.lastname: Pucciarelli
authors.forename: Marta
authors.initials: M
authors.lastname: Godoy
authors.forename: Blanca
authors.initials: B
authors.lastname: Eisman
authors.forename: Josep
authors.initials: J
authors.lastname: Casadesús
authors.forename: Francisco
authors.initials: F
authors.lastname: García-del Portillo
mesh_terms: D000818:Animals; D001426:Bacterial Proteins / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D005260:Female; D005347:Fibroblasts / Q000378:metabolism / Q000382:microbiology; D015964:Gene Expression Regulation, Bacterial; D016680:Genome, Bacterial; D055106:Genome-Wide Association Study / Q000379:methods; D044404:Genomic Islands / Q000235:genetics; D006863:Hydrogen-Ion Concentration; D036341:Intercellular Signaling Peptides and Proteins; D007413:Intestinal Mucosa / Q000378:metabolism; D007422:Intestines / Q000382:microbiology; D007668:Kidney / Q000378:metabolism / Q000382:microbiology; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D009092:Mucous Membrane / Q000378:metabolism / Q000382:microbiology; D010455:Peptides / Q000235:genetics / Q000378:metabolism; D051381:Rats; D012480:Salmonella Infections / Q000235:genetics / Q000378:metabolism / Q000382:microbiology; D012486:Salmonella typhimurium / Q000166:cytology* / Q000235:genetics* / Q000378:metabolism / Q000472:pathogenicity; D059467:Transcriptome / Q000235:genetics; D014774:Virulence / Q000235:genetics
chemical_list: D001426:Bacterial Proteins; D036341:Intercellular Signaling Peptides and Proteins; D008565:Membrane Proteins; D010455:Peptides; C079792:PhoQ protein, Bacteria; C440638:SPI-2 protein, Salmonella; C061064:PhoP protein, Bacteria; C086597:lambda Spi-1