title: The stringent response is essential for Pseudomonas aeruginosa virulence in the rat lung agar bead and Drosophila melanogaster feeding models of infection.
abstract: The stringent response is a regulatory system that allows bacteria to sense and adapt to nutrient-poor environments. The central mediator of the stringent response is the molecule guanosine 3',5'-bispyrophosphate (ppGpp), which is synthesized by the enzymes RelA and SpoT and which is also degraded by SpoT. Our laboratory previously demonstrated that a relA mutant of Pseudomonas aeruginosa, the principal cause of lung infections in cystic fibrosis patients, was attenuated in virulence in a Drosophila melanogaster feeding model of infection. In this study, we examined the role of spoT in P. aeruginosa virulence. We generated an insertion mutation in spoT within the previously constructed relA mutant, thereby producing a ppGpp-devoid strain. The relA spoT double mutant was unable to establish a chronic infection in D. melanogaster and was also avirulent in the rat lung agar bead model of infection, a model in which the relA mutant is fully virulent. Synthesis of the virulence determinants pyocyanin, elastase, protease, and siderophores was impaired in the relA spoT double mutant. This mutant was also defective in swarming and twitching, but not in swimming motility. The relA spoT mutant and, to a lesser extent, the relA mutant were less able to withstand stresses such as heat shock and oxidative stress than the wild-type strain PAO1, which may partially account for the inability of the relA spoT mutant to successfully colonize the rat lung. Our results indicate that the stringent response, and SpoT in particular, is a crucial regulator of virulence processes in P. aeruginosa.
authors.affiliation: Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada.
authors.forename: Stefanie L
authors.initials: SL
authors.lastname: Vogt
authors.forename: Christopher
authors.initials: C
authors.lastname: Green
authors.forename: Katarzyna M
authors.initials: KM
authors.lastname: Stevens
authors.forename: Brad
authors.initials: B
authors.lastname: Day
authors.forename: David L
authors.initials: DL
authors.lastname: Erickson
authors.forename: Donald E
authors.initials: DE
authors.lastname: Woods
authors.forename: Douglas G
authors.initials: DG
authors.lastname: Storey
mesh_terms: D000362:Agar; D000818:Animals; D058491:Bacterial Load; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D004195:Disease Models, Animal; D004331:Drosophila melanogaster / Q000254:growth & development / Q000382:microbiology* / Q000502:physiology; D005247:Feeding Behavior; D015964:Gene Expression Regulation, Bacterial; D006158:Guanosine Pentaphosphate / Q000378:metabolism; D018869:Heat-Shock Response / Q000502:physiology*; D006801:Humans; D008025:Ligases / Q000235:genetics / Q000378:metabolism; D008168:Lung / Q000382:microbiology*; D009154:Mutation; D011552:Pseudomonas Infections / Q000382:microbiology; D011550:Pseudomonas aeruginosa / Q000235:genetics / Q000378:metabolism / Q000472:pathogenicity* / Q000502:physiology; D051381:Rats; D014774:Virulence
chemical_list: D001426:Bacterial Proteins; D006158:Guanosine Pentaphosphate; D000362:Agar; C100969:guanosine pentaphosphate synthetase; D008025:Ligases; C028812:guanosine 3',5'-polyphosphate synthetases