title: RelA regulates virulence and intracellular survival of Francisella novicida.
abstract: Analysis of the genome of Francisella tularensis has revealed few regulatory systems, and how the organism adapts to conditions in different niches is poorly understood. The stringent response is a global stress response mediated by (p)ppGpp. The enzyme RelA has been shown to be involved in generation of this signal molecule in a range of bacterial species. We investigated the effect of inactivation of the relA gene in Francisella by generating a mutant in Francisella novicida. Under amino acid starvation conditions, the relA mutant was defective for (p)ppGpp production. Characterization showed the mutant to grow similarly to the wild-type, except that it entered stationary phase later than wild-type cultures, resulting in higher cell yields. The relA mutant showed increased biofilm formation, which may be linked to the delay in entering stationary phase, which in turn would result in higher cell numbers present in the biofilm and reduced resistance to in vitro stress. The mutant was attenuated in the J774A macrophage cell line and was shown to be attenuated in the mouse model of tularaemia, but was able to induce a protective immune response. Therefore, (p)ppGpp appears to be an important intracellular signal, integral to the pathogenesis of F. novicida.
authors.affiliation: Biomedical Sciences, Dstl Porton Down, Salisbury, Wiltshire SP4 0JQ, UK.
authors.forename: R E
authors.initials: RE
authors.lastname: Dean
authors.affiliation: Biomedical Sciences, Dstl Porton Down, Salisbury, Wiltshire SP4 0JQ, UK.
authors.forename: P M
authors.initials: PM
authors.lastname: Ireland
authors.affiliation: Biomedical Sciences, Dstl Porton Down, Salisbury, Wiltshire SP4 0JQ, UK.
authors.forename: J E
authors.initials: JE
authors.lastname: Jordan
authors.affiliation: School of Biosciences, University of Exeter, Geoffrey Pope Building, Stocker Road, Exeter EX4 4QD, UK.
authors.forename: R W
authors.initials: RW
authors.lastname: Titball
authors.affiliation: Biomedical Sciences, Dstl Porton Down, Salisbury, Wiltshire SP4 0JQ, UK.
authors.forename: P C F
authors.initials: PCF
authors.lastname: Oyston
mesh_terms: D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics* / Q000502:physiology*; D001483:Base Sequence; D018441:Biofilms / Q000254:growth & development; D002460:Cell Line; D017931:DNA Primers / Q000235:genetics; D004269:DNA, Bacterial / Q000235:genetics; D005260:Female; D005603:Francisella / Q000235:genetics* / Q000254:growth & development / Q000472:pathogenicity* / Q000502:physiology; D005798:Genes, Bacterial; D016905:Gram-Negative Bacterial Infections / Q000276:immunology / Q000382:microbiology; D006158:Guanosine Pentaphosphate / Q000096:biosynthesis; D006159:Guanosine Tetraphosphate / Q000096:biosynthesis; D008264:Macrophages / Q000382:microbiology; D051379:Mice; D008807:Mice, Inbred BALB C; D009154:Mutation; D013312:Stress, Physiological; D051996:Transcription Factor RelA / Q000235:genetics* / Q000502:physiology*; D014774:Virulence / Q000235:genetics / Q000502:physiology
chemical_list: D001426:Bacterial Proteins; D017931:DNA Primers; D004269:DNA, Bacterial; D051996:Transcription Factor RelA; D006159:Guanosine Tetraphosphate; D006158:Guanosine Pentaphosphate