title: Distinct roles of ppGpp and DksA in Legionella pneumophila differentiation.
abstract: To transit between hosts, intracellular Legionella pneumophila transform into a motile, infectious, transmissive state. Here we exploit the pathogen's life cycle to examine how guanosine tetraphosphate (ppGpp) and DksA cooperate to govern bacterial differentiation. Transcriptional profiling revealed that during transmission alarmone accumulation increases the mRNA for flagellar and Type IV-secretion components, secreted host effectors and regulators, and decreases transcripts for translation, membrane modification and ATP synthesis machinery. DksA is critical for differentiation, since mutants are defective for stationary phase survival, flagellar gene activation, lysosome avoidance and macrophage cytotoxicity. The roles of ppGpp and DksA depend on the context. For macrophage transmission, ppGpp is essential, whereas DksA is dispensable, indicating that ppGpp can act autonomously. In broth, DksA promotes differentiation when ppGpp levels increase, or during fatty acid stress, as judged by flaA expression and evasion of degradation by macrophages. For flagella morphogenesis, DksA is required for basal fliA (sigma(28)) promoter activity. When alarmone levels increase, DksA cooperates with ppGpp to generate a pulse of Class II rod RNA or to amplify the Class III sigma factor and Class IV flagellin RNAs. Thus, DksA responds to the level of ppGpp and other stress signals to co-ordinate L. pneumophila differentiation.
authors.affiliation: Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, MI, USA.
authors.forename: Zachary D
authors.initials: ZD
authors.lastname: Dalebroux
authors.forename: Brian F
authors.initials: BF
authors.lastname: Yagi
authors.forename: Tobias
authors.initials: T
authors.lastname: Sahr
authors.forename: Carmen
authors.initials: C
authors.lastname: Buchrieser
authors.forename: Michele S
authors.initials: MS
authors.lastname: Swanson
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D002448:Cell Adhesion; D002470:Cell Survival; D015169:Colony Count, Microbial; D005407:Flagella / Q000502:physiology; D017353:Gene Deletion; D020869:Gene Expression Profiling; D015964:Gene Expression Regulation, Bacterial; D006159:Guanosine Tetraphosphate / Q000378:metabolism*; D016952:Legionella pneumophila / Q000254:growth & development / Q000378:metabolism / Q000472:pathogenicity / Q000502:physiology*; D008264:Macrophages / Q000382:microbiology; D008969:Molecular Sequence Data; D037521:Virulence Factors / Q000235:genetics / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D037521:Virulence Factors; D006159:Guanosine Tetraphosphate