title: Reciprocal expression of integration host factor and HU in the developmental cycle and infectivity of Legionella pneumophila.
abstract: Legionella pneumophila is an intracellular parasite of protozoa that differentiates late in infection into metabolically dormant cysts that are highly infectious. Regulation of this process is poorly understood. Here we report that the small DNA binding regulatory proteins integration host factor (IHF) and HU are reciprocally expressed over the developmental cycle, with HU expressed during exponential phase and IHF expressed postexponentially. To assess the role of these regulatory proteins in development, chromosomal deletions were constructed. Single (ihfA or ihfB) and double deletion (Deltaihf) IHF mutants failed to grow in Acanthamoeba castellanii unless complemented in trans when expressed temporally from the ihfA promoter but not under P(tac) (isopropyl-beta-d-thiogalactopyranoside). In contrast, IHF mutants were infectious for HeLa cells, though electron microscopic examination revealed defects in late-stage cyst morphogenesis (thickened cell wall, intracytoplasmic membranes, and inclusions of poly-beta-hydroxybutyrate), and were depressed for the developmental marker MagA. Green fluorescent protein promoter fusion assays indicated that IHF and the stationary-phase sigma factor RpoS were required for full postexponential expression of magA. Finally, defects in cyst morphogenesis noted for Deltaihf mutants in HeLa cells correlated with a loss of both detergent resistance and hyperinfectivity compared with results for wild-type cysts. These studies establish IHF and HU as markers of developmental stages and show that IHF function is required for both differentiation and full virulence of L. pneumophila in natural amoebic hosts.
authors.affiliation: Department of Microbiology and Immunology, Faculty of Medicine, Dalhousie University, Halifax, Nova Scotia, Canada B3H 4H7.
authors.forename: Michael G
authors.initials: MG
authors.lastname: Morash
authors.forename: Ann Karen C
authors.initials: AK
authors.lastname: Brassinga
authors.forename: Michelle
authors.initials: M
authors.lastname: Warthan
authors.forename: Poornima
authors.initials: P
authors.lastname: Gourabathini
authors.forename: Rafael A
authors.initials: RA
authors.lastname: Garduño
authors.forename: Steven D
authors.initials: SD
authors.lastname: Goodman
authors.forename: Paul S
authors.initials: PS
authors.lastname: Hoffman
mesh_terms: D048248:Acanthamoeba castellanii / Q000382:microbiology; D000818:Animals; D001426:Bacterial Proteins / Q000096:biosynthesis* / Q000235:genetics; D015169:Colony Count, Microbial; D004268:DNA-Binding Proteins / Q000096:biosynthesis* / Q000235:genetics; D017353:Gene Deletion; D020869:Gene Expression Profiling; D015964:Gene Expression Regulation, Bacterial; D005816:Genetic Complementation Test; D006367:HeLa Cells; D006801:Humans; D034982:Integration Host Factors / Q000096:biosynthesis* / Q000235:genetics; D016952:Legionella pneumophila / Q000254:growth & development / Q000472:pathogenicity* / Q000502:physiology*; D014774:Virulence
chemical_list: D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; D034982:Integration Host Factors; C040330:histone-like protein HU, bacteria