Reciprocal expression of integration host factor and HU in the developmental cycle and infectivity of Legionella pneumophila

Michael G. Morash, Ann Karen C. Brassinga, Michelle Warthan, Poornima Gourabathini, Rafael A. Garduño, Steven D. Goodman, Paul S. Hoffman

Research output: Contribution to journalArticlepeer-review

33 Citations (Scopus)

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 (δihf) 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-Β-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, intracy-toplasmic membranes, and inclusions of poly-Β- 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 Δihf mutants in HeLa cells correlated with a loss of both detergent resistance and hyper-infectivity 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.

Original languageEnglish
Pages (from-to)1826-1837
Number of pages12
JournalApplied and Environmental Microbiology
Volume75
Issue number7
DOIs
Publication statusPublished - Apr 2009

ASJC Scopus Subject Areas

  • Biotechnology
  • Food Science
  • Ecology
  • Applied Microbiology and Biotechnology

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