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Applied and Environmental Microbiology, April 2009, p. 1826-1837, Vol. 75, No. 7
0099-2240/09/$08.00+0     doi:10.1128/AEM.02756-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Reciprocal Expression of Integration Host Factor and HU in the Developmental Cycle and Infectivity of Legionella pneumophila{triangledown} ,{dagger}

Michael G. Morash,1 Ann Karen C. Brassinga,3,{ddagger} Michelle Warthan,3 Poornima Gourabathini,3 Rafael A. Garduño,1,2 Steven D. Goodman,5 and Paul S. Hoffman1,2,3,4*

Departments of Microbiology and Immunology,1 Medicine, Faculty of Medicine, Dalhousie University, Halifax, Nova Scotia, Canada B3H 4H7,2 Department of Medicine, Division of Infectious Diseases and International Health,3 Department of Microbiology, University of Virginia School of Medicine, Charlottesville, Virginia 22908-1340,4 Division of Diagnostic Sciences, University of Southern California School of Dentistry, Los Angeles, California 90089-06415

Received 3 December 2008/ Accepted 23 January 2009

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 ({Delta}ihf) IHF mutants failed to grow in Acanthamoeba castellanii unless complemented in trans when expressed temporally from the ihfA promoter but not under Ptac (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, intracytoplasmic 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 {Delta}ihf 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.

* Corresponding author. Mailing address: Division of Infectious Diseases and International Health, Room 2146, MR-4 Bldg., University of Virginia Health Systems, 409 Lane Road, Charlottesville, VA 22908-1340. Phone: (434) 924-2893. Fax: (434) 924-0075. E-mail: psh2n{at}virginia.edu

{triangledown} Published ahead of print on 5 February 2009.

{dagger} Supplemental material for this article may be found at http://aem.asm.org/.

{ddagger} Present address: Department of Microbiology, Faculty of Science, University of Manitoba, Winnipeg, Manitoba, Canada R3T 2N2.

Applied and Environmental Microbiology, April 2009, p. 1826-1837, Vol. 75, No. 7
0099-2240/09/$08.00+0     doi:10.1128/AEM.02756-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Chong, A., Lima, C. A., Allan, D. S., Nasrallah, G. K., Garduno, R. A. (2009). The Purified and Recombinant Legionella pneumophila Chaperonin Alters Mitochondrial Trafficking and Microfilament Organization. Infect. Immun. 77: 4724-4739 [Abstract] [Full Text]  


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