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Infection and Immunity, March 2008, p. 1059-1067, Vol. 76, No. 3
0019-9567/08/$08.00+0     doi:10.1128/IAI.01167-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Burkholderia cenocepacia Requires the RpoN Sigma Factor for Biofilm Formation and Intracellular Trafficking within Macrophages{triangledown}

M. Soledad Saldías,1 Julie Lamothe,1 Robert Wu,1 and Miguel A. Valvano1,2*

Infectious Diseases Research Group,1 Department of Microbiology and Immunology, and Medicine, Siebens-Drake Research Institute, University of Western Ontario, London, Ontario, Canada2

Received 22 August 2007/ Returned for modification 27 September 2007/ Accepted 16 December 2007

Chronic respiratory infections by Burkholderia cenocepacia in cystic fibrosis patients are associated with increased morbidity and mortality, but virulence factors determining the persistence of the infection in the airways are not well characterized. Using a chronic pulmonary infection model, we previously identified an attenuated mutant with an insertion in a gene encoding an RpoN activator protein, suggesting that RpoN and/or components of the RpoN regulon play a role in B. cenocepacia virulence. In this study, we demonstrate that a functional rpoN gene is required for bacterial motility and biofilm formation in B. cenocepacia K56-2. Unlike other bacteria, RpoN does not control flagellar biosynthesis, as evidenced by the presence of flagella in the rpoN mutant. We also demonstrate that, in macrophages, the rpoN mutant is rapidly trafficked to lysosomes while intracellular wild-type B. cenocepacia localizes in bacterium-containing vacuoles that exhibit a pronounced delay in phagolysosomal fusion. Rapid trafficking to the lysosomes is also associated with the release of red fluorescent protein into the vacuolar lumen, indicating loss of bacterial cell envelope integrity. Although a role for RpoN in motility and biofilm formation has been previously established, this study is the first demonstration that the RpoN regulon in B. cenocepacia is involved in delaying phagolysosomal fusion, thereby prolonging bacterial intracellular survival within macrophages.

* Corresponding author. Mailing address: Department of Microbiology and Immunology, Dental Sciences Building, Rm. 3014, University of Western Ontario, London, Ontario, Canada N6A 5C1. Phone: (519) 661-3427. Fax: (519) 661-3499. E-mail: mvalvano{at}uwo.ca

{triangledown} Published ahead of print on 14 January 2008.

Editor: A. Camilli

Infection and Immunity, March 2008, p. 1059-1067, Vol. 76, No. 3
0019-9567/08/$08.00+0     doi:10.1128/IAI.01167-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Keith, K. E., Hynes, D. W., Sholdice, J. E., Valvano, M. A. (2009). Delayed association of the NADPH oxidase complex with macrophage vacuoles containing the opportunistic pathogen Burkholderia cenocepacia. Microbiology 155: 1004-1015 [Abstract] [Full Text]  


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