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Applied and Environmental Microbiology, February 2008, p. 753-761, Vol. 74, No. 3
0099-2240/08/$08.00+0     doi:10.1128/AEM.01944-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

The Type II Secretion System of Legionella pneumophila Elaborates Two Aminopeptidases, as Well as a Metalloprotease That Contributes to Differential Infection among Protozoan Hosts{triangledown}

Ombeline Rossier, Jenny Dao, and Nicholas P. Cianciotto*

Department of Microbiology-Immunology, Northwestern University Medical School, Chicago, Illinois 60611

Received 23 August 2007/ Accepted 29 November 2007

Legionella pneumophila, the agent of Legionnaires' disease, is an intracellular parasite of aquatic amoebae and human macrophages. A key factor for L. pneumophila in intracellular infection is its type II protein secretion system (Lsp). In order to more completely define Lsp output, we recently performed a proteomic analysis of culture supernatants. Based upon the predictions of that analysis, we found that L. pneumophila secretes two distinct aminopeptidase activities encoded by the genes lapA and lapB. Whereas lapA conferred activity against leucine, phenylalanine, and tyrosine aminopeptides, lapB was linked to the cleavage of lysine- and arginine-containing substrates. To assess the role of secreted aminopeptidases in intracellular infection, we examined the relative abilities of lapA and lapB mutants to infect human U937 cell macrophages as well as Hartmannella vermiformis and Acanthamoeba castellanii amoebae. Although these experiments identified a dispensable role for LapA and LapB, they uncovered a previously unrecognized role for the type II-dependent ProA (MspA) metalloprotease. Whereas proA mutants were not defective for macrophage or A. castellanii infection, they (but not their complemented derivatives) were impaired for growth upon coculture with H. vermiformis. Thus, ProA represents the first type II effector implicated in an intracellular infection event. Furthermore, proA represents an L. pneumophila gene that shows differential importance among protozoan infection models, suggesting that the legionellae might have evolved some of its factors to especially target certain of their protozoan hosts.

* Corresponding author. Mailing address: Department of Microbiology-Immunology, Northwestern University Medical School, 320 East Superior Ave., Chicago, IL 60611-3010. Phone: (312) 503-0385. Fax: (312) 503-1339. E-mail: n-cianciotto{at}northwestern.edu

{triangledown} Published ahead of print on 14 December 2007.

Applied and Environmental Microbiology, February 2008, p. 753-761, Vol. 74, No. 3
0099-2240/08/$08.00+0     doi:10.1128/AEM.01944-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Allard, K. A., Dao, J., Sanjeevaiah, P., McCoy-Simandle, K., Chatfield, C. H., Crumrine, D. S., Castignetti, D., Cianciotto, N. P. (2009). Purification of Legiobactin and Importance of This Siderophore in Lung Infection by Legionella pneumophila. Infect. Immun. 77: 2887-2895 [Abstract] [Full Text]  
  • Rossier, O., Dao, J., Cianciotto, N. P. (2009). A type II secreted RNase of Legionella pneumophila facilitates optimal intracellular infection of Hartmannella vermiformis. Microbiology 155: 882-890 [Abstract] [Full Text]  
  • Stewart, C. R., Rossier, O., Cianciotto, N. P. (2009). Surface Translocation by Legionella pneumophila: a Form of Sliding Motility That Is Dependent upon Type II Protein Secretion. J. Bacteriol. 191: 1537-1546 [Abstract] [Full Text]  
  • Soderberg, M. A., Dao, J., Starkenburg, S. R., Cianciotto, N. P. (2008). Importance of Type II Secretion for Survival of Legionella pneumophila in Tap Water and in Amoebae at Low Temperatures. Appl. Environ. Microbiol. 74: 5583-5588 [Abstract] [Full Text]  


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