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Infection and Immunity, April 2001, p. 2092-2098, Vol. 69, No. 4
0019-9567/01/$04.00+0   DOI: 10.1128/IAI.69.4.2092-2098.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

Type II Protein Secretion Is a Subset of the PilD-Dependent Processes That Facilitate Intracellular Infection by Legionella pneumophila

Ombeline Rossier and Nicholas P. Cianciotto*

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

Received 27 October 2000/Returned for modification 1 December 2000/Accepted 20 December 2000

Previously, we had demonstrated that a Legionella pneumophila prepilin peptidase (pilD) mutant does not produce type IV pili and shows reduced secretion of enzymatic activities. Moreover, it displays a distinct colony morphology and a dramatic reduction in intracellular growth within amoebae and macrophages, two phenotypes that are not exhibited by a pilin (pilEL) mutant. To determine whether these pilD-dependent defects were linked to type II secretion, we have constructed two new mutants of L. pneumophila strain 130b. Mutations were introduced into either lspDE, which encodes the type II outer membrane secretin and ATPase, or lspFGHIJK, which encodes the pseudopilins. Unlike the wild-type and pilEL strains, both lspDE and lspG mutants showed reduced secretion of six pilD-dependent enzymatic activities; i.e., protease, acid phosphatase, p-nitrophenol phosphorylcholine hydrolase, lipase, phospholipase A, and lysophospholipase A. However, they exhibited a colony morphology different from that of the pilD mutant, suggesting that their surfaces are distinct. The pilD, lspDE, and lspG mutants were similarly and greatly impaired for growth within Hartmannella vermiformis, indicating that the intracellular defect of the peptidase mutant in amoebae is explained by the loss of type II secretion. When assessed for infection of U937 macrophages, both lsp mutants exhibited a 10-fold reduction in intracellular multiplication and a diminished cytopathic effect. Interestingly, the pilD mutant was clearly 100-fold more defective than the type II secretion mutants in U937 cells. These results suggest the existence of a novel pilD-dependent mechanism for promoting L. pneumophila intracellular infection of human cells.

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

Infection and Immunity, April 2001, p. 2092-2098, Vol. 69, No. 4
0019-9567/01/$04.00+0   DOI: 10.1128/IAI.69.4.2092-2098.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.


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