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Infection and Immunity, May 2003, p. 2394-2403, Vol. 71, No. 5
0019-9567/03/$08.00+0     DOI: 10.1128/IAI.71.5.2394-2403.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

lvgA, a Novel Legionella pneumophila Virulence Factor

Paul H. Edelstein,1* Baofeng Hu,1 Futoshi Higa,1,2 and Martha A. C. Edelstein1

Department of Pathology and Laboratory Medicine, School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania,1 First Department of Internal Medicine, School of Medicine, Ryukyu University, Okinawa, Japan2

Received 14 November 2002/ Returned for modification 24 January 2003/ Accepted 3 February 2003

Several novel Legionella pneumophila virulence genes were previously discovered by use of signature-tagged mutagenesis (P. H. Edelstein, M. A. Edelstein, F. Higa, and S. Falkow, Proc. Natl. Acad. Sci. 96:8190-8195, 1999). One of these mutants appeared to be defective in multiplication in guinea pig lungs and spleens, yet it multiplies normally in guinea pig alveolar macrophages. Here we report further characterization of the mutated gene and its protein and the virulence role of the gene. The complete sequence of the gene, now called lvgA, is 627 bp long, and its protein product is approximately 27 kDa in size. lvgA was present in all 50 strains of L. pneumophila tested. No significant nucleic acid or protein homology was found in the GenBank database for the gene, nor were any distinctive motifs discovered in a search of other databases. The expression of both DotA and IcmX in the lvgA mutant was normal. Subcellular fractionation studies localized LvgA to the outer membrane fraction, and protease digestion studies suggested that at least some of the protein is surface expressed. No change in bacterial lipopolysaccharide composition or reactivity to serogroup-specific antisera was detected in the mutant. Growth competition studies with alveolar macrophages showed that the mutant was outcompeted by its parent 3-fold in 24 h and 24-fold in 48 h, in contrast to what was observed with the null phenotype in parallel testing with alveolar macrophages or with the A549 alveolar epithelial cell line. This macrophage defect of the mutant bacterium was due to slower growth, as the mutant invaded alveolar macrophages normally. Electron microscopy showed that the mutant bacterium resided in a ribosome-studded phagosome in alveolar macrophages, with no distinction from its parent. The lvgA mutant was outcompeted by its parent about sixfold in guinea pig lungs and spleens; prolonged observation of infected animals showed no late-onset virulence of the mutant. Transcomplementation of the mutant restored the parental phenotype in guinea pigs. The lvgA mutant was twofold more susceptible to killing by human ß-defensin 2 but not to killing by other cationic peptides, serum complement, or polymorphonuclear neutrophils. lvgA is a novel virulence gene that is responsible for pleiotropic functions involving both extracellular and intracellular bacterial resistance mechanisms.

* Corresponding author. Mailing address: Clinical Microbiology Laboratory, Gates Bldg., 4th Floor, University of Pennsylvania Medical Center, 3400 Spruce St., Philadelphia, PA 19104-4283. Phone: (215) 662-6651. Fax: (215) 662-6655. E-mail: phe{at}mail.med.upenn.edu.

Editor: W. A. Petri, Jr.

Infection and Immunity, May 2003, p. 2394-2403, Vol. 71, No. 5
0019-9567/03/$08.00+0     DOI: 10.1128/IAI.71.5.2394-2403.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.



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