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Infect Immun, April 1998, p. 1768-1775, Vol. 66, No. 4
0019-9567/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

Expression of Multiple Pili by Legionella pneumophila: Identification and Characterization of a Type IV Pilin Gene and Its Role in Adherence to Mammalian and Protozoan Cells

Barbara J. Stone and Yousef Abu Kwaik*

Department of Microbiology and Immunology, University of Kentucky Chandler Medical Center, Lexington, Kentucky 40536-0084

Received 12 September 1997/Returned for modification 14 January 1998/Accepted 27 January 1998

Legionella pneumophila expresses pili of variable lengths, either long (0.8 to 1.5 µm) or short (0.1 to 0.6 µm), that can be observed by transmission electron microscopy. We have identified a gene in L. pneumophila with homology to the type IV pilin genes (pilEL). An insertion mutation was constructed in pilEL and introduced into the L. pneumophila wild-type strain by allelic exchange. The pilin mutant is defective for expression of long pili. Reintroduction of the pilin locus on a cosmid vector restores expression of the long pili. The L. pneumophila pilEL mutant exhibited approximately a 50% decrease in adherence to human epithelial cells (HeLa and WI-26 cells), macrophages (U937 cells), and Acanthamoeba polyphaga but had a wild-type phenotype for intracellular replication within these cells. Southern hybridization analysis showed that the pilEL locus is present in L. pneumophila serogroups 1 through 13 but is variable in 16 other Legionella species. The presence of a type IV pilin gene and its expression by L. pneumophila may provide an advantage for colonization of lung tissues during Legionnaires' disease and invasion of amoebas in the environment.

* Corresponding author. Mailing address: Department of Microbiology and Immunology, University of Kentucky Chandler Medical Center, Lexington, KY 40536-0084. Phone: (606) 323-3873. Fax: (606) 257-8994. E-mail: yabukw{at}pop.uky.edu.




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Copyright © 1998 by the American Society for Microbiology. All rights reserved.