title: 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.
abstract: Legionella pneumophila expresses pili of variable lengths, either long (0.8 to 1.5 microm) or short (0.1 to 0.6 microm), 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.
authors.affiliation: Department of Microbiology and Immunology, University of Kentucky Chandler Medical Center, Lexington 40536-0084, USA.
authors.forename: B J
authors.initials: BJ
authors.lastname: Stone
authors.forename: Y
authors.initials: Y
authors.lastname: Abu Kwaik
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001422:Bacterial Adhesion; D001425:Bacterial Outer Membrane Proteins / Q000235:genetics* / Q000502:physiology; D001483:Base Sequence; D056890:Eukaryota / Q000382:microbiology*; D036781:Fimbriae Proteins; D010861:Fimbriae, Bacterial / Q000502:physiology*; D005798:Genes, Bacterial; D006367:HeLa Cells; D006801:Humans; D016952:Legionella pneumophila / Q000235:genetics / Q000502:physiology*; D008969:Molecular Sequence Data; D009154:Mutation
chemical_list: D001425:Bacterial Outer Membrane Proteins; D036781:Fimbriae Proteins