EXPRESSION OF MULTIPLE PILI BY LEGIONELLA-GNEUMOPHILA - IDENTIFICATION AND CHARACTERIZATION OF A TYPE-IV PILIN GENE AND ITS ROLE IN ADHERENCE TO MAMMALIAN AND PROTOZOAN CELLS

Legionella pneumophila expresses pill of variable lengths, either long (0.8 to 1.5 mu m) or short (0.1 to 0.6 mu m), that can be observed by transmission electron microscopy. We have identified a gene in L. pne umophila with homology to the type IV pilin genes (pilE(L)). An insert ion mutation was constructed in pilE(L) and introduced into the L. pne umophila wild-type strain by allelic exchange. The pilin mutant is def ective for expression of long pill. Reintroduction of the pilin locus on a cosmid vector restores expression of the long pill. The L. pneumo phila pilE(L) mutant exhibited approximately a 50% decrease in adheren ce 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 a nalysis shelved that the pilE(L) locus is present in L. pneumophila se rogroups 1 through 13 but is variable in 16 other Legionella species. The presence of a type TV pilin gene and its expression by L. pneumoph ila may provide an advantage for colonization of lung tissues during L egionnaires' disease and invasion of amoebas in the environment.