The Legionella pneumophila icmGCDJBF Genes Are Required for Killing of Human Macrophages

Abstract

ABSTRACT Previously, a collection of mutants of Legionella pneumophila that had lost the ability to multiply within and kill human macrophages was generated by Tn 903 dII lac Z transposon mutagenesis and classified into DNA hybridization groups. A subset of these mutants was complemented by a plasmid, pMW100, containing a 13.5-kb genomic DNA insert. This plasmid restored the ability to multiply within and produce cytopathic effects on human macrophages to members of DNA hybridization groups II, IV, VI, and XVII. A region of the genomic insert of pMW100 was sequenced, and eight potential genes were identified and named icmE , icmG , icmC , icmD , icmJ , icmB , icmF , and tphA . None of the genes encode potential protein products with significant homology to previously characterized proteins, except for tphA , whose product has significant homology to a family of metabolite/H + symport proteins from gram-negative bacteria. The positions of the Tn 903 dII lac Z insertions within the genes were determined by nucleotide sequencing. No Tn 903 dII lac Z insertions mapped to icmG , icmJ , or tphA ; therefore, these loci were mutated to test whether they were required for macrophage killing. Complementation analysis was used to evaluate the roles of the potential gene products and provide information on the organization of transcriptional units within the region. The results indicate that all identified open reading frames except tphA are required for killing of human macrophages.