Characterization of the Legionella pneumophila gene ligA

Legionella pneumophila is a bacterial pathogen that resides and multiplies in macrophages as well as in its natural aquatic hosts, the protozoa. Diffe rent bacterial factors contribute to pathogenicity and accompanying eukaryo tic intracellular events. Sequencing of mie flanking regions revealed a gen e of 2610 bp, ligA, that has no significant similarity to any of the genes identified previously Epidemiological studies indicate that this gene is pr esent in Legionella pneumophila, the species most often associated with cas es of the Legionnaires' disease, but not in Legionella species other than L .pneumophila. The isogenic ligA deletion mutant was resistant to NaCl, and showed decreased cytotoxicity to human monocytes and decreased hemolytic ac tivity to red blood cells. How-ever, the most prominent effect of the L. pn eumophila ligA mutant strain LEPF1 was the nearly completely reduced replic ation within the natural host Acanthamoeba castellanii. Since this gene is L. pneumophila specific and regulates numerous bacterial properties we desi gnated this gene ligA for Legionella pneumophila infectivity gene A.