The flagellum of Legionella pneumophila and its link to the expression of the virulent phenotype.

Legionalla pneumophila is a human pathogen causing atypical pneumonia. It is a monopolar flagellated gram-negative bacterium. Flagellation of L. pneumophila is life cycle dependent and the expression of flagella is genetically linked to the virulence phenotype. Non-flagellated mutants of L. pneumophila are less infectious for macrophages and amoebae compared to the wild type. The flagellar operon is expressed in a hierarchical manner, and different sigma factors and transcriptional regulators are involved in this cascade of gene regulation. The genome sequence of L. pneumophila was used to identify putative regulatory elements of various flagellar operons. Preliminary reports about regulators which are involved in the link between virulence gene regulation and flagellation are discussed.