The expression of the flagellum of Legionella pneumophila is modulated by different environmental factors.

Legionella pneumophila, the aetiologic agent of legionnaires' disease, contains a single, monopolar flagellum which is composed of one major subunit, the FlaA protein. Expression studies using a reporter gene fusion of the flaA promoter with the luxAB gene revealed that the flaA expression is not only temperature regulated but is also influenced by the growth phase, the viscosity and the osmolarity of the medium, and by amino acids.