The perils of locomotion

The protein that keeps the Legionnaires' disease bacterium in motion also causes its demise, according to a study on page 1093. Molofsky and colleagues show that bacterial flagellin, which leaks out of phagosomal pores in infected mouse cells, triggers bacterial degradation and cell death.

Like many motile bacteria, Legionella pneumophila uses whip-like flagella in its natural aquatic environment. Genes that control the assembly of flagella are also required for the bug to replicate in human macrophages, a process that occurs when humans inhale aerosols from contaminated water.

In macrophages, L. pneumophila avoids degradation by blocking the fusion of bacteria-containing phagosomes with degradative lysosomes—a feat that requires its pore-forming type IV secretion system.

Molofsky and colleagues now show that the cytosolic pathogen recognition receptor Naip5—which mice require to fight off L....