Living with Legionella

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Science  22 Jun 2012:
Vol. 336, Issue 6088, pp. 1484
DOI: 10.1126/science.336.6088.1484-a

Legionnaire's disease is an adventitious severe infection of humans caused by a ubiquitous bacterium that naturally lives within aquatic protozoa that colonize inadequately maintained water cooling systems. Legionella pneumophila uses the IVB Dot/Icm translocation system to introduce proteins into the host cell that remodel an intracellular vacuole to make it habitable. The bacterium then replicates within the modified host cell vacuole. The Dot/Icm system has a large repertoire of translocatable substrates, which appears to endow this pathogen with a wide host range, allowing it even to colonize mammalian macrophages. In a series of evolution experiments, Ensminger et al. discovered that when grown exclusively in mouse macrophages for several months, L. pneumophila improved its ability to replicate in this abnormal host cell to the extent that it failed to thrive when returned to amoebae. Population genotyping revealed mutations in the flagellar regulator and defects in lysine biosynthesis that could act to increase uptake into and replication within macrophages.

PLoS Pathogens 8, e1002731 (2012).

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