Do We Have a Quorum?

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Science  20 Mar 2009:
Vol. 323, Issue 5921, pp. 1539
DOI: 10.1126/science.323.5921.1539d

Bacteria can communicate with one another and act cooperatively as a group—a process known as quorum sensing (QS). However, such communication and cooperation can be exploited by “cheaters,” who benefit from the shared metabolic or otherwise beneficial activities without contributing to them. In the case of the pathogenic bacterium Pseudomonas aeruginosa, the signal molecules that facilitate population-wide QS regulate important disease-related processes, such as biofilm formation, swarming motility, and the production of secreted virulence factors. Rumbaugh et al. demonstrate that this potentially deadly cocktail of activities can be undermined by mutant bacteria that cheat. In a burn injury model in mice, infection with QS P. aeruginosa leads to rapid death of the host; infection with QS mutant bacteria resulted in significantly less mortality. The mortality caused by QS bacteria was substantially diminished in the presence of the mutant bacteria, which, through their exploitation of the QS bacteria, were able to flourish at their benefactors' expense, reducing the overall virulence of the infection. Furthermore, the mutant bacteria, which cannot normally mount an effective systemic infection, were able to spread to the liver in the presence of the QS bacteria, presumably by piggy-backing on the social activities of the QS bacteria. QS mutants are known to arise in clinical settings and may thus affect the virulence and course of infections. — GR

Curr. Biol. 19, 341 (2009).

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