Easy Riders

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Science  17 Dec 2010:
Vol. 330, Issue 6011, pp. 1588
DOI: 10.1126/science.330.6011.1588-a
CREDIT: XAVIER ET AL., MOL. MICROBIOL. 10.1111/J.1365-2958.2010.07436.X (2010)

Microorganisms rarely act alone, and bacterial cells continually fire off signaling molecules, behave cooperatively, exchange metabolites, and swarm together. Despite its many advantages, collaboration is vulnerable to cheaters who may exploit the advantages generated by the collective without contributing themselves. Once cheating gains a foothold, it is difficult to eradicate. Xavier et al. have explored the occurrence of cheating in the bacterium Pseudomonas aeruginosa, which forms motile swarms that move on a self-produced, copious film of rhamnolipid surfactant. A mutant rendered incapable of emitting surfactant (green) could swarm along the film from a wild-type strain (red) without adversely affecting the producer, yet it overwhelmed a different strain engineered to produce surfactant continuously with no regulation. So how do colonies of wild-type producers avoid such takeover? Rhamnolipid production is costly; thus it is only synthesized when carbon is abundantly available and when growth is limited by a lack of nitrogen. In this scenario, perhaps bacteria need to be motile to find better food to resume growth, at which point surfactant production is switched off. Hence, by being frugal with surfactant production, producers can escape cheaters waiting for a free ride.

Mol. Microbiol. 10.1111/j.1365-2958.2010.07436.x (2010).

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