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Just as self-interest can hamper cooperation and fitness in human societies, the presence of 'cheater' microorganisms decreases the population fitness of tight-knit bacterial communities.

Certain bacteria form organized assemblies known as biofilms by releasing small-molecule signals that trigger cellular aggregation. The films offer survival advantages, helping the microbes to resist antibiotics, for example. Researchers led by Stephen Diggle at the University of Nottingham, UK, created biofilms consisting of varying proportions of cooperative Pseudomonas aeruginosa — a human pathogen — and a 'cheating' mutant that cannot respond to the aggregation signal but still benefits from being part of the biofilm. Biofilms containing more 'cheaters' grew more slowly and were less resistant to antibiotics than films with few or no cheaters.

Strategies that take advantage of the evolution of cheating pathogens may be useful in combating biofilms, which can cause persistent infections, the authors suggest.

Proc. R. Soc. B. 279, 4765–4771 (2012)