Cooperation and conflict in quorum-sensing bacterial populations

Communication between bacteria via the release and sensing of small diffusible signal molecules, or quorum sensing, is thought to be a way of coordinating cooperative behaviours at the population level. Evolutionary theory predicts that individuals who communicate and cooperate are vulnerable to cheaters, who either do not signal or fail to respond to signals. Experiments in colonies of the pathogen Pseudomonas aeruginosa, which signals between cells to regulate virulence factor expression, now confirm that both signal and signal-receptor mutants (or 'cheats') do have a fitness advantage. But a solution to the cheating problem does exist in the form of kin selection — 'honest' communication is favoured when it is between close relatives. The findings provide an explanation for the spread of cheats that has been observed in bacterial infections of humans.