TY - JOUR T1 - Combinatorial quorum sensing in <em>Pseudomonas aeruginosa</em> allows for novel cheating strategies JF - bioRxiv DO - 10.1101/313502 SP - 313502 AU - James Gurney AU - Sheyda Azimi AU - Sam P. Brown AU - Stephen P. Diggle Y1 - 2019/01/01 UR - http://biorxiv.org/content/early/2019/10/22/313502.abstract N2 - In the opportunistic pathogen Pseudomonas aeruginosa, quorum sensing (QS) is a social trait that is exploitable by non-cooperating cheats. Previously it has been shown that by linking QS to the production of both public and private goods, cheats can be prevented from invading populations of cooperators and this has been termed ‘a metabolic incentive to cooperate’. We hypothesized P. aeruginosa could evolve novel cheating strategies to circumvent private goods metabolism by rewiring its combinatorial response to two QS signals (3O-C12-HSL and C4-HSL). We performed a selection experiment that cycled P. aeruginosa between public and private goods growth media and evolved an isolate which rewired its control of cooperative protease expression from a synergistic (AND-gate) response to dual signal input, to a 3O-C12-HSL only response. We show that this isolate circumvents metabolic incentives to cooperate and acts as a combinatorial signaling cheat, with a higher fitness in competition with its ancestor. Our results show three important principles; first, combinatorial QS allows for diverse social strategies to emerge; second, that restrictions levied by private goods are not sufficient to explain the maintenance of cooperation in natural populations and third that modifying combinatorial QS responses could result in important physiological outcomes in bacterial populations.Importance Bacteria engage in social interactions which are often controlled in a coordinated manner by quorum sensing (QS). In Pseudomonas aeruginosa, QS regulates the expression of a significant proportion of the genome, allowing for cooperation between cells to occur. An unresolved question is how cooperation is evolutionarily maintained in the presence of non-cooperating cheats and environmental challenges, and several ideas have been put forward to address this question. Here we examine the role metabolic incentives play in maintaining cooperation. We demonstrate that using multiple signals to regulate QS (combinatorial signaling) allows for novel cheating strategies to evolve that bypass metabolic incentives and reduce investment in social interactions. ER -