Evolutionary response to quorum-sensing inhibition conflicts with antibiotic resistance

The opportunistic pathogen Pseudomonas aeruginosa, employs a hierarchical quorum-sensing network to regulate virulence factors which cooperatively benefit the population at a cost to the individual. Quorum-sensing suppression was therefore proposed as an anti-virulence target. Furthermore, it was argued that the evolution of a cooperative mutant in a quorum-sensing-suppressed population would be hampered through its exploitation by neighboring non-mutant cells. It remains unclear whether mechanisms which overcome this exploitation exist. Here we investigate regain of cooperation by evolving a mutant of the lasR master quorum-sensing regulator in a medium requiring LasR-dependent cooperation for growth. The mutant regained partial cooperative growth through null mutations in mexT, an activator of the MexEF-OprN multi-drug resistant pump. We find that these mutations lead to selection for cooperative growth in the lasR mutant background through enhanced activity of the RhlIR system. We show that the regain of cooperation in mexT^- mutants is mediated by the reduction in MexEF-OprN activity, while an additional source of private benefit is mostly mexEF-oprN-independent. Finally, we show that selection for antibiotic resistance through MexEF-OprN prevents the evolution of cooperation. Thus, a pleiotropic regulatory element links public and private goods, and leads to collateral sensitivity between quorum-sensing cooperation and antibiotic resistance.