Spatial-temporal dynamics of a microbial cooperative behavior robust to cheating

Abstract

Individuals living in dense populations control their behaviors by sensing, integrating and responding to many cues. How can these processes enable the evolution and stability of cooperative behaviors that could easily be exploited by cheaters? Here we shed light on how bacteria regulate cooperation by studying swarming in Pseudomonas aeruginosa, a behavior requiring cooperative secretions of rhamnolipid surfactants to facilitate collective movement over surfaces. By combining fluorescent imaging and computational analyses we show, counterintuitively, that rhamnolipid expression peaks at swarming edges. We then show that the integration of competing diffusive cues--quorum sensing signals and growth-limiting nutrients--enables P. aeruginosa to communicate across centimeters and adopt expression patterns unseen in well-mixed liquid culture. Integration of multiple cues enables robustness against cheating even when we experimentally perturb the quorum sensing system. Taken together, these results illuminate how the integration of cues in spatially structured communities can stabilize cooperation.