The great divide: rhamnolipids mediate separation betweenP. aeruginosaandS. aureus

Abstract

AbstractThe coexistence of multiple bacterial species during infection can have significant impacts on pathogenesis.Pseudomonas aeruginosaandStaphylococcus aureusare opportunistic bacterial pathogens that can co-infect hosts and cause serious illness. The factors that dictate whether one species will outcompete the other or whether the two species can coexist are not fully understood. We investigated the role of surfactants in the interactions between these two species on a surface that enablesP. aeruginosato swarm. We found thatP. aeruginosaswarms are repelled by colonies of clinicalS. aureusisolates, creating physical separation between the two strains. This effect was abolished in mutants ofS. aureusthat were defective in the production of phenol-soluble modulins (PSMs), which form amyloid fibrils around wild-type colonies. We investigated the mechanism that establishes physical separation between the two species using the Imaging of Reflected Illuminated Structures (IRIS) method, which tracks the flow of the rhamnolipid surfactant layer produced byP. aeruginosa. We found that PSMs produced byS. aureusdeflected the rhamnolipid surfactant layer flow, which in turn, altered the direction ofP. aeruginosaswarms. These findings show that rhamnolipids mediate physical separation betweenP. aeruginosaandS. aureus, which enables these species to coexist in distinct microenvironments. Additionally, we found that aBacillus subtilissurfactant and abiotic hydrophobic molecules repelledP. aeruginosaswarms through surfactant deflection. Our results suggest that surfactant interactions could have major impacts on bacteria-bacteria and bacteria-host relationships. In addition, our findings uncover a mechanism responsible forP. aeruginosaswarm development that does not rely on sensing but instead is guided largely by the flow of the surfactant layer and its boundaries.