Quorum sensing control of antibiotic resistance protects
cooperating bacterial cells during interspecies competition.
Many bacteria use chemical signals to coordinate gene transcription in a population-wide manner. In Proteobacteria these signals are commonly acyl-homoserine lactones. These systems are called quorum sensing (QS) systems because gene activation is cell-density dependent. Most of the QS controlled genes are classified as “public goods” because the gene products are secreted and benefit all neighboring bacteria. This situation creates an opportunity for bacteria to “cheat” by benefiting from secreted proteins without having to incur the production cost. Cheaters are often QS-deficient mutants and are a drain on the fitness of the population. In most environments, cheaters are restricted within a population, but in isolated cultures the cheaters often far outnumber non-cheaters. We hypothesize that competition between species limits the emergence of QS-deficient cheaters. Previously, we characterized a dual-species model with two soil bacteria, Burkholderia and Chromobacterium. Both species have QS controlled antibiotic production which inhibits growth in the other species. To address our hypothesis, we co-cultured a mixture of QS-intact and QS-deficient Chromobacterium with a QS-intact Burkholderia strain that produces the antibiotic bactobolin. Our results demonstrate that in the presence of Burkholderia producing bactobolin, QS-intact Chromobacterium survive at a higher rate than QS-deficient. This survival indicates the presence of a novel, QS controlled antibiotic resistance. Because QS also controls the production of antimicrobials, increased survival of QS-intact Chromobacterium results in a net increase in the competitiveness of the population during co-culture growth. Our results illustrate a novel mechanism where interspecies competition serves to stabilize and preserve QS systems, which in turn promotes the competitive ability of the population. This has important implications for how QS systems evolved and are maintained during growth in mixed-microbial communities.