Quorum sensing-controlled genes increase the survival of Chromobacterium violaceum during bacterial interspecies competition

Abstract

Many Proteobacteria use a cell-cell communication system called quorum sensing (QS) to coordinate gene expression in a cell density-dependent manner. Cell density is detected through the production and diffusion of acyl-homoserine lactones (AHLs). The AHL concentration increases until threshold is reached, and AHLs bind the AHL receptor causing transcription of QS-controlled genes. Many QS-controlled genes include: antimicrobials, biofilm components, and other virulence factors. For this reason, we believe that QS is critical for survival during competition with other bacteria. To test our hypothesis, we have developed a competition model between two soil-saprophytes, Burkholderia thailandensis and Chromobacterium violaceum. Our research demonstrates that QS in C. violaceum and B. thailandensis controls the production of antimicrobials that inhibit the other species’ growth. C. violaceum using QS to increase resistance to bactobolin, a B. thailandensis antibiotic, through a RND efflux pump. This QS-controlled efflux pump is important for limiting QS-deficient mutants in our competition model allowing for the increase in antimicrobial producing cells and increased survival of C. violaceum during competition. Our results demonstrate that interspecies competition can reinforce QS-controlled behaviors by placing constraints on QS-deficient mutants. Additionally, we demonstrate that the AHL receptor, CviR, in C. violaceum Cv017 can bind to N-octanoyl-L-homoserine lactone (C8-HSL) and N-3-hydroxyoctanoyl-L- (3OH-C8)-HSL produced by B. thailandensis. RNA sequencing of transcripts from C. violaceum grown in the presence of C8-HSL or hexanoyl (C6)-HSL revealed an enrichment in the transcriptome for competition associated genes when exposed to C8-HSL. Our transcriptomic and competition results show that the ability of C. violaceum to detect non-cognate AHLs provides an advantage during interspecies competition through the activation of competition associated genes.