Quorum-sensing control of antibiotic resistance stabilizes cooperation in Chromobacterium violaceum

Abstract

Many Proteobacteria use quorum sensing to regulate production of public goods, such as antimicrobials and proteases, that are shared among members of a community. Public goods are vulnerable to exploitation by cheaters, such as quorum sensing-defective mutants. Quorum sensing- regulated private goods, goods that benefit only producing cells, can prevent the emergence of cheaters under certain growth conditions. Previously, we developed a laboratory co-culture model to investigate the importance of quorum-regulated antimicrobials during interspecies competition. In our model, Burkholderia thailandensis and Chromobacterium violaceum each use quorum sensing-controlled antimicrobials to inhibit the other species' growth. Here, we show that C. violaceum uses quorum sensing to increase resistance to bactobolin, a B. thailandensis antibiotic, by increasing transcription of a putative antibiotic efflux pump. We demonstrate conditions where C. violaceum quorum-defective cheaters emerge and show that in these conditions, bactobolin restrains cheaters. We also demonstrate that bactobolin restrains quorum-defective mutants in our co-culture model, and the increase in antimicrobial-producing cooperators drives the C. violaceum population to become more competitive. Our results describe a mechanism of cheater restraint involving quorum control of efflux pumps and demonstrate that interspecies competition can reinforce cooperative behaviors by placing constraints on quorum sensing-defective mutants.

Two resistance nodulation division-family efflux pumps inChromobacteriumspecies and their role in antibiotic resistance and tolerance

“…We previously demonstrated that deleting the cdeAB-oprM genes from CV017 increases susceptibility to the ribosome-targeting antibiotics bactobolin and another ribosome-targeting antibiotic, tetracycline, and the DNA intercalating agent ethidium bromide (18). These data support the idea that CdeAB-OprM system is an efflux pump that increases resistance to a range of toxic substrates.…”

“…As ciprofloxacin is one of the recommended treatments for infections with pathogenic Chromobacterium (2), the results suggest this pump might be important in cases of antibiotic failures. To date, there are very few publications on Chromobacterium mechanisms of antibiotic resistance and drug export (18,22,23). Results of this study will be useful for identifying resistance mechanisms in clinical isolates and for future Chromobacterium research.…”

“…cdeR is encoded adjacent to the cdeAB-oprM gene cluster and predicted to encode a TetR-family transcriptional regulator, which typically function as transcriptional repressors by binding to the promoters of their target genes (the hallmark of this family, TetR, binds to the promoter of the tetA gene encoding the tetracycline pump) (20). Previously, we reported a CdeR mutant (CdeR H127Y) that increased transcription of cdeA and cdeB, and also increased bactobolin resistance (18). These results are consistent with the idea that CdeR is a repressor, and the CdeR H127Y mutation abolishes repressor activity.…”

“…In B. thailandensis, the antibiotic is bactobolin, which targets the 50S ribosomal subunit to block translation (17). We showed that an efflux pump in CV017 is important for bactobolin resistance, which we called CdeAB-OprM (18).…”

Does quorum sensing interference affect the fitness of bacterial pathogens in the real world?

“…In this respect, it is important to mention that although quorum sensing is often considered to mainly control the production of public goods (including various virulence factors, e.g., lytic enzymes and toxins), several private goods that can significantly affect the fitness of bacteria in the host and/or external environment have recently been reported to be controlled by quorum sensing as well. These include flagellar motility in V. harveyi (Yang and Defoirdt, 2015), resistance to oxidative stress in P. aeruginosa (Garcia-Contreras et al, 2015), resistance to osmotic stress in V. harveyi (van Kessel et al, 2015), resistance to phages in P. aeruginosa (Moreau et al, 2017;Saucedo-Mora et al, 2017), Vibrio anguillarum (Tan et al, 2015) and V. cholerae (Hoque et al, 2016) and production of an antibiotic efflux pump in Chromobacterium violaceum (Evans et al, 2018).…”