THE ROLE OF VIBRIO CHOLERAE QUORUM SENSING IN THE MICROBIOTA INTERACTIONS OF CHIRONOMIDS

Vibrio cholerae causes the fatal cholera diarrhea and is a natural inhabitant of aquatic ecosystems. We commonly isolate V. cholerae along with other bacterial species from all four life stages (eggs, larvae, pupae and adults) of chironomid insects. V. cholerae secretes Haemagglutinin/Protease (HAP) that degrades the gelatinous matrix of chironomid egg masses, likely acquiring nutrients and consequently preventing hatching. HAP is activated by Quorum Sensing (QS), a bacterial cell-cell communication process in which accumulation of extracellular chemical molecules (called autoinducers, AIs) triggers an intracellular signal transduction cascade. Our aim was to define the role of QS AI signals produced by chironomid microbiota on the production of HAP by V. cholerae, and to characterize the complex relationships of chironomids, V. cholerae, and other members of the egg mass microbial community. To study the role of QS signals we used V. cholerae bioluminescence reporter strains (QS-proficient O1 El-Tor wild type and QS-deficient mutants). The results demonstrated that V. cholerae responds to AIs produced by other members of the chironomid bacterial consortium by expressing the hapA gene. The egg mass microbiota may use the degraded gelatinous matrix of the egg mass for their own growth. By doing so, these other species may in turn control the population levels of V. cholerae in the egg mass. So too V. cholerae supports the maintenance of endogenous bacteria in the egg mass by secreting HAP. Understanding V. cholerae QS in the insect system may help uncover the interactions between this pathogen and the human gut.