Fluoride export is required for competitive fitness of pathogenic microorganisms in dental biofilm models.

Microorganisms resist fluoride toxicity using fluoride export proteins from one of several different molecular families. Cariogenic species and extrude intracellular fluoride using a CLC F/H antiporter and FEX fluoride channel, respectively, whereas commensal eubacteria, such as , export fluoride using a Fluc fluoride channel. In this work, we examine how genetic knockout of fluoride export impacts pathogen fitness in single-species and three-species dental biofilm models. For biofilms generated using with genetic knockout of the CLC transporter, exposure to low fluoride concentrations decreased counts, synergistically reduced the populations of , increased the relative proportion of commensal , and reduced properties associated with biofilm pathogenicity, including acid production and hydroxyapatite dissolution. Biofilms prepared with with genetic knockout of the FEX channel also exhibited reduced fitness in the presence of fluoride, but to a lesser degree. Imaging studies indicate that is highly sensitive to fluoride, with the knockout strain undergoing complete lysis when exposed to low fluoride for a moderate amount of time, and biochemical purification the CLC transporter and functional reconstitution establishes that the functional protein is a dimer encoded by a single gene. Together, these findings suggest that fluoride export by oral pathogens can be targeted by specific inhibitors to restore biofilm symbiosis in dental biofilms, and that is especially susceptible to fluoride toxicity.