Contribution of chloride channel permease to fluoride resistance in Streptococcus mutans.

Abstract

Genes encoding fluoride transporters have been identified in bacterial and archaeal species. The genome sequence of the cariogenicStreptococcus mutansbacteria suggests the presence of a putative fluoride transporter, which is referred to as a chloride channel permease. Two homologues of this gene (GenBank locus tags SMU_1290c and SMU_1289c) reside in tandem in the genome ofS. mutans The aim of this study was to determine whether the chloride channel permeases contribute to fluoride resistance.We constructed SMU_1290c- and SMU_1289c-knockoutS. mutansUA159 strains. We also constructed a double-knockout strain lacking both genes. SMU_1290c or SMU_1289c was transformed into a fluoride transporter- disruptedEscherichia coli strain. All bacterial strains were cultured under appropriate conditions with or without sodium fluoride, and fluoride resistance was evaluated.All three gene-knockoutS. mutansstrains showed lower resistance to sodium fluoride than did the wild-type strain. No significant changes in resistance to other sodium halides were recognized between the wild-type and double-knockout strains. Both SMU_1290c and SMU_1289c transformation rescued fluoride transporter-disruptedE.colicell from fluoride toxicity.We conclude that the chloride channel permeases contribute to fluoride resistance inS. mutans.