Fluoride has been used as an effective anticaries agent for more than 70 years, which might result in the emergence of fluoride‐resistant strains. However, the fluoride resistance mechanism and the cariogenic properties of fluoride‐resistant mutant for cariogenic bacterial species Streptococcus mutans remain largely unknown. We describe here the construction and characterization of a mariner‐based transposon system designed to be used in S. mutans, which is also potentially applicable to other streptococci. To identify genetic determinants of fluoride resistance in S. mutans, we constructed a library of S. mutans transposon insertion mutants and screened this library to identify mutants exhibiting fluoride resistance phenotype. Two mutants were found to carry transposon insertion in two different genetic loci (smu.396 and smu.1291c), respectively. Our subsequent genetic study indicates the fluoride‐resistant phenotype for the mutant with the insertion in smu.1291c is resulting from the constitutive overexpression of downstream operon smu.1290c‐89c, which is consistent with the previous reports. We also demonstrate for the first time that the deletion of smu.396 is responsible for the fluoride‐resistant phenotype and that the combining of smu1290c‐89c overexpression and smu.396 deletion in one strain could attribute an additive effect on the fluoride resistance. In addition, our results suggest that the biological fitness of those fluoride‐resistant mutants is reduced compared to that of wild‐type strain. Overall, our identification and characterization of genetic determinants responsible for fluoride resistance in S. mutans expand our understanding of the fluoride resistance mechanism and the biological consequence of the fluoride resistance strains.

中文翻译：

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通过筛选转座子突变体文库鉴定与耐氟性有关的变形链球菌基因

氟化物已被用作有效的防龋剂已有70多年的历史了，这可能导致出现耐氟菌株。但是，对于致龋细菌物种变形链球菌，耐氟化物的机制和耐氟化物突变体的致龋特性仍然未知。我们在这里描述了设计用于变形链球菌的基于水手的转座子系统的构建和表征，该系统也可能适用于其他链球菌。为了确定变形链球菌耐氟性的遗传决定因素，我们构建了变形链球菌的文库转座子插入突变体，并筛选该文库以鉴定表现出氟化物抗性表型的突变体。发现两个突变体分别在两个不同的遗传基因座（smu.396和smu.1291c）中携带转座子插入。我们随后的遗传研究表明，在smu.1291c中插入的突变体的耐氟化物表型是由下游操纵子smu.1290c-89c的组成型过表达引起的，这与以前的报道一致。我们还首次证明smu.396的缺失是导致氟抗性表型的原因，并且是smu1290c-89c过表达与smu.396的结合一个菌株中的缺失可归因于对氟化物抗性的累加效应。此外，我们的结果表明，与野生型菌株相比，这些抗氟突变体的生物学适应性降低。总体而言，我们对变异链球菌耐氟化物的遗传决定因素的鉴定和表征扩展了我们对耐氟化物机理和耐氟菌株的生物学结果的理解。