Intrinsic Fluoride Tolerance Regulated by a Transcription Factor

Area of Science:

• Microbiology
• Molecular Biology
• Dental Research

Background:

• Fluoride is crucial for dental hard tissue remineralization and bacterial activity modulation, making it a key anti-caries agent.
• While Streptococcus mutans' response to fluoride is studied, the mechanisms of intrinsic fluoride tolerance remain unclear.
• TetR family transcription factors are known to be involved in multidrug resistance, suggesting a potential role in fluoride tolerance.

Purpose of the Study:

• To investigate the role of TetR family transcription factors in regulating fluoride tolerance in Streptococcus mutans.
• To identify specific genes and regulatory pathways involved in S. mutans' intrinsic fluoride tolerance.

Main Methods:

• Construction of a mutant library for all S. mutans TetR genes.
• Identification and characterization of the fluoride related transcriptional regulator (FrtR).
• RNA sequencing of an in-frame frtR deletion mutant to identify downstream genes.
• Purification of recombinant FrtR protein and determination of DNA binding motifs using electrophoretic mobility shift and DNase I footprinting assays.
• Minimum inhibitory concentration (MIC) assays with mutant and complement strains.

Main Results:

• A novel transcription factor, FrtR, was identified as crucial for fluoride tolerance in S. mutans.
• Deletion of the frtR gene significantly decreased S. mutans viability in the presence of fluoride, in both planktonic and biofilm states.
• RNA sequencing revealed that the fluoride related permease gene (frtP) is directly regulated by FrtR.
• Increased expression of frtP led to enhanced fluoride sensitivity in S. mutans.

Conclusions:

• FrtR is a key regulator of frtP expression in S. mutans, influencing the bacterium's intrinsic fluoride tolerance.
• This study elucidates a novel molecular mechanism underlying fluoride tolerance in S. mutans.
• Targeting the FrtR-frtP pathway presents a potential strategy to enhance S. mutans' susceptibility to fluoride, aiding in dental caries prevention.