SppR in Streptococcus mutans coordinates stress tolerance response and BrpA expression

Area of Science:

• Microbiology
• Molecular Biology
• Genetics

Background:

• SppR acts as a transcriptional repressor for fructanase (FruA) and fructose-1-phosphatase (SppA).
• Understanding SppR's role is vital for addressing *Streptococcus mutans* physiology, particularly its resilience to environmental stressors.

Purpose of the Study:

• To investigate the function of SppR in *S. mutans* stress tolerance and biofilm formation.
• To elucidate SppR's regulatory role in *brpA* gene expression.

Main Methods:

• Construction and analysis of a frameshift *sppR* mutant using *in vitro* biofilm models and stress challenge assays.
• Luciferase reporter fusion assays and *in vitro* transcription assays to study *brpA* regulation.
• RNA-sequencing (RNA-seq) to analyze global gene expression changes in the *sppR* mutant.

Main Results:

• *sppR* deficiency negatively impacted growth at low pH and under oxidative stress, reducing survival rates.
• SppR represses *brpA* expression, evidenced by reduced promoter activity in the mutant and direct binding of recombinant SppR to the *brpA* promoter.
• RNA-seq revealed altered expression of over 136 genes in the *sppR* mutant, including those involved in DNA repair and acid tolerance.

Conclusions:

• SppR is essential for *S. mutans*' acid and oxidative stress tolerance.
• SppR plays a significant role in regulating *brpA* expression, contributing to the bacterium's overall physiology and stress response.