An XRE-Type Regulator in Streptococcus mutans Plays an Important Role in brpA Expression and Oxidative Stress Tolerance Response

This study used a functional genomics approach to explore the role of a XRE-type regulator (SMU.405c) in S. mutans physiology including the expression of biofilm regulatory protein BrpA. Results showed that deletional mutation of xre significantly reduced the ability of the deficient mutant to grow in the presence of methyl viologen, a commonly used oxidative stressor (P<0.001).

When challenged in a hydrogen peroxide killing assay, the survival rate of the ∆xre mutant was >2-log less than the parent strain after 60 minutes (P<0.001). Luciferase reporter fusion assays showed that xre deficiency had no significant effect on luciferase expression when it was under the control of the intact brpA promoter, but the reporter activity increased by >6-fold (P<0.001) when the reporter gene was fused to a brpA promoter derivative with deletion of a putative XRE-binding box.