frtR Gene Affects Acid Production and Demineralization Ability of Streptococcus mutans

  Objective  To study the effect of the frtR gene of TetR family on the acid production ability of Streptococcus mutans (S. mutans) and the bacteria's ability to induce tooth demineralization.

  Methods  The growth of two strains of S. mutans UA159, ΔfrtR, the frtR gene in-frame deletion strain, and ΔfrtR/pDL278-frtR, the complement strain, was examined. The structure of biofilm was observed by laser scanning confocal microscopy (LSCM). The quantitative determination of water-insoluble extracellular polysaccharide (EPS) in the bacterial biofilms was done by anthrone-sulfuric acid method. The acid production capacity of S. mutans was measured by glycolytic pH drop. The demineralization-inducing ability of the strains on bovine teeth was determined by transverse microradiography (TMR).

  Results  The growth curves of the strains showed that frtR did not affect the growth of S. mutans. According to the findings of LSCM observation, frtR did not affect the biofilm formation. According to the findings of the anthrone-sulfuric acid method, frtR did not have any significant impact on the EPS synthesis of S. mutans. The results of the glycolytic pH drop assay showed that the deletion of frtR delayed the rate of acid production by S. mutans when sucrose was the only carbon source. In addition, according to the TMR results, knocking out frtR reduced the depth and amount of demineralization induced by S. mutans on the surface of bovine teeth.

  Conclusion  The deletion of frtR can weaken the acid production ability and the demineralization ability of S. mutans.