Deficiency of PdxR in Streptococcus mutans affects vitamin B 6 metabolism, acid tolerance response and biofilm formation

Streptococcus mutans, a key etiological agent of the human dental caries, lives primarily on the tooth surface in tenacious biofilms. The SMU 864 locus, designated pdxR, is predicted to encode a member of the novel MocR/GabR family proteins, which are featured with a winged helix DNA ‐binding N‐terminal domain and a C‐terminal domain highly homologous to the pyridoxal phosphate‐dependent aspartate aminotransferases. A pdxR ‐deficient mutant, TW 296, was constructed using allelic exchange. PdxR deficiency in S. mutans had little effect on cell morphology and growth when grown in brain heart infusion. However, when compared with its parent strain, UA 159, the PdxR ‐ deficient mutant displayed major defects in acid tolerance response and formed significantly fewer biofilms ( P