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Deficiency of PdxR in Streptococcus mutans affects vitamin B 6 metabolism, acid tolerance response and biofilm formation
Author(s) -
Liao S.,
Bitoun J.P.,
Nguyen A.H.,
Bozner D.,
Yao X.,
Wen Z.T.
Publication year - 2015
Publication title -
molecular oral microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.18
H-Index - 77
eISSN - 2041-1014
pISSN - 2041-1006
DOI - 10.1111/omi.12090
Subject(s) - streptococcus mutans , biofilm , mutant , operon , pyridoxal , biochemistry , biology , streptococcus gordonii , chemistry , microbiology and biotechnology , enzyme , gene , bacteria , genetics
Summary 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 < 0.01). When analyzed by real‐time polymerase chain reaction, PdxR deficiency was found to drastically reduce expression of an apparent operon encoding a pyridoxal kinase ( SMU 865) and a pyridoxal permease ( SMU 866) of the salvage pathway of vitamin B 6 biosynthesis. In addition, PdxR deficiency also altered the expression of genes for ClpL protease, glucosyltransferase B and adhesin SpaP, which are known to play important roles in stress tolerance and biofilm formation. Consistently, PdxR‐deficiency affected the growth of the deficient mutant when grown in defined medium with and without vitamin B 6 . Further studies revealed that although S. mutans is known to require vitamin B 6 to grow in defined medium, B 6 vitamers, especially pyridoxal, were strongly inhibitory at millimolar concentrations, against S. mutans growth and biofilm formation. Our results suggest that PdxR in S. mutans plays an important role in regulation of vitamin B 6 metabolism, acid tolerance response and biofilm formation.