Contribution of glucan‐binding protein A to firm and stable biofilm formation by S treptococcus mutans

Summary Glucan‐binding proteins ( G bps) of S treptococcus mutans , a major pathogen of dental caries, mediate the binding of glucans synthesized from sucrose by the action of glucosyltransferases ( GTF s) encoded by gtf B , gtf C , and gtf D . Several stress proteins, including D na K and G ro EL encoded by dna K and gro EL , are related to environmental stress tolerance. The contribution of G bp expression to biofilm formation was analyzed by focusing on the expression levels of genes encoding GTF s and stress proteins. Biofilm‐forming assays were performed using G bp A ‐, G bp B ‐, and G bp C ‐deficient mutant strains and the parental strain MT 8148. The expression levels of gtf B , gtf C , gtf D , dna K , and gro EL were evaluated by reverse transcription‐quantitative polymerase chain reaction ( RT ‐q PCR ). Furthermore, the structure of biofilms formed by these G bp‐deficient mutant strains was observed using confocal laser scanning microscopy ( CLSM ). Biofilm‐forming assay findings demonstrated that the amount formed by the G bp A ‐deficient mutant strain ( AD 1) was nearly the same as that by the parental strain, while the G bp B ‐ and G bp C ‐deficient mutant strains produced lower amounts than MT 8148. Furthermore, RT ‐q PCR assay results showed that the expressions of gtf B , dna K , and gro EL in AD 1 were elevated compared with MT 8148. CLSM also revealed that the structure of biofilm formed by AD 1 was prominently different compared with that formed by the parental strain. These results suggest that a defect in G bp A influences the expression of genes controlling biofilm formation, indicating its importance as a protein for firm and stable biofilm formation.