Compare differential gene expression between S. 6715 and fluoride-resistant strains

Objective: To detect the cariogenic characteristics and the differential gene expression between Streptococcus sobrinus 6715 and its fluoride-resistant strains. The morphology, physiological, biochemical and gene expression were studied in vitro. Method: Fluoride-resistant strains of Streptococcus sobrinus 6715 which can live in a high level concentration of fluoride(1000 µg/ml)was induced by increasing the concentration of fluoride in the TSA step by step. After serial passaged twenty times in fluoride-free TSA, it also kept its fluoride-resistant characteristic. Then comparison the Acid Adaptation between Streptococcus sobrinus 6715 and its fluoride-resistant stains. Preliminary exposure of mid-exponential phase cells to a low, sub-lethal pH would enhance the survival rate in a lethal pH. Suppression subtractive hybridization(SSH) technology was used to detect the differential gene expression between them. Result: The results of the morphology, physiological, biochemical revealed that the biochemical reactions of fluoride-resistant strains have been changed after fluoride induced mutation.The greatest viability (10.55%) of fluoride-resistant strains appeared when cells were pre-acified at pH5.0. The fluoride-resistant stains had a stronger acid adaptation compared with their parent.After comparing with the GenBank by BLAST, it was identified that there were two differential gene expression fragments , fruA and SMU.438c. fruA might be one of the chief cariogenic genes and the function of SMU.438c was still unsure. Conclusion: Construct the cDNA decrease lib of S.6715 and its fluoride-resistant strains through SSH, it is a basic for the deeply study of fluoride-resistant mechanism.