Methods: S. mutans GS5 was grown at 37ºC, 5% CO2 in TY medium supplemented with glucose, fructose, sorbitol or sucrose as the carbohydrate source. Cells were harvested at early-exponential or in mid-exponential growth phase. An equal amount of total RNA (1 µg) from each phase culture was used for quantification of the transcript levels of the ftf and gtfB/C genes. Real-time reverse-transcription/polymerase chain-reaction system was applied for quantifying relative levels of transcription for gtfB/C and ftf, under the tested conditions.
Results: significant increase in the expression of ftf and gtfB/C genes at early-exponential growth phase, in comparison to mid-exponential growth phase was observed. The tested carbohydrates have also effected on the expression of these genes. At early-exponential growth phase, ftf mRNA expression increased approximately by 2.5-fold in the presence of glucose and sucrose, while with fructose and sorbitol the mRNA level doubled. The amount of gtfB and gtfC mRNA was increased prominently, in the presence of all tested carbohydrates. Sucrose enhanced gtfB expression 8-fold, while gtfC expression level was increased by 23-fold. At mid-exponential growth phase in TY supplemented sorbitol, ftf expression level was observed to be increased by 25-fold. The sorbitol induced also, the expression levels of gtfB and gtfC genes in all growth phases.
Conclusion: Our study demonstrates that the type, amount of carbohydrate and the growth phase have a major influence on transcription of the gtfB/C and ftf genes, and provides evidence for regulatory circuits for exopolysaccharide gene expression in S. mutans.