Streptococcus mutans CcpA Promotes Biofilm Exopolysaccharide Production and Virulence Gene Expression

Streptococcus mutans is a key cariogenic pathogen of dental caries due to its strong ability to synthesize extracellular glucans and form biofilms. Glucosyltransferases, encoded by gtfB/C/D genes in S. mutans, are responsible for producing biofilm exopolysaccharides (EPS) and are considered to be critical virulence factors. Previous studies have highlighted the roles of various regulatory factors of gtf genes in S. mutans. Here, we investigated the role of the global transcriptional regulator CcpA encoded by ccpA in regulating the EPS synthesis and biofilm formation of S. mutans. A ccpA in-frame deletion strain was observed to develop shiny, round colonies and longer cell length. In addition, the deletion of ccpA resulted in impaired growth, diminished synthesis of EPS, and reduced biofilm formation. Transcriptome analysis revealed that differentially expressed genes in the ccpA deletion strain were significantly enriched in pathways of carbohydrate transport and metabolism, in which the expressions of gtfB and gtfC were downregulated markedly. Electrophoretic mobility shift assays confirmed that CcpA directly binds to the promoter sequences of gtfB and gtfC, with a higher affinity for gtfC. Moreover, the expression level of ccpA in part explained differences in the ability to synthesize sufficient EPS and form stable biofilm in clinically isolated strains. These findings highlight that CcpA plays a crucial role in the EPS production and biofilm formation of S. mutans through directly binding to the promoter regions of gtfB and gtfC. This study provides novel insights into the pathogenic mechanisms of S. mutans and potential strategies for the prevention and treatment of dental caries.