Transcriptional Profiling of Streptococcus mutans Biofilms Co-cultured with Streptococcus gordonii

Objectives: Viridans group streptococci are primary colonizers of the tooth surface. Streptococcus mutans is the principal causative agent of dental caries in humans and one of the important virulence properties of this organism is their ability to form biofilms. A number of genes have been found to be involved in monospecies biofilm formation by S. mutans. In this study, we analyzed the gene expression profiles of S. mutans biofilms with or without S. gordonii using S. mutans whole-genome microarrays.

Methods:S. mutans UA159 was inoculated with or without S. gordonii DL1 in chemically defined medium (CDM) supplemented with 0.5% sucrose. S. mutans and S. gordonii were separated using a two-compartment system. Planktonic cells were removed and the biofilms on the 6-well polystyrene plates were harvested. Total RNA was purified and utilized for microarray analysis. Microarray data are referenced at the National Center for Biotechnology Information Gene Expression Omnibus Database under platform GPL4769.

Results: When a S. mutans UA159 biofilm was grown in the presence of S. gordonii, the gene encoding glucan-binding protein A (gbpA, SMU.2112) showed dramatically increased transcription with an induction level of 15-fold. The transcription of the comD histidine kinase gene (SMU.1916) of the com regulon was also up-regulated 11-fold. Furthermore, of the S. mutans UA159 phosphoenolpyruvate-sugar phosphotransferase systems (PET-PTS), enzyme II (EII) genes for sucrose (SMU.1961) -, fructose (SMU.872) -, and mannose (SMU.1879)- specific EII showed 9.1-, 5.7-, 7.4-fold up-regulation, respectively.

Conclusions: Our results showed that when S. mutans and S. gordonii were grown together in mixed cultures, there were synergistic effects during S. mutans biofilm formation. These results imply that cell-to-cell communication is operative in S. mutans biofilm formation. Supported by JSTS Grant-in-Aid for Scientific Research (C) 19592409.