Gene-Expression of Streptococcus mutans in Biofilm: Reflection of Virulence Properties

Objectives: Profile of gene expression can alter markedly when bacteria are immobilized on surface, therefore allowing the bacteria to express different propeties accomodating their acclimation to the new ecological niche. In this study, we have investigated the molecular processes occurring during the in vitro biofilm development of Streptococcus mutans.

Methods: Biofilm-grown S. mutans was characterized by DNA-microarrays and real time RT-PCR to identify differentially expressed genes associated with biofilm development. Biofilm formation was visualized by confocal laser scanning microscopy (CLSM). The reporter strain assay was performed to detect cell-cell communication between biofilm bacteria on different surfaces.

Results: Our results demonstrate the significant transcriptional changes in bacteria following immobilization on surfaces and biofilm maturation by S. mutans. Gene expression and intercellular signaling between the bacteria were dependent on the type of solid surface the biofilm was formed on. The DNA-microarrays analysis enabled to identify the genes, mostly involved in biofilm development process of S. mutans. Differential expression of the selected genes was further confirmed by real-time RT-PCR. Numerous differentially expressed genes appear to modulate adherence and biofilm formation in S. mutans, whereas others are involved in intracellular trafficking or membrane transporter systems. Moreover, assessment of the CLSM images demonstrated that mature biofilm development on solid surfaces is accompanied by significant alterations in cell vitality at different biofilm layers. Other notable findings indicated that carbohydrates have a major influence on transcription of the genes, known to be mostly involved in S. mutans biofilm formation.

Conclusions: In vitro comparative analysis has confirmed our hypothesis that significant changes in the patterns of gene expression occur following transition of S. mutans to various biofilm modes. Findings of such a study enhance our understanding of the crucial stages of biofilm formation process at the molecular level which affect virulence properties of oral biofilms.