luxS-based quorum-sensing signaling affects Biofilm formation in Streptococcus mutans

Quorum sensing (QS) is a process by which bacteria communicate with diffusible chemical signaling molecules called autoinducers (AIs). The autoinducer-2 signal (AI-2) produced by the LuxS protein mediates interspecies communication among Gram-positive and Gram-negative bacteria. In this study, we report that luxS-dependent QS is involved in the formation of Streptococcus mutans biofilms.

An S. mutans luxS mutant was constructed, and the differences in growth and biofilm formation were compared between the wild-type strain and the mutant strain. To quantificationally analyze the kinetic biofilm formation of the mutant strain, an assay of BioFilm Ring Test(R) was applied.

There is a small increase in the growth of the luxS mutant strain after the stationary phase, compared with the parent strain. However during the exponential period, there were no significant differences. Using the BioFilm Ring Test(R), it was demonstrated that this luxS mutation was able to accelerate biofilm formation on a polystyrene surface during the mid-exponential growth phase. With 1% glucose treatment, even greater differences were observed between the mutant strain and its parental strain.

These data suggest that a luxS-dependent signal may play an important role in the biofilm formation of S. mutans.