Phenotypic Characterization of the ClpL Chaperone in Streptococcus mutans

Objectives: To characterize the role of the ClpL chaperone in stress responses, biofilm formation and virulence of S. mutans.
Methods: A markerless approach was used to delete the clpL gene from S. mutans UA159, and the mutant (ΔclpL) was complemented using the integration vector pMC340B (CΔclpL). Strains were tested for their abilities to tolerate different types of environmental stress, form biofilms in vitro, and kill the larvae of Galleria melonella.
Results: When compared to the parental strain, the ΔclpL strain did not show significant differences in growth or survival under any of the stress conditions tested. However, the mutant showed significant differences in its ability to form biofilm; it formed less biofilm in the presence of glucose but more biofilm when grown in sucrose. Moreover, the mutant formed more cellular aggregates in sucrose, and Western blot analysis revealed an increased accumulation of GtfB/GtfC in ΔclpL when compared to UA159. Finally, virulence of the ΔclpL strain is attenuated in the G. melonella model.
Conclusions: These results reveal that ClpL modulates biofilm formation in S. mutans, a major virulence trait of this dental pathogen Future studies will focus on identifying the proteins that interact with ClpL, and how those interactions influence S. mutans virulence.