The Role of CodY in Hydrogen Peroxide Tolerance and Biofilm Formation of Streptococcus mutans

Streptococcus mutans is the major cariogenic bacterium in the oral cavity. S. mutans causes disease by three main virulence factors: acid production, acid tolerance, and biofilm formation. S. mutans outcompetes various other species in the oral cavity, however it is affected by hydrogen peroxide production by these species. Based on previous findings and this research, hydrogen peroxide is shown to extend the lag phase of S. mutans but does not kill it unless present in extremely high amounts that are generally not produced by commensal species like S. sanguinis and S. gordonii in the oral cavity. CodY is a global regulatory protein in S. mutans that functions in regulation of survival, especially during nutrient limitation. We hypothesized that CodY may regulate hydrogen peroxide tolerance genes as these would also be related to survival. Our findings show that upon exposure to hydrogen peroxide a codY mutant survives similarly or better when compared to the wild-type UA159. The codY mutant also forms larger biofilms than the wild-type UA159 when exposed to hydrogen peroxide during exponential phase of growth. This may indicate that CodY represses a gene, or genes, involved in hydrogen peroxide tolerance or that in its absence multiple genes are deregulated causing the observed phenotype