Growth with Commensal Streptococci Alters Streptococcus mutans Behaviors

As oral bacteria grow and persist within biofilms attached to the tooth’s surface, they interact with other species to form synergistic or antagonistic exchanges that govern homeostasis for the overall population. The author performed whole transcriptome sequencing (RNA-seq) on cocultures of S. mutans with either Streptococcus gordonii, Streptococcus sanguinis, or Streptococcus oralis and a quadculture containing all four species in comparison to S. mutans grown alone. The results reveal that a conserved response to oral streptococci can generally be observed in addition to species-dependent changes to the S. mutans transcriptome. The authors monitored the behavior of S. mutans by microscopy imaging of biofilms and in a bacteriocin overlay assay. They verified that S. mutans acts similarly with each of these species but noted divergences in phenotypes when cocultured with another cariogenic Streptococcus or with oral non-streptococci species. The study results found that a majority impacted the fitness of S. mutans in various assays, highlighted by increased biomass of commensal streptococci in mixed-species biofilms. These results confirm a common, species-independent modification of S. mutans behaviors with oral commensal streptococci that further emphasizes the need to evaluate oral bacteria within multispecies settings.