Growth with Commensal Streptococci Alters 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. One example are the interactions between the cariogenic species and oral commensal streptococci. Previously, we showed that the cell-cell signaling pathways of were inhibited during coculture with other oral streptococci species, leading us to posit that the transcriptome and behaviors are broadly altered during growth with these species. To test this hypothesis, we performed whole transcriptome sequencing (RNA-seq) on cocultures of with either , , or and a quadculture containing all 4 species in comparison to grown alone. Our results reveal that in addition to species-dependent changes to the transcriptome, a conserved response to oral streptococci in general can be observed. We monitored the behavior of by both microscopy imaging of biofilms and in a bacteriocin overlay assay and verified that acts similarly with each of these species but noted divergences in phenotypes when cocultured with another cariogenic () or with oral nonstreptococci species. RNA-seq with oral nonstreptococci showed lack of a consistent gene expression profile and overlap of differentially expressed genes found with commensal streptococci. Finally, we investigated the role of upregulated genes within our data sets to determine if they provided a fitness benefit during interspecies interactions. Eleven total genes were studied, and we found that a majority impacted the fitness of in various assays, highlighted by increased biomass of commensal streptococci in mixed-species biofilms. These results confirm a common, species-independent modification of behaviors with oral commensal streptococci that emphasizes the need to further evaluate oral bacteria within multispecies settings.