Human saliva modifies growth, biofilm architecture and competitive behaviors of oral streptococci

Our group recently transcriptomically characterized coculture growth between Streptococcus mutans and several species of commensal streptococci (Rose et al, 2023). However, these experiments were carried out in our lab-based experimental medium, tryptone and yeast extract (TY-). To understand whether culturing these species within a medium that more closely mimics their natural environment alters the interaction, we evaluated both monoculture and coculture growth between the dental caries pathogen Streptococcus mutans and oral commensal species Streptococcus oralis in a half TY- / half human saliva mix that was optimally chosen based on our initial characterization of oral streptococci behaviors in medium mixes containing saliva. Our results surprising show that inclusion of saliva enhances the competition of Streptococcus mutans against commensal streptococci through upregulation of carbohydrate uptake and glycolytic pathways. Streptococcus mutans UA159 and Streptococcus oralis 34 were grown either as monocultures or cocultures, inoculated 1:1. All samples were grown in either TY- (regular lab-based experimental medium) or TY-Saliva (half TY / half human saliva). Resulting comparisions included differentially expressed genes (DEGs) between TY-Saliva and TY- conditions for each monoculture as well as cocultures.