Nutritional Niches within Supragingival Biofilms - PROJECT SUMMARY / ABSTRACT The bacteria that colonize the oral cavity, forming biofilms on surfaces such as the hard tissues of teeth, participate in complex exchanges with other microbes inhabiting the same niche. One such example is the relationship between Streptococcus mutans, one of the primary drivers of dental caries development, and other oral commensal streptococci species. Organic acids produced by S. mutans, an end product from the fermentation of dietary carbohydrates, accumulate and are concentrated within microcolony-like biofilm structures that are the sites of enamel demineralization. Encasing the microcolonies are oral commensal streptococci – thus, understanding how these structures form, the interactions that occur between S. mutans and other oral streptococci that enclose them, and development of new strategies/targets to disrupt these structures is of critical significance to the field of oral health. Our group has begun to address these needs through characterization of S. mutans gene expression when it is cocultured with other oral bacteria and have made several crucial observations such as alterations to the S. mutans transcriptome through a specific, characterized pattern only in the presence of oral commensal streptococci, and not with other disease- associated streptococci or oral non-streptococci. One such change is in the expression of phosphotransferase systems (PTS) for specific carbohydrate uptake and utilization. During growth in coculture, both S. mutans and oral commensal streptococci gene expression stratifies into different carbohydrate utilization preferences, suggesting that each species partitions into a different nutritional niche during the interaction. However, these conclusions are only based on transcriptomic datasets and require further experimentation to validate. Our central hypothesis is that during active competition, health- and disease-associated oral streptococci modify carbohydrate utilization preferences via gene expression changes as to not compete for the same carbohydrate source. Our objective is to validate this hypothesis though using functionalized carbohydrates for click chemistry that will allow for single cell analysis of carbohydrate utilization during super-resolution microscopy imaging of mixed-species biofilms, as well as to validate/confirm our findings through genetically engineered mutants in both S. mutans and oral streptococci. Our long-term goal is to be able to manipulate these interactions through either prebiotic/probiotic strategies and/or therapeutic interventions to target pathways that selectively remove S. mutans from oral biofilms while leaving health-associated, commensal species intact. Included in our approach are research objectives that: i) explicate nutritional niches between health- and disease-associated oral bacteria, ii) exploit nutritional niches to alter microbial ecology through oral streptococci interactions, and iii) elucidate partitioning of the oral microbiome by specific carbohydrate utilization preferences. Together, this proposal will strengthen our understanding of the interconnectedness of the oral microbiome while working to answer new and relevant questions in understanding how intermicrobial interactions can drive dysbiosis of a healthy microbial community, eventually leading to disease (caries) formation.
