Gene Regulation and Physiology of Oral Streptococci

/ABSTRACT Supragingival dental plaque represents a degradative microbial community capable of fermenting a wide variety of sugars over a wide range of concentrations while adapting to the constant changes in carbohydrate source and availability in the oral cavity. Dental caries is developed due to a loss of balance between these fermentative activities, which release corrosive organic acids, and the activities of the host and microorganisms to neutralize acidic pH, resulting in a microbiome particularly good at producing and tolerating these acids. This biochemical imbalance is frequently accompanied by a microbial dysbiosis, where the biofilm is predominated by certain acid-producing and acid-tolerant species. Previous iterations of DE012236 established the foundation for the present work by focusing on the integration of carbohydrate metabolism and virulence development in the major caries etiological agent, Streptococcus mutans, in contrast to related commensal streptococci such as Streptococcus sanguinis and Streptococcus gordonii. Further, by studying a spectrum of sugar catabolism pathways, it was discovered that the mechanisms regulating sugar utilization in S. mutans, e.g., carbohydrate catabolite repression (CCR), cheating and bet-hedging behavior, deviate substantially from those of paradigm organisms. We posit that the deviation of S. mutans from these paradigms was driven by evolutionary adaptations that have imparted to this organism the necessary degree of flexibility to respond to the wide fluctuations in the amount and type of carbohydrates introduced into the human oral cavity. The present proposal builds on these previous studies and our recent discoveries in fructose metabolism and fructose-mediated cariogenicity and stress response, demonstrating the unique fitness of S. mutans that has evolved to better utilize this ubiquitous carbohydrate to enhance its competitiveness against the commensals. These fructose-specific phenotypes were further substantiated by the ability of fructose to activate in S. mutans the core functions of stress response and as many as 176 gene shared with a toxic glycolytic byproduct, methylglyoxal, including an uncharacterized conserved protein (GloA2) closely related to the enzyme required for degradation of methylglyoxal. There's now a large body of high-quality research evidence associating fructose with the ongoing epidemic of metabolic disorders: obesity, type 2 diabetes, cardiovascular diseases, and liver pathologies. As the component of two most widely used dietary sweeteners, sucrose and high- fructose corn syrup, fructose is likely contributing to the prevalence of caries among the western populations. To understand the molecular basis for, and ecological consequences of, fructose metabolism in dental biofilms, we present three Specific Aims: 1) In vitro characterization of the effects of fructose on streptococcal stress physiology; 2) Identifying genetic mechanisms required for fructose and GloA2-mediated response in S. mutans; 3) Assessing the contributions of fructose to microbial ecology and dysbiosis in biofilm models. Project Number: 2R01DE012236-27A1 | Fiscal Year: 2025 | NIH Institute/Center: National Institute of Dental and Craniofacial Research (NIDCR) | Principal Investigator: Lin Zeng | Institution: UNIVERSITY OF FLORIDA, GAINESVILLE, FL | Award Amount: $434,625 | Activity Code: R01 | Study Section: Oral, Dental and Craniofacial Sciences Study Section[ODCS] View on NIH RePORTER: https://reporter.nih.gov/project-details/11225796