Investigating the roles of extracellular pyruvate in regulating Streptococcus mutans physiology and stress resistance

About This Grant

LrgA/B (membrane proteins found in a wide variety of bacteria) has been recently identified as a pyruvate importer in Bacillus subtilis, Staphylococcus aureus, and Streptococcus mutans. An increased appreciation for extracellular pyruvate’s non-traditional and diverse roles in metabolism and stress resistance has emerged in recent years. Although our published and preliminary data demonstrate key roles for LrgAB and/or extracellular pyruvate in modulating S. mutans physiology, oxidative stress resistance, and virulence, the precise mechanism(s) by which extracellular pyruvate exerts these functions in S. mutans remain unknown. Amongst oral streptococci, lrgAB and its upstream two-component regulator lytST, are notably absent from the genomes of non-cariogenic streptococcal species, and likewise extracellular pyruvate supplementation does not confer a strong stationary phase growth advantage in non-cariogenic oral streptococci. Collectively, these observations support the hypothesis that extracellular pyruvate serves as a metabolic signal that enhances stress resistance and metabolic flexibility of S. mutans, contributing to survival in fluctuating host environments. This would provide a distinct competitive advantage to S. mutans in dental plaque biofilm and other pyruvate-replete environments such as the bloodstream. This hypothesis will be addressed by two specific aims. In Aim 1, the metabolic fate of extracellular pyruvate in S. mutans planktonic cultures will be tracked and identified by 13C-labeled pyruvate feeding experiments and NMR spectroscopy. Time-resolved metabolomic and transcriptomic analyses will also be employed to characterize pyruvate-, LytST-, and LrgAB-driven gene expression and metabolic shifts during growth-phase transitions. In Aim 2, fluorescence-based reporters and confocal microscopy will be used to examine the influence of lrgAB and extracellular pyruvate supplementation on S. mutans niche competition and behavior within dual-species biofilms grown in human saliva. Pyruvate supplementation, LrgAB, and LytST effects on S. mutans oxidative stress resistance and survival in human whole blood, plasma and serum will also be assessed. Understanding the interactions between extracellular pyruvate, LytST, and LrgAB could provide new insights into the pathogenesis of S. mutans, its persistence in the oral cavity and bloodstream, and its interactions with other microbial species. This could lead to new targeted therapeutic strategies to control S. mutans infections, both within the oral cavity and in systemic conditions such as infective endocarditis.