The human dental plaque biofilm is a physically and chemically complex environment that is inhabited by a many bacterial species, including Streptococcus mutans, which is regarded as the primary etiological cause of human dental caries. S. mutans has a number of behaviors that give rise to its virulence, and it regulates and activates these behaviors through the use of chemical cues received from its environment. However, the local environment of S. mutans at different locations within a biofilm may be chemically and physically different, subject to substantial variation in pH, oxygen concentration and nutrient availability, as well as different balances of colonizing species and different concentrations of the small molecules that allow the bacteria to communicate and regulate virulence behaviors. This project seeks to determine how this diversity of microenvironments affects the centrally important S. mutans virulence behavior known as genetic competence. Competence is the ability to take up extracellular DNA, and the genetic network that regulates competence in S. mutans is closely intertwined with the mechanisms that regulate virtually every other cariogenic trait of the organism. The competence genes are extremely sensitive to environmental conditions and to the nature of the chemical signals received. Expression of competence genes across a population of cells can be uniform or can involve activation of only a subset of the bacteria. Therefore a broad scientific goal is to understand how S. mutans processes or interprets environmental signals to regulate competence and other virulence behaviors, how microenvironments in the biofilm affect this processing, and how competence genes are activated at the cell-to-cell level throughout an oral biofilm. This project will focus o identifying and understanding the genetic """"""""switches"""""""" that control S. mutans competence, exploring how pH, oxygen concentration, and carbohydrate availability affect the regulation of competence by peptide signals, and studying and modeling the ways that competence is regulated by peptide signals inside an S. mutans biofilm. The project will accomplish these goals through a novel microfluidic, single-cell approach. This method allows multiple, well-defined environmental inputs to be supplied to subpopulations of S. mutans cells while the profile of competence gene activation across those subpopulations is measured and modeled quantitatively. The project will yield detailed information about how S. mutans competence is spatially distributed in an oral biofilm and what kinds of chemical conditions trigger this and related virulence behaviors. Success in achieving these objectives will advance research in human oral health by improving the understanding of how Streptococcus mutans causes dental disease.

Public Health Relevance

The causative agent of human dental caries, Streptococcus mutans, is able to alter its gene expression and virulence behavior by secreting signals that are part of an intercellular communication system. The goal of this project is to use a sophisticated microfluidics system and fluorescent read-outs of gene expression to dissect the way in which individual bacteria respond to complex combinations of signals and environmental conditions to modify their virulence. The studies will shed new light on ways to control oral diseases, such as dental caries, and have high relevance to other infectious diseases as these signaling pathways are present in a variety of streptococcal bacteria.

National Institute of Health (NIH)
National Institute of Dental & Craniofacial Research (NIDCR)
Research Project (R01)
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Study Section
Oral, Dental and Craniofacial Sciences Study Section (ODCS)
Program Officer
Lunsford, Dwayne
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University of Florida
Schools of Arts and Sciences
United States
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Kaspar, Justin; Shields, Robert C; Burne, Robert A (2018) Competence inhibition by the XrpA peptide encoded within the comX gene of Streptococcus mutans. Mol Microbiol 109:345-364
Underhill, Simon A M; Shields, Robert C; Kaspar, Justin R et al. (2018) Intracellular Signaling by the comRS System in Streptococcus mutans Genetic Competence. mSphere 3:
Son, M; Kaspar, J; Ahn, S J et al. (2018) Threshold regulation and stochasticity from the MecA/ClpCP proteolytic system in Streptococcus mutans competence. Mol Microbiol 110:914-930
De Furio, Matthew; Ahn, Sang Joon; Burne, Robert A et al. (2017) Oxidative Stressors Modify the Response of Streptococcus mutans to Its Competence Signal Peptides. Appl Environ Microbiol 83:
Shields, Robert C; O'Brien, Greg; Maricic, Natalie et al. (2017) Genome-wide screens reveal new gene products that influence genetic competence in Streptococcus mutans. J Bacteriol :
Hagen, Stephen J; Son, Minjun (2017) Origins of heterogeneity in Streptococcus mutans competence: interpreting an environment-sensitive signaling pathway. Phys Biol 14:015001
Kaspar, Justin; Underhill, Simon A M; Shields, Robert C et al. (2017) Intercellular communication via the comX-Inducing Peptide (XIP) of Streptococcus mutans. J Bacteriol :
Moye, Zachary D; Son, Minjun; Rosa-Alberty, Ariana E et al. (2016) Effects of Carbohydrate Source on Genetic Competence in Streptococcus mutans. Appl Environ Microbiol 82:4821-4834
Shields, Robert C; Burne, Robert A (2016) Growth of Streptococcus mutans in Biofilms Alters Peptide Signaling at the Sub-population Level. Front Microbiol 7:1075
Son, Minjun; Ghoreishi, Delaram; Ahn, Sang-Joon et al. (2015) Sharply Tuned pH Response of Genetic Competence Regulation in Streptococcus mutans: a Microfluidic Study of the Environmental Sensitivity of comX. Appl Environ Microbiol 81:5622-31

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