Biofilms are highly organized bacterial structures that are attached to a surface. They are ubiquitous in nature and may be detrimental, causing numerous types of illnesses in living organisms. Biofilms in the human oral cavity are the main cause of dental caries and periodontal diseases and can act as a source for pathogenic organisms to spread within the body and cause various types of systemic diseases. Streptococcus mutans is the primary etiological agent of dental caries, the single most chronic childhood disease. In many cases, quorum sensing (QS) is required for initial formation and subsequent development of biofilms and the signaling molecule autoinducer 2 (AI- 2) has been well studied as an inter-species QS signaling molecule. However, recent reports also suggest that AI-2-mediated signaling is important for intra-species biofilm formation in both Gram-negative and positive bacteria. Therefore, there is significant interest in understanding the role of different QS signals such as AI-2 in oral biofilm formation. Microfluidic devices provide biomimetic environments and offer a simple method for executing multiple stimuli experiments simultaneously, thus, can be an extremely powerful tool in the study of QS in biofilms. In this study, we report conditions that support the development of S. mutans biofilms in microchannel microfluidic devices, and the effects of extracellular addition of chemically synthesized (S)-4,5-dihydroxy-2,3-pentanedione (DPD; precursor of AI-2) on mono-species S. mutans luxS (AI-2 deficient strain) biofilm formation using a gradient generating microfluidic device. S. mutans wild type (WT) and luxS biofilms were developed in nutrient rich medium (25% brain heart infusion medium, BHI + 1% sucrose) for up to 48 h. Maximum biofilm formation with both strains was observed after 24 h, with distinct structure and organization. No changes in S. mutans luxS biofilm growth or structure were observed upon exposure to different concentrations of AI-2 in a gradient generating device (0 to 5 M). These results were also validated by using a standard 96-well plate assay and by verifying the uptake of AI-2 by S. mutans luxS. Our data suggest that extracellular addition of AI-2 does not complement the luxS deletion in S. mutans with respect to biofilm formation.

Type II toxin-antitoxin (TA) systems are composed of a stable toxin and its cognate unstable antitoxin that impedes the toxin through direct interaction. The human oral pathogen Streptococcus mutans uses a quorum-sensing peptide (CSP) as a stress-inducible pheromone to synchronize gene expression in response to specific stressors. The objectives of this study were to investigate the role of S. mutans MazEF TA in cell survival and characterize the functionality of CSP-inducible chromosomal type II TAs. Our results suggest that MazEF represents a stress-response element. Interestingly, S. mutans negatively regulates its MazEF system under high-cell-density environment that is characteristic of oral biofilms. S. mutans also encodes a novel chromosomal type II TA involved in biofilm formation and development of dormant persister cells. The results from this study suggest a complex interplay between quorum-sensing (signal), type II TA activation (response), and persister formation (phenotype) as a reaction to environmental perturbations.

Type II toxin-antitoxin (TA) systems are composed of a stable toxin and its cognate unstable antitoxin that impedes the toxin through direct interaction. The human oral pathogen Streptococcus mutans uses a quorum-sensing peptide (CSP) as a stress-inducible pheromone to synchronize gene expression in response to specific stressors. The objectives of this study were to investigate the role of S. mutans MazEF TA in cell survival and characterize the functionality of CSP-inducible chromosomal type II TAs. Our results suggest that MazEF represents a stress-response element. Interestingly, S. mutans negatively regulates its MazEF system under high-cell-density environment that is characteristic of oral biofilms. S. mutans also encodes a novel chromosomal type II TA involved in biofilm formation and development of dormant persister cells. The results from this study suggest a complex interplay between quorum-sensing (signal), type II TA activation (response), and persister formation (phenotype) as a reaction to environmental perturbations.

Thesis (doctoral)--Karolinska Institutet, Stockholm, 1985. / Extra t.p. with thesis statement inserted. Includes bibliographical references.

Thesis (doctoral)--Rijksuniversiteit te Utrecht.

Thesis (doctoral)--Lunds Universitet, Malmö, 1988. / Extra t.p. with thesis statement inserted. Includes bibliographical references.

Thesis (doctoral)--Karolinska Institutet, Stockholm, 1985. / Extra t.p. with thesis statement inserted. Includes bibliographical references.

Thesis--Göteborg. / Includes abstract. Includes reprints of author's articles. Extra t.p. with thesis statement inserted. Includes bibliographical references.

Thesis--University of Turku, Finland, 1999. / Includes bibliographical references.

Thesis (doctoral)--Lunds Universitet, Malmö, 1988. / Extra t.p. with thesis statement inserted. Includes bibliographical references.