Dental plaque is a complex multi-species community and is the etiological factor of multiple oral diseases. The high diversity presents intricate mechanisms of interactions among the species. Two major types of interactions are chemical and physical. Chemical interactions are mediated by the production and detection of small signaling molecules such as autoinducer-2 (AI-2). Generated by luxS, AI-2 is produced by many species of bacteria and regulates important traits as biofilm formation and survival. Physical interactions such as coaggregation are mediated by the expression of surface molecules that allow cell-cell binding among cells from different species. The majority of early bacterial communities forming on saliva-bathed dental surfaces are streptococcal species such as Streptococcus gordonii and Streptococcus oralis. These two commensal species produce AI-2 and coaggregate with one another and with many other species of dental bacteria. In the present dissertation, S. gordonii and S. oralis were used as a model of early mixed-species dental plaque biofilms addressing the impact of AI-2-mediated communication and coaggregation in biofilm formation. Streptococcal AI-2 activity was detected on wild-type but not on ΔluxS strains. Importantly, AI-2 detection was dependent on pH levels and boric acid availability. The present hypothesis stipulates that physical and chemical interactions among these two species are required for mixed-species biofilm structure/composition. To test this, luxS/AI-2 deficient mutants of both species and coaggregation-deficient mutants of S. gordonii were employed in biofilm experiments using human saliva as the sole nutrition source. The results show that S. gordonii grew biofilms independently and regardless of deficiencies. In contrast, S. oralis did not grow biofilms as a single-species and required AI-2-mediated interactions as well as coaggregation interactions with S. gordonii to survive within the biofilms. S. oralis biomass was rescued by exogenous addition of AI-2. Proteomics work revealed six proteins from S. gordonii that bound to S. oralis dependent upon calcium/magnesium availability. This work contributes to the understanding of dental plaque formation at the early stages and the role of physical and chemical interactions among the commensal dental species. Potential therapeutic compounds targeting these two types of interactions would be useful to treat oral diseases.
|Advisor:||Tammariello, Steven P.|
|Commitee:||Davies, David G., Garruto, Ralph M., Marques, Claudia NH|
|School:||State University of New York at Binghamton|
|School Location:||United States -- New York|
|Source:||DAI-B 74/02(E), Dissertation Abstracts International|
|Keywords:||Biofilms, Coaggregation, Commensal species, Dental plaques, Oral bacteria, Quorum sensing|
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