Streptococcal Antagonism In Oral Biofilms: Streptococcus sanguinis and Streptococcus gordonii interference with Streptococcus mutans

Department of Diagnostic and Biological Sciences, School of Dentistry, University of Minnesota, Minneapolis, Minnesota 55455; and Mucosal and Vaccine Research Center, Minneapolis Veterans Affairs Medical Center, Minneapolis, Minnesota 55417

^* To whom correspondence should be addressed. Email: kreth001{at}umn.edu.

	Abstract

Biofilms are polymicrobial, with diverse bacterial species competing for limited space and nutrients. Under healthy conditions, the different species in biofilms maintain an ecological balance. This balance can be disturbed by environmental factors and interspecies interactions. These perturbations can enable dominant growth of certain species leading to disease. To model clinically relevant interspecies antagonism, we studied three well-characterized and closely related oral species, Streptococcus gordonii, Streptococcus sanguinis and cariogenic Streptococcus mutans. S. sanguinis and S. gordonii used oxygen availability and the differential production of hydrogen peroxide (H₂O₂) to compete effectively against S. mutans. Interspecies antagonism was influenced by glucose with reduced production of H₂O₂. Furthermore, aerobic conditions stimulated the competence system and the expression of the bacteriocin mutacin IV of S. mutans, as well as the H₂O₂-dependent release of heterologous DNA from mixed cultures of S. sanguinis and S. gordonii. These data provide new insights into ecological factors that determine the outcome of competition between pioneer colonizing oral streptococci and the survival mechanisms of S. mutans in the oral biofilm.