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Chapter 22 : Antagonistic, Synergistic, and Counteroffensive Strategies for Streptococcal Interspecies Interactions
Category: Genomics and Bioinformatics
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Interactions between oral streptococci have developed because of ecological pressures within the oral environment. The high abundance of oral streptococci makes it very likely that they have evolved close relationships manifested in diverse interspecies interactions. Interspecies interactions in the oral biofilm can be defined by the purpose and nature of the interactions. Although there are many potential interactions between oral streptococci and other members of the oral biofilm community as well as the host, this chapter specifically focuses on streptococcus-streptococcus interactions. By promoting genetic exchange, the interspecies interaction, although not beneficial for the lysed bacterial species, is important in the context of evolution. A counteroffensive strategy was recently identified for Streptococcus oligofermentans, another oral streptococcal species and competitor of S. mutans. Surprisingly, S. oligofermentans is able to utilize the lactic acid produced by cariogenic species, such as S. mutans, to generate hydrogen peroxide, leading to growth inhibition of the lactic acid producer. Expanding research into multispecies models is desirable and would most likely reveal interesting synergistic behavior of oral streptococci. The close relationship of the oral streptococci enables the reconstruction of biochemical networks from already-existing metabolic functions identified in other streptococci. The spatial-temporal developmental patterns of oral streptococci in the biofilm, including the molecular mechanisms, are characterized. The oral biofilm is easily accessible, and the variety of genetic manipulation options for oral streptococci allows for experimental verification of in silico predictions.
Interspecies interactions among S. mutans, S. sanguinis, S. gordonii, S. oralis, and S. oligofermentans. Shown is the production of lactic acid, mutacin, CSP (involved in stimulation of mutacin gene expression), challisin, and hydrogen peroxide, important in the antagonistic relationship between these oral streptococci. Lactic acid inhibits the growth of acid-sensitive streptococci. S. oligofermentans uses lactic acid for the production of growth-inhibiting concentrations of H2O2 via the lactate oxidase (Lox). Conversely, H2O2 is also generated by S. sanguinis and S. gordonii by the pyruvate oxidase (Pox). H2O2 inhibits growth of S. mutans. S. sanguinis and S. gordonii are sensitive to the mutacins produced by S. mutans. S. gordonii utilizes challisin to interfere with the mutacin production by reducing the levels of the stimulating compound CSP. In a synergistic manner, S. oralis and S. sanguinis are able to degrade mucin, a glycoprotein present in saliva. S. gordonii is more efficient in binding to the saliva-coated tooth via the adhesin Hsa than is S. sanguinis. For further details, see the text. Modified after reference 30 .
Alignment of the upstream promoter regions of the pyruvate oxidase-encoding genes of S. gordonii (S.g.), S. sanguinis (S.s.), and S. mitis (S.m.). ATG indicates the start of the coding sequence for pyruvate oxidase.
Distribution of functional groups involved in oral streptococcal interspecies interactions