The role of capsule production on the physiology of an oral commensal

Abstract The hydrogen peroxide (H2O2)-producing oral commensal, Streptococcus parasanguinis, plays a major role in maintaining oral homeostasis in a nitrite (NO2)-dependent manner. Specifically, salivary NO2 produced by nitrate- reducing bacteria reacts with H2O2 to produce reactive nitrogen species (RNS), such as peroxynitrite (ONOO-), which is an antimicrobial that targets diverse pathogens, such as Streptococcus mutans, Enterococcus faecalis, and Aggregatibacter actinomycetemcomitans. In S. parasanguinis the production of H2O2 is mediated by the poxL (pyruvate oxidase) gene, which is homologous to the Streptococcus pneumoniae spxB gene. Multiple studies have shown that in S. pneumoniae H2O2 production has an inverse relationship with capsule production. Capsule production in S. pneumoniae is important for biofilm formation and oxidative stress resistance. However, the relationship between capsule production and H2O2 production, oxidative stress tolerance, and biofilm development remains unknown in S. parasanguinis. Additionally, the role of capsule in NO2-mediated nitrosative stress tolerance remains unstudied. S. parasanguinis harbors a capsule biosynthesis (CPS) operon that is homologous to the S. pneumoniae CPS operon, indicating that the roles of capsule may function in a similar manner to S. pneumoniae as it pertains to fitness. CpsE, a galactosyl transferase, is required for initiating the addition of the first monosaccharide in the formation of S. parasanguinis polysaccharide capsule biosynthesis. The goal of this project is to characterize the role of S. parasanguinis CpsE in modulating H2O2 production, NO2- mediated stress tolerance and biofilm formation, and commensal fitness within multispecies biofilms. We hypothesize that capsule production plays a critically important role in S. parasanguinis biofilm formation, stress response, and polymicrobial interactions. The specific aims of this project are to: 1) Determine the role of capsule production on S. parasanguinis biofilm development and stress tolerance, and 2) Determine the role of capsule production on S. parasanguinis’ microbial competition. Ultimately, the completion of the proposed aims will provide new knowledge about the role of capsule in oral commensal fitness, colonization, and ability to antagonize oral pathogens, which has never been studied.