PROJECT SUMMARY Dental caries is a prevalent but preventable oral disease. In caries-active subjects, there is a shift towards a microbial community dominated by acidogenic and acid-tolerant bacteria. Streptococcus mutans is a major cariogenic pathogen. Commensal bacteria normally help to control S. mutans via bioactive products such as H2O2. However, high-sugar consumption, which is frequently found in populations with a high rate of caries development, could inhibit the generation of H2O2 through carbohydrate catabolite repression and thereby disrupt homeostasis. Several metal titanates have recently emerged as effective green chemistry solutions to produce reactive oxygen species (ROS), including H2O2, O2˙–, ˙OH, and 1O2. They trigger oxidation stress in certain bacteria and subsequently inhibit them. Metal titanates have the potential for broad dental applications due to high compatibility with various dental materials, including dental adhesive systems, resin composites, ceramics, and metals. Furthermore, as photocatalysts, metal titanates will not be consumed in the catalyzed reaction but can act continuously, thus offering long-lasting benefits. Our group has demonstrated that gold titanate could catalyze and produce H2O2, which could inactivate S. mutans while having limited impact on commensal oral bacterial S. gordonii and S. sanguinis. It is hypothesized that selective photoactivated semiconducting metal-titanates will produce extrinsic H2O2 from O2 reduction and other ROS to inhibit S. mutans, while giving an advantage to commensal bacteria and thereby maintain homeostasis in dental biofilms and thus prevent dental caries. To test our hypothesis, Aim 1 will optimize the application conditions of metal titanates to maximize the potentials of the antibacterial efficacy. We will measure different species of ROS production from gold titanate with in situ probe compounds. Then, we will synthesize semiconducting metal titanates to enhance the photocatalytic activities (i.e., activation by visible light, more ROS generation) and improve clinical performances (e.g., esthetics, compatibility, physical property, stability, and toxicity). Aim 2 will identify the gene expressions of S. mutans and commensals exposed to metal titanates. The transcriptional profiles of S. mutans with metal titanates will be revealed by mRNA sequencing (RNA-seq) and the oxidative stress relevant genes will be specifically monitored. Aim 3 will focus on diverse multi-species oral biofilms, especially in high sugar condition. First, we will examine the effect of metal titanates on the spatial organization and composition of the dual-species biofilms of S. mutans and commensal bacteria in flow cell system. Second, we will apply plaque-derived multispecies microbial biofilms and S. mutans-infected multispecies oral microbial community to understand the response of species within complex oral biofilms to metal titanates in the oral cavity, for which 16S rRNA gene sequencing will be employed to measure the composition shift. Collectively, the study will provide a comprehensive understanding of the effects of metal titanates on the formation and ecology of dental biofilms and guide the development of an effective dental application.

PROJECT NARRATIVE Dental caries is an enormous health problem worldwide and there is a shift towards oral microbial community dominated by cariogenic bacterium, eg: Streptococcus mutans, in caries-active subjects. Commensal bacteria normally help to control S. mutans via bioactive products such as H2O2; however, high-sugar consumption, which is frequently found in populations with high caries rates, could inhibit the generation of H2O2 through carbohydrate catabolite repression and disrupt the homeostasis. This project will investigate if selective photoactivated semiconducting metal titanates will produce extrinsic H2O2 from O2 reduction and other reactive oxygen species (ROS), to inhibit S. mutans, while giving an advantage to commensal bacteria and thereby maintain homeostasis in dental biofilms and thus prevent dental caries.