Streptococcal secretion of pyruvate - a novel antioxidant strategy in the oral biofilm

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Project Summary Commensal streptococci play an important role in oral biofilm homeostasis. Disturbance of biofilm homeostasis leads to dysbiosis and eventually disease development, including caries and periodontal disease. Several oral streptococci are producing significant amounts of H2O2 able to inhibit susceptible pathobionts involved in disease development. However, the production of H2O2 does not always correlate with the antagonistic ability of the producer. Our group recently identified the mechanism behind this observation: oral streptococci secrete the central metabolite pyruvate as potent H2O2 scavenger. The mechanism of pyruvate secretion as oxidative stress response has been reported for eukaryotic cells, but has not been investigated in prokaryotes and little is known about prokaryotic pyruvate transport in general. Our observation raises key ecological questions about the role of commensal streptococci in the oral cavity: why do some streptococcal H2O2 producers secrete protective amounts of pyruvate and others do not? What is the genetic basis for this ability? What are the implications for oral health? The following specific aims are proposed to identify and characterize the pyruvate secretion mechanism and its genetic control in oral streptococci: Aim I: Identify the pyruvate secretion mechanism and its specific regulation. We will identify the genetic components required for pyruvate secretion by combining transposon mutagenesis with an established genetic screening protocol. The regulation of these genes will be compared between species. Aim I will determine how different streptococci modulate the H2O2/pyruvate balance that is critical for oral microbial ecology. Aim II: Characterize the regulatory network that determines the H2O2/pyruvate balance. We will perform ChIP-seq (CCR+/-) under conditions of low and high pyruvate secretion to identify the key regulatory components of this pathway. This will also serve as independent approach to identify the pyruvate secretion mechanism. An improved understanding of how the streptococcal community regulates its H2O2/pyruvate balance will help to define the molecular determinates of disease development and provide a novel target for disease prevention.