Probing oral microbial functionality - Expression of spxB in plaque samples

The Human Oral Microbiome Database (HOMD) provides an extensive collection of genome sequences from oral bacteria. The sequence information is a static snapshot of the microbial potential of the so far sequenced species. A major challenge is to connect the microbial potential encoded in the metagenome to an actual function in the in vivo oral biofilm. In the present study we took a reductionist approach and identified a considerably conserved metabolic gene, spxB to be encoded by a majority of oral streptococci using the HOMD metagenome information. spxB encodes the pyruvate oxidase responsible for the production of growth inhibiting amounts of hydrogen peroxide (H₂O₂) and has previously been shown as important in the interspecies competition in the oral biofilm. Here we demonstrate a strong correlation of H₂O ₂ production and the presence of the spxB gene in dental plaque. Using Real-Time RT PCR we show that spxB is expressed in freshly isolated human plaque samples from several donors and that the expression is relative constant when followed over time in one individual. This is the first demonstration of an oral community encoded gene expressed in vivo suggesting a functional role of spxB in oral biofilm physiology. This also demonstrates a possible strategy to connect the microbial potential of the metagenome to its functionality in future studies by identifying similar highly conserved genes in the oral microbial community.