Project Summary/Abstract Dental plaque is a polymicrobial community of the human mouth that can contribute to multiple oral diseases. As with many other multispecies microbial communities, the microorganisms that make up dental plaque are spatially organized similarly among different people, suggesting that the forces that govern the development of these communities are conserved. Streptococcus gordonii has been hypothesized to play a crucial role in dental plaque development due to its ability to rapidly bind the saliva-coated oral surfaces aiding late colonizers of the dental plaque in joining the maturing community. RNA-seq analysis of S. gordonii cells in a biofilm revealed that approximately 10% of its genes are differentially expressed compared to their planktonic counterparts. Of particular interest, biofilm-derived cells upregulated SGO_2031, which encodes a putative Ne-lysine acetyltransferase, a member of the GCN5-related N-acetyltransferase (GNAT) family. Deletion of SGO_2031 causes a defect in single-species biofilm formation compared to the wild-type parent strain due to a reduction in the expression of the poly-gamma- glutamate gene (pgsA), which has been implicated in the production of extracellular polysaccharides. Our preliminary data suggest that acetylation of the sensor histidine kinase gene SGO_0299 regulates pgsA transcription and biofilm formation. This proposal will investigate the effect of SGO_0299 acetylation on its ability to phosphorylate its cognate response regulator, SGO_0298, ultimately affecting EPS production and biofilm formation. Given S. gordonii important role in oral biofilm development as an early colonizer of tooth surfaces, we will establish a murine model system to investigate how SGO_2031 dependent acetylation affects S. gordonii’s ability to colonize and shape the oral microbial community.