During the previous grant period, the biology and mechanisms of adhesion to teeth by Streptococcus sanguis were modeled in comparison to S. gordonii. Facilitated by our development of an In Vivo Expression Technology (1VET) library and an early biofilm model on saliva-coated hydroxyapatite (sHA), reporter gene and mutational approaches, and direct detection of gene expression, we showed that betaglucoside metabolism systems contribute to the global control of adhesion and biofilm formation in vitro and in vivo. We also identified and characterized adhesin genes and proteins of S. gordonii that appear to distinguish sessile, planktonic and free-growing cells in an sHA biofilm model. These genes and proteins appear to comprise an Adhesion Maintenance System (AMS). In S. sanguis and S. gordonii, the AMS is hypothesized to be a module of genes and proteins that function as a network to control the specificity of adhesion and initial biofilm formation, explaining competitive differences we now show in S. gordonii and S. sanguis as pioneer colonizers. To test our hypothesis that the AMS, including bfrAB, srtA, sspA, sspB, scaA, abpB, msrA and their protein products, regulates the specificity of adhesion and initial biofilm formation, we will: (1) determine how SrtA acts on SspA to transcriptionally regulate sspB; (2) show that mutations in sspA and sspB and other adhesins modify the structure and function of surface fibrils; (3) describe the proof-of-principle of a network that comprises the AMS module; and (4) compare the expression and function of AMS genes and proteins in S. gordonii with S. sanguis. Collectively, these studies will characterize the AMS as a unique biological network that enables the pioneer oral streptococci to competitively adhere and colonize the teeth and withstand eradication by swallowing in saliva.
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