Cell wall-anchored CshA polypeptide (259 kilodaltons) in Streptococcus gordonii forms surface fibrils that confer hydrophobic and adhesive properties

It has been shown previously that inactivation of the cshA gene, encoding a major cell surface polypeptide (259 kDa) in the oral bacterium Streptococc us gordonii, generates mutants that are markedly reduced in hydrophobicity, deficient in binding to oral Actinomyces species and to human fibronectin, and unable to colonize the oral cavities of mice. We now show further that surface fibrils 60.7 +/- 14.5 nm long, which are present on wild-type S. g ordonii DL1 (Challis) cells, bind CshA-specific antibodies and are absent f rom the cell surfaces of cshA mutants. To more precisely determine the stru ctural and functional properties of CshA, already inferred from insertional -mutagenesis experiments, we have cloned the entire cshA gene into the repl icative plasmid pAM401 and expressed full-length CshA polypeptide on the ce ll surface of heterologous Enterococcus faecalis JH2-2. Enterococci express ing CshA exhibited a 30-fold increase in cell surface hydrophobicity over E . faecalis JH2-2 carrying the pAM401 vector alone and 2.4-fold-increased ad hesion to human fibronectin. CshA expression in E. faecalis also promoted c ell-cell aggregation and increased the ability of enterococci to bind Actin omyces naeslundii cells. Electron micrographs of negatively stained E. faec alis cells expressing CshA showed peritrichous surface fibrils 70.3 +/- 9.1 nm long that were absent from control E. faecalis JH2-2(pAM401) cells. The fibrils bound CshA-specific antibodies, as detected by immunoelectron micr oscopy, and the antibodies inhibited the adhesion of E. faecalis cells to f ibronectin. The results demonstrate that the CshA polypeptide is the struct ural and functional component of S. gordonii adhesive fibrils, and they pro vide a molecular basis for past correlations of surface fibril production, cell surface hydrophobicity, and adhesion in species of oral "sanguis-like" streptococci.