IADR Abstract Archives
Adhesion of Streptococcus Gordonii to Bacterial Sialic Acid Sugars
Objectives: Interbacterial adhesion is central to the process of oral biofilm formation. Many Streptococcus gordonii strains encode adhesins that bind to sialic acid (Sia) sugars. In the mouth, Sias decorate most abundantly mucin proteins in saliva and on mucosal surfaces. However, certain bacteria also express Sias on their cell surface glycans. Thus, we hypothesized that S. gordonii not only binds to Sias on host proteins, as previously shown, but also to Sias expressed on other bacteria, thereby facilitating oral biofilm formation. To explore this possibility, we aimed to determine the contribution of Sias to interbacterial adhesion, and to develop techniques for identifying Sia-expressing oral bacteria.
Methods: We evaluated interbacterial adhesion between Sia-binding S. gordonii strain Challis (DL1) and S. agalactiae strain COH1, which is known to express Sias on its surface, by microscopy and using bacterial coaggregation and coadhesion assays. We used far-western blotting and flow cytometry experiments with a Sia-specific plant lectin and a recombinant S. gordonii Sia-binding adhesin, Hsa, to detect Sias on the surface of S. agalactiae. We also used isogenic knockout mutants of the S. gordonii adhesin and of a S. agalactiae Sia synthesis gene, and enzymatically removed surface Sias by treatment with sialidases.
Results: Interbacterial adhesion occurred between S. gordonii and S. agalactiae parent strains in each binding assay tested. Adhesion did not occur when Sia was not expressed or enzymatically removed from S. agalactiae. Also, the Sia-binding plant lectin and recombinant S. gordonii Sia-binding adhesin bound to the parent S. agalactiae strain, but binding was abolished by sialidase treatment and did not occur with the Sia-deficient mutant strain.
Conclusions: We conclude that Sia-mediated interbacterial adhesion occurs between S. gordonii that express a Sia-binding adhesin and bacteria that express Sias on their surface. Thus, Sia-mediated interbacterial adhesion may constitute a hitherto unrecognized mechanism in oral biofilm formation.
Methods: We evaluated interbacterial adhesion between Sia-binding S. gordonii strain Challis (DL1) and S. agalactiae strain COH1, which is known to express Sias on its surface, by microscopy and using bacterial coaggregation and coadhesion assays. We used far-western blotting and flow cytometry experiments with a Sia-specific plant lectin and a recombinant S. gordonii Sia-binding adhesin, Hsa, to detect Sias on the surface of S. agalactiae. We also used isogenic knockout mutants of the S. gordonii adhesin and of a S. agalactiae Sia synthesis gene, and enzymatically removed surface Sias by treatment with sialidases.
Results: Interbacterial adhesion occurred between S. gordonii and S. agalactiae parent strains in each binding assay tested. Adhesion did not occur when Sia was not expressed or enzymatically removed from S. agalactiae. Also, the Sia-binding plant lectin and recombinant S. gordonii Sia-binding adhesin bound to the parent S. agalactiae strain, but binding was abolished by sialidase treatment and did not occur with the Sia-deficient mutant strain.
Conclusions: We conclude that Sia-mediated interbacterial adhesion occurs between S. gordonii that express a Sia-binding adhesin and bacteria that express Sias on their surface. Thus, Sia-mediated interbacterial adhesion may constitute a hitherto unrecognized mechanism in oral biofilm formation.