Harvesting Novel Bacterial Glycan-Binding Coadhesion Partners from Multi-Species Oral Biofilms

Objectives: Studies of the human oral microbiome revealed a great diversity of microbial communities among different individuals. During the formation of oral biofilms, bacterial species within the biofilms physically interact with each other through distinct coadhesive mechanism. Previous studies have revealed the molecular basis for some bacterial coadhesive interactions. An example is the binding of a Gal/GalNAc-specific protein adhesin on Actinomyces naeslundii to corresponding receptor polysaccharides on certain strains of streptococci. However, the vast amount of other possible bacteria-bacteria interactions still remains unexplored. A coadhesion assay, designed to screen multi-species biofilms for coadhesion partners, was used here to search for oral bacteria that bind to exotic, non-mammalian glycan motifs carried by certain oral streptococci. One example is Streptococcus oralis H1 that expresses a polysaccharide containing Rhaα1-2Rha. Thus far, no coadhesion partners are known that bind to this exotic non-mammalian glycan motif.
Methods: Dental biofilms were collected and bacteria were cultured on agar plates. Colony-lifts were probed by bacteria overlay with fluorophore-labeled S. oralis H1. Colonies that showed positive binding were picked and streaked out onto new culture plates. After repeated rounds of probing and re-streaking, pure monocultures were obtained. Glycan-binding of these isolates was tested by denaturation of bacterial protein adhesins.
Results: The coadhesion method was initially validated using A. naeslundii WVU45 and S. oralis 34. For the Rhaα1-2Rha motif on S. oralis H1, twelve bacterial isolates that express putative adhesins were obtained. The presence of a glycan-binding adhesin specifically binding to S. oralis H1 could be confirmed for one of these isolates.
Conclusions: A coadhesion partner of S. oralis H1 could be isolated from multi-species oral biofilms, demonstrating the usefulness of the current coadhesion method for studying adhesive inter-species interactions between members of the oral microbiome.