Cross-Kingdom Cell-to-Cell Interactions in Cariogenic Biofilm Initiation.

is known to form polymicrobial biofilms with various spp., including mitis and mutans group streptococci. (mitis group) has been shown to bind avidly to hyphae via direct cell-to-cell interaction, while the cariogenic pathogen (mutans group) interacts with the fungal cells via extracellular glucans. However, the biophysical properties of these cross-kingdom interactions at the single-cell level during the early stage of biofilm formation remain understudied. Here, we examined the binding forces between (or ) and in the presence and absence of in situ glucans on the fungal surface using single-cell atomic force microscopy and their influence on biofilm initiation and subsequent development under cariogenic conditions. The data show that binding force to the surface is significantly higher than that of to the fungal surface (2-fold). However, binding forces are dramatically enhanced when the cell surface is locally coated with extracellular glucans (6-fold vs. uncoated ), which vastly exceeds the forces between and. The enhanced binding affinity of to glucan-coated resulted in a larger structure during early biofilm initiation compared to biofilms. Ultimately, this resulted in dominance composition in the 3-species biofilm model under cariogenic conditions. This study provides a novel biophysical aspect of -streptococcal interaction whereby extracellular glucans may selectively favor binding interactions with during cariogenic biofilm development.