Although a number of studies have described transcriptional responses of S. mutans under various conditions [11–15], the molecular Pictilisib concentration response of this bacterium under physiologically relevant hyperosmotic condition has not been profiled at transcriptomic level. In this study, we used microarray to profile the transcriptome of S. mutans under hyperosmotic conditions. Several genes and pathways were identified and further correlated with phenotypic
changes of the organism observed under hyperosmotic challenges. The aim of this work is to provide a comprehensive insight into the sophisticated machineries adopted by S. mutans to better fit the physiologically relevant elevated osmolality, and thus perseveres within the oral cavity. Results and discussion Hyperosmotic conditions initiate biofilm dispersal By constructing
the growth curve of S. mutans under increasing concentrations of NaCl, we found that 0.4 M of NaCl provided the sub-inhibitory level of osmolality that slightly retarded the growth rate of S. mutans (Figure 1A). We thus chose this concentration of NaCl for the rest of study. We investigated the short-term and long-term effects of 0.4 M of NaCl on the biofilm configuration of S. mutans. Hyperosmotic conditions LY2874455 in vitro significantly inhibited the biomass of S. mutans biofilm, and this inhibitory effect was time and concentration-dependent (Figure 1B and C). In addition, we performed live/dead fluorescence stain of biofilm and enumerated the biofilm colony forming unit (CFU), and we found that either the percentage or absolute number of viable cells after exposure to 0.4 M NaCl was comparable to that of non-treated control (Figure 1D and E). Tideglusib These data indicate that the observed biomass reduction after hyperosmotic exposure was less likely caused by growth inhibition, but more likely attributed to the dispersal of biofilm under adversary conditions. The osmolality-provoked biofilm dispersal was
further confirmed with fluorescence double-labeling and scanning electronic microscopy (Figure 2). Exposure to sub-inhibitory level of hyperosmotic stimuli not only inhibited cellular components within the biofilm, but also reduced the extracellular polysaccharides (EPS) matrix synthesized. Figure 1 Effect of osmotic stress on S. mutans GSK126 concentration planktonic and biofilm cells. (A) 0.4 M was the sub-inhibitory sodium chloride concentration (the highest concentration without significantly inhibiting the growth of bacteria) for S. mutans growth. (B) Biofilm formation was compromised under hyperosmotic conditions. (C) Short-term sub-inhibitory hyperosmotic stress disintegrated the pre-established biofilm. (D) Representative confocal laser scanning microscopy images (left panel) of live (green)/dead (red) stain of S. mutans biofilm after exposure to 0.