Role of sucrose-dependent exopolysaccharides in the biofilm development of <i>Streptococcus mutans</i> revealed at the microscale level

<i>Streptococcus mutans</i> is a major pathogen in caries development due to its ability to rapidly metabolize sucrose into EPS. EPS serves as a major component of the <i>S. mutans</i> biofilm matrix, and previous studies mostly explored the effects of EPS on the macroscale. However, how EPS shapes <i>S. mutans</i> biofilm formation at the microscale is not well understood. By combining single-cell tracking with fluorescence staining techniques, we demonstrate that sucrose-dependent EPS governs the transition from 2D growth to 3D biofilm architecture and facilitates the formation of a liquid region at the bottom of the biofilm. These findings bridge a fundamental knowledge gap between the microscale organization and macroscale attributes of biofilms, offering novel perspectives for developing targeted anti-caries strategies.