Figure 7.

B. subtilis enables S. mutans adherence and biofilm formation due to its proteolytic activity. A suggested mechanism: (a) in the S. mutans mono-species culture, certain receptor molecules on the surface (green) and the bacterial surfaces (yellow) are blocked by the caseins (pale blue). (b) In the dual-species culture, Bacillus spp. cells (purple) can break down casein proteins, particularly κ-casein. The proteolysis decreases the interaction with the receptors and enables S. mutans to adhere to the surface and form a biofilm.