Role of opuB in Modulating Membrane Vesicle Composition and Function in Streptococcus mutans Under Neutral and Acidic Conditions.

Streptococcus mutans (S. mutans) plays an important role in dental caries through acid production and biofilm formation. The membrane vesicles (MVs) of S. mutans are essential for microbial physiology, biofilm activity, and acid adaptation. The OpuB transporter regulates osmotic pressure in Bacillus subtilis; however, its role in S. mutans and its MVs remains unexplored. This study investigated the effects of the opuB pathway on MV biogenesis, as well as the proteomic and lipidomic profiles under neutral (pH 7.5) and acidic (pH 5.5) conditions. Nanoflow cytometry showed that the opuB-deficient strain (Smu_opuB) produced significantly more and smaller MVs than UA159 at pH 7.5, while the difference was not significant at pH 5.5. Lipidomic analysis revealed that opuB affected the lipid composition and concentration of S. mutans MVs. Proteomic analysis identified the differential enrichment of key metabolic processes associated with stress, including DNA repair. These findings highlight that opuB is an important regulator of MV biosynthesis and composition and may affect the environmental adaptability of S. mutans by regulating MVs.