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

<i>Streptococcus mutans</i> (<i>S. mutans</i>) plays an important role in dental caries through acid production and biofilm formation. The membrane vesicles (MVs) of <i>S. mutans</i> are essential for microbial physiology, biofilm activity, and acid adaptation. The OpuB transporter regulates osmotic pressure in <i>Bacillus subtilis</i>; however, its role in <i>S. mutans</i> and its MVs remains unexplored. This study investigated the effects of the <i>opuB</i> 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 <i>opuB</i>-deficient strain (<i>Smu_opuB</i>) 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 <i>opuB</i> affected the lipid composition and concentration of <i>S. mutans</i> MVs. Proteomic analysis identified the differential enrichment of key metabolic processes associated with stress, including DNA repair. These findings highlight that <i>opuB</i> is an important regulator of MV biosynthesis and composition and may affect the environmental adaptability of <i>S. mutans</i> by regulating MVs.