Normoxic stress enhance the secretion of adhesion-promoting membrane vesicles by Streptococcus mutans

Background Streptococcus mutans (S. mutans) is the primary pathogen of dental caries and one of the pioneer colonizers of dental plaque biofilms. The normoxic stress experienced by S. mutans during initial adhesion is detrimental to biofilm formation. Membrane vesicles (MVs) can modulate the stress adaptability and biofilm formation of parental bacteria. However, it remains unclear whether normoxic stress influences the secretion, composition and function of MVs.Materials and methods We conducted characterization, omics analysis, and functional validation of MVs secreted by S. mutans under normoxic and hypoxic conditions. Furthermore, we performed a comparative analysis of protein expression profiles between MVs and their parental bacteria under normoxic stress.Results Compared with those of hypoxic MVs, the secretion of normoxic MVs is increased approximately 100-fold, and significantly enrich the adhesion proteins GtfC and SpaP. Normoxic MVs promote the initial adhesion and early biofilm formation of S. mutans through enhancing glucan synthesis, self-aggregation and the surface adhesion force. On the contrary, the magnitude of expression changes of GtfC and SpaP at the transcriptional and cellular levels under normoxic stress are modest.Conclusion Normoxic stress enhances the secretion of adhesion-promoting MVs by S. mutans. The cargo composition of S. mutans MVs may dynamically modulate in response to environmental stresses to facilitate their colonization.