The Sec secretion system enhances GtfB secretion and exopolysaccharide production to promote the formation of Streptococcus mutans persisters induced by cationic antimicrobials

Abstract

Bacterial persistence-caused antibacterial tolerance and recurrent infections are critical for clinical treatments. Streptococcus mutans persisters have been reported to enhance bacterial cariogenicity and tolerance to multi-antimicrobial agents, yet their formation mechanisms remain unclear. Here, we investigated the crucial role of the Sec secretion system in persister formation induced by dimethylamino dodecyl methacrylate (DMADDM) and chlorhexidine. DMADDM treated biofilms significantly increased exopolysaccharide (EPS) production and formed a large amount of persisters, while fewer persisters were formed in less EPS produced medium, indicating the important role of EPS in persistence. Persisters significantly upregulated the expressions of gtfB and the Sec secretion system. The Sec secretion system has been previously proposed to secret GtfB. Therefore, nine key gene-knockout mutants of the Sec secretion system and their complementary strains were constructed, including yidC1, yidC2, secY, secA, secE, secG, yajC, ftsY and ffH, respectively; ΔgtfB was also constructed for EPS defect control. ΔyidC2, ΔsecY, ΔsecA and ΔffH significantly decreased the expression and secretion of GtfB, then reduced the amounts of EPS, indicating that these four components from the Sec secretion system were the key proteins responsible for GtfB secretion. Moreover, all Sec secretion system mutants and ΔgtfB reduced persister formation in DMADDM and chlorhexidine induced biofilms, indicating that the Sec secretion system regulates gtfB expression and EPS production, thereby influencing persister formation. Our findings indicated the key roles of the Sec secretion system in S. mutans persistence and suggested that the Sec secretion system and EPS production were key targets to removing biofilms and overcome bacterial persistence.