ABSTRACTl-Arginine, a ubiquitous amino acid in human saliva, serves as a substrate for alkali production by arginolytic bacteria. Recently, exogenousl-arginine has been shown to enhance the alkalinogenic potential of oral biofilm and destabilize its microbial community, which might help control dental caries. However,l-arginine exposure may inflict additional changes in the biofilm milieu when bacteria are growing under cariogenic conditions. Here, we investigated how exogenousl-arginine modulates biofilm development using a mixed-species model containing both cariogenic (Streptococcus mutans) and arginolytic (Streptococcus gordonii) bacteria in the presence of sucrose. We observed that 1.5% (wt/vol)l-arginine (also a clinically effective concentration) exposure suppressed the outgrowth ofS. mutans, favoredS. gordoniidominance, and maintainedActinomyces naeslundiigrowth within biofilms (versus vehicle control). In parallel, topicall-arginine treatments substantially reduced the amounts of insoluble exopolysaccharides (EPS) by >3-fold, which significantly altered the three-dimensional (3D) architecture of the biofilm. Intriguingly,l-arginine repressedS. mutansgenes associated with insoluble EPS (gtfB) and bacteriocin (SMU.150) production, whilespxBexpression (H2O2production) byS. gordoniiincreased sharply during biofilm development, which resulted in higher H2O2levels in arginine-treated biofilms. These modifications resulted in a markedly defective EPS matrix and areas devoid of any bacterial clusters (microcolonies) on the apatitic surface, while thein situpH values at the biofilm-apatite interface were nearly one unit higher in arginine-treated biofilms (versus the vehicle control). Our data reveal new biological properties ofl-arginine that impact biofilm matrix assembly and the dynamic microbial interactions associated with pathogenic biofilm development, indicating the multiaction potency of this promising biofilm disruptor.IMPORTANCEDental caries is one of the most prevalent and costly infectious diseases worldwide, caused by a biofilm formed on tooth surfaces. Novel strategies that compromise the ability of virulent species to assemble and maintain pathogenic biofilms could be an effective alternative to conventional antimicrobials that indiscriminately kill other oral species, including commensal bacteria.l-Arginine at 1.5% has been shown to be clinically effective in modulating cariogenic biofilms via alkali production by arginolytic bacteria. Using a mixed-species ecological model, we show new mechanisms by whichl-arginine disrupts the process of biofilm matrix assembly and the dynamic microbial interactions that are associated with cariogenic biofilm development, without impacting the bacterial viability. These results may aid in the development of enhanced methods to control biofilms usingl-arginine.
Coordination of fungal biofilm development by extracellular vesicle cargo
