A Highly Arginolytic Streptococcus Species That Potently Antagonizes Streptococcus mutans

The ability of certain oral biofilm bacteria to moderate pH through arginine metabolism by the arginine deiminase system (ADS) is a deterrent to the development of dental caries. Here, we characterize a novelStreptococcus strain, designated strain A12, isolated from supragingival dental plaque of a caries-free individual. A12 not only expressed the ADS pathway at high levels under a variety of conditions but also effectively inhibited growth and two intercellular signaling pathways of the dental caries pathogenStreptococcus mutans . A12 produced copious amounts of H2 O2 via the pyruvate oxidase enzyme that were sufficient to arrest the growth ofS. mutans . A12 also produced a protease similar to challisin (Sgc) ofStreptococcus gordonii that was able to block the competence-stimulating peptide (CSP)–ComDE signaling system, which is essential for bacteriocin production byS. mutans . Wild-type A12, but not ansgc mutant derivative, could protect the sensitive indicator strainStreptococcus sanguinis SK150 from killing by the bacteriocins ofS. mutans . A12, but notS. gordonii , could also block the XIP (comX -i nducingp eptide) signaling pathway, which is the proximal regulator of genetic competence inS. mutans , but Sgc was not required for this activity. The complete genome sequence of A12 was determined, and phylogenomic analyses compared A12 to streptococcal reference genomes. A12 was most similar toStreptococcus australis andStreptococcus parasanguinis but sufficiently different that it may represent a new species. A12-like organisms may play crucial roles in the promotion of stable, health-associated oral biofilm communities by moderating plaque pH and interfering with the growth and virulence of caries pathogens.