A Highly Arginolytic Streptococcus Species That Potently Antagonizes Streptococcus mutans

Abstract

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 novel Streptococcus 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 pathogen Streptococcus mutans. A12 produced copious amounts of H 2 O 2 via the pyruvate oxidase enzyme that were sufficient to arrest the growth of S. mutans. A12 also produced a protease similar to challisin (Sgc) of Streptococcus gordonii that was able to block the competence-stimulating peptide (CSP)-ComDE signaling system, which is essential for bacteriocin production by S. mutans. Wild-type A12, but not an sgc mutant derivative, could protect the sensitive indicator strain Streptococcus sanguinis SK150 from killing by the bacteriocins of S. mutans. A12, but not S. gordonii, could also block the XIP (comX-inducing peptide) signaling pathway, which is the proximal regulator of genetic competence in S. 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 to Streptococcus australis and Streptococcus 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. Dental caries remains an enormous health problem worldwide (1-4). The current view of the initiation and progression of dental caries is one of a dynamic process in which the normal balance between the complex environmental factors that control demineralization and remineralization of the tooth is disrupted in a way that favors the loss of tooth mineral. Demineralization is driven primarily by microbial fermentation of carbohydrates to organic acids, which can lower the pH of oral biofilms to the extent that there is significant dissolution of tooth mineral. Alkalization of oral biofilms occurs during fasting periods and is attributable to salivary clearance of acids, buffering of oral biofilms by host-derived and microbially derived components, and the production of basic compounds by microbial metabolism of amino acids, polyamines, urea, and other compounds (5-10). Development or worsening of a carious lesion occurs when acid-mediated enamel demineralization predominates and is associated with changes in the composition and biochemical activities of the associated microflora. Evidence is now accumulating from a variety of sources that supports that alkali generation, particularly in the form of ammonia, plays a major role in pH homeostasis in oral biofilms and inhibits the initiation and progre...

Effects of Arginine on Streptococcus mutans Growth, Virulence Gene Expression, and Stress Tolerance

“…The NlmC/ImmB (CipB/CipI) system constitutes an intracellular bacteriocin (NlmC/CibB) and immunity protein (ImmB/CipI) and, in cells stimulated with high levels of CSP, enhances the release of extracellular DNA (eDNA), which in turn provides structural and functional integrity to biofilms of S. mutans (45). Thus, 1.5% arginine provides an environmental input that interferes with the signal transduction cascade that regulates mutacin gene expression, resulting in less eDNA release and less stable biofilms (12). Perhaps more importantly, the reduction in bacteriocin production may lead to better survival and growth of arginolytic commensal streptococci and other potentially beneficial bacteria that are targeted by mutacins.…”

“…Likewise, oral arginine metabolism via the ADS was positively correlated with dental health in children (6). Several reports also suggested the beneficial role of arginine on the growth and biofilm development of oral commensals (12,(22)(23)(24)(25). Secreted arginine deiminase from S. intermedius significantly diminished the expression of key virulence factors and genes essential for biofilm formation in Porphyromonas gingivalis (26).…”

Biology of Oral Streptococci

“…Most isolates of S. mutans carry the ComDE two-component system, which is required for the activation of transcription of a number of different genes encoding lantibiotic and non-lantibiotic bacteriocins, small peptides that exhibit antimicrobial activity against other species. ComDE depends on a quorum sensing peptide CSP ( c ompetence s timulating p eptide) for activity (105). S. gordonii DL-1 produces a protease, designated as challisin, which is able to degrade CSP and block the activation of bacteriocin gene expression by S. mutans (106).…”

Ecological Approaches to Dental Caries Prevention: Paradigm Shift or Shibboleth?

“…However, very recently 2 natural oral commensal species, Streptococcus dentisani and Streptococcus A12 that were isolated from the supragingival plaque of caries-free individuals, have demonstrated promising probiotic effects against dental caries. Both these "active colonizers" have a double probiotic action, as they can not only inhibit the growth of MS, but also moderate plaque pH through their arginolytic actions [Huang et al, 2016a;López-López et al, 2017].…”