The pyruvate oxidase (SpxB)-dependent production of H2O2 is widely distributed among oral commensal streptococci. Several studies confirmed the ability of H2O2 to antagonize susceptible oral bacterial species, including caries-associated Streptococcus mutans as well as several periodontal pathobionts. Here we report a potential mechanism to bolster oral commensal streptococcal H2O2 production by magnesium (Mg2+) supplementation. Magnesium is a cofactor for SpxB catalytic activity, and supplementation increases the production of H2O2 in vitro. We demonstrate that Mg2+ affects spxB transcription and SpxB abundance in Streptococcus sanguinis and Streptococcus gordonii. The competitiveness of low-passage commensal streptococcal clinical isolates is positively influenced in antagonism assays against S. mutans. In growth conditions normally selective for S. mutans, Mg2+ supplementation is able to increase the abundance of S. sanguinis in dual-species biofilms. Using an in vivo biophotonic imaging platform, we further demonstrate that dietary Mg2+ supplementation significantly improves S. gordonii oral colonization in mice. In summary, our results support a role for Mg2+ supplementation as a potential prebiotic to promote establishment of oral health-associated commensal streptococci.
Keywords: Streptococcus gordonii; Streptococcus sanguinis; hydrogen peroxide; magnesium; oral biofilm; pyruvate oxidase.