Magnesium-Dependent Promotion of H₂O₂ Production Increases Ecological Competitiveness of Oral Commensal Streptococci

Abstract

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 <i>Streptococcus mutans</i> 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 <i>spxB</i> transcription and SpxB abundance in <i>Streptococcus sanguinis</i> and <i>Streptococcus gordonii</i>. The competitiveness of low-passage commensal streptococcal clinical isolates is positively influenced in antagonism assays against <i>S. mutans</i>. In growth conditions normally selective for <i>S. mutans</i>, Mg²⁺ supplementation is able to increase the abundance of <i>S. sanguinis</i> in dual-species biofilms. Using an in vivo biophotonic imaging platform, we further demonstrate that dietary Mg²⁺ supplementation significantly improves <i>S. gordonii</i> 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.