Extracellular Phosphate Modulation and Polyphosphate Accumulation by Corynebacterium matruchotii and Streptococcus mutans

(1) Background: An alternative and understudied microbial mechanism that may influence demineralization is the microbially mediated ion exchange of Ca²⁺ and orthophosphate (P_i), which alters the saturation state of the mineral species within the surface enamel. There is a need to examine the ability of members of the oral microbiome to modulate Ca²⁺ and P_i, which control mineral solubility, in order to effectively evaluate mineralization therapies to improve oral health. (2) Methods: P_i uptake was measured using an ascorbic acid assay during a BHI liquid culture growth of Corynebacterium matruchotii and Streptococcus mutans for up to 20 h. The initial and endpoint medium Ca²⁺ levels were measured using ICP-OES. Bacterial cells were examined at different growth stages using DAPI/polyP binding emission at 525 nm to detect the presence of internalized macromolecules of polyphosphates (polyP) that could drive P_i uptake. (3) Results: C. matruchotii (p = 0.0061) substantially accumulated P_i (3.84 mmol/L), with a concomitant formation of polyP. In contrast, S. mutans did not take up P_i or accumulate polyP. No significant Ca²⁺ drawdown in the media was observed in either strain. (4) Conclusions: This study suggests that when examining the future efficacy of prevention technologies to improve, in vitro assays may consider including specific oral bacteria capable of substantial P_i uptake.