Polyphosphate-accumulating Bacteria: Potential Contributors to Mineral Dissolution in the Oral cavity

Abstract

The role of oral bacteria in the dissolution of dental enamel and dentin that can result in carious lesions has long been solely ascribed to metabolic acid production. However, other microbial processes may also influence tooth dissolution. Recently, bacteria that accumulate polyphosphate in marine sediments have been shown to dynamically influence the solubility of phosphatic minerals. Here we show, using microscopy and genomic databases, that dental plaque and caries lesions, all contain abundant polyphosphate-accumulating bacteria. Using a culture of the model organism, Lactobacillus rhamnosus, a known polyphosphate-accumulating bacteria that is known to inhabit advanced caries lesions, we show that polyphosphate accumulation can lead to undersaturated conditions with respect to hydroxyapatite under some, but not all, oral cavity conditions. Samples of L. rhamnosus grown in various environmental conditions, including exposure to changing oxygenation conditions, input/removal of organics and trace nutrients, were collected over a course of 24 hours and stained with 4',6-diamidino-2-phenylindole (DAPI) to confirm/deny the presence of poly-p in the cells. A comparison of changes in extracellular inorganic phosphate between cultures grown under conditions that result in polyP accumulation vs conditions that did not, was used a a means of measuring the phosphate fluctuation that was likely contributed by intracellular phosphate accumulation. We suggest, through an extrapolation from our model organism results, that polyphosphate-accumulating bacteria, which we observed to be ubiquitous in oral fluids, have a similar influence on the solubility of minerals that comprise the tooth structure. These results suggest that the generation of undersaturated conditions by polyphosphate-accumulating bacteria constitutes a new potential mechanism of tooth dissolution that may augment the effects of metabolic acid production.