Fluoride accumulation by a strain of human oral Streptococcus sanguis

Abstract

Cells of Streptococcus sanguis strain H7PR3 accumulated fluoride when incubated with sodium fluoride at pH 5.5. In media containing 1 ppm of added F − (5 × 10 −5 M NaF) the intracellular concentration of the anion at equilibrium was about 6 ppm. Incubation of the cells in the presence of iodoacetamide, or in the absence of added glucose, or at different temperatures between 22–37 °C, had very little effect on the amount of fluoride taken up by the cells so that the accumulation system appeared to be independent of energy-producing metabolic processes. Part of the fluoride taken up by the cells was irreversibly bound and maximum binding was observed at 1 ppm of added fluoride. The apparent affinity constant for the system was 0.3 ppm (1.5 × 10 −5 M). Fluoride was shown to bind to cytoplasmic components within the cells. A second fraction, the loosely bound fluoride, was concentrated two-fold within the cells and could be removed from the cells by washing with buffer. Uptake and binding were observed also at pH 7.0. Accumulative processes such as these probably contribute to the reported uptake of fluoride by dental plaque, and may be important in determining the metabolic susceptibilities of oral microorganisms to the anion.