Studies with fluoride-sensitive and fluoride-resistant strains of Streptococcus salivarius. I. Inhibition of both intracellular polyglucose synthesis and degradation by fluoride.

Abstract

Sodium fluoride (0.48 mM) completely inhibited intracellular polyglucose synthesis by resting cells of Streptococcus salivarius incubated anaerobically with glucose. Inhibition was complete if fluoride was preincubated with the cells before the addition of the substrate or if added during active synthesis. However, the degradation of the intracellular material in the absence of exogenous glucose continued at an appreciable rate at 15 times this NaF concentration. The degree of fluoride inhibition of both polyglucose degradation and synthesis was increased as the pH of the reaction mixture decreased. The rate and quantity of the intracellular polysaccharide synthesized during subsequent incubations with glucose in the absence of NaF was not reduced significantly by preincubating the cells with NaF up to 2.4 mM. However, both parameters were reduced by prior exposure to 4.8 mM NaF.Fluoride-resistant cells, obtained either by stepwise selection or by ultraviolet-induced mutation, synthesized polyglucose in the presence of 2.4 mM NaF at rates and amounts only slightly less than those of control cells incubated in buffer free of this inhibitor. Furthermore, the ability of resistant cells to synthesize polyglucose in the presence of high NaF levels was retained despite growth for 300 generations in medium free of sodium fluoride. The ultraviolet-induced strains synthesized polyglucose at greater rates and amounts than the stepwise selected cells, suggesting that they differ in the nature of their resistance.