ABSTRACTThe dental caries pathogenStreptococcus mutanscan ferment a variety of sugars to produce organic acids. Exposure ofS. mutansto certain nonmetabolizable carbohydrates, such as xylitol, impairs growth and can cause cell death. Recently, the presence of a sugar-phosphate stress inS. mutanswas demonstrated using a mutant lacking 1-phosphofructokinase (FruK) that accumulates fructose-1-phosphate (F-1-P). Here, we studied an operon inS. mutans,sppRA, which was highly expressed in thefruKmutant. Biochemical characterization of a recombinant SppA protein indicated that it possessed hexose-phosphate phosphohydrolase activity, with preferences for F-1-P and, to a lesser degree, fructose-6-phosphate (F-6-P). SppA activity was stimulated by Mg2+and Mn2+but inhibited by NaF. SppR, a DeoR family regulator, repressed the expression of thesppRAoperon to minimum levels in the absence of the fructose-derived metabolite F-1-P and likely also F-6-P. The accumulation of F-1-P, as a result of growth on fructose, not only inducedsppAexpression, but it significantly altered biofilm maturation through increased cell lysis and enhanced extracellular DNA release. Constitutive expression ofsppA, via a plasmid or by deletingsppR, greatly alleviated fructose-induced stress in afruKmutant, enhanced resistance to xylitol, and reversed the effects of fructose on biofilm formation. Finally, by identifying three additional putative phosphatases that are capable of promoting sugar-phosphate tolerance, we show thatS. mutansis capable of mounting a sugar-phosphate stress response by modulating the levels of certain glycolytic intermediates, functions that are interconnected with the ability of the organism to manifest key virulence behaviors.IMPORTANCEStreptococcus mutansis a major etiologic agent for dental caries, primarily due to its ability to form biofilms on the tooth surface and to convert carbohydrates into organic acids. We have discovered a two-gene operon inS. mutansthat regulates fructose metabolism by controlling the levels of fructose-1-phosphate, a potential signaling compound that affects bacterial behaviors. With fructose becoming increasingly common and abundant in the human diet, we reveal the ways that fructose may alter bacterial development, stress tolerance, and microbial ecology in the oral cavity to promote oral diseases.
Identification of Lead Compounds Targeting the Cathepsin B-Like Enzyme of Eimeria tenella