Fluoride and zinc on glucans production by S. mutans

Zinc (Zn) and fluoride (F) appear to affect the activity of F-ATPase and maintenance of delta pH across the cell membrane, which could influence the secretion and/or synthesis of glucosyltransferases (GTFs). Objective: We explored the potential actions of Zn and F on glucans production by Streptococcus mutans UA159 growing in suspension cultures and in biofilms. Methods: S. mutans UA159 was grown in ultrafiltered tryptone-yeast extract broth with 1% glucose (in suspension) or 1% sucrose (in biofilms) in the presence or absence (control) of 0.1 mM Zn or F, alone or in combination. For the suspension cultures, the culture supernatant was collected at different growth phases (early-, mid-, and late-exponential) by centrifugation. The culture supernatant (used as a source of GTFs) was mixed with [¹⁴C-glucose]-sucrose for 4h, at 37^oC. The amount of radiolabeled soluble and insoluble glucans was determined by scintillation counting. Biofilms were formed on saliva-coated hydroxyapatite discs in batch cultures for 5 days in the presence of [¹⁴C-glucose]-sucrose. The dry-weight, protein concentration and polysaccharides were determined in the biofilms after the experimental period. Total soluble (SG) and insoluble (IG) glucans, and iodophilic (IPS) polysaccharides were determined by liquid scintillation counting. Results: Zn and F, alone or in combination, clearly affected the synthesis of IG (25-45% reduction), but not SG; the effects were evident at mid-, but especially, at late exponential growth phases. Furthermore, Zn and F significantly reduced the amount of IG in biofilms compared to control (p<0.05); the effects on SG were minimal. Zn and/or F at 0.1 mM exhibited negligible effects on the activity of GTFs. Conclusions: Zinc and fluoride reduced the insoluble glucan synthesis by S. mutans growing either in planktonic or biofilm mode likely due to diminished secretion and/or synthesis of GTFs. Supported by NIDCR Grant 1 R03 DE015441-01.