Inactivation of the Streptococcus mutans fxpC gene confers resistance to xylitol, a caries-preventive natural carbohydrate sweetener.
Xylitol is transported by Streptococcus mutans via a constitutive phosphoenolpyruvate:fructose phosphotransferase system (PTS) composed of a IIABC protein. Spontaneous xylitol-resistant strains are depleted in constitutive fructose-PTS activity, exhibit additional phenotypes, and are associated with the caries-preventive properties of xylitol. Polymerase chain-reactions and chromosome walking were used to clone the fxp operon that codes for the constitutive fructose/xylitol-PTS. The operon contained three open reading frames: fxpA, which coded for a putative regulatory protein of the deoxyribose repressor (DeoR) family, fxpB, which coded for a 1-phosphofructokinase, and fxpC, which coded for a IIABC protein of the fructose-PTS family. Northern blot analysis revealed that these genes were co-transcribed into a 4.4-kb mRNA even in the absence of fructose. Inactivation of the fxpC gene conferred resistance to xylitol, confirming its function. The fxp operon is also present in the genomes of other xylitol-sensitive streptococci, which could explain their sensitivity to xylitol.
Benchabane
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Groupe de Recherche en Ecologie Buccale, Département de Biochimie et Microbiologie (Sciences) and Faculté de Médecine Dentaire, Université Laval, Quebec City, Quebec, Canada, G1K 7P4.
Lortie
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LA
Buckley
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Trahan
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Frenette
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D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics / Q000502:physiology*; D001483:Base Sequence; D016386:Chromosome Walking; D024881:Drug Resistance, Bacterial / Q000235:genetics*; D036781:Fimbriae Proteins; D020868:Gene Silencing; D005798:Genes, Bacterial; D008565:Membrane Proteins / Q000235:genetics / Q000502:physiology*; D008969:Molecular Sequence Data; D009876:Operon / Q000502:physiology; D010731:Phosphoenolpyruvate Sugar Phosphotransferase System / Q000235:genetics*; D016133:Polymerase Chain Reaction; D013295:Streptococcus mutans / Q000201:enzymology* / Q000235:genetics*; D014158:Transcription, Genetic; D014169:Transformation, Bacterial; D014993:Xylitol / Q000494:pharmacology*
D001426:Bacterial Proteins; D008565:Membrane Proteins; D036781:Fimbriae Proteins; D010731:Phosphoenolpyruvate Sugar Phosphotransferase System; D014993:Xylitol