title: Identification and functional analysis of the L-ascorbate-specific enzyme II complex of the phosphotransferase system in Streptococcus mutans.
abstract: BACKGROUND
  Streptococcus mutans is the primary etiological agent of human dental caries. It can metabolize a wide variety of carbohydrates and produce large amounts of organic acids that cause enamel demineralization. Phosphoenolpyruvate-dependent sugar phosphotransferase system (PTS) plays an important role in carbohydrates uptake of S. mutans. The ptxA and ptxB genes in S. mutans encode putative enzyme IIA and enzyme IIB of the L-ascorbate-specific PTS. The aim of this study was to analyze the function of these proteins and understand the transcriptional regulatory mechanism.
  
  
  RESULTS
  ptxA (-), ptxB (-), as well as ptxA (-) , ptxB (-) double-deletion mutants all had more extended lag phase and lower growth yield than wild-type strain UA159 when grown in the medium using L-ascorbate as the sole carbon source. Acid production and acid killing assays showed that the absence of the ptxA and ptxB genes resulted in a reduction in the capacity for acidogenesis, and all three mutant strains did not survive an acid shock. According to biofilm and extracellular polysaccharides (EPS) formation analysis, all the mutant strains formed much less prolific biofilms with small amounts of EPS than wild-type UA159 when using L-ascorbate as the sole carbon source. Moreover, PCR analysis and quantitative real-time PCR revealed that sgaT, ptxA, ptxB, SMU.273, SMU.274 and SMU.275 appear to be parts of the same operon. The transcription levels of these genes were all elevated in the presence of L-ascorbate, and the expression of ptxA gene decreased significantly once ptxB gene was knockout.
  
  
  CONCLUSIONS
  The ptxA and ptxB genes are involved in the growth, aciduricity, acidogenesis, and formation of biofilms and EPS of S. mutans when L-ascorbate is the sole carbon source. In addition, the expression of ptxA is regulated by ptxB. ptxA, ptxB, and the upstream gene sgaT, the downstream genes SMU.273, SMU.274 and SMU.275 appear to be parts of the same operon, and L-ascorbate is a potential inducer of the operon.
authors.affiliation: Department of Stomatology, Nanfang Hospital and College of Stomatology, Southern Medical University, Guangzhou, Guangdong, China.
authors.forename: Xinyu
authors.initials: X
authors.lastname: Wu
authors.affiliation: Department of Stomatology, Nanfang Hospital and College of Stomatology, Southern Medical University, Guangzhou, Guangdong, China.
authors.forename: Jin
authors.initials: J
authors.lastname: Hou
authors.affiliation: Department of Stomatology, the Second Affiliated Hospital of Shantou University, Shantou, Guangdong, China.
authors.forename: Xiaodan
authors.initials: X
authors.lastname: Chen
authors.affiliation: Department of Stomatology, Nanfang Hospital and College of Stomatology, Southern Medical University, Guangzhou, Guangdong, China.
authors.forename: Xuan
authors.initials: X
authors.lastname: Chen
authors.affiliation: Department of Stomatology, Nanfang Hospital and College of Stomatology, Southern Medical University, Guangzhou, Guangdong, China. zhaowh@smu.edu.cn.
authors.forename: Wanghong
authors.initials: W
authors.lastname: Zhao
mesh_terms: D001205:Ascorbic Acid / Q000378:metabolism*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D018441:Biofilms; D003731:Dental Caries / Q000382:microbiology; D006801:Humans; D009876:Operon; D010770:Phosphotransferases / Q000235:genetics / Q000378:metabolism*; D013295:Streptococcus mutans / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development / Q000502:physiology
chemical_list: D001426:Bacterial Proteins; D010770:Phosphotransferases; D001205:Ascorbic Acid
keywords: Acidogenesis; Aciduricity; Biofilm formation; Extracellular polysaccharides; L-ascorbate; Phosphotransferase system; Streptococcus mutans