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Role of VicRKX and GlnR in pH-Dependent Regulation of the Streptococcus salivarius 57.I Urease Operon

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      Abstract

      Dental plaque rich in alkali-producing bacteria is less cariogenic, and thus, urease-producing Streptococcus salivarius has been considered as a therapeutic agent for dental caries control. Being one of the few ureolytic microbes in the oral cavity, S. salivarius strain 57.I promotes its competitiveness by mass-producing urease only at acidic growth pH. Here, we demonstrated that the downregulation of the transcription of the ure operon at neutral pH is controlled by a two-component system, VicRKX, whereas the upregulation at acidic pH is mediated by the global transcription regulator of nitrogen metabolism, GlnR. In the absence of VicR-mediated repression, the α subunit of RNA polymerase gains access to interact with the AT-rich sequence within the operator of VicR, leading to further activation of transcription. The overall regulation provides an advantage for S. salivarius to cope with the fluctuation of environmental pH, allowing it to persist in the mouth successfully.

      ABSTRACT

      Ureolysis by Streptococcus salivarius is critical for pH homeostasis of dental plaque and prevention of dental caries. The expression of S. salivarius urease is induced by acidic pH and carbohydrate excess. The differential expression is mainly controlled at the transcriptional level from the promoter 5′ to ureI (pureI). Our previous study demonstrates that CodY represses pureI by binding to a CodY box 5′ to pureI, and the repression is more pronounced in cells grown at pH 7 than in cells grown at pH 5.5. Recent sequence analysis revealed a putative VicR consensus and two GlnR boxes 5′ to the CodY box. The results of DNA affinity precipitation assay, electrophoretic mobility shift assay, and chromatin immunoprecipitation-PCR analysis confirmed that both GlnR and VicR interact with the predicted binding sites in pureI. Isogenic mutant strains (vicRKX null and glnR null) and their derivatives (harboring S. salivarius vicRKX and glnR, respectively) were generated in a recombinant Streptococcus gordonii strain harboring a pureI-chloramphenicol acetyltransferase gene fusion on gtfG to investigate the regulation of VicR and GlnR. The results indicated that GlnR activates, whereas VicR represses, pureI expression. The repression by VicR is more pronounced at pH 7, whereas GlnR is more active at pH 5.5. Furthermore, the VicR box acts as an upstream element to enhance pureI expression in the absence of the cognate regulator. The overall regulation by CodY, VicR, and GlnR in response to pH ensures an optimal expression of urease in S. salivarius when the enzyme is most needed.IMPORTANCE Dental plaque rich in alkali-producing bacteria is less cariogenic, and thus, urease-producing Streptococcus salivarius has been considered as a therapeutic agent for dental caries control. Being one of the few ureolytic microbes in the oral cavity, S. salivarius strain 57.I promotes its competitiveness by mass-producing urease only at acidic growth pH. Here, we demonstrated that the downregulation of the transcription of the ure operon at neutral pH is controlled by a two-component system, VicRKX, whereas the upregulation at acidic pH is mediated by the global transcription regulator of nitrogen metabolism, GlnR. In the absence of VicR-mediated repression, the α subunit of RNA polymerase gains access to interact with the AT-rich sequence within the operator of VicR, leading to further activation of transcription. The overall regulation provides an advantage for S. salivarius to cope with the fluctuation of environmental pH, allowing it to persist in the mouth successfully.

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      Most cited references 47

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      A rapid and sensitive method for the quantitation of microgram quantities of protein utilizing the principle of protein-dye binding

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        Genome sequence of Streptococcus mutans UA159, a cariogenic dental pathogen.

        Streptococcus mutans is the leading cause of dental caries (tooth decay) worldwide and is considered to be the most cariogenic of all of the oral streptococci. The genome of S. mutans UA159, a serotype c strain, has been completely sequenced and is composed of 2,030,936 base pairs. It contains 1,963 ORFs, 63% of which have been assigned putative functions. The genome analysis provides further insight into how S. mutans has adapted to surviving the oral environment through resource acquisition, defense against host factors, and use of gene products that maintain its niche against microbial competitors. S. mutans metabolizes a wide variety of carbohydrates via nonoxidative pathways, and all of these pathways have been identified, along with the associated transport systems whose genes account for almost 15% of the genome. Virulence genes associated with extracellular adherent glucan production, adhesins, acid tolerance, proteases, and putative hemolysins have been identified. Strain UA159 is naturally competent and contains all of the genes essential for competence and quorum sensing. Mobile genetic elements in the form of IS elements and transposons are prominent in the genome and include a previously uncharacterized conjugative transposon and a composite transposon containing genes for the synthesis of antibiotics of the gramicidin/bacitracin family; however, no bacteriophage genomes are present.
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          Molecular biology of microbial ureases.

          Urease (urea amidohydrolase; EC 3.5.1.5) catalyzes the hydrolysis of urea to yield ammonia and carbamate. The latter compound spontaneously decomposes to yield another molecule of ammonia and carbonic acid. The urease phenotype is widely distributed across the bacterial kingdom, and the gene clusters encoding this enzyme have been cloned from numerous bacterial species. The complete nucleotide sequence, ranging from 5.15 to 6.45 kb, has been determined for five species including Bacillus sp. strain TB-90, Klebsiella aerogenes, Proteus mirabilis, Helicobacter pylori, and Yersinia enterocolitica. Sequences for selected genes have been determined for at least 10 other bacterial species and the jack bean enzyme. Urease synthesis can be nitrogen regulated, urea inducible, or constitutive. The crystal structure of the K. aerogenes enzyme has been determined. When combined with chemical modification studies, biophysical and spectroscopic analyses, site-directed mutagenesis results, and kinetic inhibition experiments, the structure provides important insight into the mechanism of catalysis. Synthesis of active enzyme requires incorporation of both carbon dioxide and nickel ions into the protein. Accessory genes have been shown to be required for activation of urease apoprotein, and roles for the accessory proteins in metallocenter assembly have been proposed. Urease is central to the virulence of P. mirabilis and H. pylori. Urea hydrolysis by P. mirabilis in the urinary tract leads directly to urolithiasis (stone formation) and contributes to the development of acute pyelonephritis. The urease of H. pylori is necessary for colonization of the gastric mucosa in experimental animal models of gastritis and serves as the major antigen and diagnostic marker for gastritis and peptic ulcer disease in humans. In addition, the urease of Y. enterocolitica has been implicated as an arthritogenic factor in the development of infection-induced reactive arthritis. The significant progress in our understanding of the molecular biology of microbial ureases is reviewed.
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            Author and article information

            Affiliations
            [a ]Department of Microbiology and Immunology and Research Center for Pathogenic Bacteria, College of Medicine, Chang Gung University, Taoyuan, Taiwan
            [b ]Graduate Institute of Biomedical Sciences, College of Medicine, Chang Gung University, Taoyuan, Taiwan
            [c ]Molecular Infectious Disease Research Center, Chang Gung Memorial Hospital, Taoyuan, Taiwan
            University of Kentucky
            Author notes
            Address correspondence to Yi-Ywan M. Chen, mchen@ 123456mail.cgu.edu.tw .

            Citation Huang S-C, Chen Y-YM. 2016. Role of VicRKX and GlnR in the pH-dependent regulation of the Streptococcus salivarius 57.I urease operon. mSphere 1(3):e00033-16. doi: 10.1128/mSphere.00033-16.

            Contributors
            Role: Editor
            Journal
            mSphere
            mSphere
            msph
            msph
            mSphere
            mSphere
            American Society for Microbiology (1752 N St., N.W., Washington, DC )
            2379-5042
            18 May 2016
            May-Jun 2016
            : 1
            : 3
            27303745
            4888889
            mSphere00033-16
            10.1128/mSphere.00033-16
            (Editor)
            Copyright © 2016 Huang and Chen.

            This is an open-access article distributed under the terms of the Creative Commons Attribution 4.0 International license.

            Counts
            Figures: 7, Tables: 2, Equations: 0, References: 47, Pages: 14, Words: 8635
            Product
            Funding
            Funded by: Chang Gung Memorial Hospital, Linkou (Linkou Chang Gung Memorial Hospital) http://dx.doi.org/10.13039/501100005795
            Award ID: CMRPD 1D0051-0053
            Award Recipient : Yi-Ywan Margaret Chen
            Categories
            Research Article
            Molecular Biology and Physiology
            Custom metadata
            May/June 2016

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