title: Downregulation of GbpB, a component of the VicRK regulon, affects biofilm formation and cell surface characteristics of Streptococcus mutans.
abstract: The virulence of the dental caries pathogen Streptococcus mutans relies in part on the sucrose-dependent synthesis of and interaction with glucan, a major component of the extracellular matrix of tooth biofilms. However, the mechanisms by which secreted and/or cell-associated glucan-binding proteins (Gbps) produced by S. mutans participate in biofilm growth remain to be elucidated. In this study, we further investigate GbpB, an essential immunodominant protein with similarity to murein hydrolases. A conditional knockdown mutant that expressed gbpB antisense RNA under the control of a tetracycline-inducible promoter was constructed in strain UA159 (UACA2) and used to investigate the effects of GbpB depletion on biofilm formation and cell surface-associated characteristics. Additionally, regulation of gbpB by the two-component system VicRK was investigated, and phenotypic analysis of a vicK mutant (UAvicK) was performed. GbpB was directly regulated by VicR, and several phenotypic changes were comparable between UACA2 and UAvicK, although differences between these strains existed. It was established that GbpB depletion impaired initial phases of sucrose-dependent biofilm formation, while exogenous native GbpB partially restored the biofilm phenotype. Several cellular traits were significantly affected by GbpB depletion, including altered cell shape, decreased autolysis, increased cell hydrophobicity, and sensitivity to antibiotics and osmotic and oxidative stresses. These data provide the first experimental evidence for GbpB participation in sucrose-dependent biofilm formation and in cell surface properties.
authors.affiliation: Department of Oral Diagnosis, Piracicaba Dental School, University of Campinas (UNICAMP), Av. Limeira 901, CEP 13414-903 Piracicaba, São Paulo, Brazil.
authors.forename: Cristiane
authors.initials: C
authors.lastname: Duque
authors.forename: Rafael N
authors.initials: RN
authors.lastname: Stipp
authors.forename: Bing
authors.initials: B
authors.lastname: Wang
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Smith
authors.forename: José F
authors.initials: JF
authors.lastname: Höfling
authors.forename: Howard K
authors.initials: HK
authors.lastname: Kuramitsu
authors.forename: Margaret J
authors.initials: MJ
authors.lastname: Duncan
authors.forename: Renata O
authors.initials: RO
authors.lastname: Mattos-Graner
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D018441:Biofilms / Q000254:growth & development*; D015536:Down-Regulation; D015964:Gene Expression Regulation, Bacterial / Q000502:physiology*; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D009154:Mutation; D012329:RNA, Bacterial; D018085:Regulon / Q000502:physiology*; D013295:Streptococcus mutans / Q000187:drug effects / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D013395:Sucrose / Q000494:pharmacology
chemical_list: D001426:Bacterial Proteins; D008565:Membrane Proteins; D012329:RNA, Bacterial; D013395:Sucrose