A mechanism for extremely weak SpaP-expression in Streptococcus mutans strain Z1

摘要

Background:Streptococcusmutanssurface-proteinantigen(SpaP,PAc,orantigenI/II)hasbeenwellknowntoplayanimportantroleininitialattachmenttotoothsurfaces.However,strainswithweakSpaP-expressionwererecentlyreportedtobefoundinnaturalpopulationsofS.mutans.TheS.mutansgbpC-negativestrainZ1,whichwepreviouslyisolatedfromsalivaandplaquesamples,apparentlyexpressesrelativelylowlevelsofSpaPproteincomparedtoS.mutansstrainsMT8148orUA159.Objective:ToelucidatethemechanismforweakSpaP-expressioninthisstrain,thespaPgeneregioninstrainZ1wasamplifiedbypolymerasechainreaction(PCR)andanalyzed.Methods:AllelicexchangemutantsbetweenstrainsZ1andUA159involvingthespaPgeneregionwereconstructed.TheSpaPproteinexpressedinthemutantswasdetectedwithCoomasieBrilliantBlue(CBB)-stainingandWesternblotanalysisfollowingSDS-PAGE.Results:The4689bpspaPgenecodingsequenceforZ1appearedtobeintact.Incontrast,a20bpnucleotidesequenceappearedtobedeletedfromtheregionimmediatelyupstreamfromtheZ1spaPgenewhencomparedtothesameregioninUA159.The216bpand237bpintergenicfragmentsupstreamfromthespaPgene,respectively,fromZ1andUA159wereisolated,modified,andtransformedintotheotherstrainbyallelicreplacement.TheresultantUA159-promoterregion-mutantexhibitedextremelyweakSpaP-expressionsimilartothatofstrainZ1andtheZ1complementedmutantexpressedSpaproteinlevelslikethatofstrainUA159.Conclusion:TheseresultssuggestthatweakSpaP-expressioninstrainZ1resultedfroma20bp-deletioninthespaPgenepromoterregion.Keywords:antigenI/II;viridansstreptococci;glucan-bindingproteins;adhesins;mutantchimericproteins(Published:14April2011)Citation:JournalofOralMicrobiology2011,3:5495-DOI:10.3402/jom.v3i0.5495