CrypticStreptococcus mutans5.6-kb plasmids encode a toxinantitoxin system for plasmid stabilization

Journal of Oral Microbiology

关键词: Streptococcus mutans;    Plasmid addiction system;    Toxin--antitoxin cassette;    RelBE;    MazEF;    HicBA;    Regulator of translation;   

DOI  :  

来源: Co-Action Publishing

【 摘 要 】

Background:InallStreptococcusmutansstrains,5–13%carrya5.6-kbplasmid.Despiteitsfrequency,littleisknownaboutitsmediatedfunctionswithmostoftheinformationcomingfromasinglestudyfocussingonplasmidpUA140.Objective:Here,wedescribethesequenceandgeneticorganizationoftwoS.mutans5.6-kbplasmids,pDC09andpNC101.Results:BasedonPicoGreendsDNAquantificationandReal-TimequantitativePCR(RTQ-PCR),theplasmidcopynumberwasfoundtorangebetween10and74,dependingonthestraintested.Incontrasttoliterature,weidentifiedsixinsteadoffiveopenreadingframes(ORFs).WhiletheputativegeneproductsofORF1(asaRep-protein)andORF2(asaMob-protein)couldbeconfirmedasbeingidenticaltothosefrompUA140,thefunctionsofORF3(unknown)andORF4(possiblyAtpEhomologue)couldnotbefurtherrevealed.However,theproductofORF5showedafairlyhighidentity(38–50%)andstructuralsimilarity(58–74%)toRelEofStreptococcuspneumoniae,Streptococcusequi,andStreptococcusdownei.Inaddition,weidentifiedafunctionallycorrespondingORF6encodingaproteinwith61–68%identity(81–86%similarity)totheS.equiandS.downeiantitoxinoftheRelBfamily.RelEandRelBtogetherformaplasmid-encodedtoxin-antitoxin(TA)system,RelBEplas.DespiteitsratherlimitedsequencesimilaritywithchromosomalTAsystemsinS.mutans(RelBEchro,MazEF,HicBA),wefoundsimilartertiarystructuresapplyingI-Tasserproteinpredictionanalysis.Conclusion:TypeII-toxins,astheplasmid-encodedRelE,areRNAendonucleases.DependingontheirmRNAcleavageactivity,theymight1)killeveryplasmid-freeprogeny,therebystabilizingplasmidtransferattheexpenseofthehostand/or2)helpS.mutansenteradormantstateandsurviveunfavourableenvironmentalconditions.Whilstafunctioninplasmidstabilizationhasbeenconfirmed,afunctioninpersistenceundernutritionalstress,testedherebyinducingaminoacidstarvation,couldnotbedemonstratedsofar.Keywords:Streptococcusmutans;plasmidaddictionsystem;toxinantitoxincassette;RelBE;MazEF;HicBA;regulatoroftranslation(Published:15January2013)Citation:JournalofOralMicrobiology2013,5:19729-http://dx.doi.org/10.3402/jom.v5i0.19729

【 授权许可】

Unknown