BacterialCommunityStructureintheDrinkingWate

BacterialCommunityStructureintheDrinkingWaterMicrobiomeIsGovernedbyFiltrationProcessesAmeetJ.Pinto,†ChuanwuXi,‡andLutgardeRaskin†,*†DepartmentofCivilandEnvironmentalEngineering,UniversityofMichigan‡DepartmentofEnvironmentalHealthSciences,UniversityofMichigan*SSupportingInformationABSTRACT:Thebacterialcommunitystructureofadrinkingwatermicrobiomewascharacterizedoverthreeseasonsusing16SrRNAgenebasedpyrosequencingofsamplesobtainedfromsourcewater(amixofagroundwaterandasurfacewater),differentpointsinadrinkingwaterplantoperatedtotreatthissourcewater,andintheassociateddrinkingwaterdistributionsystem.Eventhoughthesourcewaterwasshowntoseedthedrinkingwatermicrobiome,treatmentprocessoperationslimitthesourcewater’sinfluenceonthedistributionsystembacterialcommunity.Rather,inthisplant,filtrationbydualmediarapidsandfiltersplayedaprimaryroleinshapingthedistributionsystembacterialcommunityoverseasonaltimescalesasthefiltersharboredastablebacterialcommunitythatseededthewatertreatmentprocessespastfiltration.Bacterialtaxathatcolonizedthefilterandsloughedoffinthefiltereffluentwereabletopersistinthedistributionsystemdespitedisinfectionoffinishedwaterbychloraminationandfilterbackwashingwithchloraminatedbackwashwater.Thus,filtercolonizationpresentsapossibleecologicalsurvivalstrategyforbacterialcommunitiesindrinkingwatersystems,whichpresentsanopportunitytocontrolthedrinkingwatermicrobiomebymanipulatingthefiltermicrobialcommunity.GroupingbacterialtaxabasedontheirassociationwiththefilterhelpedtoelucidaterelationshipsbetweentheabundanceofbacterialgroupsandwaterqualityparametersandshowedthatpHwasthestrongestregulatorofthebacterialcommunityinthesampleddrinkingwatersystem.■INTRODUCTIONBacterialcommunitiesindrinkingwatersystems(DWSs)canplayapositiverolethroughbiologicallymediatedchemicalcontaminantremoval;mostcommonlyimplementedinfiltrationsystems,1butcanalsohaveanegativeimpactifDWSsharborpotentialpathogens2,3andbycontributingtoinfrastructuredeteriorationduetobiologicallyinducedcorrosion.4Inanefforttominimizethesenegativeaspects,mostdrinkingwaterutilitiestrytolimitmicrobialgrowthinthedrinkingwatertreatmentplant(DWTP)andthedrinkingwaterdistributionsystem(DWDS).Specifically,mostfiltersaredesignedtoremoveturbidityandbacterialgrowthsubstratestolimitbacterialgrowthdownstreamfromthefilteranddisinfection(e.g.,ozonation,chlorination,chloramination,orUVtreatment)isusedtoinactivatebacteria.Further,adisinfectionresidualismaintainedinmostDWDSstopreventbacterialregrowth.5Despitetheseefforts,allDWSsharboravastdiversityofbacteria6,7andbacterialconcentrationsindrinkingwaterareestimatedtobearound106−108cellsperliter.6,8Asitisnotpossibletoeliminatebacteriafromdrinkingwaterwithcurrenttreatmenttechnologies,itiscriticaltoidentifythedifferenttypesofbacteriaandtheirrelativeabundanceinDWSs,andtodeterminewhichwaterqualityparametersand/ortreatmentprocessesshapethebacterialcommunitystructureinDWSs.PreviousstudieshavedeterminedbacterialabundanceatdifferentpointsinaDWS,6elucidatedseasonalanddiurnalchangesinbacterialcommunitymembershipatmultiplesamplinglocations,8,9andtriedtoidentifysourcesofbacteriaintheDWDS.10Thesestudieshavesoughttoanswerquestionssuchas“whoispresent?”and“howdoescompositionchangebetweensitesorovertime?”.However,theygenerallydidnotevaluatetheroleofwaterqualityorprocessoperationinshapingcommunitystructure.Characterizingthedrinkingwatermicrobiomewithoutidentifyingtheforcesthatinfluenceitisnotonlychallenging,butalsorepresentsalostopportunity.Whilefactorsshapingbacterialcommunitystructureareundeniablysitespecificduetodifferencesinplantconfig-urations,operationalpractices,andwaterquality,developinganapproachthatcanidentifytheforcesthatdeterminethebacterialcommunitystructureprovidesaframeworkthatcanbeReceived:May22,2012Revised:July11,2012Accepted:July15,2012Published:July16,2012Articlepubs.acs.org/est©2012AmericanChemicalSociety8851dx.doi.org/10.1021/es302042t|Environ.Sci.Technol.2012,46,8851−8859appliedtomostDWSs.Toourknowledge,suchanapproachhasnotyetbeendeveloped.Tothisend,weconductedasamplingcampaignfortheAnnArbor,MichiganDWS,includingmultiplesamplelocationsattheDWTPandDWDS.Weusedβ-diversityanalysesbasedon16SrRNAbasedpyrosequencingtocomparebacterialcommunitiesacrosssamplinglocationsandseasonstodetermine(i)whichsource(s)and/orprocess(es)seedandshapethebacterialcommunityintheDWTPandDWDS,and(ii)howwaterqualitycontributestothestructureofbacterialcommunities.■MATERIALSANDMETHODSDrinkingWaterTreatmentPlantandDistributionSystem.TheAnnArborDWTPsupplieswatertotheCityofAnnArbor,Michigan.ThetwosourcewaterstreatedatthisplantconsistofsurfacewaterfromtheHuronRiverandgroundwaterfromlocalwells.Thesurfacewatertoground-waterratiovariesthroughtheyearrangingfromapproximately2:1inthewinterto8:1inthesummer.Treatmentincludeslimesoftening,coagulation,flocculation,sedimentation,ozonation,dualmediafiltration,andadditionoffreechlorineandammoniabeforedistribution(SupportingInformation(SI)FigureS1).TheDWTPhas26dualmediafiltersconsistingofalayerofgranularactivatedcarbon(GAC)onsand(bedheightratiosrangefrom2:1to3:1)s