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10.1128/AEM.70.9.5373-5382.2004.2004,70(9):5373.DOI:Appl.Environ.Microbiol. VerhaegeandWillyVerstraeteKorneelRabaey,NicoBoon,StevenD.Siciliano,Marc ThatSelf-MediateElectronTransferBiofuelCellsSelectforMicrobialConsortia:Theseinclude:REFERENCES:Thisarticlecites36articles,10ofwhichcanbeaccessedfreeCONTENTALERTSmore»articlescitethisarticle),Receive:RSSFeeds,eTOCs,freeemailalerts(whennew::onMay1,2014byTONGJIUNIVERSITY://aem.asm.org/DownloadedfromAPPLIEDANDENVIRONMENTALMICROBIOLOGY,Sept.2004,p.5373–5382Vol.70,No.90099-2240/04/$08.000DOI:10.1128/AEM.70.9.5373–5382.2004Copyright©2004,AmericanSocietyforMicrobiology.AllRightsReserved.BiofuelCellsSelectforMicrobialConsortiaThatSelf-MediateElectronTransferKorneelRabaey,1NicoBoon,1StevenD.Siciliano,2MarcVerhaege,3andWillyVerstraete1*LaboratoryofMicrobialEcologyandTechnology(LabMET),GhentUniversity,Ghent,1andLaboratoryforNon-ferrousMetallurgy,GhentUniversity,Zwijnaarde,3Belgium,andDepartmentofSoilScience,UniversityofSaskatchewan,Saskatoon,Saskatchewan,Canada2Received28November2003/Accepted25April2004Microbialfuelcellsholdgreatpromiseasasustainablebiotechnologicalsolutiontofutureenergyneeds.Currenteffortstoimprovetheefficiencyofsuchfuelcellsarelimitedbythelackofknowledgeaboutthemicrobialecologyofthesesystems.Thepurposesofthisstudywere(i)toelucidatewhetherabacterialcommunity,eithersuspendedorattachedtoanelectrode,canevolveinamicrobialfuelcelltobringabouthigherpoweroutput,and(ii)toidentifyspeciesresponsiblefortheelectricitygeneration.Enrichmentbyrepeatedtransferofabacterialconsortiumharvestedfromtheanodecompartmentofabiofuelcellinwhichglucosewasusedincreasedtheoutputfromaninitiallevelof0.6Wm2ofelectrodesurfacetoamaximallevelof4.31Wm2(664mV,30.9mA)whenplaingraphiteelectrodeswereused.Thisresultwasobtainedwithanaverageloadingrateof1gofglucoseliter1day1andcorrespondedto81%efficiencyforelectrontransferfromglucosetoelectricity.Cyclicvoltammetryindicatedthattheenhancedmicrobialconsortiumhadeithermembrane-boundorexcretedredoxcomponentsthatwerenotinitiallydetectedinthecommunity.Dominantspeciesoftheenhancedculturewereidentifiedbydenaturinggradientgelelectrophoresisandculturing.Thecommunityconsistedmainlyoffacultativeanaerobicbacteria,suchasAlcaligenesfaecalisandEnterococcusgallinarum,whicharecapableofhydrogenproduction.PseudomonasaeruginosaandotherPseudomonasspecieswerealsoisolated.Forseveralisolates,electrochemicalactivitywasmainlyduetoexcretedredoxmediators,andoneofthesemediators,pyocyaninproducedbyP.aeruginosa,couldbecharacterized.Overall,theenrichmentprocedure,irrespectiveofwhetheronlyattachedorsuspendedbacteriawereexamined,selectedfororganismscapableofmediatingtheelectrontransfereitherbydirectbacterialtransferorbyexcretionofredoxcomponents.Biologicalfuelcellsareapotentialgreenenergytechnology.Inamicrobialfuelcellbacteriadonotdirectlytransfertheelectronswhichtheyproducetotheircharacteristicterminalelectronacceptor;instead,theseelectronsaredivertedtowardanelectrode(anode).Theelectronsaresubsequentlycon-ductedoveraresistanceorpowerusertowardacathode,andthus,bacterialenergyisdirectlyconvertedtoelectricalenergy(35).Threemaintypesofbiofuelcellscanbedistinguished:photoautotrophic-typebiofuelcells(38),morecommonhet-erotrophic-typebiofuelcells,(9)andsedimentbiofuelcells(3).Biofuelcellshavesomecharacteristicsthataresimilartothoseoftraditionalpowersources,aswellastothoseofanaerobicreactors.Theycanbedescribedontheonehandbyelectro-chemicalparameters,suchaspowerdensity(inwattspersquaremeterofelectrodesurface),currentoutput,andcellvoltage,andontheotherhandbybiologicalparameters,suchasthenutrientloadingrateandbiological/chemicaloxygendemand(inkilogramspercubicmeterperday)(34).However,incontrasttoanaerobicreactors,weknowrelativelylittleaboutthemicrobialecologyofmicrobialfuelcells(26).Sofar,inmostofthestudiesperformedtheworkersusedwell-definedpurestrains,suchasShewanellaputrefaciens(21,22)orEscherichiacoli(13,30).Recently,twobacteriathatexhibitedhighcoulombicefficiencyaspurecultureshavebeendescribed;thesebacteria,Geobactersulfurreducens(3,4)andRhodoferaxferrireducens(7),arecapableoftransferringthemajorityoftheelectronsgainedfromthecarbonsourcesace-tateandglucose,respectively,totheelectrode.Thesestudiesimpliedthattherewashighcoulombicefficiency,meaningthattherewashighelectrontransferefficiency.However,thisdoesnotimplythattherewashighenergytransferefficiency,whichisdependentontheproductofcurrentandpotential,bothofwhichdeterminetheenergy,expressedinjoules.Inalimitednumberofcases,mixedconsortiaobtainedfromwastewatertreatmentplantshavebeenusedinflowthroughsystems(26).Recently,membersofourgroupdescribedbatchsystemsinwhich,dependingontheorganicload,coul