本科毕业设计论文细菌吸附重金属外文翻译.docx

本科毕业设计论文细菌吸附重金属外文翻译.docx

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本科毕业设计论文细菌吸附重金属外文翻译

BacterialSorptionofHeavyMetals

Fourbacteria,Bacilluscereus,B.subtilis,Escherichiacoli,andPseudomonasaeruginosa,wereexaminedfortheabilitytoremoveAg+,Cd2+,Cu2+,andLa3+fromsolutionbybatchequilibrationmethods.CdandCusorptionovertheconcentrationrange0.001to1mMwasdescribedbyFreundlichisotherms.At1mMconcentrationsofbothCd2+andCu2+,P.aeruginosaandB.cereuswerethemostandleastefficientatmetalremoval,respectively.FreundlichKconstantsindicatedthatE.coliwasmostefficientatCd2+removalandB.subtilisremovedthemostCu2+.RemovalofAg+fromsolutionbybacteriawasveryefficient;anaverageof89%ofthetotalAg+wasremovedfromthe1mMsolution,whileonly12,29,and27%ofthetotalCd2+,Cu2+,andLa3+,respectively,weresorbedfrom1mMsolutions.ElectronmicroscopyindicatedthatLa3+accumulatedatthecellsurfaceasneedlelike,crystallineprecipitates.Silverprecipitatedasdiscretecolloidalaggregatesatthecellsurfaceandoccasionallyinthecytoplasm.NeitherCd2+norCu2+providedenoughelectronscatteringtoidentifythelocationofsorption.TheaffinityseriesforbacterialremovalofthesemetalsdecreasedintheorderAg>La>Cu>Cd.Theresultsindicatethatbacterialcellsarecapableofbindinglargequantitiesofdifferentmetals.Adsorptionequationsmaybeusefulfordescribingbacterium-metalinteractionswithmetalssuchasCdandCu;however,thisapproachmaynotbeadequatewhenprecipitationofmetalsoccurs.

Thefateoftoxicmetalliccationsinthesoilenvironmentdependslargelyontheinteractionsofthesemetalswithinorganicandorganicsurfaces.Theextenttowhichametalliccationinteractswiththesesurfacesdeterminestheconcentrationofmetalinsolutionand,consequently,thepotentialformovementintogroundwateroruptakebyplants.Aconsiderableamountofworkhasbeendonetoevaluatetheadsorptionorcomplexationofvariousheavymetalsbysoilsandsoilconstituents,suchasclaysandorganicmatterfractions.Onepotentiallyimportantorganicsurfacewhichhasreceivedlittleattentionisthatofthesoilmicrobialpopulation.Soilmicroorganismsaretypicallyassociatedwiththeclayandorganicfractionsofthesoilmicroenvironmentsandwouldbeexpectedtoparticipateinthemetaldynamicstypicallyascribedtothesefractions.Bacteriahaveahighsurfacearea-to-volumeratioand,asastrictlyphysicalcellularinterface,shouldhaveahighcapacityforsorbingmetalsfromsolution.Thereisevidencethatbacterialcellsaremoreefficientatmetalremovalthanclaymineralsonadry-weightbasis.Kurekandco-workersobservedthatsorptionofCd2+bydeadcellsofaParacoccussp.andSerratiamarcescenswasgreaterthanthatofmontmorillonitewhenthesolid-to-solutionratiowasthesameforbothbacteriaandclay.LivecellsaccumulatedaboutthesamequantityofCd2+asdidclay.

Severalinvestigationshaveshownthatrelativelylargequantitiesofmetalliccationsarecomplexedbyalgae,bacteria,andfungi.Metalbindingbyisolatedgram-positiveandgram-negativebacterialcellwallshasalsobeenevaluated.Cellwallsofthegram-positivebacteriaBacillussubtilisandB.licheniformiswereobservedtobindlargerquantitiesofseveralmetalsthancellenvelopesofthegram-negativebacteriumEscherichiacoli.

Weareinterestedintheroleofmicroorganismsinthebehaviorofvariousheavymetalsinthesoilenvironment.Theobjectivesofthisworkweretodeterminethemetal-bindingcapacitiesofwholecellsoftwogram-positiveandtwogram-negativebacteriaandtodeterminewhetheranequilibriummodel,theFreundlichadsorptionisotherm,wouldadequatelydescribebacterialmetalsorption.B.cereus,B.subtilis,andPseudomonasaeruginosawereexaminedasrepresentativesofcommonspeciesfrequentlyisolatedfromsoils.E.coliwasalsousedasasecondgram-negativebacteriumbecauseitisawell-characterizedmicroorganismanditscellenvelopehasbeenshowntobindlessmetalthandoB.subtiliscellwalls.ThefourmetallicionsusedinthisinvestigationwereAg+,Cd2+,Cu2+,andLa3+.Cadmiumandcopperarebothtoxiccationsofenvironmentalimportance.Silverandlanthanum,representativeofmonovalentandtrivalentheavymetals,respectively,arealsotoxicbutarelessfrequentlyfoundintheenvironment.

MATERIALSANDMETHODS

Bacteriaandgrowthconditions.ThebacteriausedintheseexperimentswereB.cereusATCC11778;P.aeruginosaATCC14886,bothobtainedfromtheAmericanTypeCultureCollection;B.subtilis168;andE.coliK-12strainAB264,bothfromtheUniversityofGuelph.Thebacteriawereroutinelyculturedin0.5xbrainheartinfusionbroth（BBLMicrobiology.Systems）am.ended.with.2.4g.of.HEPES（N-2-hydroxyethylpiperazine-N'-2-ethanesulfonicacid）liter-1and2.0gofMES（2-N-morpholinoethanes