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APPLIEDANDENVIRONMENTALMICROBIOLOGY,Aug.2010,p.4919–4925Vol.76,No.150099-2240/10/$12.00doi:10.1128/AEM.01015-10Copyright©2010,AmericanSocietyforMicrobiology.AllRightsReserved.MINIREVIEWBiosynthesisandBiodegradationof3-Hydroxypropionate-ContainingPolyestersBjo¨rnAndreeßenandAlexanderSteinbu¨chel*Institutfu¨rMolekulareMikrobiologieundBiotechnologie,Westfa¨lischeWilhelms-Universita¨tMu¨nster,D-48149Mu¨nster,Germany3-Hydroxypropionate(3HP)isanimportantcompoundinthechemicalindustry,andthepolymerized3HPcanbeusedasabioplastic.Inthisreview,wefocusonpolyestersconsistingof3HPmonomers,includingthehomopolyesterpoly(3-hydroxypropionate)andcopolyesterspoly(3-hydroxybutyrate-co-3-hydroxypropionate),poly(3-hydroxypropionate-co-3-hydroxybutyrate-co-3-hydroxyhexanoate-co-3-hydroxyoctanoate),poly(4-hydroxy-butyrate-co-3-hydroxypropionate-co-lactate),andpoly(3-hydroxybutyrate-co-3-hydroxypropionate-co-4-hydroxy-butyrate-co-lactate).Homopolyesterslikepoly(3-hydroxybutyrate)areoftenhighlycrystallineandbrittle,whichlimitssomeoftheirapplications.Theincorporationof3HPmonomersreducestheglasstransitiontemperature,thecrystallinity,andalso,atupto60to70mol%3HP,themeltingpointofthecopolymer.Thisreviewprovidesasurveyofthesynthesisandphysicalpropertiesofdifferentpolyesterscontaining3HP.Bacterialpolyhydroxyalkanoates(PHAs)arenaturalbiode-gradablethermoplasticsproducedbyvariousmicroorganismsasintracellularenergyandcarbonstoragecompounds.PHAshaveattractedincreasedattentionaspossiblealternativestopetroleum-basedpolymers.Theyarebiodegradable,insolubleinwater,nontoxic,biocompatible,piezoelectric,thermoplastic,and/orelastomeric.ThesefeaturesmakePHAssuitableforseveralapplicationsinthepackagingindustry,medicine,pharmacy,agriculture,andfoodindustry,asrawmaterialsfortheproductionofenantiomericallypurechemicals,andfortheproductionofpaints(2,44).ThebestcharacterizedPHAispoly(3-hydroxybutyrate)[poly(3HB)],whichissyn-thesizedbymanybacteria(28,31,38,41).Unfortunately,poly(3HB)isahighlycrystallineandbrittlepolymerwithalowelongation-to-breakfactor,whichhaspreventeditsuseinawiderangeofapplications.ToobtainbacterialPHAswithimprovedphysicalandmechanicalproperties,previousstudieshavedemonstratedthebiosynthesisofcopolyestersconsistingof3-hydroxybutyrate(3HB)andasecondconstituent.PathwaysforthebiosynthesisofsuchPHAcopolyesters,likepoly(3-hydroxybutyrate-co-3-hydroxyvalerate)[poly(3HB-co-3HV)],poly(3-hydroxybutyrate-co-4-hydroxyvalerate)[poly(3HB-co-4HV)],andpoly(3-hydroxybutyrate-co-3-hydroxypropionate)[poly(3HB-co-3HP)],occurnaturallyinmanybacteriaorhavebeenengineered(5,40).Someofthesepolyestersexhibitmaterialcharacteristicscomparabletothoseofpetrochemical-derivedpolymers.How-ever,incontrasttopetrochemical-basedpolymers,PHAsarecompletelybiodegradabletoCO2andwater.Anotheradvan-tageisthattheycanbeproducedfromrenewableresources.Unfortunately,PHAproductionbybacterialfermentationiscostlyand,duetoinefficientutilizationoftheresources,notnecessarilyenvironmentallyconvenientinallcases(13).Anexampleofabacterium-synthesizedcopolymerwhichiscompetitivewithpolymersproducedfrompetrochemicalsinbulkispoly(3HB-co-3HV).Cupriavidusnecator(32),formerlyRalstoniaeutrophaorAlcaligeneseutrophus,accumulatesthisco-polyesterwhenfedwithglucoseandpropionicacidinaphos-phate-depletedbatchculture(30).Thephysicalpropertiesofpoly(3HB-co-3HV)resemblethoseofpolyethyleneandpolypro-pylene(18).Poly(3HB-co-3HV)hasbeencommerciallyproducedthroughfermentationusingaglucose-utilizingmutantofC.ne-catorthatrequirescofeedingofpropionicacidfor3-hydroxyval-erateformation.ThispolymerwassoldbyICI(in1983)underthetradenameBiopol.Ingeneral,themorphologyandseveralphysicalpropertiesofcopolymersstronglydependontheircomonomercompositionandsequencestructure(20).Acomonomerloweringthemeltingtemperature,crystallinity,andfragilityis3-hydroxypropionate(3HP).3HPisanindustriallyrelevantproduct.Theputativeap-plicationsof3HPareenormous.Amongthepossibleusesasamonomerfor(co)polymerization,itcouldbeusedasaprecursorforthesynthesisofothercommerciallyvaluablechemicals,like1,3-propanediol,acrylicacid,oracrylamide(6).3HPisonlyproducedasahomopolymerfromanunrelatedcarbonsourcebymetabolicengineeringinrecombinantEsch-erichiacoli(3);alternatively,itischemicallysynthesizedviaring-openingpolymerizationof-propiolactone(4,15,49).Inthispaper,wereviewthesynthesisandphysicalpropertiesof3HP-containingcopolymersandthepreparationofthe3HPunits(Fig.1).CHEMICALSYNTHESISOFPOLY(3-HYDROXYPROPIONATE)Forthesynthesisof3HP-containingpolyesters,a3HPsup-plyisrequired.Thereareseveralchemicalapproachestopro-vide3HPforcopolymersynthesis(45).*Correspondingauthor.Mailingaddress:Institutfu¨rMolekulareMikrobiologieundBiotechnologie,Westfa¨lischeWilhelms-Universita¨tMu¨nster,Corrensstraße3,D-48149Mu¨nster,Germany.Phone:49-251-8339821.Fax:49-251-8338388.E-mail:steinbu@uni-muenster.de.Publishedaheadofprinton11June2010.4919Polymerizationof-propiolactoneisawell-knownmethodforthepreparationofpoly(3HP).Greshametal.(15)observedthepolymerizationof-propiolactonebyheating(150°C)