History and current taxonomic status of genus Agrobacterium

ContentslistsavailableatScienceDirect

Systematic

and

Applied

Microbiology

j o ur na l h o me pa g e :h t t p : / / w w w . e l s e v i e r . c o m / l o c a t e / s y a p m

History

and

current

taxonomic

status

of

genus

Agrobacterium

José

David

Flores-Félix

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_Esther

_Menéndez

_,

_Alvaro

_Peix

_,

_Paula

_{García-Fraile}

_,

Encarna

Velázquez

a_{DepartamentodeMicrobiologíayGenéticaandInstitutoHispanolusodeInvestigacionesAgrarias(CIALE),UniversidaddeSalamanca,Salamanca,Spain} b_{InstitutodeRecursosNaturalesyAgrobiología,IRNASA-CSIC,Salamanca,Spain}

c_{UnidadAsociadaGrupodeInteracciónPlanta-Microorganismo(UniversidaddeSalamanca-IRNASA-CSIC),Salamanca,Spain}

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Articlehistory: Received21May2019 Receivedinrevisedform 15November2019 Accepted22November2019 Keywords: Agrobacterium Taxonomy Rhizobium Allorhizobium

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ThegenusAgrobacteriumwascreatedacenturyagobyConnwhoincludeditinthefamilyRhizobiaceae togetherwiththegenusRhizobium.Initially,thegenusAgrobacteriumcontainedthenon-pathogenic species Agrobacteriumradiobacter andthe plantpathogenic species Agrobacteriumtumefaciens and Agrobacteriumrhizogenes.Attheendofthepastcenturytwonewpathogenicspecies,Agrobacterium rubiandAgrobacteriumvitis,wereaddedtothegenus.Alreadyinthepresentcenturythesespeciesplus AgrobacteriumlarrymooreiwerereclassifiedintogenusRhizobium.Thisreclassificationwas controver-sialandforatimebothgenusnameswereusedwhennewspeciesweredescribed.Fewyearsago, afterataxonomicrevisionbasedongenomicdata,theoldspeciesA.rhizogeneswasmaintainedinthe genusRhizobium,theoldspeciesA.vitiswastransferredtothegenusAllorhizobiumandseveral Rhizo-biumspeciesweretransferredtothegenusAgrobacterium,whichcurrentlycontains14speciesincluding theoldspeciesA.radiobacter,A.tumefaciens,A.rubiandA.larrymoorei.Mostofthesespeciesareable toproducetumoursindifferentplants,neverthelessthegenusAgrobacteriumalsoencompasses non-pathogenicspecies,onespeciesabletonodulatelegumesandonehumanpathogenicspecies.Taking intoaccountthatthespeciesaffiliationstofiveAgrobacteriumgenomospecieshavenotbeendetermined yet,anincreaseinthenumberofspecieswithinthisgenusisexpectedinthenearfuture.

©2019PublishedbyElsevierGmbH.

TheAgrobacteriumtaxonomyinthepastcentury

The genus Agrobacterium was created by Conn [9] who includeditwithinthefamily Rhizobiaceae[8]togetherwiththe genus Rhizobium [14]. In the 5th edition of the Bergey’s Man-ualofDeterminativeBacteriology, thespecies includedintothe genus Agrobacterium were Agrobacterium radiobacter, Agrobac-teriumtumefaciensandAgrobacteriumrhizogenes.Inthe6thedition ofthisManualtheplanttumorigenicspeciesAgrobacteriumrubi [17,48]wasincluded,beingdifferentiatedfromA.tumefacienson the basis of the ability to reduce nitrate to nitrite [6]. In the 7theditionofthisManualthespeciesAgrobacteriumstellulatum, Agrobacteriumpseudotsugae andAgrobacteriumgypsophilaewere addedto thegenus[7],but this inclusionwas laterconsidered

∗ Correspondingauthorat:DepartamentodeMicrobiologíayGenética,Lab.209, EdificioDepartamentaldeBiología.CampusMigueldeUnamuno,37007Salamanca, Spain.

E-mailaddress:evp@usal.es(E.Velázquez).

1 _{Currentaffiliation:ICAAM–InstitutodeCiênciasAgráriaseAmbientais}

Mediter-rânicas,LaboratóriodeMicrobiologiadoSolo,UniversidadedeÉvora.

unjustified becausethey probably belongto othergenera [23]. Therefore, in the subsequent 8th edition of the Bergey’s Man-ual only fourspecies were included,A. radiobacter,which was non-pathogenic,A.rhizogenes,whichinducedhairyroots,andA. tumefaciensandA.rubi,whichinducedplantgalls.The differentia-tionofthesespecieswasbasedonsomephenotypiccharacteristics togetherwiththeirabilitytoproducediversesymptomsin differ-entplants[1].Thesefourspecieswereincludedinthevalidation listsofSkermanetal.[45],whoindicatedthatA.tumefaciensisthe typespeciesofgenusAgrobacterium.

Duringthe70and80softhepastcentury,severalstudies includ-ing strainsisolatedfromdifferent sourceswere performedand theexistenceofdifferentvarieties,biovarsand/orbiotypeswas deeply revisedby Young [58].Some authorsproposedthat the speciesA.tumefaciensandA.radiobacterconstituteasinglespecies, A.radiobacter[20],laternamedA.radiobactervar.tumefaciens[21]. However,consideringthatA.tumefacienswasconsideredthetype speciesofthegenusAgrobacteriumbySkermanetal.[45],Holmes andRobertsconsideredthatthecorrectnamefortheunifiedtaxon isA.tumefaciens[18].

https://doi.org/10.1016/j.syapm.2019.126046 0723-2020/©2019PublishedbyElsevierGmbH.

Nonetheless,inthe1steditionoftheBergey’sManualof Sys-tematicBacteriologypublishsedin1984,KerstersanddeLey[22] maintainedthefourspecies,buttheyincludedthreebiovarsinthe speciesA.tumefaciensandtwobiovarsinthespeciesA.radiobacter, assigningthespeciesA.rhizogenestoanamelybiovar2and main-tainingthespeciesA.rubi.InthiseditionoftheBergey´sManual ahighernumberofphenotypiccharacteristicswererecordedfor theAgrobacteriumspecies,buttheirdifferentiationcontinuedtobe mainlybasedonphenotypicandphytopatogenicitytests[22].

Atthe beginning ofthe 90sseveral changes wereproposed withinthegenusAgrobacteriumincludingthedescriptionofnew species,neverthelessnoneofthesechangeswererecordedinthe 9thandlasteditionoftheBergey’sManualofDeterminative Bacte-riologypublishedin1994,whichincludedthesamespeciesthatthe previousversionofthisManual[19].Inyear1990thestrainsfrom thebiovar3ofA.tumefaciensproducingtumoursinVitisvinifera wereincludedintoanewspeciesofgenusAgrobacteriumnamed A.vitis[32].In thedescriptionofthisspecies,inadditiontothe classicphenotypicandphytopatogenicytests,theauthorscarried outDNA–DNAhybridizationamongthetypestrainsofthe Agrobac-teriumspeciesdescribedtodateandamongseveralstrainsofthe newproposedones.Theresultsobtainedinthisworkshowedthat thetypestrainofA.vitispresentedlessthan50%DNA–DNA related-nesswithrespecttothetypestrainsoftheremainingAgrobacterium species,whereastheanalysedstrainsofA.vitispresentedvalues rangingfrom80to92%amongthem.Surprisingly,thetypestrains A.tumefaciensNCPPB2437T_{andA.radiobacterATCC19358}T_also

presentedDNA–DNArelatednessvalueswithinthisrange[32]. In1992,RügerandHöfle[41]includedseveralstrainsisolated frommarinesourcesinseveralspeciesofthegenusAgrobacterium recoveringthenamesA.stellulatum,Agrobacteriumferrugineumand Agrobacteriumgelatinovorum,whichwerenotincludedinthe val-idationlistsofSkermanetal.[45],andproposingthenewspecies AgrobacteriumatlanticumandAgrobacteriummeteori.Inthiswork theAgrobacteriumspeciespreviouslydescribedwerenotincluded andtheclassificationofthenewproposedoneswasbasedinthe initialassignement of A.stellulatumtothe genusAgrobacterium [47] being differentiated the newspecies onthe basis of phe-notypictraits and thelow DNA–DNArelatedness foundamong them[41].Allthesespecieswerelaterreclassifiedinothergenera. ThespeciesAgrobacteriumatlanticumand Agrobacteriummeteori werereclassifiedintoRuegeriaatlantica[51,52].Thetypestrainof Agrobacteriumferrugineumwasreclassifiedinto Pseudorhodobac-terferrugineus[50,53]andthestrainLMG128intoHoefleamarina [37].AgrobacteriumstellulatumwasreclassifiedintoStappia stellu-lata[51,52]andAgrobacteriumgelatinovorumwasreclassifiedinto Ruegeriagelatinovorans[51,52]andlaterintoThalassobius gelati-novorus[2].

Ayearafter,Sawadaetal.[43]revisedthetaxonomicstatusof Agrobacteriumspeciesdescribeduntilyear1990.Inthisworkthe 16SrRNA(rrs)genesequencesofrepresentativestrainsofthe bio-var1(A.tumefaciens-A.radiobacter),biovar2(A.rhizogenes),biovar 3(A.vitis)andA.rubiwereobtainedandcomparedwiththoseofthe severalspeciesfromdifferentalphaProteobacteriagenera, includ-ingthegenusRhizobium.Theanalysisofthisgeneshowedthatthe strainsfrombiovar1wererelatedtoA.rubi,butthosefromthe bio-vars2and3werephylogeneticallydivergentbeingthestrainsfrom thebiovar2verycloselyrelatedtothetypestrainofRhizobium trop-ici.Nevertheless,despitethespeciesA.rhizogeneswasemended,it wasmaintainedwithinthegenusAgrobacterium.Moreover,itwas reportedthatthetypestrainsofA.tumefaciensNCPPB2437T_andA.

radiobacterIAM12048T_{have87%DNA–DNArelatednessin}

agree-mentwiththeresultsfromOphelandKerr[32]forA.tumefaciens NCPPB2437T_{andA.radiobacterATCC19358}T_{.Therefore,Sawada}

etal.concludedthatthesetwostrainscannotbeplacedin differ-entspeciesandtheyindicatedthataccordingtotheRule38ofthe

InternationalCodeofNomenclatureofBacteriathespecies estab-lishedearliershouldbemaintained[28].SinceA.radiobacterwas describedin1902(asBacillusradiobacter)byBeijerinckandvan Delden[4]andA.tumefacienswasdescribedin1907(asBacterium tumefaciens)bySmithandTownsend[46],Sawadaetal.[43] pro-posedtonamethestrainsofbiovar1asA.radiobacterandtoreject thespeciesnameA.tumefaciens.Thus,attheendofthepastcentury A.radiobacter,A.rhizogenes,A.rubiandA.vitiswereconsideredthe validspeciesofgenusAgrobacterium.

ThetaxonomyofgenusAgrobacteriumfrom2000onwards

Themostrelevantandconflictivechangeinthetaxonomic sta-tusofgenusAgrobacteriumtookplaceinyear2001whenYoung et al. [60] proposedthe reclassification of the complete genus AgrobacteriumintothegenusRhizobium.Thisreclassificationwas based on the resultsof Sawada et al. [43] and, therefore, the Agrobacterium species were reclassified as Rhizobium radiobac-ter,Rhizobiumrhizogenes,RhizobiumrubiandRhizobiumvitis.The reclassification,whichwasbasedontherrsgenesequences ana-lysed by Maximum-likelihood and Neighbour-joining methods, wasnotacceptedbymanyauthorswhosignedtheletterof Far-randetal.[13].Theseauthorsconsideredthatonlythebiovar2 belongstogenusRhizobiumandthatclassicalandmoleculardata supportthatAgrobacteriumandRhizobiumaredifferentgenera.This letterwaslaterrepliedbyYoung etal.[61]andthecontroversy wassettledbykeepingthereclassification.Consideringthis decis-sion,Young[57]alsoproposedthereclassificationofthespecies Agrobacteriumlarrymoorei,whichwasdescribedin2001[5],as Rhi-zobiumlarrymoorei.Nevertheless,thisspecieswasnotincludedin the2ndeditionoftheBergey’sManualwhichonlyincludedthe speciesA.tumefaciens,A.rhizogenes,A.rubiandA.radiobacter. Curi-ously,inthiseditionofBergey’sManualtheofficialreclassification ofAgrobacteriumspeciesintothegenusRhizobiumwasdisregarded, althoughtheauthorsmakeahistoricalreviewofthenomenclature problemsaffectingthegenusAgrobacteriumoverthetime[59].

Duetotheconfusiongeneratedafterthereclassificationofgenus Agrobacterium intogenusRhizobium, thenewspecies described since2001outsidetheofficialjournalfordescriptionofnewtaxa ofProkaryotes(IJSEM)werenamedAgrobacterium,asoccurredin thecaseofAgrobacteriumalbertimagniisolatedfromaquaticplants, in whose description,as occurredin the case of A. larrymoorei describedayearbefore,onlytherrsgenewasincluded[42]. How-ever,thespeciesdescribedoutside thementionedjournalwere namedRhizobiumandtheanalysisofseveralhousekeepinggenes wasincludedintheirdescriptionsin additiontothatoftherrs gene.ThesespecieswereRhizobiumpusense,isolatedfrom chick-pearhizosphere[35],Rhizobiumnepotum,isolatedfromtumoursof differentplants[38]andRhizobiumskierniewicenseisolatedfrom tumoursofchrysanthemumandcherryplum[39].

Inparallel,theAgrobacteriumstrainsfromdifferentspecieswere distributedintothegenomicgroups(genomicspecies, genomo-species,genomovars)G1toG9,G11,twounnamedgenomicgroups andG13[10,11,30].Atthetimeoftheseworks,theG4includedthe typestrainsofA.tumefaciensandA.radiobacter,theG11thatofA. rubi,theG10thatofA.rhizogenesandthetwounnamedgroups includedseveralstrainsofA.larrymooreiandA.vitis[30].Laterit wasshownthattheG8correspondstothespeciesA.fabrum[29], theG2tothespeciesR.pusense[3,35]andanewgenomovar,named G14,correspondstothespeciesR.nepotum[38,44].

Thetaxonomicstatusofthesespecieswaschangedagainwhen Mousaviet al. [31] basedon theanalysisof the rrs,recA, atpD andrpoBgenesproposedtotransferR.pusense, R.nepotumand R.skierniewicensetogenusAgrobacteriumandR.vitis(initiallyA. vitis)togenusAllorhizobium,asnewcombinations, whichwere

Table1

SpeciescurrentlyincludedinthegenusAgrobacteriumandspeciescausingtumoursorhairyrootscurrentlyincludedinothergeneraofFamilyRhizobiaceae.

Species Sourceofisolation Pathogenicitysymptoms References

GenusAgrobacterium

A.radiobactera _{Soilandplantrhizosphere Non-pathogenic [4,9]}

A.tumefaciensa _{Malussp.tumours Tumours [9,46]}

A.rubi Rubussp.tumours Tumours [17,48]

A.larrymoorei Ficusbenjaminatumours Tumours [5]

‘A.albertimagni’ Potamogetonpectinatus Nodata [42]

‘A.fabrum’ Prunussp.,Humuluslupulus,Euonymusalata,Rubusmacropetalustumours Tumours [29]

A.pusense Cicerarietinumrhizosphere Nodata [31,35]

A.nepotum Prunus,VitisandRubustumours Tumours [31,38]

A.skierniewicense ChrysanthemumandPrunustumours Tumours [39]

A.arsenijevicii PrunusandRubustumours Tumours [25]

‘A.deltaense’ Sesbaniacannabinanodules Nodata [55]

A.salinitolerans Sesbaniacannabinanodules Nodata [56]

‘A.bohemicum’ Papaversomniferum Non-pathogenic [62]

A.rosae Rosaxhybridatumours Tumours [26]

GenusAllorhizobium

A.vitis Vitisviniferatumours Tumours [31,32]

GenusRhizobium

R.rhizogenes Malussp. Hairyroots [9,40]

‘R.tumorigenes’ Rubussp.tumours Tumours [27]

a_{WehaveincludedthesetwospeciesnamestakingintoaccountthecurrentdecisionoftheJudicialCommision[49].Ganetal.[22]proposedthattheybelongtodifferent}

subspeciesofthespeciesA.radiobacter.Thequotednamescorrespondtospeciesthathavenotbeenofficiallyvalidatedtodate.

later validatedin IJSEM [33]. Theold species A. rhizogeneswas maintainedasRhizobiumrhizogenesinthegenusRhizobium,which currentlyalsocontainsthenewspeciesRhizobiumtumorigenesable toinduceplanttumours[27].Mousavietal.[31]didnotconsidered thespeciesAgrobacteriumfabrumisolatedfromtumoursof vari-ousplants[29]becauseitwasnotofficiallyproposed,althoughthe completegenomeofitstypestrainC58wasthefirstobtainedfor amemberofthegenusAgrobacteriumanditwassequencedtwice independentlyduetotheimportanceofthisstrainforplantgenetic engineering[16,54].

Since2015,severalnewspeciesofgenusAgrobacteriumhave been described based on the analyses of the rrs and several housekeepinggenesand,insomecases,thecomplete genomes. Someofthesespecieswereisolatedfromplanttumours,suchas Agrobacteriumarsenijevicii[25]andAgrobacteriumrosae[26],but otherswereisolatedfromlegumenodules,suchasAgrobacterium deltaense[55]andAgrobacteriumsalinitolerans[56],orplantwastes, suchasAgrobacteriumbohemicum[62].Insomeoftheseworksa strainnamedKB-105(ATCC31113)fromAgrobacteriumviscosum wasmentioned[12],neverthelessthisspecieshasnotbeen offi-ciallyproposedandmoreoverthestrainKB-105,whichis nota type strain,iscurrently includedina patent (U.S.Patent Num-ber4,028,185).Therefore,A.viscosumcannotbeconsideredavalid speciestodateandthenithasnotbeenincludedinthepresent study.

ConcerningtotheoldspeciesofgenusAgrobacteriumthatwere nottransferredtoothergenerabyMousavietal.[31],theyreturn totheirinitialnamesA.tumefaciens,A.radiobacter,A.rubiandA. larrymoorei.Nevertheless,there isaproblemwiththenamesof thetwofirstspeciesaswaspointedoutbySawadaetal.[43]who, consideringthatthenameA.radiobacterhaspriority,proposedthe rejectionofthenameA.tumefaciens.Nevertheless, accordingto Rule56aoftheInternationalCodeofNomenclatureofBacteria,only theJudicialCommissioncanplaceanameonthelistofrejected names[28,36].Afteryearsofdiscussionaboutthisissue,thelast decisionofthisCommissiontakenin2014isthat“the combina-tionAgrobacteriumradiobacter(BeijerinckandvanDelden1902) Conn1942haspriorityoverthecombinationAgrobacterium tume-faciens(SmithandTownsend1907)Conn1942whenthetwoare treatedasmembersof thesamespeciesbasedontheprinciple ofpriorityasappliedtothecorrespondingspecificepithets.The typespeciesofthegenusisAgrobacteriumtumefaciens(Smithand Townsend1907)Conn1942,eveniftreatedasalaterheterotypic

synonymofAgrobacteriumradiobacter(BeijerinckandvanDelden 1902)Conn1942.Agrobacteriumtumefaciens(SmithandTownsend 1907)Conn1942istypifiedbythestraindefinedontheApproved ListsofBacterialNamesandbystrainsknowntobederivedfrom thenomenclaturaltype”[49].

In 2014,thesame yearthedecision oftheJudicial Commis-sionwaspublished, Zhangetal. [63]sequencedthegenomeof thetypestrainofA.radiobacterheldinDSMZculturecollection (DSM30147T_{)andproposedtheemendationofthisspeciesinorder}

toincludetheresultsofassimilationofdifferentcarbonsources, theproductionofseveralenzymesandthefattyacidprofile.These authorsindicatedthatthegenomeofthestrainDSM30147T_was

unusuallylarge,sinceithasmorethan7Mbwhereastheremaining analysedgenomeshavesizesrangingfrom4.8to6.8Mb. Neverthe-less,inthepresentyear2019,Ganetal.[15]reportedthereason ofthisdifference,whichwasacontaminationofthegenomeofthe strainDSM30147T_{(GCF000421945)withpartofthegenomeofthe}

strainTS43alsoisolatedbyZhangetal.[63](GCF001526605).The genomicdatawerenotincludedintheprotologueoftheemended speciesA.radiobacter,butinanycasetheemendationisnotvalid todatesinceitwasnotofficiallyperformed.

IntheworkofGanetal.[15]thegenomesofthetypestrains ofA.tumefaciensB6T_{(LMVK01000030.1,FCNL01000034.1)andA.}

radiobacter NCPPB 3001T _{(LMVJ01000011.1)were obtainedand}

compared withtheavailabegenomeofthestrainA.radiobacter LMG140T_{(MRDG01000013.1)concludingthatthetypestrainsof}

A.tumefaciensandA.radiobacterrepresenttwosubspeciesfromthe samespecies.Theseauthors,takingintoaccountthatthe combina-tionAgrobacteriumradiobacterhaspriorityoverthecombination Agrobacteriumtumefaciens[49],proposedthatA.tumefaciensB6T

shouldbereclassifiedintoanewsubspeciesofA.radiobacter. How-ever,thisproposalcannotbeacceptedbecausetheprotologues ofthetwoproposedsubspecieswerenotincludedinthepaperof Ganetal.[15]andmoreoveritisnecessaryanewemendationof thespeciesA.radiobacter.Inanycase,thisproposaldoesnot mod-ifytheresolutionoftheJudicialCommissiongiventhatthespecific nameAgrobacteriumtumefacienscannotberejectedaslongasthis Commissionhasnotmadesuchdecision.

Therefore, the genus Agrobacterium currently contains 14 species if we considerthe namesA. radiobacter and A. tumefa-ciensandthespeciesA.fabrum,althoughthisspecieshasnotbeen still proposed(Table 1). One of them, A. albertimagni, is more closelyrelatedtosomeRhizobiumspeciesformingarrsgenecluster

Agrobacterium rubiNBRC 13261T(BBJU01000046) Agrobacterium rosae NCPPB 1650T_{(NXEJ01000009)}

Agrobacterium bohemicumR90T(PGEL01000020) Agrobacterium larrymooreiAF3.10T_{(ATCC 51759}T

Agrobacterium fabrumC58T(AE007869) Agrobacterium pusenseNRCPB10T_(FJ969841)

Agrobacterium salinitoleransYIC 5082T(MRDH01000011) Agrobacterium deltaenseYIC 4121T_{(MRDI01000025)}

Agrobacterium tumefaciensB6T_{(FCNL01000034)}

Agrobacterium radiobacterNCPPB3001T(LMVJ01000011) Agrobacterium nepotum39/7T_(FR870231)

Agrobacterium arsenijeviciiKFB 330T(JWIT01000061) Agrobacterium albertimagniAOL15T_{(ALJF01000029)}

Rhizobium rosettiformansW3T(NR_116445)

Rhizobium aggregatumIFAM1003T_(X73041)

Rhizobium daejeonenseL61T(NR_042851) Rhizobium selenitireducensB1 (NR_044216)

Rhizobium naphthalenivoransTSY03b (NR_132669)

Allorhizobium undicolaORS 992T(ATCC 700741T) (JHXQ01000045) Allorhizobiumvitis NCPPB 3554T_{(NZ_LMVL02000018)}

Rhizobium tumorigenes1078T(PCDQ01000084)

Rhizobium leguminosarumUSDA 2370T_{(NZ_QBLB01000002)}

Rhizobium rhizogenesNBRC 13257T(NZ_BAYX01000035) Rhizobium tropiciCIAT 899T_(CP004015)

Bradyrhizobium japonicumUSDA 6T(AP012206)

99 62 99 87 95 91 76 96 60 94 96 80 62 95 99 72 69 99 77 97 62

Fig.1.Neighbour-joiningphylogeneticrootedtreebasedonrrsgenesequences(1380nt)showingthetaxonomiclocationofthespeciesfromAgrobacterium,Rhizobium andAllorhizobiumabletoinducepathogenicsymptomsinplants.Bootstrapvaluescalculatedfor1000replicationsareindicated.Bar,1ntsubstitutionper100nt.Accession numbersfromGenbankaregiveninbrackets.

(Fig.1)thatbelongtoneitherAgrobacteriumnorRhizobiumbuttoa separategenus[12,34].Nevertheless,thereclassificationofA. alber-timagniinanewgenuswillneedfurtherstudiessincecurrently thegenomesofseveralRhizobiumspeciesbelongingtothis puta-tivenewgenusarenotavailable.Theremainingspeciescurrently includedwithingenusAgrobacteriumformedarrscluster phylo-geneticallydivergenttogeneraAllorhizobiumandRhizobiumalso containingplantpathogenicspecies(Fig.1).MostofAgrobacterium speciesareabletoproducetumoursindifferentplants(Table1), neverthelessthenumberofnon-pathogenicspecieshadincresed inthelasttwoyears,withoneofthem,A.salinitolerans, ableto nodulatethelegumeSesbaniacannabina[56]andother,A.pusense, frequentlyisolatedfromclinicalsources[3],abletocausehuman sepsis[24].Ifwetakeintoaccountthatthestrainsbelongingto fivedefinedgenomospecieshavenotbeenassignedtoan Agrobac-teriumspeciesyet,asignificantincreaseinitsnumberisexpected inanearfuture.

Aknowledgements

Thisworkwassupportedby MINECO(Spanish Central Gov-ernment)Grant AGL2013-48098-P toEV. EMwasgranted by a postdoctoralcontractassociatedtothisproject.

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