Studies on biosynthesis system of magnetite in magnetic bacterium Magnetospirillum
magnetotacticum MS‑1
著者 田岡 東
著者別名 Taoka, Azuma journal or
publication title
博士学位論文要旨 論文内容の要旨および論文審査 結果の要旨/金沢大学大学院自然科学研究科
volume 平成16年12月
page range 277‑282 year 2004‑12‑01
URL http://hdl.handle.net/2297/16633
氏名 生年月曰 本籍 学位の種類 学位記番号 学位授与の日付 学位授与の要件 学位授与の題目
田岡東
香川県 博士(理学)
博甲第624号 平成16年3月25曰
課程博士(学位規則第4条第1項)
StudiesonBiosynthesisSystemofMagnetiteinMagnetic BacteriumMZg"etoSPjγjノノ"沈沈cZg"emZzzcrjcz`腕MS-1
(磁性細菌Mzg"emSPjγjノノ"沈加g"cmtzzcjjc"”MS-1におけるマグネタ イト生合成経路に関する研究)
論文審査委員(主査)
論文審査委員(副査)
福森義宏 和田敬四郎 東浩
(理学部・教授)
(自然科学研究科・教授)
(理学部・助教授)金森
櫻井勝(理学部・教授)
正明(理学部・講師)
学位 ニムロno 文要 ]曰
ADsZFHzcr:IpurifiedthenitratereductasefromMZgアzeZD叩かiJ肋川川昭肥ZDZZzcZi切川 MS-1・TheenzymewascomposedofS6kDa-andl7kDa-subunitsandcontained lnolybdopteringuanmedinucleotideandhemecascof豆ctors.M〃zcZg"eZDZZzcr允皿剛 胆p1ocuswasclusteledinsevenopenreadingfiPames,アzc1pFDAGHBC・The phylogeneticanalysesofNapA,NapBandNapCsuggestedacloserelationshipbetween M川αg"eZomcZibm川7zcZpgenesandE、coJmcZpgenes,whichisnotconsistentwithtlle lGSIDNAdata・nrtllennore,IinvestigatedtheeffcctsofmolyMate-deficiencyintI1e mediumonthetotalironcontentsofthemagnetosomefiPaction・Theresultsuggested thattlleperiplasmicmtrate配ductaseactivityisnotessentialfbrmagnetitebiosynthesis inM〃zcZg"eMZzcr比"〃butnecessaryfbroptimumsynthesisofmagnetite・
Secondary,ItrieddevelopingthenlethodofthetargetedgenedisruptionfbrM '7zcZg肥ZDmcZicLd川.Broad-host-rangeplasmidsofthelncPgroupweretransfbITedby coUjugationandreplicatedinthisbacte血mStudiesareunderwaytoconstructof
"叩genesdisruptionmutantofM〃Zag"eZmZzcriCzJ〃・
Hnally,Ifbundtllattwo蔚七siderophorereceptorswerelliglllyexpressedintlle
magneticcells・Thesereceptorswerealsoinducedwhentllecellswerecultivatedwitlltlle恥2+richmediumTheseresultssuggestthattllebacteriatlBnsportandutilizeFe3+
formagnetitesynthesisevenundertheFe2+richgrowthcondition
lntmduction
MZgMDSp腕ノノ川7MgMomcZic川MS-1wasisolatedfromthesedimentsofthe freshwaterswalnp[1]、Oneofthenovel化aturesofM川cZg"α伽cZic伽isthatthis
bacteriumsynthesizesintracellularparticles,telTnedmagnetosomes,whichare envelopedsinglecrystalsofmagnetitewitlllipidbilayers・
BazylinskiandBlakemoreinvestigatedtheoptinmngrowthconditionsfbr lnagnetiteproductionbyM川Czg"α○匁αjc"剛andfbundthatthebacteriumproduces morelnagnetitesUnderlnicroaerobicconditionssupplementedwithnitrate,whichis finallyreducedtoN20(M)[Z]、Theyalsoreportedthatthebacteriumcannotgrow understIictanaerobicconditionswithnitrate[Z].Therefbre,itseelnslikelythatthe bacteriumisanncroaerobicdenitlifier:theaerobicrespirationwithO2andthe anaerobicrespirationwitllnitrateasthefinalelectronacceptorsoccursimultaneouslyin
thecelLIhlrtllennore,Yanlazakietal・havereportedthatthMii-typemtlitereductase
isllighlyexpressedi、theperiplasmofthemagneticcellsofM〃zcZg"emmcr允肋zand showsanovelFe(11):nitliteoxidoreductaseactivity[3]・Theseresultssuggestthatthe denitlificationmayberequiredfbrmagnetitesynthesisinM川cZg"e〃〃αに"川.
However,tllerearecurrentlynoreportsontllechamcterizationandfimctionofother denitrifj/ingenzymesofjM7zag"抑伽加川.
M2BteriaIMndlMetllodS
M#c"w"淫umiSmsdzMgアDWUソbcoJm蹴り〃
M〃28"e加伽此醐wascultivatedinachemicallydeflnedliquidmedium[1]・
TheMo-deficientcellswerepreparedbycultivationwithtlleMo-deficientmetal
mixtureunderthesamegrowtllconditionsasdescribedabove・L4mMNH4C1was addedtothemediumasNsourcefbrthegrowthoflzcZpdeletionstrain・
ESCノカ〃jc/DiZzco〃XL-1B1ueMRFwasusedfbrcloningStudies・E8coZiS17-1 nwasusedfbrtlledonorofdiparentalconjugationE・coJiHB101(pRKZO1S)mdE coJim1006wereusedashelperstrainanddonorstlainoftriparentalcomu弩ation
studies,respectively6E8co〃strainsweregrownat37oCunderaerobicconditionsin LuriaBertani(LB)medium[S].
P噸/5M#のアDTFDimzZWwJbJcZUzse./、TOM・magnetotacticmm
M〃zcZg"emjZzcZ比皿川cellswe1℃brokenbytllreepassagesthroughtlleHench pressurecell(100MPa).Aftertlleunbrokencellsandmagnetosomeswereremoved byacentIifilgationatlO,OOOxgfbrlSmin,thesupematantwasrecoveredandfnrther celltlifilgedatlW,OOOxgfbrlhThenitrate1℃ductasewaspurifIedfromtlle supematantbyanlonexcllange-,cationexcllange-andhydroxylapatite‐
chromatographies・
AmdZyげUIbeJUimUUwwJbUczUz8Mc虚U'iry
Thenitratereductaseactivitywasassayedbythemethodof氏mandezetaL withslightmodifications[6]・NitIiteconcentrationwasdetenninedbytlle diazocouplingprocedureofMcholasajldNason[刀.
OMaJwJ2w-dZHjDz伽jbPMJZDo卯呵肱"0雌9℃Z地cUmpjbo剛esCDE)
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One-andtwo-dimensionalelectrophoreseswerepelfblmedaccordingto methodsofLaemmli[S]andO,Farrell[9],respectively6
DezごnF8jjzOzz伽〃伽"〃"z②U航Mbe伽9M℃M『WiUzc耐i、〃
Thecellswerecolnpletelydisruptedwithasomcoscimator(20kHz,100W).
ThelysatewascentrifilgedatS,OOOxgfbrZOInin・Theresultingpelletwasusedasthe crudemagnetosomefraction・Aftertheorganlccomponentsinthefractionwere
decolnposedbydryaslling,theresultingbrownashwasdissolvedinlNHC1anddilutedintodistilledanddeionizedwatemTheironconcentrationofresultingsolution
wasmeasuredbyphotolnetlicdetern血ationwitlll,l0-phenanthroline[10]・MUzzimgeweFfHP0e"た
ThematingexperimentswereconductedbythemethodsofSimonetaL[11]
anddeBruijnandRossbach[12]withsomemodifications.
ResultsandDiscussion
PePiPJUzsJUDiMjZmzw巴UJi8伽sea"α川α〃e伽肋qyJ8zIbesis
IpurifIedtheperiplasmicnitratereductase,thefirstenzymeofdenitrificatio、,
fromM〃zcZg"emZZzctjC"脚.TheenzymeshowsabsorptionpeaksatSS1,SZ1and419 nmintllereducedfbnnandwascompoSeClof別kDa-andl71KDa-ploteinsonSDS-
肌GE,althouglltllel7kDa-proteinbandwaslesslnalkedlystainedwitllCoomassie
BrilliantB1ue(Hg・リH1rther,theenzymecontainedmolybdopteringuanme
dinucleotideandhenlecascomctors・
TheM〃zcZg"αomajCzu川皿p1ocuswasclusteredinsevenopenreadingframes,
"cpFDAGHBC・T11eorganizalionoftheM〃zcZg"eMZzcrjC皿加’zc2Pgeneclusteris exactlytllesameasthatoftheganⅡnasubclassofP7qoreobacZmZzasE・CO魔,whicllis notconsistentwitlltllephylogeneticanalysesofthel6SrDNAsequences[13landtlle cytochromecsequences[1判.ThephylogeneticanalysesofNapA,NapBandNapC suggestedacloserelationsllipbetweenM川αg〃〃ZZza妬"川〃c2PgenesandE・coJmcZp genes(Hg.z).Therefbre,the皿pgeneclusterofM〃Zag"eZDmc飾伽mightbe transfbrredbyhorizontalgenetransferwithinthebacterialcomnunity・RIrthemore,
twobindingsitesoftheputativetranscliptionalmctors,H1randNarL/NarEwelefbund inupstreamof〃cZpFregion
ninvestigatetllepllysiologicalfimctionoftlleperiplasmicnitratereductasein
M剛cZg"eZoZZzcZiC"川,IcultivatedtllebacteliumintlleabsenceofMoandcomparedtlle
nitratereductaseactivitiesofthecell-freeextractsandtlletotalironcontentsoftlle
…………。
}
》》》 ’一一
6分oro9aTrJm100
窟野津⑪
鶴榧蠅VP7.gzcらpEryR回 匡no堅℃麺「幻遁
-52.ZkDa
』Jヒワ8PrTo塀、耐娠PP?。S河EHWp画α順
〕.-3631dDa
--302kD幻
I3subumit
Oq2PB)-し醗騨-21.9kDa
IF蓬一 」
aP7CZ@!ハロ仁エワ翠6no癖[、「幻?ロ--7.41のa
ロ1
Fig.1SDS-HkGEofpurifledMmcqgPueわJZzc"Czum periplasmicnitrateI巳ductaseThegelsweIestainedwith
CoomassieBrilliantBlueR-2SO.
Fig.2.PhylogenetictI巳eoftheNapA、ECO〃DMSO だ。uctaseUnsAwasdelinedasout-gToup.
crudemagnetosomefractionspreparedfromtheMo-deficientcellswiththoseofMO-・
suppIementedcellsofM〃zcZg"e〃ねα疋伽,resPectively6AsshowninHgure3A,the mtrate1℃ductaseactivityoftheMo-defIcientcellsofM〃zcZgMDZZzα加川wasalmost undetectable,wlliletlleironcontentsintllemagnetosomefractionswasabout判%of tllecontrolexpeliment・Theseresultsshowtllatthebacterialmagnetitescouldbe synthesizedintheabsenceoftllepeliplasmicmtratereductase・Neitllerofnitratenor
nitlitemightbeessentiallyrequiredfbrbiosyntllesisofmagnetiteincontrasttotI1e previouslyresultsHowev則itshouldbenotedtI1attU1ecytochromeczjiwashigllly expressedinthemolybdate-deficientcells(Fig3B).Therefb肥,tllebacteliumlnight utilizeoxygenasaltemativeelectronacceptorfbr圧(11)oxidationbycytochlomecz1iin theabsenceofMo,becauseMWzag"eZDZZzc此川cytochromeaj,showsMMⅣ,,Ⅳ,‐
tetrametllyLp-phenylenedianmne-O2oxidoreductaseactivity[3]・
DeveU、pEI8卿TdzUUz聯ZMg巴アDMZmqp伽"伽鋤MJil「M・ma=netotacticum
Atfirst,IestablishedthemethodfbrplasndtransfbrbyconjugationinM
"zCZg〃われα尤皿剛.ThetwoRK2derivativeplasmidspRK‘llSandpKSSOOwere
tmnsferredtorecipientstrain,M〃zcZg肥ZDZZzaた"川,bydiparetalandtriparetal co11jugations,respectively6Thisisthefirstreportonplasmidtransferbyconjugation
inM7mg7ze〃ZZzcZiC皿川MS-1・Secondlylltriedtlletargeteddisruptionof皿pFDAGgenesinM '、g〃ZDZZzcriCzd肌Thegenedisruptionplaslnid,namely,pKFZOS,wasconstructedand
transferredintoM’7zcZg肥ZDZZzaたzJ"z・nfbrcerecombination,substitutionplasmid,
pKSSO7,wasfmrthertransferTedintoresultanttransconjugant[15】・Theoccurrencesof
recolnbinationeventswereverifiedbySouthernhyblidizationanalysis,suggestingthat therecombinationeventsoccurredbetweentlledismptionplasmidandgenomcDNA
-280-
(B)の
旨&■8自白国 (墓四一の量】⑭量面’-8四画日》 (A)10a43265554s352s150● Conml withoutMoO4withWO4
03
トⅢ ↓
:昌一山名。駒一一く
つ一二聟⑪生且g一・一一8m白眉員。日二》ら臣冒呵②的ロ百号目⑨旨』署zEゴミ)2216匹頤000q0 ●昌息己。g詞
I
cbmuIwmhmnMoo4前山“Moo4,withSOO600700500600700WO4 0
Wavclengdh(nm) Wavelength(nm)
gmumhoon範ons
Fig3. (A)Comparisonoftheironcontentandnit『atereductaseactivitybetweenMo紅eficientcelIsandMo‐
拠画Q、苧dpellM且)Th色JifIb妃npespect[aomedUCedWithNaM4]minU§[Oxjd唾。祠、韓bj)Jら応薊‐
嶢.TiPpLspppPにdfmmMo-supplementedcelIsandMMeficieiit~c§ils・The~画面己655hdii8h-感Hisラ6hiHFs
a耐butedtocytochlomec`,.
Howeverbtheculturewaslnixtureofwildtypecellsandsingleanddoublecrossover recombinantcells・NowlhavetliedisolationofdoUblecrossoverhomologues recombinantstrainfromthecultureofM伽g"α伽α蜘加(pKF205,pKS807)by
dilutiomnethod・
Up2UzlteTimJzzyM・ma印etotacticumFelアゼc姉"〃cEPZDパー
Ibidentifj/theproteinsfbrmagnetitebiomineralization,IhaVecomparedtlle proteinprofileofthenon-magneticcellswiththatofthemagneticcellsofM 川cZg〃〃ZZzcrjb"〃byZ-DEandfbundthattworbnB-dependentoutermembranereceptor holnologueswerehighlyexpressedinmagneticcells(Hg4).nrthennore,tlle expressionsweree血ancedinFe2+richcondition・ThelcfblC,itseemslikelythatM 川629"eZDZZzcrjCm川transportsandutilizesre3+fbrmagnetitesyntllesisfiomthecultureby
thesereceptors・
歪雛B:…恵了---
1柵kDa..~.rザザ..“
…’瓢葛等11ハ,Ⅷ
……〆■可姜壽二言三聟ル
ー守一Tfr-己…い」/つぎZもS7kDa両.]--.”華昌 一.‘.(や9
-§…・
鱈kDa : s Fig42-DEpattemo「theceIl-neeextI己cts pl巴paI己dliomthemagneticcellso「M Pmg"elDmcliCzdm・TheciIcIedpYoteinswe尼 magneticcellsspecincfelTic-sidemphoに
.、.。r_で receptorhomologUes.
C⑪ncumim■-- ̄----二■夕勾ユ
pH
IpurifiedtheperiplasmicnitratereductaseandcharacterizedtllelzcZpフlocus、
Molybdemlmstarvationexpelilnentsuggestedtllatthenitratereductaseactivityisnot
essentialfbrmagnetitebiosynthesisinM'72629"emzzza比"胴butnecessaryfbropti]【num
synthesisofmagnetite・H1】【tIhe]【more,Itlieddevelopingtl。leme[hodoftlletargeted
genedisruptionfbrMWzcZg'zeZomcrjb"川.HnallybIcomparedtlleproteinprofileofthe non-magneticcellswiththatofthemagneticcellsandfbundthattwoTbnB-dependent outermembranereceptorhomologueswerehighlyexpressedinmagneticcells,
suggestingthatMWzcZg〃MZzajC"川transportsFe3+fbrmagnetitesynthesis.
Refmmces
[1]JBacteliol.(1W9)140:720-729.
[2】APPI・Envilon・Miclobiol.(1983)妬:1118-1124.
旧]Eu正JBiochem.(1995)233:665-671.
nBio/Technology(1983)1:784-791.
nMolecularqoning,AlaboIatoWmanual(1989).
nAnal・Biochem.(1982)120:85-90.
[刀MethodsEnzymol.(1957)3:981-984.
[8]Natule(1WO)227:680-685.
[,]J、Biol,Che、(p75)250:4007-4021.
[10]ChemisMnalyst(1963)鬼:88-94.
[11]MethodsEnzymol.(1986)118:640-659.
[12]Methodsfbrgeneralandmolecularbacteriology
(1994)387-405.
[13]J・SystemBacteliol(1$l)41:324=3西.
[14]AIch・MicrObioL(1995)1$:400-406.
[1コPIantCenPhysiol.(2002)43:1s即2-15s7.
学位論文審査結果の要旨
本論文は、磁性細菌肱沈CZg"etomcrjc"”の脱窒系の開始酵素であるペリプラズム型硝酸塩還元酵素(Nap)
の生化学的,性質と遺伝子塩基配列を解明するとともに、本酵素の発現制御機構および分子進化を考察するこ とにより、磁気微粒子生合成機構と脱窒経路との関わりを明らかにし、さらに磁気微粒子生合成に関与する 新規蛋白質を同定した論文である。
肱沈(Zg"cmZZzcrjc""のNapを精製し、本酵素が2種類のサブユニットで構成され、補欠分子族としてモ リブデンコファクター、鉄硫黄クラスター、ヘムcを持つ事を明らかにした。さらに、その遺伝子塩基配列 から、本酵素が〃(ZPFDAGHBCgeneclusterにコードされていること、転写因子FNRとNarL/Pにより発 現制御きれることを明らかにした。また、NapA,NapBNapCアミノ酸配列による系統解析により、本細菌 の〃cZP遺伝子群はuproteobacteriaの〃⑰遺伝子群の水平伝搬によることを示唆した。一方、これまで同 定されていない磁気微粒子生合成に関与する蛋白質として2種類のFe(、)-siderophoreレセプターを同 定し、本細菌が磁気微粒子生合成にためFe(、)を積極的に取り込んでいることを示唆した。
以上、本研究により、磁性細菌肌沈cZgMomcjjc"”のマグネタイト合成に関して、多くのことを明らか にし、それらの知見は当該分野の研究発展に大いに寄与するものと考えられる。従って、審査委員会は、本 論文が博士論文として妥当であると判断した。
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