作者： Barbara J. Woodford , Michaelr . Hoffmann , Juan C. Diazricci
DOI:
关键词: Magnetite 、 Remanence 、 Strain (chemistry) 、 Materials science 、 Biomineralization 、 Electron microscope 、 After treatment 、 Magnetosome 、 Population 、 Nuclear magnetic resonance
摘要: In order toexplore theextent ofthis control, cultures ofAquaspirillum magnetotacticum intheexponential growth phasewereexposed toincreasing magnetic pulses withtheaimofseparating cell populations onthebasis of their coercivities. Isothermal remanent magnetization andanhysteretic remanentmagnetization studies wereperformed withfreeze-dried cells after theremagnetization treatment. Subpopulations ofA.magnetotacticum thatshowed anincrease incoercivity correlated withtheintensity ofthemagnetic wereisolated. After successive subcultures oftheremaining north-seeking cells, amaximumbulkcoercivity (Hbnax) of40mT wasobtained treatment witha55-mTpulse. Although weobtained A.magnetotacticum variants displaying higher coercivities thanthewild-type strain, changes incrystal sizeorshapeofthe magnetite crystals werebelowreliable detection limits withtransmission electron microscopy. Attempts toshift thecoercivity towards values caused ittodecrease, achange whichwasaccompanied byanincrease in magnetostatic interactions ofthemagnetosome chains aswellasanincrease inthecell population anabnormal distribution chains. Ultrastructural analyses ofcells andmagnetosomes revealed theappearance ofcystlike bodies whichoccasionally contained magnetosomes. Theincrease incystlike andabnormal magnetosome whenhigher wereusedsuggested thatmagnetosomes werecollapsing because ofstronger interparticle forces. Inthe10years since Aquaspirillum was reported andcharacterized (1,2,20), thediscovery ofother magnetotactic microorganisms thatmakedifferently sized andshaped (Fe304) hasshownthatthe crystallographic andmagnetic features ofthecrystals are species specific (3,17,22,25,26,28). Fromatechnological point ofview,itwouldbehighly desirable todefine the mechanisms involved inthebioprecipitation ofmagnetite ordertobeabletocontrol theshapeandsizeofthese single-domain particles. Unfortunately, theregulatory mechanismsinvolved inmagnetite biomineralization areun