Ultrastructure of a magnetotactic spirillum.

摘要: electron microscopy. The organism resembled otherspirilla ingeneralt cellmorphology, although some differences were detected attheultrastructural level. Electron-dense particles within magnetotactic cellswere shownbyenergy-dispersive X-rayanalysis tobe localizations containing iron. A non-magnetotactic variant ofstrain MS-1lacked these novelbacterial inclusion bodies. chainofthese traversed each cell inaspecific arrangement that was consistent fromcelltocell, seemingly associated withtheinner surface ofthecytoplasmic membrane. Each particle surrounded byan electron-dense layer separated fromtheparticle electron-transparent region. Theterm"magnetosome" isproposed fortheelectron-dense withtheir enveloping layer(s) asfoundinthis and other bacteria. Magnetotactic bacteria ofdiverse morphological typeslive inmarineandfreshwater sediments, fromwhichtheycanbeseparated by using small permanent magnets (4). Allmagnetically responsive cells examined todate(4,10, 23)havecontained oneortwointracellular chains ofelectron-dense, iron-rich particles, measuring 40to100nm inwidth. Recently, a helical, heterotrophic, freshwater, bacterium wasisolated anddesignated strain MS-1(10). Thisisolate hasbeencharacterized andappears tobeanewspecies ofthegenus Aquaspirillum (17) bycriteria separate fromits magnetic properties (5;unpublished data). Strain MS-1possesses asingle chain ofelectrondense eachapproximately 40nmwide. Results of57FeMossbauer resonance spectroscopyestablished thatiron inmagnetotactic MS-1ispresent primarily asmagnetite (10). ofthis organism(obtained byculturing inamediumwith reduced iron content) lacked andmagnetite. Ultrastructural characteristics ofmagnetotacticbacteria havenotbeendescribed indetail. Theobjective study wastocharacterize theultrastructure ofmagnetotactic andnonmagnetotactic variants MS-1.Thedetailed structure oftheelectron-dense, andtheir relationship totheremainder ofthecell wereofcentral interest because (i) theyappear todiffer fromother types ofinclusionbodies reported tooccurinbacterial (31), and(ii) theyareassumed toberesponsible