Spatial localization of Mms6 during biomineralization of Fe 3 O 4 nanocrystals in Magnetospirillum magneticum AMB-1
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Eric Mumper School of Earth Sciences, The Ohio State University, Columbus, Ohio 43210, USA
Carol Gassman Department of Chemistry, Columbia Basin College, Pasco, Washington 99301, USA
Dennis A. Bazylinski School of Life Sciences, University of Nevada, Las Vegas, Las Vegas, Nevada 89154, USA
Steven K. Lower School of Earth Sciences, The Ohio State University, Columbus, Ohio 43210, USA; and School of Environment and Natural Resources, The Ohio State University, Columbus, Ohio 43210, USA
Brian H. Lowera) School of Environment and Natural Resources, The Ohio State University, Columbus, Ohio 43210, USA (Received 26 June 2015; accepted 25 January 2016)
Magnetotactic bacteria mineralize nanometer-size crystals of magnetite (Fe3O4) through a series of protein-mediated reactions that occur inside of organelles called magnetosomes. Mms6 is a transmembrane protein thought to play a key role in magnetite mineralization. We used both electron and fluorescent microscopy to examine the subcellular location of Mms6 protein within single cells of Magnetospirillum magneticum AMB-1 using Mms6-specific antibodies. We also purified magnetosomes from M. magneticum to determine if Mms6 was physically attached to magnetite crystals. Our results show that Mms6 proteins are present during crystal growth, and Mms6 is found in direct contact with the magnetite crystals or within the lipid/protein membrane surrounding the magnetite crystals. Mms6 was not detected at other subcellular locations within the bacteria or isolated fractions. Because Mms6 was found to completely surround the magnetosomes rather than being localized to one specific area of the magnetosome, it appears that this protein could act on the entire magnetite crystal during the biomineralization process. This supports a model in which Mms6 functions to regulate Fe3O4 crystal morphology. This knowledge is important for future in vitro experiments utilizing Mms6 to synthesize tailored nanomagnets with specific physical or magnetic properties.
I. INTRODUCTION
Magnetic nanoparticles hold great promise for many applications including, magnetic separations in biotechnology, delivery of cancer treatments, magnetic resonance imaging, data storage, and clean up of environmental contaminants.1–10 Humans have therefore spent much of the past decade trying to synthesize magnetic nanoparticles with controllable size and morphology (e.g., Ref. 11). There is another organism that has spent considerably more time perfecting the art of fabricating nanometer scale magnets. A group of prokaryotes called magnetotactic bacteria (MTB) have evolved Contributing Editor: Laurie Gower a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2016.41
a unique set of genes to direct the biological synthesis of nanometer size, monodisperse magnets. The human quest to synthesize the ideal nanomagnet may benefit from our ability to mimic the biomineralization reaction within this single-celled organism. MTBs use a specialized set of proteins to mineralize chemically pure, sin
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