title: Overproduction of Magnetosomes by Genomic Amplification of Biosynthesis-Related Gene Clusters in a Magnetotactic Bacterium.
abstract: Magnetotactic bacteria biosynthesize specific organelles, the magnetosomes, which are membrane-enclosed crystals of a magnetic iron mineral that are aligned in a linear chain. The number and size of magnetosome particles have to be critically controlled to build a sensor sufficiently strong to ensure the efficient alignment of cells within Earth's weak magnetic field while at the same time minimizing the metabolic costs imposed by excessive magnetosome biosynthesis. Apart from their biological function, bacterial magnetosomes have gained considerable interest since they provide a highly useful model for prokaryotic organelle formation and represent biogenic magnetic nanoparticles with exceptional properties. However, potential applications have been hampered by the difficult cultivation of these fastidious bacteria and their poor yields of magnetosomes. In this study, we found that the size and number of magnetosomes within the cell are controlled by many different Mam and Mms proteins. We present a strategy for the overexpression of magnetosome biosynthesis genes in the alphaproteobacterium Magnetospirillum gryphiswaldense by chromosomal multiplication of individual and multiple magnetosome gene clusters via transposition. While stepwise amplification of the mms6 operon resulted in the formation of increasingly larger crystals (increase of ∼35%), the duplication of all major magnetosome operons (mamGFDC, mamAB, mms6, and mamXY, comprising 29 genes in total) yielded an overproducing strain in which magnetosome numbers were 2.2-fold increased. We demonstrate that the tuned expression of the mam and mms clusters provides a powerful strategy for the control of magnetosome size and number, thereby setting the stage for high-yield production of tailored magnetic nanoparticles by synthetic biology approaches.
  
  
  
  Before our study, it had remained unknown how the upper sizes and numbers of magnetosomes are genetically regulated, and overproduction of magnetosome biosynthesis had not been achieved, owing to the difficulties of large-scale genome engineering in the recalcitrant magnetotactic bacteria. In this study, we established and systematically explored a strategy for the overexpression of magnetosome biosynthesis genes by genomic amplification of single and multiple magnetosome gene clusters via sequential chromosomal insertion by transposition. Our findings also indicate that the expression levels of magnetosome proteins together limit the upper size and number of magnetosomes within the cell. We demonstrate that tuned overexpression of magnetosome gene clusters provides a powerful strategy for the precise control of magnetosome size and number.
authors.affiliation: Ludwig-Maximilians-Universität München, Department of Biology I, Martinsried, Germany.
authors.forename: Anna
authors.initials: A
authors.lastname: Lohße
authors.affiliation: Ludwig-Maximilians-Universität München, Department of Biology I, Martinsried, Germany.
authors.forename: Isabel
authors.initials: I
authors.lastname: Kolinko
authors.affiliation: Ludwig-Maximilians-Universität München, Department of Biology I, Martinsried, Germany.|Max Planck Institute of Biochemistry, Department of Molecular Structural Biology, Martinsried, Germany.
authors.forename: Oliver
authors.initials: O
authors.lastname: Raschdorf
authors.affiliation: Ludwig-Maximilians-Universität München, Department of Biology I, Martinsried, Germany.
authors.forename: René
authors.initials: R
authors.lastname: Uebe
authors.affiliation: Ludwig-Maximilians-Universität München, Department of Biology I, Martinsried, Germany.
authors.forename: Sarah
authors.initials: S
authors.lastname: Borg
authors.affiliation: Ludwig-Maximilians-Universität München, Department of Biology I, Martinsried, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Brachmann
authors.affiliation: Max Planck Institute of Biochemistry, Department of Molecular Structural Biology, Martinsried, Germany.
authors.forename: Jürgen M
authors.initials: JM
authors.lastname: Plitzko
authors.affiliation: Saarland University-Helmholtz Institute for Pharmaceutical Research Saarland, Helmholtz Centre for Infection Research and Department of Pharmaceutical Biotechnology, Saarbrücken, Germany.
authors.forename: Rolf
authors.initials: R
authors.lastname: Müller
authors.affiliation: Shandong University-Helmholtz Joint Institute of Biotechnology, State Key Laboratory of Microbial Technology, Life Science College, Shandong University, Qingdao, China.
authors.forename: Youming
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: Ludwig-Maximilians-Universität München, Department of Biology I, Martinsried, Germany dirk.schueler@uni-bayreuth.de.
authors.forename: Dirk
authors.initials: D
authors.lastname: Schüler
mesh_terms: D018628:Gene Dosage; D005798:Genes, Bacterial; D055944:Magnetosomes / Q000378:metabolism*; D042201:Magnetospirillum / Q000235:genetics* / Q000378:metabolism*; D005810:Multigene Family; D001678:Organelle Biogenesis