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Formation and positioning of the magnetosome chain in Magnetospirillum Magneticum AMB-1Le Nagard, Lucas January 2018 (has links)
Magnetotactic bacteria are a group of prokaryotes that share the ability to align
with external magnetic fields, due to the presence within their cytoplasm of one or
several chains of nanometer-sized magnetic crystals called the magnetosomes. The
orientation of the chain within the cell is critical for magnetotaxis, which allows these
bacteria to swim along the geomagnetic field lines. To do so, the magnetic moment
and thus the chain need to lie parallel to the swimming direction which, for elongated
bacteria such as AMB-1, is roughly parallel to the long axis of the cell. In most
studies, the alignment between the magnetic moment and the cell axis is taken for
granted, however no precise measurement has been performed to confirm this. In this
thesis, experiments performed to test this assumption are presented, and the results
show that for most studied bacteria the alignment is not perfect. The effect on the
orientation distributions is discussed and accounted for in the analysis performed to
measure the magnetic moment of individual bacteria.
A second project presented in this thesis is focused on the biomineralization process in
AMB-1. Magnetotactic bacteria synthesize crystals characterized by a well-controlled
morphology and a high chemical purity, which makes them interesting for biomedical
applications. To study how these crystals are produced, we used scanning trans-
mission X-ray microscopy, and preliminary results show that this tool is suitable for
studying this complex process. The methods developed and improved during this MSc
to perform these experiments are presented, and the first results show an evolution
in the spectroscopy of the magnetosomes as they grow. / Thesis / Master of Science (MSc)
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Greigite et magnétite : les déterminants environnementaux et génétiques contrôlant la biominéralisation chez les bactéries magnétotactiques / Greigite and magnetite : environmental and genetic determinants controlling biomineralization in magnetotactic bacteriaDescamps, Elodie 12 February 2018 (has links)
Les bactéries magnétotactiques représentent un groupe d’une grande diversité écologique et phylogénétique. Elles sont capables de biominéraliser des nanocristaux de magnétite [un oxyde de fer (Fe(II)Fe(III)2O4)] ou de greigite [un sulfure de fer (Fe(II)Fe(III)2S4)] dans leurs magnétosomes, organites alignés en chaînes permettant la navigation le long des lignes de champ magnétique terrestre. Jusqu'à récemment, seules des souches produisant de la magnétite étaient disponibles en culture pure, conduisant à des études sur les mécanismes de biominéralisation de cet oxyde de fer. En 2011, une nouvelle bactérie capable de former de la magnétite et de la greigite, Desulfamplus magnetovallimortis souche BW-1, a été cultivée avec succès en laboratoire. Dans cette thèse, nous proposons d'utiliser une approche intégrée et multidisciplinaire pour comprendre les mécanismes de biominéralisation de la greigite en utilisant comme modèle d’étude la souche BW-1. Nous avons donc cherché à déterminer les conditions environnementales et biologiques favorisant la formation de la magnétite et de la greigite. Ces travaux ont également conduit à la caractérisation physiologique et phylogénétique de BW-1. Puis, l’utilisation d’approches globales et ciblées de transcriptomique ont permis d'évaluer le taux d'expression des gènes impliqués dans la formation des magnétosomes (magnétite vs. greigite) dans diverses conditions de croissance. Une approche de protéomique a permis d’apporter des informations supplémentaires à cette étude. Ces résultats ont permis de progresser dans la compréhension fondamentale de la biominéralisation in vivo, en particulier pour des bactéries formant de la greigite. / Magnetotactic bacteria represent a phylogenetically and ecologically diverse group of prokaryotes able to biomineralize magnetic nanocrystals composed of magnetite [an iron oxide (Fe(II)Fe(III)2O4)] or greigite [an iron sulfide (Fe(II)Fe(III)2S4)] in their magnetosomes, a prokaryotic organelle whose cytoplasmic alignement in chain allows the cell to navigate along the Earth’s magnetic field lines. Until recently, only magnetite-producing strains were available in pure culture. Thus, only the magnetite biomineralization has been studied. In 2011, a new bacterium able to form both magnetite and greigite, Desulfamplus magnetovallimortis strain BW-1, was isolated from Death Valley, California and cultivated in pure culture. In this work, we propose to use an integrated and multidisciplinary approach to understand the mechanisms involved in greigite biomineralization in BW-1 strain. First, we determined the environmental and biological conditions in which magnetite and greigite are formed. This first part of my thesis also contributed to the physiologic and phylogenetic characterization of this bacterium. Secondly, we used global and targeted transcriptomic approaches to evaluate the transcription levels of genes putatively involved in magnetosomes formation (magnetite vs. greigite) under various growth conditions. A proteomic approach provided additional informations to this study.Results obtained during my thesis contribute to the understanding of in vivo biomineralization, particularly for greigite production in magnetotactic bacteria.
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Mixotrophic Magnetosome-Dependent Magnetoautotrophic Metabolism of Model Magnetototactic Bacterium Magnetospirillum magneticum AMB-1Mumper, Eric Keith 20 June 2019 (has links)
No description available.
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Collective Behavior of Magneto-Aerotactic Bacteria: Experiments and Computational ModelingWijesinghe, Wijesinghe Mudiyanselage Hiran Shanaka January 2021 (has links)
No description available.
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