Biological materials have ever been used by humans because of their remarkable properties. This is surprising since the materials are formed under physiological conditions and with commonplace constituents. Nature thus not only provides us with inspiration for designing new materials but also teaches us how to use soft molecules to tune interparticle and external forces to structure and assemble simple building blocks into functional entities. Magnetotactic bacteria and their chain of magnetosomes represent a striking example of such an accomplishment where a very simple living organism controls the properties of inorganics via organics at the nanometer-scale to form a single magnetic dipole that orients the cell in the Earth magnetic field lines. My group has developed a biological and a bio-inspired research based on these bacteria. My research, at the interface between chemistry, materials science, physics, and biology focuses on how biological systems synthesize, organize and use minerals. We apply the design principles to sustainably form hierarchical materials with controlled properties that can be used e.g. as magnetically directed nanodevices towards applications in sensing, actuating, and transport. In this thesis, I thus first present how magnetotactic bacteria intracellularly form magnetosomes and assemble them in chains. I developed an assay, where cells can be switched from magnetic to non-magnetic states. This enabled to study the dynamics of magnetosome and magnetosome chain formation. We found that the magnetosomes nucleate within minutes whereas chains assembles within hours. Magnetosome formation necessitates iron uptake as ferrous or ferric ions. The transport of the ions within the cell leads to the formation of a ferritin-like intermediate, which subsequently is transported and transformed within the magnetosome organelle in a ferrihydrite-like precursor. Finally, magnetite crystals nucleate and grow toward their mature dimension. In addition, I show that the magnetosome assembly displays hierarchically ordered nano- and microstructures over several levels, enabling the coordinated alignment and motility of entire populations of cells. The magnetosomes are indeed composed of structurally pure magnetite. The organelles are partly composed of proteins, which role is crucial for the properties of the magnetosomes. As an example, we showed how the protein MmsF is involved in the control of magnetosome size and morphology. We have further shown by 2D X-ray diffraction that the magnetosome particles are aligned along the same direction in the magnetosome chain. We then show how magnetic properties of the nascent magnetosome influence the alignment of the particles, and how the proteins MamJ and MamK coordinate this assembly. We propose a theoretical approach, which suggests that biological forces are more important than physical ones for the chain formation. All these studies thus show how magnetosome formation and organization are under strict biological control, which is associated with unprecedented material properties. Finally, we show that the magnetosome chain enables the cells to find their preferred oxygen conditions if the magnetic field is present. The synthetic part of this work shows how the understanding of the design principles of magnetosome formation enabled me to perform biomimetic synthesis of magnetite particles within the highly desired size range of 25 to 100 nm. Nucleation and growth of such particles are based on aggregation of iron colloids termed primary particles as imaged by cryo-high resolution TEM. I show how additives influence magnetite formation and properties. In particular, MamP, a so-called magnetochrome proteins involved in the magnetosome formation in vivo, enables the in vitro formation of magnetite nanoparticles exclusively from ferrous iron by controlling the redox state of the process. Negatively charged additives, such as MamJ, retard magnetite nucleation in vitro, probably by interacting with the iron ions. Other additives such as e.g. polyarginine can be used to control the colloidal stability of stable-single domain sized nanoparticles. Finally, I show how we can “glue” magnetic nanoparticles to form propellers that can be actuated and swim with the help of external magnetic fields. We propose a simple theory to explain the observed movement. We can use the theoretical framework to design experimental conditions to sort out the propellers depending on their size and effectively confirm this prediction experimentally. Thereby, we could image propellers with size down to 290 nm in their longer dimension, much smaller than what perform so far. / Biologische Materialien wie Knochen, Muscheln und Holz wurden von den Menschen seit den ältesten Zeiten verwendet. Diese biologisch gebildeten Materialien haben bemerkenswerte Eigenschaften. Dies ist besonders überraschend, da sie unter physiologischen Bedingungen und mit alltäglichen Bestandteilen gebildet sind. Die Natur liefert uns also nicht nur mit Inspiration für die Entwicklung neuer Materialien, sondern lehrt uns auch, wie biologische Additiven benutzen werden können, um einfache synthetische Bausteine in funktionale Einheiten zu strukturieren. Magnetotaktischen Bakterien und ihre Kette von Magnetosomen sind ein Beispiel, wo einfache Lebewesen die Eigenschaften von anorganischen Materialien steuern, um sich entlang den magnetischen Feldlinien der Erde zu orientieren. Die von den Bakterien gebildeten Magnetosomen sind von besonderem Interesse, da mit magnetischen Eisenoxid-Nanopartikeln in den letzten zehn Jahren einer Vielzahl von Bio-und nanotechnologischen Anwendungen entwickelt worden sind. In dieser Arbeit stelle ich eine biologische und eine bio-inspirierte Forschung auf der Grundlage der magnetotaktischen Bakterien vor. Diese Forschung verbindet die neuesten Entwicklungen von Nanotechnik in der chemischen Wissenschaft, die neuesten Fortschritte der Molekularbiologie zusammen mit modernen Messverfahren. Mein Forschungsschwerpunkt liegt somit an der Schnittstelle zwischen Chemie, Materialwissenschaften, Physik und Biologie. Ich will verstehen, wie biologische Systeme Materialien synthetisieren und organisieren, um Design-Prinzipien zu extrahieren, damit hierarchischen Materialien mit kontrollierten Eigenschaften nachhaltig gebildet werden.

Magnetic hyperthermia (MH) is an anti-cancer treatment which exploits the heat produced by tumour-targeted magnetic nanoparticles (MNPs) subjected to an alternating magnetic field (AMF). A problem limiting the clinical use of MH, however, is the inability to adequately localise the MNPs at the tumour site. A cellular approach using mesenchymal stem cells (MSCs) as carriers has been proposed as these cells are believed to home to sites of tissue injury and tumour growth, however problems with MNPs uptake and toxicity retard progress and need to be overcome. The aim of this project was to find an alternative approach in MH treatment, creating engineered human MSCs able to biosynthesise MNPs. To achieve this goal, MSCs were transfected with either, or both, M. magneticum AMB-1 mms6 and mmsF genes. M. magneticum AMB-1 is a genus of magnetotactic bacteria, containing magnetosomes, which are lipidic organelles containing single crystals of magnetite. M. magneticum-AMB1 mms6 and mmsF genes are important for final crystal morphology and are known to play a role in crystal synthesis and growth respectively. The originality of this study was in using mms6 and mmsF genes, which were codon-optimized for mammalian expression, alone or in combination, for transfection of human MSCs, which have known tumour homing capacity. The transfected MNPs-bearing MSCs, able to migrate into the tumour tissue, were subjected to AMF in MH experiments in an attempt to induce cancer cell death. mms6 and mmsF gene expression, following transfection, was investigated in the human osteosarcoma cell line MG63 by reverse transcription polymerase chain reaction (RT-PCR). The cellular ultrastructure of transfected MG63 cells was investigated by transmission electron microscopy (TEM), revealing the presence of nanoparticles. The magnetism of transfected MG63 cells was proved by superconducting quantum interference device (SQUID) and supported by in vitro MH experiments. Then, human MSCs were transfected with mms6 and mmsF genes, alone or in combination. The effect of transfection experiments and MNPs synthesis on MSCs markers of stemness, cell proliferation and differentiation ability were investigated. The MTB genes expression in human MSCs was assessed by RT-PCR and cell magnetism was confirmed by SQUID, in vitro MH experiments and by magnetic force microscopy (MFM). Then, in vitro studies of MH were undertaken to establish whether mms6 transfected MSCs expressing MNPs supported a MH effect when exposed to an AMF. Cells were initially exposed to an AMF of 565.3 kHz frequency in monolayers and in 3D arrangements and cell death/viability was assessed. Subsequently, the effect of the same AMF on 3D models of mixed populations of mms6-expressing MSCs and cancer cells was assessed. The results indicate that viability of MNPs-expressing MSCs and adjacent cancer cells is reduced following AMF exposure. In vivo studies of MH were undertaken following intracardiac injection of mms6-expressing MSCs in tumour-bearing mice (epidermoid carcinoma). The expression of mms6-expressing MSCs inside mice organs was confirmed by RT-PCR, fluorescence microscopy and immunohistochemistry. The effect of the application of an AMF of 565.3 kHz on mice tumours was studied with different techniques (tumour size and volume measurement, multiphoton microscopy, haematoxylin and eosin staining, and activated Caspase 3 expression), to understand if MNPs created inside mms6- expressing MSCs, following AMF exposure, could lead to cancer cell death. Results indicate that mice tolerate the treatment well, however no appreciable tumour reduction or necrosis was evident. Overall the results suggest that mms6 transfection alone confers the highest magnetisation to MSCs compared to mmsF alone or mms6+mmsF co-transfected, and that mms6 expression in human MSCs does not have an adverse effect on important cell functions. mms6-expressing MSCs, when exposed to an AMF, show reduced viability and enhanced cell cytotoxicity in vitro. When co-cultured with cancer cells in 3D models in vitro, mms6-expressing MSCs are able to reduce viability of adjacent cancer cells confirming the potential applicability of mms6- expressing MSCs for MH treatment. In vivo proof of concept experiments show that mms6-expressing MSCs can locate to the tumour tissue, and mms6-expressing intracardiac injected MSCs mice exposed to AMF tolerate the treatment well. However, the number of mms6-expressing MSCs able to localize to the tumour tissue in this experiment was too low to give an appreciable tumour reduction, so more experiments are needed to enhance the experimental protocol. A number of improvements are required to progress this novel technique towards clinical application. Gene transfection and MNPs production need to be optimised, the best frequency for MH needs to be established and MSCs delivery to the tumour has to be significantly increased to allow concentration of MNPs. The study has helped to increase our knowledge on the creation of magnetic human MSCs to potentially use these cells in MH cancer treatment.

La société Nanobactérie développe un traitement thermique innovant contre le cancer qui repose sur l‘utilisation de nanoparticules d‘oxyde de fer d‘origine bactérienne, appelées magnétosomes. Celles-ci sont injectées directement dans la tumeur puis activées par le champ magnétique alternatif. Cette activation crée une augmentation locale de la température provoquant la destruction de la tumeur, sans affecter les tissus sains environnants. Afin d‘éviter les problèmes de toxicité liés à la présence d‘endotoxines bactériennes à la surface des magnétosomes, un processus de purification est utilisé. Il permet l‘élimination de toute la membrane organique immunogène et de garder ainsi le minéral responsable de l‘activité thermique. Cependant, l‘élimination de cette membrane entraîne l‘agrégation des magnétosomes. La première étape de ce travail de thèse a donc consisté à stabiliser les magnétosomes purifiés, et l'‘identification du meilleur revêtement a été évaluée. Dans une deuxième partie, une nouvelle modalité de chauffage a été mise au point pour augmenter l‘efficacité de l‘hyperthermie magnétique dans la destruction de cellules cancéreuses. / The Nanobactérie company develops a novel strategy of cancer treatment using iron oxide nanoparticles of bacterial origin, called magnetosomes. These nanoparticles are injected directly into the tumor and then activated by an alternating magnetic field. Activated nanoparticles trigger a highly localized rise of temperature, inducing the destruction of the tumor without any adverse effects on adjacent healthy tissues. To avoid the problems of toxicity caused by the presence of bacterial endotoxin which present on the surface of magnetosomes extracted from bacteria, a process of purification is realized to eliminate all the immunogenic organic membrane and keep only the mineral responsible for the thermal activity. However, since elimination of this membrane causes the aggregation of the magnetosomes which become unstable in aqueous solution, the first part of this work consisted in stabilizing the purified magnetosomes by a modification of their surface. The identification of the best coating was then evaluated. Moreover, in the second part of this work, a new heating modality was assessed to increase the efficiency of the magnetic hyperthermia in the destruction of cancer cells.

During the past few years, gold nanoparticles (AuNPs) have received considerable attention in many fields due to their optical properties, photothermal effect and biocompatibility. AuNPs, particularly AuNCs and AuNRs, exhibit great potential in diagnostics and imaging. In the present study, AuNCs were used to selectively image and quantify intracellular antioxidants. It was reported by Chen et al. that the strong fluorescence of AuNCs is quenched by highly reactive oxygen species (hROS). Most of applications depend on fluorescence quenching, however, for our project we designed turn-on fluorescent sensors using AuNCs that sense antioxidants. In the presence of antioxidants, AuNCs fluorescence switch on, while in the absence of antioxidants their fluorescence immediately turn off due to hROS effect. AuNRs were also used for cellular imaging in which AuNRs were conjugated to Cy3-labelled molecular beacon (MB) DNA. Next, the previous complex was loaded in two different strains of magnetotactic bacteria (MTB). MTB were used as a targeted delivery vehicle in which magnetosomes direct the movement of bacteria. The DNA sequence was specific to a certain sequence in mitochondria. The exposure of MTB to an alternating magnetic field (AMF) leads to the increase of temperature inside the bacteria, which destruct the cell wall, and hence, bacterial payload is released. When MD-DNA hybrid with the target sequence, AuNR and Cy3 separate from each other, the fluorescence of the Cy3 is restored.

Iron is a common cation in biomineral sand; it is present for example in magnetite produced by magnetotactic bacteria and in iron sulfides produced by sulfate reducing microorganisms. The work presented in this thesis focused on two types of microorganisms capable of forming iron biominerals. In the first project I have studied the effect of O2 on the respiratory physiology and the formation of magnetosomes by Magnetospirillum magneticum AMB-1. In the second project I have studied the relationship between olivine and the activity of dissimilatory sulfate reducing (DSR) microorganisms. For the first project, I grew cells of AMB-1 in cultures with various concentrations of O2 and monitored growth and the formation of magnetic mineral particles (MMP). Results have shown that AMB-1 cells grew better at 100-225 uMO2(aq) than at lower [O2], yet the formation of MMP was repressed at ~45 uM O2(aq) and strongly inhibited at >100 uM O2(aq).These results have helped better understand the dissimilarity between the optimal growth conditions of magnetotactic bacteria and the conditions needed for the formation of MMPs. My results have also shown that the reaction between H2S produced by DSRs and olivine is abiotic, not catalyzed and exergonic. The pH did not vary significantly during this reaction and pH variation (in the 5-9 range) did not significantly influence this chemical reaction. Bicarbonate inhibited the reaction between H2S and olivine, but not the chemical equilibrium. Phosphate, a weak iron chelator, influenced the equilibrium of the reaction and it is assumed to help increase the rate of olivine weathering in the presence of DSRs. The activity of DSRs was positively influenced by the presence and abundance of olivine. Based on my results I propose that olivine help DSR obtain energy more efficiently, but does not represent a source of energy or nutrients for the cells. These results helped better understand the formation of iron biominerals and signatures of this activity.

<p>Magnetotactic bacteria (MTB) are ubiquitous, multi-phylogenetic bacteria that actively synthesize chains of magnetic, membrane bound; single domain magnetite (Fe₃O₄) or greigite (Fe₃S₄) crystals, termed magnetosomes in order to better navigate to their preferred chemical environment using the Earth’s magnetic field. Discovered in 1963, the field is now focused on understanding magnetosome chain formation and associated processes through genetic studies as well as analytical techniques such as Transmission Electron Microscopy (TEM) and Scanning Transmission X-ray Microscopy – X-ray Magnetic Circular Dichroism (STXM-XMCD).</p> <p>This thesis performed studies on <em>Candidatus Magnetovibrio blakemorei</em> strain MV-1 using STXM at the C 1s, O 1s, Ca 2p and Fe 2p edges. STXM-XMCD was used to determine the magnetism of individual magnetosomes and quantitatively determine magnetic properties such as the magnetic moment of individual chains. A sub-population of MV-1 cells was identified as having anomalous magnetic orientations of magnetosome sub-chains when separated spatial gaps. The frequency of this event and the underlying implications to magnetosome formation are discussed.</p> / Master of Science (MSc)

Les bactéries magnétotactiques (MTB) appartiennent à différents phyla procaryotes et ont la capacité de synthétiser des magnetosomes (cristaux de magnétite entourés par une membrane). Durant la thèse, nous avons procédé à l’analyse génomique de 2 bactéries magnétotactiques: Magnetospira sp. QH-2 et Magnetococcus MO-1. La synthénie et la correlation génique des gènes impliqués dans la formation des magnétosomes montrent que l'insertion de cet îlot chez QH-2 a eu lieu après la divergence entre les Magnetospirillum sp et Magnetospira sp. L'analyse comparative a mis en évidence trois groupes distincts de MTB : Groupe I, comprenant les souches Magnetospirillum spp. et Magnetospira; Groupe II avec MO-1 et M. marinus MC-1 et le Groupe III, avec D. magneticus RS-1. QH-2 montre aussi une évolution adaptative distincte par comparaison aux souches marines ou d'eau douce. L'analyse comparative des réseaux métaboliques révèle une très grande similitude intra-Groupe et une importante variabilité inter-Groupe. Cela est probablement dû aux enzymes impliqués dans les voies métaboliques anoxiques, qui représentent ainsi la contrainte à une distribution taxonomique large des MTB. Ces enzymes permettent ainsi de prédire le phénotype métabolique nécessaire à la production des magnétosomes. Différentes analyses (des protéines ribosomales au genome entier) indiquent une composition taxonomique chimérique des gènes de MO-1 et MC-1, et peut représenter une nouvelle lignée taxonomique chez les Protéobactéries. J’ai aussi participé à l'analyse des génomes de deux bactéries piezophiles, d’une bactérie photosynthétique pourpre et l’analyse phylogénomique des tyrosine-Kinases bactériennes. / Magnetotactic bacteria (MTB) are a diverse group of aquatic prokaryotes, which synthesize membrane-Enclosed magnetic crystals known as magnetosomes. In this thesis, the genome sequences of two marine MTB strains, Magnetospira sp. QH-2 and magneto-Ovoid strain MO-1 were analyzed. The magnetosome gene cluster synteny and mam gene correlation indicate that the insertion of the magnetosome island into QH-2 chromosome occurred after divergence between freshwater and marine magnetospirilla. Comparative genomic analysis revealed three distinct groups of sequenced MTB strains: Group I with Magnetospirillum spp. strains and Magnetospira strain, Group II with MO-1 strain and M. marinus MC-1, and Group III including Desulfovibrio magneticus RS-1. In addition, it shows an adaptive evolution of two marine MTB strains to marine sediments in comparison with closely related freshwater species. Moreover, comparative metabolic network analysis reveals high level of intra-Group similarity and inter-Group variety in MTB. With anoxic network enzymes, potential “MTB” strains are predicted, and are consistent with recently isolated MTB strains. It suggested that the anoxic metabolic network might be one restricted constraint for MTB distribution in bacterial lineages. Interestingly, analyses from ribosomal proteins to the whole MTB genome strongly support a taxonomic chimeric nature of MO-1 and MC-1 genes, and may represent a novel Proteobacteria lineage. Additionally, I also participate to genome analyses of piezophilic Desulfovibrio and Phaeospirillum molischianum strains as well as genome-Wide analysis of bacterial tyrosine kinases.

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.

Les bactéries magnétotactiques (MTB) sont des organismes capables de synthétiser des cristaux magnétiques au sein d’un organite particulier, le magnétosome. L’assemblage de ces magnétosomes leur confère des propriétés d’aimantation et d’orientation dans les champs magnétiques. Dans le contexte de l’essor des biotechnologies, nous avons procédé à la fonctionnalisation des MTB pour des applications de bioremédiation du cobalt.Nous avons ainsi développé des vecteurs adaptés aux MTB pour l’expression de machineries enzymatiques de Staphylococcus aureus et Pseudomonas aeruginosa permettant la production de métallophores analogues à la nicotianamine. Nous avons observé un phénotype double, d’augmentation de la résistance aux métaux et d’augmentation de l’accumulation du cobalt que ce soit chez Escherichia coli ou les MTB Magnetospirillum magneticum AMB-1 et Magnetospirillum gryphiswaldense MSR-1. Nous avons également observé que l’expression de systèmes d’import des métaux tel que la NiCoT perméase NxiA de Rhodopseudomonas palustris dans des souches exprimant les analogues de la nicotianamine permet d’accroître encore l’accumulation des métaux.De plus, nous avons montré que la production de ces analogues permet un enrichissement en cobalt des magnétosomes, mais ne conduit pas à de modification de la spéciation de ce métal chez les MTB.Nous proposons donc ici l’utilisation des MTB comme châssis cellulaire pour de nouvelles applications biotechnologiques. / Magnetotactic bacteria (MTB) are organisms able to synthesize magnetic crystals within a specific organelle, the magnetosome. The assembly of these magnetosomes gives them magnetization and orientation properties in magnetic fields. In the context of the development of biotechnology, we have performed the functionalization of MTBs for cobalt bioremediation applications.We have thus developed vectors suitable for MTB for the expression of enzymatic machineries of Staphylococcus aureus and Pseudomonas aeruginosa allowing the production of metallophores analogous to nicotianamine. We observed a double phenotype, increased resistance toward metals and increased cobalt accumulation in Escherichia coli or MTBs Magnetospirillum magneticum AMB-1 and Magnetospirillum gryphiswaldense MSR-1. We have also observed that the expression of metal import systems such as Rhodopseudomonas palustris NiCoT permease NxiA in strains expressing nicotianamine analogs further increases the accumulation of metals.Moreover, we have shown that the production of these analogs allows a cobalt enrichment of the magnetosomes, but does not lead to a modification of the speciation of this metal in MTB.We introduce here the use of MTBs as cellular chassis for new biotechnological applications.

Cette thèse étudie quelques situations dans lesquelles un système actif, composé de particules auto-propulsées, est soumis à des contraintes extérieures. Dans un premier chapitre, nous étudions le comportement d'une assemblée de bactéries magnétotactiques —capables de s'aligner sur un champ magnétique extérieur— forcées au travers d'une constriction en forme de sablier. Nous caractérisons les propriétés dynamiques de ce système, à l'échelle individuelle mais également à celle de l'embouteillage formé et du jet émergeant. En particulier, nous montrons dans les zones concentrées en bactéries des couplages reliant densité en bactéries, vitesse de nage et forçage magnétique beaucoup plus complexes que ce qui avait été considéré jusqu'à maintenant dans les modèles théoriques.Le deuxième chapitre aborde un nouveau système actif constitué de disques de camphres posés à la surface de l'eau. Dans une première étape, nous avons étudié en détails les propriétés de nage individuelle de ces objets qui brisent spontanément la symétrie du système pour se mettre en mouvement. En particulier, nous montrons que les données recueillies peuvent être rationnalisées à l'aide d'une approche théorique très simple de ce problème couplé d'hydrodynamique et de transport de tensio-actif. Dans un troisième chapitre, nous avons abordé la dynamique d'une assemblée de ces nageurs interfaciaux interagissant via les champs hydrodynamiques et chimiques qu'ils génèrent. À concentration intermédiaire en nageurs, un régime de nage intermittente caractérisé par des bouffées pseudo-périodiques d'activité des nageurs apparaît. En utilisant des outils et concepts issus du domaine de la turbulence nous montrons que de façon remarquable, ce système très simple exhibe des comportements canoniques de la turbulence tels que prédits par Kolmogorov (1941), ouvrant ainsi des perspectives concrètes sur des analogies très riches entre turbulence et systèmes actifs / This work address different situations where active matter, made out of self-propelled particles, is submitted to external constraints.In a first part, we consider the response of magnetotactic bacteria –capable of swim alignment along magnetic field lines- directed through an hourglass shape geometry. We characterize the dynamic properties of the system, both at the individual bacteria scale and at the scale of the jammed region or of the induced outgoing jet. We show that in high density regions, couplings between the bacteria interactions, swim velocity and magnetic forcing take a much more complex form than had been considered so far in theoretical models.In a second chapter, we are addressing a new active system made out of camphor disks lying at the air-water interface. First of all, we study in details the individual swim properties of such particles, which spontaneously break the system symmetry to start moving. In particular, we show that all experimental data can be rationalized within the framework of a very simple model of this complex problem where hydrodynamic flows and surfactant transports are coupled through Marangoni stress.In a last chapter, we addressed the collective dynamics of an assembly of such interfacial swimmers that interact through the flow and chemical fields they generate. At intermediate swimmers concentrations, an intermittent swim regime appears characterized by pseudo-periodic activity bursts. Using tools and concepts from the turbulence domain, we show that, remarkably, this simple system exhibits dynamical properties matching the ones of canonical turbulence as predicted by Kolmogorov in the 40s. This demonstration opens up rich perspectives in the historical domain of turbulence together with in the emerging one of active matter