Publications by authors named "Nicolas Menguy"

60 Publications

Massive Intracellular Remodeling of CuS Nanomaterials Produces Nontoxic Bioengineered Structures with Preserved Photothermal Potential.

ACS Nano 2021 06 25;15(6):9782-9795. Epub 2021 May 25.

Laboratoire Matière et Systèmes Complexes MSC, UMR 7057, CNRS and University of Paris, 75205, Paris Cedex 13, France.

Despite efforts in producing nanoparticles with tightly controlled designs and specific physicochemical properties, these can undergo massive nano-bio interactions and bioprocessing upon internalization into cells. These transformations can generate adverse biological outcomes and premature loss of functional efficacy. Hence, understanding the intracellular fate of nanoparticles is a necessary prerequisite for their introduction in medicine. Among nanomaterials devoted to theranostics is copper sulfide (CuS), which provides outstanding optical properties along with easy synthesis and low cost. Herein, we performed a long-term multiscale study on the bioprocessing of hollow CuS nanoparticles (CuS NPs) and rattle-like iron oxide [email protected] core-shell hybrids ([email protected] NPs) when inside stem cells and cancer cells, cultured as spheroids. In the spheroids, both CuS NPs and [email protected] NPs are rapidly dismantled into smaller units (day 0 to 3), and hair-like nanostructures are generated (day 9 to 21). This bioprocessing triggers an adaptation of the cellular metabolism to the internalized metals without impacting cell viability, differentiation, or oxidative stress response. Throughout the remodeling, a loss of IONF-derived magnetism is observed, but, surprisingly, the CuS photothermal potential is preserved, as demonstrated by a full characterization of the photothermal conversion across the bioprocessing process. The maintained photothermal efficiency correlated well with synchrotron X-ray absorption spectroscopy measurements, evidencing a similar chemical phase for Cu but not for Fe over time. These findings evidence that the intracellular bioprocessing of CuS nanoparticles can reshape them into bioengineered nanostructures without reducing the photothermal function and therapeutic potential.
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http://dx.doi.org/10.1021/acsnano.1c00567DOI Listing
June 2021

Mass collection of magnetotactic bacteria from the permanently stratified ferruginous Lake Pavin, France.

Environ Microbiol 2021 Mar 9. Epub 2021 Mar 9.

Aix-Marseille University, CNRS, CEA, UMR7265 Institute of Biosciences and Biotechnologies of Aix-Marseille, CEA Cadarache, Saint-Paul-lez-Durance, F-13108, France.

Obtaining high biomass yields of specific microorganisms for culture-independent approaches is a challenge faced by scientists studying organism's recalcitrant to laboratory conditions and culture. This difficulty is highly decreased when studying magnetotactic bacteria (MTB) since their unique behaviour allows their enrichment and purification from other microorganisms present in aquatic environments. Here, we use Lake Pavin, a permanently stratified lake in the French Massif Central, as a natural laboratory to optimize collection and concentration of MTB that thrive in the water column and sediments. A method is presented to separate MTB from highly abundant abiotic magnetic particles in the sediment of this crater lake. For the water column, different sampling approaches are compared such as in situ collection using a Niskin bottle and online pumping. By monitoring several physicochemical parameters of the water column, we identify the ecological niche where MTB live. Then, by focusing our sampling at the peak of MTB abundance, we show that the online pumping system is the most efficient for fast recovering of large volumes of water at a high spatial resolution, which is necessary considering the sharp physicochemical gradients observed in the water column. Taking advantage of aerotactic and magnetic MTB properties, we present an efficient method for MTB concentration from large volumes of water. Our methodology represents a first step for further multidisciplinary investigations of the diversity, metagenomic and ecology of MTB populations in Lake Pavin and elsewhere, as well as chemical and isotopic analyses of their magnetosomes.
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http://dx.doi.org/10.1111/1462-2920.15458DOI Listing
March 2021

Diagenetic formation of uranium-silica polymers in lake sediments over 3,300 years.

Proc Natl Acad Sci U S A 2021 01;118(4)

Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie, UMR 7590 Sorbonne Université-CNRS-MNHN-IRD (Museum National d'Histoire Naturelle-Institut de Recherche pour le Développement), 75005 Paris, France.

The long-term fate of uranium-contaminated sediments, especially downstream former mining areas, is a widespread environmental challenge. Essential for their management is the proper understanding of uranium (U) immobilization mechanisms in reducing environments. In particular, the long-term behavior of noncrystalline U(IV) species and their possible evolution to more stable phases in subsurface conditions is poorly documented, which limits our ability to predict U long-term geochemical reactivity. Here, we report direct evidence for the evolution of U speciation over 3,300 y in naturally highly U-enriched sediments (350-760 µg ⋅ g U) from Lake Nègre (Mercantour Massif, Mediterranean Alps, France) by combining U isotopic data (δU and (U/U)) with U -edge X-ray absorption fine structure spectroscopy. Constant isotopic ratios over the entire sediment core indicate stable U sources and accumulation modes, allowing for determination of the impact of aging on U speciation. We demonstrate that, after sediment deposition, mononuclear U(IV) species associated with organic matter transformed into authigenic polymeric U(IV)-silica species that might have partially converted to a nanocrystalline coffinite (USiO·HO)-like phase. This diagenetic transformation occurred in less than 700 y and is consistent with the high silica availability of sediments in which diatoms are abundant. It also yields consistency with laboratory studies that proposed the formation of colloidal polynuclear U(IV)-silica species, as precursors for coffinite formation. However, the incomplete transformation observed here only slightly reduces the potential lability of U, which could have important implications to evaluate the long-term management of U-contaminated sediments and, by extension, of U-bearing wastes in silica-rich subsurface environments.
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http://dx.doi.org/10.1073/pnas.2021844118DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7848604PMC
January 2021

Diverse phylogeny and morphology of magnetite biomineralized by magnetotactic cocci.

Environ Microbiol 2021 02 10;23(2):1115-1129. Epub 2020 Oct 10.

Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Innovation Academy for Earth Science, Chinese Academy of Sciences, Beijing, China.

Magnetotactic bacteria (MTB) are diverse prokaryotes that produce magnetic nanocrystals within intracellular membranes (magnetosomes). Here, we present a large-scale analysis of diversity and magnetosome biomineralization in modern magnetotactic cocci, which are the most abundant MTB morphotypes in nature. Nineteen novel magnetotactic cocci species are identified phylogenetically and structurally at the single-cell level. Phylogenetic analysis demonstrates that the cocci cluster into an independent branch from other Alphaproteobacteria MTB, that is, within the Etaproteobacteria class in the Proteobacteria phylum. Statistical analysis reveals species-specific biomineralization of magnetosomal magnetite morphologies. This further confirms that magnetosome biomineralization is controlled strictly by the MTB cell and differs among species or strains. The post-mortem remains of MTB are often preserved as magnetofossils within sediments or sedimentary rocks, yet paleobiological and geological interpretation of their fossil record remains challenging. Our results indicate that magnetofossil morphology could be a promising proxy for retrieving paleobiological information about ancient MTB.
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http://dx.doi.org/10.1111/1462-2920.15254DOI Listing
February 2021

Intracellular amorphous Ca-carbonate and magnetite biomineralization by a magnetotactic bacterium affiliated to the Alphaproteobacteria.

ISME J 2021 01 24;15(1):1-18. Epub 2020 Aug 24.

Aix-Marseille University, CNRS, CEA, UMR7265 Institute of Biosciences and Biotechnologies of Aix-Marseille (BIAM), CEA Cadarache, F-13108, Saint-Paul-lez-Durance, France.

Bacteria synthesize a wide range of intracellular submicrometer-sized inorganic precipitates of diverse chemical compositions and structures, called biominerals. Their occurrences, functions and ultrastructures are not yet fully described despite great advances in our knowledge of microbial diversity. Here, we report bacteria inhabiting the sediments and water column of the permanently stratified ferruginous Lake Pavin, that have the peculiarity to biomineralize both intracellular magnetic particles and calcium carbonate granules. Based on an ultrastructural characterization using transmission electron microscopy (TEM) and synchrotron-based scanning transmission X-ray microscopy (STXM), we showed that the calcium carbonate granules are amorphous and contained within membrane-delimited vesicles. Single-cell sorting, correlative fluorescent in situ hybridization (FISH), scanning electron microscopy (SEM) and molecular typing of populations inhabiting sediments affiliated these bacteria to a new genus of the Alphaproteobacteria. The partially assembled genome sequence of a representative isolate revealed an atypical structure of the magnetosome gene cluster while geochemical analyses indicate that calcium carbonate production is an active process that costs energy to the cell to maintain an environment suitable for their formation. This discovery further expands the diversity of organisms capable of intracellular Ca-carbonate biomineralization. If the role of such biomineralization is still unclear, cell behaviour suggests that it may participate to cell motility in aquatic habitats as magnetite biomineralization does.
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http://dx.doi.org/10.1038/s41396-020-00747-3DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7853122PMC
January 2021

Formation of a Single-Crystal Aluminum-Based MOF Nanowire with Graphene Oxide Nanoscrolls as Structure-Directing Agents.

Angew Chem Int Ed Engl 2020 Jun 14;59(26):10353-10358. Epub 2020 Apr 14.

Institut des Matériaux Poreux de Paris, UMR 8004 CNRS-ENS-ESPCI, PSL research university, Paris, France.

An innovative strategy is proposed to synthesize single-crystal nanowires (NWs) of the Al dicarboxylate MIL-69(Al) MOF by using graphene oxide nanoscrolls as structure-directing agents. MIL-69(Al) NWs with an average diameter of 70±20 nm and lengths up to 2 μm were found to preferentially grow along the [001] crystallographic direction. Advanced characterization methods (electron diffraction, TEM, STEM-HAADF, SEM, XPS) and molecular modeling revealed the mechanism of formation of MIL-69(Al) NWs involving size-confinement and templating effects. The formation of MIL-69(Al) seeds and the self-scroll of GO sheets followed by the anisotropic growth of MIL-69(Al) crystals are mediated by specific GO sheets/MOF interactions. This study delivers an unprecedented approach to control the design of 1D MOF nanostructures and superstructures.
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http://dx.doi.org/10.1002/anie.202000795DOI Listing
June 2020

Ecotoxicological Studies of ZnO and CdS Nanoparticles on Photosynthetic Microorganism in Seine River Water.

Nanomaterials (Basel) 2020 Jan 28;10(2). Epub 2020 Jan 28.

Université de Paris, ITODYS, UMR 7086, CNRS, 15 rue Jean-Antoine de Baïf, F-75205 Paris CEDEX 13, France.

Seine river water was used as natural environmental medium to study the ecotoxicological impact of ZnO and CdS nanoparticles and Zn and Cd free ions using as a biological target. It was demonstrated by viability tests and photosynthetic activity measurements that free Zn ( = 2.7 × 10 M) is less toxic than free Cd and ZnO nanoparticles ( = 1.4 × 10 M). In the case of cadmium species, free Cd ( = 3.5 × 10 M) was similar to CdS nanoparticles (CdS-1: = 1.9 × 10 M and CdS-2: = 1.9 × 10 M), as follows: CdS > Cd > ZnO > Zn. Adenosine-5'-triphosphate (ATP) assay and superoxide dismutase (SOD) enzymatic activity confirmed these results. Transmission electron microscopy (TEM), coupled with energy-dispersive X-ray spectroscopy (EDS), confirmed the internalization of CdS-1 nanoparticles after 48 h of contact with at 10 M. With a higher concentration of nanoparticles (10 M), ZnO and CdS-2 were also localized inside cells.
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http://dx.doi.org/10.3390/nano10020227DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7075296PMC
January 2020

Transformation Cycle of Magnetosomes in Human Stem Cells: From Degradation to Biosynthesis of Magnetic Nanoparticles Anew.

ACS Nano 2020 02 16;14(2):1406-1417. Epub 2020 Jan 16.

Laboratoire Matière et Systèmes, Complexes MSC, UMR 7057, CNRS and University of Paris , 75205 , Paris Cedex 13 , France.

The nanoparticles produced by magnetotactic bacteria, called magnetosomes, are made of a magnetite core with high levels of crystallinity surrounded by a lipid bilayer. This organized structure has been developed during the course of evolution of these organisms to adapt to their specific habitat and is assumed to resist degradation and to be able to withstand the demanding biological environment. Herein, we investigated magnetosomes' structural fate upon internalization in human stem cells using magnetic and photothermal measurements, electron microscopy, and X-ray absorption spectroscopy. All measurements first converge to the demonstration that intracellular magnetosomes can experience an important biodegradation, with up to 70% of their initial content degraded, which is associated with the progressive storage of the released iron in the ferritin protein. It correlates with an extensive magnetite to ferrihydrite phase transition. The ionic species delivered by this degradation could then be used by the cells to biosynthesize magnetic nanoparticles anew. In this case, cell magnetism first decreased with magnetosomes being dissolved, but then cells remagnetized entirely, evidencing the neo-synthesis of biogenic magnetic nanoparticles. Bacteria-made biogenic magnetosomes can thus be totally remodeled by human stem cells, into human cells-made magnetic nanoparticles.
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http://dx.doi.org/10.1021/acsnano.9b08061DOI Listing
February 2020

On the first evidence of exchange-bias feature in magnetically contrasted consolidates made from CoFeO-CoO core-shell nanoparticles.

Sci Rep 2019 Dec 19;9(1):19468. Epub 2019 Dec 19.

Université de Paris, CNRS UMR-7086, Interfaces Traitement Organisation et DYnamique des Systèmes (ITODYS), 75013, Paris, France.

Hetero-nanostructures based on magnetic contrast oxides have been prepared as highly dense nanoconsolidates. Cobalt ferrite-cobalt oxide core-shell type nanoparticles (NPs) were synthesized by seed mediated growth in polyol and subsequently consolidated by Spark Plasma Sintering (SPS) at 500 °C for a few minutes while applying a uniaxial pressure of 100 MPa. It is interesting to note that the exchange bias feature observed in the core-shell NPs is reproduced in their ceramic counterparts, or even attenuated. A systematic structural characterization was then carried out to elucidate the decrease in the exchange magnetic field, involving mainly advanced X-ray diffraction, zero-field and in-field Fe Mössbauer spectrometry, magnetic measurements and electron microscopy.
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http://dx.doi.org/10.1038/s41598-019-55649-yDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6923415PMC
December 2019

Protective Effect of Polyoxometalates in {Mo}/Maghemite Binary Superlattices Under Annealing.

Front Chem 2019 29;7:830. Epub 2019 Nov 29.

Laboratory MONARIS, Sorbonne Université, CNRS UMR8233, Paris, France.

The binary assembly DDA-{Mo}/OA-γ-FeO (DDA = didodecyldimethylammonium, {Mo} = [MoO(CHCOO)(HO)], OA = oleic acid) constitutes one of the two examples in the literature of binary superlattices made of a mixing of nanocrystals and oxo-clusters. In a precedent work, we reported in details the preparation of such magnetic binary systems and studied the effect of the nature of the polyoxometalates (POMs) on the magnetic properties. In the present paper, we study the stability of this model binary assembly under heating at various temperatures. Indeed, especially if magnetic and/or transport properties are targeted, an annealing can be essential to change the phase of the nanocrystals in a more magnetic one and/or to desorb the organic capping of the nano-objects that can constitute an obstacle to the electronic communication between the nano-objects. We gave evidence that the maghemite organization in the binary assembly is maintained until 370°C under vacuum thanks to the presence of the POMs. This latter evolve in the phase MoO, but still permits to avoid the aggregation of the nanocrystals as well as preserve their periodical arrangement. On the contrary, an assembly made of pure γ-FeO nanocrystals displays a clear aggregation of the nano-objects from 370°C, as attested by transmission and scanning electronic microscopies and confirmed by magnetic measurements. The stability of the magnetic nanocrystals in such POMs/nanocrystals assemblies opens the way to (i) the elaboration of new binary assemblies from POMs and numerous kinds of nanocrystals with a good control on the magnetic properties and to (ii) the investigation of new physical properties as exchange coupling, or magneto-transport in such systems.
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http://dx.doi.org/10.3389/fchem.2019.00830DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6895896PMC
November 2019

Discovery of High Abundances of Aster-Like Nanoparticles in Pelagic Environments: Characterization and Dynamics.

Front Microbiol 2019 15;10:2376. Epub 2019 Oct 15.

Laboratoire Microorganismes: Génome et Environnement, Université Clermont Auvergne, UMR CNRS 6023, Aubière, France.

This study reports the discovery of Aster-Like Nanoparticles (ALNs) in pelagic environments. ALNs are pleomorphic, with three dominant morphotypes which do not fit into any previously defined environmental entities [i.e., ultramicro-prokaryotes, controversed nanobes, and non-living particles (biomimetic mineralo-organic particles, natural nanoparticles or viruses)] of similar size. Elemental composition and selected-area electron diffraction patterns suggested that the organic nature of ALNs may prevail over the possibility of crystal structures. Likewise, recorded changes in ALN numbers in the absence of cells are at odds with an affiliation to until now described viral particles. ALN abundances showed marked seasonal dynamics in the lakewater, with maximal values (up to 9.0 ± 0.5 × 10 particles·mL) reaching eight times those obtained for prokaryotes, and representing up to about 40% of the abundances of virus-like particles. We conclude that (i) aquatic ecosystems are reservoirs of novel, abundant, and dynamic aster-like nanoparticles, (ii) not all virus-like particles observed in aquatic systems are necessarily viruses, and (iii) there may be several types of other ultra-small particles in natural waters that are currently unknown but potentially ecologically important.
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http://dx.doi.org/10.3389/fmicb.2019.02376DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6803438PMC
October 2019

On the limits of Reactive-Spark-Plasma Sintering to prepare magnetically enhanced nanostructured ceramics: the case of the CoFeO-NiO system.

Sci Rep 2019 Oct 1;9(1):14119. Epub 2019 Oct 1.

ITODYS, Université Paris Diderot, Sorbonne Paris Université, CNRS UMR-7086, 75013, Paris, France.

Magnetic materials are crucial for the efficiency of the conversion-storage-transport-reconversion energy chain, and the enhancement of their performance has an important impact on technological development. The present work explores the possibility of preparing hetero-nano-structured ceramics based on magnetic oxides, by coupling a ferrimagnetic phase (F) with an antiferromagnetic one (AF) on the nanometric scale. The field-assisted sintering technique or SPS (Spark-Plasma Sintering), adopted at this purpose, ensures the preservation of nano-sized crystals within the final solid structure. The aim is to establish how exchange bias may affect the resulting nano-consolidates and to investigate the potential of this process to increase the total magnetic anisotropy of the CoFeO grains, and thus their coercive field, while keeping the saturation magnetization the same. The structure, microstructure and magnetic properties of the ceramics obtained were studied by several techniques. The results show that the sintering process, along with its typical reductive atmosphere, modifies the composition of the constituents. A new metallic phase appears as a consequence of the reciprocal diffusion of Co and Ni cations, leading to a change in the amount and structure of the AF phase. We propose a schematic representation of the atomic movements that hinder an exchange bias effect between the F and AF phases.
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http://dx.doi.org/10.1038/s41598-019-50657-4DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6773756PMC
October 2019

Decoding Biomineralization: Interaction of a Mad10-Derived Peptide with Magnetite Thin Films.

Nano Lett 2019 11 7;19(11):8207-8215. Epub 2019 Oct 7.

Department of Biomaterials , Max Planck Institute of Colloids and Interfaces , Am Mühlenberg 1 , 14476 Potsdam , Germany.

Protein-surface interactions play a pivotal role in processes as diverse as biomineralization, biofouling, and the cellular response to medical implants. In biomineralization processes, biomacromolecules control mineral deposition and architecture via complex and often unknown mechanisms. For studying these mechanisms, the formation of magnetite nanoparticles in magnetotactic bacteria has become an excellent model system. Most interestingly, nanoparticle morphologies have been discovered that defy crystallographic rules (e.g., in the species strain BW-1). In certain conditions, this strain mineralizes bullet-shaped magnetite nanoparticles, which exhibit defined (111) crystal faces and are elongated along the [100] direction. We hypothesize that surface-specific protein interactions break the nanoparticle symmetry, inhibiting the growth of certain crystal faces and thereby favoring the growth of others. Screening the genome of BW-1, we identified Mad10 (gnetosome-ssociated eep-branching) as a potential magnetite-binding protein. Using atomic force microscope (AFM)-based single-molecule force spectroscopy, we show that a Mad10-derived peptide, which represents the most conserved region of Mad10, binds strongly to (100)- and (111)-oriented single-crystalline magnetite thin films. The peptide-magnetite interaction is thus material- but not crystal-face-specific. It is characterized by broad rupture force distributions that do not depend on the retraction speed of the AFM cantilever. To account for these experimental findings, we introduce a three-state model that incorporates fast rebinding. The model suggests that the peptide-surface interaction is strong in the absence of load, which is a direct result of this fast rebinding process. Overall, our study sheds light on the kinetic nature of peptide-surface interactions and introduces a new magnetite-binding peptide with potential use as a functional coating for magnetite nanoparticles in biotechnological and biomedical applications.
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http://dx.doi.org/10.1021/acs.nanolett.9b03560DOI Listing
November 2019

Nickel and iron partitioning between clay minerals, Fe-oxides and Fe-sulfides in lagoon sediments from New Caledonia.

Sci Total Environ 2019 Nov 21;689:1212-1227. Epub 2019 Jun 21.

Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie (IMPMC), UMR 7590 CNRS-SU-IRD-MNHN, Sorbonne Université, case 115, 4 place Jussieu, 75252 Paris Cedex 5, France.

In the tropics, continental weathering and erosion are major sources of trace metals towards estuaries and lagoons, where early diagenesis of sediments may influence their mobility and bioavailability. Determining trace metals speciation in tropical sedimentary settings is thus needed to assess their long-term fate and potential threat to fragile coastal ecosystems. In this study, we determined Fe, Ni and S speciation across a shore-to-reef gradient in sediments from the New Caledonia lagoon that receive mixed contribution from lateritic (iron-oxyhydroxides and clay minerals), volcano-sedimentary (silicates) and marine (carbonate) sources. Sulfur K-edge XANES data indicated a major contribution of pyrite (FeS) to S speciation close to the shore. However, this contribution was found to dramatically decrease across the shore-to-reef gradient, S mainly occurring as sulfate close to the coral reef. In contrast, Fe and Ni K-edge XANES and EXAFS data indicated a minor contribution of pyrite to Fe and Ni speciation, and this contribution could be evidenced only close to the shore. The major fractions of Fe and Ni across the shore-to-reef gradient were found to occur as Ni- and Fe-bearing clay minerals consisting of smectite (~nontronite), glauconite and two types of serpentines (chrysotile and greenalite/berthierine). Among these clay minerals, greenalite/berthierine, glauconite and possibly smectite, were considered as authigenic. The low contribution of pyrite to trace metals speciation compared to clay minerals is interpreted as a result of (1) a reduced formation rate due to the low amounts of organic carbon compared to the Fe pool and (2) repeated re-oxidation events upon re-suspension of the sediments top layers due to the specific context of shallow lagoon waters. This study thus suggests that green clay authigenesis could represent a key process in the biogeochemical cycling of trace metals that are delivered to lagoon ecosystems upon continental erosion and weathering.
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http://dx.doi.org/10.1016/j.scitotenv.2019.06.274DOI Listing
November 2019

Bio-inspired hydrophobicity promotes CO reduction on a Cu surface.

Nat Mater 2019 11 5;18(11):1222-1227. Epub 2019 Aug 5.

Laboratoire de Chimie des Processus Biologiques, CNRS UMR 8229, Collège de France, Paris, France.

The aqueous electrocatalytic reduction of CO into alcohol and hydrocarbon fuels presents a sustainable route towards energy-rich chemical feedstocks. Cu is the only material able to catalyse the substantial formation of multicarbon products (C/C), but competing proton reduction to hydrogen is an ever-present drain on selectivity. Here, a superhydrophobic surface was generated by 1-octadecanethiol treatment of hierarchically structured Cu dendrites, inspired by the structure of gas-trapping cuticles on subaquatic spiders. The hydrophobic electrode attained a 56% Faradaic efficiency for ethylene and 17% for ethanol production at neutral pH, compared to 9% and 4% on a hydrophilic, wettable equivalent. These observations are assigned to trapped gases at the hydrophobic Cu surface, which increase the concentration of CO at the electrode-solution interface and consequently increase CO reduction selectivity. Hydrophobicity is thus proposed as a governing factor in CO reduction selectivity and can help explain trends seen on previously reported electrocatalysts.
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http://dx.doi.org/10.1038/s41563-019-0445-xDOI Listing
November 2019

Juxtaposed membranes underpin cellular adhesion and display unilateral cell division of multicellular magnetotactic prokaryotes.

Environ Microbiol 2020 04 8;22(4):1481-1494. Epub 2019 Jul 8.

Aix Marseille University, CNRS, LCB, Marseille, 13402, France.

Multicellular magnetotactic prokaryotes (MMPs) exhibit peculiar coordination of swimming along geomagnetic field lines. Approximately 40-80 cells assemble, with a helical geometry or axisymmetry, into spherical or ellipsoidal MMPs respectively. To contribute to a comprehensive understanding of bacterial multicellularity here we took multiple microscopic approaches to study the diversity, assembly, reproduction and motility of ellipsoidal MMPs. Using correlative fluorescence in situ hybridization and scanning electron microscopy analysis, we found an unexpected diversity in populations of ellipsoidal MMPs in the Mediterranean Sea. The high-pressure freezing/freeze substitution fixation technique allowed us to show, for the first time, that cells adhere via juxtaposed membranes and are held together by a rimming lattice. Fluorescence confocal microscopy and ultrathin section images revealed not only the one-layer hollow three-dimensional architecture, but also periphery-core unilateral constriction of constituent cells and unidirectional binary fission of the ellipsoidal MMPs. This finding suggests the evolution toward MMPs multicellularity via the mechanism of incomplete separation of offspring. Remarkably, thousands of flagellar at the periphery surface of cells underpin the coordinated swimming of MMPs in response to mechanical, chemical, magnetic and optical stimuli, including a magnetotactic photokinesis behaviour. Together these results unveil the unique structure and function property of ellipsoidal MMPs.
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http://dx.doi.org/10.1111/1462-2920.14710DOI Listing
April 2020

Phylogenetic and Structural Identification of a Novel Magnetotactic Strain, WYHR-1, from a Freshwater Lake.

Appl Environ Microbiol 2019 07 1;85(14). Epub 2019 Jul 1.

Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, People's Republic of China.

Magnetotactic bacteria (MTB) are phylogenetically diverse prokaryotes that are able to biomineralize intracellular, magnetic chains of magnetite or greigite nanocrystals called magnetosomes. Simultaneous characterization of MTB phylogeny and biomineralization is crucial but challenging because most MTB are extremely difficult to culture. We identify a large rod, bean-like MTB (tentatively named WYHR-1) from freshwater sediments of Weiyang Lake, Xi'an, China, using a coupled fluorescence and scanning electron microscopy approach at the single-cell scale. Phylogenetic analysis of 16S rRNA gene sequences indicates that WYHR-1 is a novel genus from the class. Transmission electron microscope observations reveal that WYHR-1 cells contain tens of magnetite magnetosomes that are organized into a single chain bundle along the cell long axis. Mature WYHR-1 magnetosomes are bullet-shaped, straight, and elongated along the [001] direction, with a large flat end terminated by a {100} face at the base and a conical top. This crystal morphology is distinctively different from bullet-shaped magnetosomes produced by other MTB in the class and the phylum. This indicates that WYHR-1 may have a different crystal growth process and mechanism from other species, which results from species-specific magnetosome biomineralization in MTB. Magnetotactic bacteria (MTB) represent a model system for understanding biomineralization and are also studied intensively in biogeomagnetic and paleomagnetic research. However, many uncultured MTB strains have not been identified phylogenetically or investigated structurally at the single-cell level, which limits comprehensive understanding of MTB diversity and their role in biomineralization. We have identified a novel MTB strain, WYHR-1, from a freshwater lake using a coupled fluorescence and scanning electron microscopy approach at the single-cell scale. Our analyses further indicate that strain WYHR-1 represents a novel genus from the class. In contrast to bullet-shaped magnetosomes produced by other MTB in the class and the phylum, WYHR-1 magnetosomes are bullet-shaped, straight, and highly elongated along the [001] direction, are terminated by a large {100} face at their base, and have a conical top. Our findings imply that, consistent with phylogenetic diversity of MTB, bullet-shaped magnetosomes have diverse crystal habits and growth patterns.
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http://dx.doi.org/10.1128/AEM.00731-19DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6606866PMC
July 2019

Ectosymbiotic bacteria at the origin of magnetoreception in a marine protist.

Nat Microbiol 2019 07 29;4(7):1088-1095. Epub 2019 Apr 29.

CNRS, CEA, Aix-Marseille Université, UMR7265 Biosciences and Biotechnologies Institute of Aix-Marseille, Saint Paul lez Durance, France.

Mutualistic symbioses are often a source of evolutionary innovation and drivers of biological diversification. Widely distributed in the microbial world, particularly in anoxic settings, they often rely on metabolic exchanges and syntrophy. Here, we report a mutualistic symbiosis observed in marine anoxic sediments between excavate protists (Symbiontida, Euglenozoa) and ectosymbiotic Deltaproteobacteria biomineralizing ferrimagnetic nanoparticles. Light and electron microscopy observations as well as genomic data support a multi-layered mutualism based on collective magnetotactic motility with division of labour and interspecies hydrogen-transfer-based syntrophy. The guided motility of the consortia along the geomagnetic field is allowed by the magnetic moment of the non-motile ectosymbiotic bacteria combined with the protist motor activity, which is a unique example of eukaryotic magnetoreception acquired by symbiosis. The nearly complete deltaproteobacterial genome assembled from a single consortium contains a full magnetosome gene set, but shows signs of reduction, with the probable loss of flagellar genes. Based on the metabolic gene content, the ectosymbiotic bacteria are anaerobic sulfate-reducing chemolithoautotrophs that likely reduce sulfate with hydrogen produced by hydrogenosome-like organelles underlying the plasma membrane of the protist. In addition to being necessary hydrogen sinks, ectosymbionts may provide organics to the protist by diffusion and predation, as shown by magnetosome-containing digestive vacuoles. Phylogenetic analyses of 16S and 18S ribosomal RNA genes from magnetotactic consortia in marine sediments across the Northern and Southern hemispheres indicate a host-ectosymbiont specificity and co-evolution. This suggests a historical acquisition of magnetoreception by a euglenozoan ancestor from Deltaproteobacteria followed by subsequent diversification. It also supports the cosmopolitan nature of this type of symbiosis in marine anoxic sediments.
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http://dx.doi.org/10.1038/s41564-019-0432-7DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6697534PMC
July 2019

Identification of novel species of marine magnetotactic bacteria affiliated with Nitrospirae phylum.

Environ Microbiol Rep 2019 06 6;11(3):330-337. Epub 2019 May 6.

Aix Marseille University, CNRS, LCB, Marseille, 13402, France.

Magnetotactic bacteria (MTB) are a group of Gram-negative bacteria characterized by synthesizing magnetosomes and swimming along geomagnetic field lines. Phylogenetically, they belong to different taxonomic lineages including Proteobacteria, Nitrospirae, Omnitrophica, Latescibacteria and Planctomycetes phyla on the phylogenetic tree. To date, six Nitrospirae MTB phylotypes have been identified from freshwater or low-salinity environments and described in the literature. Here, we report the identification of two Nitrospirae MTB phylotypes collected, for the first time, from the marine environment. Both have a spherical morphology with a cell size of ~ 5 μM and similar motility but are different colours (black-brown and ivory-white) under the optic microscope. They synthesized bullet-shaped iron-oxide magnetosomes that were arranged in multiple bundles of chains. Moreover, the cytoplasm of the black-brown Nitrospirae MTB contained sulphur inclusions that conferred on cells a rough, granular appearance. Phylogenetic analysis based on their 16S rRNA gene sequences revealed that they are two novel species and cluster with the previously reported MTB affiliated with the phylum Nitrospirae, thus extending the distribution of Nitrospirae MTB from freshwater to the marine environment.
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http://dx.doi.org/10.1111/1758-2229.12755DOI Listing
June 2019

Low-cost high-efficiency system for solar-driven conversion of CO to hydrocarbons.

Proc Natl Acad Sci U S A 2019 May 27;116(20):9735-9740. Epub 2019 Mar 27.

Laboratoire de Chimie des Processus Biologiques, CNRS UMR 8229, Collège de France, Sorbonne Université, 75231 Paris Cedex 05, France;

Conversion of carbon dioxide into hydrocarbons using solar energy is an attractive strategy for storing such a renewable source of energy into the form of chemical energy (a fuel). This can be achieved in a system coupling a photovoltaic (PV) cell to an electrochemical cell (EC) for CO reduction. To be beneficial and applicable, such a system should use low-cost and easily processable photovoltaic cells and display minimal energy losses associated with the catalysts at the anode and cathode and with the electrolyzer device. In this work, we have considered all of these parameters altogether to set up a reference PV-EC system for CO reduction to hydrocarbons. By using the same original and efficient Cu-based catalysts at both electrodes of the electrolyzer, and by minimizing all possible energy losses associated with the electrolyzer device, we have achieved CO reduction to ethylene and ethane with a 21% energy efficiency. Coupled with a state-of-the-art, low-cost perovskite photovoltaic minimodule, this system reaches a 2.3% solar-to-hydrocarbon efficiency, setting a benchmark for an inexpensive all-earth-abundant PV-EC system.
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http://dx.doi.org/10.1073/pnas.1815412116DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6525546PMC
May 2019

Iron Oxide Nanoflowers @ CuS Hybrids for Cancer Tri-Therapy: Interplay of Photothermal Therapy, Magnetic Hyperthermia and Photodynamic Therapy.

Theranostics 2019 12;9(5):1288-1302. Epub 2019 Feb 12.

Sorbonne Université, CNRS UMR 8234, Physicochimie des Electrolytes et Nanosystèmes InterfaciauX (PHENIX), 4 place Jussieu, 75005 Paris, France.

Innovative synthesis routes revolutionized nanomaterial combination and design possibilities resulting in a new generation of fine-tuned nanoparticles featuring exquisite shape and constitution control. However, there is still room for improvement when it comes to the development of multi-functional nanoparticle agents merging a plurality of therapeutic functions to tackle tumors simultaneously by synergic mechanisms. Herein, we report the design of an optimized nanohybrid for cancer tri-therapy featuring a maghemite (γ-Fe2O3) nanoflower-like multicore nanoparticle conceived for efficient magnetic hyperthermia (MHT) and a spiky copper sulfide shell ([email protected]) with a high near-infrared (NIR) absorption coefficient suitable for photothermal (PTT) and photodynamic therapy (PDT). Spiky-like [email protected] nanohybrids were obtained through a straightforward and scalable water-based template sacrificial synthesis, which allows the shell shape control by tuning polyvinylpyrrolidone (PVP) concentration. A comprehensive characterization of nanohybrid size, shape and structural properties was carried out by combining complementary TEM, SEM, HR-TEM, EELS, XRD and NTA. The all-in-one therapeutic multi-functionality was assessed on cancer cells and on tumor-bearing nude mice. Tests carried out on [email protected] nanohybrid aqueous dispersion demonstrated their impressive efficiency to convert light (conversion coefficient = 42 ± 6 %) and magnetic stimulation (SAR ~ 350 W g) into heat as well as to induce concurrent reactive oxygen species (ROS) formation upon laser irradiation. Such capabilities were further confirmed in cellular environment by tests and at the organism level by tests in a murine tumor model. Notably, complete tumor regression was obtained for the PTT mode at low Cu concentration. Overall, these results allowed determining windows of applicability for each therapy individually or in combination. Altogether, the obtained data evidence the successful synthesis of a unique tri-therapeutic nanoparticle featuring highly relevant assets for clinical translation such as reduced nanoparticle administered dose, reduced laser power exposure, reduced magnetic field frequency, and the possibility of serial heating cycles and therapy monitoring by photoacoustic (PA) and magnetic resonance imaging (MRI). Furthermore, the integration of the dual heating capability (MHT + PTT) with the PDT insult offers a unique asset to tackle tumors by multiple cytotoxic strategies in order to improve the therapeutic outcome in a broader spectrum of clinical conditions.
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http://dx.doi.org/10.7150/thno.30238DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6401506PMC
January 2020

Biosynthesis of magnetic nanoparticles from nano-degradation products revealed in human stem cells.

Proc Natl Acad Sci U S A 2019 03 13;116(10):4044-4053. Epub 2019 Feb 13.

Laboratoire Matière et Systèmes Complexes, UMR 7057, CNRS and University Paris Diderot, 75205 Paris Cedex 13, France;

While magnetic nanoparticles offer exciting possibilities for stem cell imaging or tissue bioengineering, their long-term intracellular fate remains to be fully documented. Besides, it appears that magnetic nanoparticles can occur naturally in human cells, but their origin and potentially endogenous synthesis still need further understanding. In an effort to explore the life cycle of magnetic nanoparticles, we investigated their transformations upon internalization in mesenchymal stem cells and as a function of the cells' differentiation status (undifferentiated, or undergoing adipogenesis, osteogenesis, and chondrogenesis). Using magnetism as a fingerprint of the transformation process, we evidenced an important degradation of the nanoparticles during chondrogenesis. For the other pathways, stem cells were remarkably "remagnetized" after degradation of nanoparticles. This remagnetization phenomenon is the direct demonstration of a possible neosynthesis of magnetic nanoparticles and could lay some foundation to understand the presence of magnetic crystals in human cells. The neosynthesis was shown to take place within the endosomes and to involve the H-subunit of ferritin. Moreover, it appeared to be the key process to avoid long-term cytotoxicity (impact on differentiation) related to high doses of magnetic nanoparticles within stem cells.
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http://dx.doi.org/10.1073/pnas.1816792116DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6410821PMC
March 2019

Nature of Hexagonal Silicon Forming via High-Pressure Synthesis: Nanostructured Hexagonal 4H Polytype.

Nano Lett 2018 09 20;18(9):5989-5995. Epub 2018 Aug 20.

Sorbonne Université, Muséum National d'Histoire Naturelle, UMR CNRS 7590, IRD. - Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie (IMPMC), 4 Place Jussieu , 75005 Paris , France.

Hexagonal Si allotropes are expected to enhance light absorption in the visible range as compared to common cubic Si with diamond structure. Therefore, synthesis of these materials is crucial for the development of Si-based optoelectronics. In this work, we combine in situ high-pressure high-temperature synthesis and vacuum heating to obtain hexagonal Si. High pressure is one of the most promising routes to stabilize these allotropes. It allows one to obtain large-volume nanostructured ingots by a sequence of direct solid-solid transformations, ensuring high-purity samples for detailed characterization. Thanks to our synthesis approach, we provide the first evidence of a polycrystalline bulk sample of hexagonal Si. Exhaustive structural analysis, combining fine-powder X-ray and electron diffraction, afforded resolution of the crystal structure. We demonstrate that hexagonal Si obtained by high-pressure synthesis correspond to Si-4H polytype (ABCB stacking) in contrast with Si-2H (AB stacking) proposed previously. This result agrees with prior calculations that predicted a higher stability of the 4H form over 2H form. Further physical characterization, combining experimental data and ab initio calculations, have shown a good agreement with the established structure. Strong photoluminescence emission was observed in the visible region for which we foresee optimistic perspectives for the use of this material in Si-based photovoltaics.
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http://dx.doi.org/10.1021/acs.nanolett.8b02816DOI Listing
September 2018

Genomic study of a novel magnetotactic Alphaproteobacteria uncovers the multiple ancestry of magnetotaxis.

Environ Microbiol 2018 12 16;20(12):4415-4430. Epub 2018 Oct 16.

Institute of Biosciences and Biotechnologies of Aix Marseille (BIAM), UMR7265 CEA - CNRS - Aix Marseille University, CEA Cadarache, 13108, Saint-Paul-lez-Durance, France.

Ecological and evolutionary processes involved in magnetotactic bacteria (MTB) adaptation to their environment have been a matter of debate for many years. Ongoing efforts for their characterization are progressively contributing to understand these processes, including the genetic and molecular mechanisms responsible for biomineralization. Despite numerous culture-independent MTB characterizations, essentially within the Proteobacteria phylum, only few species have been isolated in culture because of their complex growth conditions. Here, we report a newly cultivated magnetotactic, microaerophilic and chemoorganoheterotrophic bacterium isolated from the Mediterranean Sea in Marseille, France: Candidatus Terasakiella magnetica strain PR-1 that belongs to an Alphaproteobacteria genus with no magnetotactic relative. By comparing the morphology and the whole genome shotgun sequence of this MTB with those of closer relatives, we brought further evidence that the apparent vertical ancestry of magnetosome genes suggested by previous studies within Alphaproteobacteria hides a more complex evolutionary history involving horizontal gene transfers and/or duplication events before and after the emergence of Magnetospirillum, Magnetovibrio and Magnetospira genera. A genome-scale comparative genomics analysis identified several additional candidate functions and genes that could be specifically associated to MTB lifestyle in this class of bacteria.
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http://dx.doi.org/10.1111/1462-2920.14364DOI Listing
December 2018

Magnetic-field induced rotation of magnetosome chains in silicified magnetotactic bacteria.

Sci Rep 2018 05 16;8(1):7699. Epub 2018 May 16.

Sorbonne Université, CNRS, Collège de France, Laboratoire de Chimie de la Matière Condensée de Paris, 4 Place Jussieu, 75252, Paris, Cedex 05, France.

Understanding the biological processes enabling magnetotactic bacteria to maintain oriented chains of magnetic iron-bearing nanoparticles called magnetosomes is a major challenge. The study aimed to constrain the role of an external applied magnetic field on the alignment of magnetosome chains in Magnetospirillum magneticum AMB-1 magnetotactic bacteria immobilized within a hydrated silica matrix. A deviation of the chain orientation was evidenced, without significant impact on cell viability, which was preserved after the field was turned-off. Transmission electron microscopy showed that the crystallographic orientation of the nanoparticles within the chains were preserved. Off-axis electron holography evidenced that the change in magnetosome orientation was accompanied by a shift from parallel to anti-parallel interactions between individual nanocrystals. The field-induced destructuration of the chain occurs according to two possible mechanisms: (i) each magnetosome responds individually and reorients in the magnetic field direction and/or (ii) short magnetosome chains deviate in the magnetic field direction. This work enlightens the strong dynamic character of the magnetosome assembly and widens the potentialities of magnetotactic bacteria in bionanotechnology.
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http://dx.doi.org/10.1038/s41598-018-25972-xDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5955880PMC
May 2018

Accumulation and Dissolution of Magnetite Crystals in a Magnetically Responsive Ciliate.

Appl Environ Microbiol 2018 04 2;84(8). Epub 2018 Apr 2.

CNRS/CEA/Aix-Marseille Université, UMR7265 Biosciences and Biotechnologies Institute of Aix-Marseille, Saint-Paul-lés-Durance, France

Magnetotactic bacteria (MTB) represent a group of microorganisms that are widespread in aquatic habitats and thrive at oxic-anoxic interfaces. They are able to scavenge high concentrations of iron thanks to the biomineralization of magnetic crystals in their unique organelles, the so-called magnetosome chains. Although their biodiversity has been intensively studied, their ecology and impact on iron cycling remain largely unexplored. Predation by protozoa was suggested as one of the ecological processes that could be involved in the release of iron back into the ecosystem. Magnetic protozoa were previously observed in aquatic environments, but their diversity and the fate of particulate iron during grazing are poorly documented. In this study, we report the morphological and molecular characterizations of a magnetically responsive MTB-grazing protozoan able to ingest high quantities of MTB. This protozoan is tentatively identified as , a ciliate known to be a predator of bacteria. Using light and electron microscopy, we investigated in detail the vacuoles in which the lysis of phagocytized prokaryotes occurs. We carried out high-resolution observations of aligned magnetosome chains and ongoing dissolution of crystals. Particulate iron in the ciliate represented approximately 0.01% of its total volume. We show the ubiquity of this interaction in other types of environments and describe different grazing strategies. These data contribute to the mounting evidence that the interactions between MTB and protozoa might play a significant role in iron turnover in microaerophilic habitats. Identifying participants of each biogeochemical cycle is a prerequisite to our understanding of ecosystem functioning. Magnetotactic bacteria (MTB) participate in iron cycling by concentrating large amounts of biomineralized iron minerals in their cells, which impacts their chemical environment at, or below, the oxic-anoxic transition zone in aquatic habitats. It was shown that some protozoa inhabiting this niche could become magnetic by the ingestion of magnetic crystals biomineralized by grazed MTB. In this study, we show that magnetic MTB grazers are commonly observed in marine and freshwater sediments and can sometimes accumulate very large amounts of particulate iron. We describe here different phagocytosis strategies, determined using magnetic particles from MTB as tracers after their ingestion by the protozoa. This study paves the way for potential scientific or medical applications using MTB grazers as magnetosome hyperaccumulators.
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http://dx.doi.org/10.1128/AEM.02865-17DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5881073PMC
April 2018

Interactions between magnetite and humic substances: redox reactions and dissolution processes.

Geochem Trans 2017 Oct 19;18(1). Epub 2017 Oct 19.

Geomicrobiology, Center for Applied Geosciences, University of Tuebingen, Sigwartstrasse 10, 72076, Tuebingen, Germany.

Humic substances (HS) are redox-active compounds that are ubiquitous in the environment and can serve as electron shuttles during microbial Fe(III) reduction thus reducing a variety of Fe(III) minerals. However, not much is known about redox reactions between HS and the mixed-valent mineral magnetite (FeO) that can potentially lead to changes in Fe(II)/Fe(III) stoichiometry and even dissolve the magnetite. To address this knowledge gap, we incubated non-reduced (native) and reduced HS with four types of magnetite that varied in particle size and solid-phase Fe(II)/Fe(III) stoichiometry. We followed dissolved and solid-phase Fe(II) and Fe(III) concentrations over time to quantify redox reactions between HS and magnetite. Magnetite redox reactions and dissolution processes with HS varied depending on the initial magnetite and HS properties. The interaction between biogenic magnetite and reduced HS resulted in dissolution of the solid magnetite mineral, as well as an overall reduction of the magnetite. In contrast, a slight oxidation and no dissolution was observed when native and reduced HS interacted with 500 nm magnetite. This variability in the solubility and electron accepting and donating capacity of the different types of magnetite is likely an effect of differences in their reduction potential that is correlated to the magnetite Fe(II)/Fe(III) stoichiometry, particle size, and crystallinity. Our study suggests that redox-active HS play an important role for Fe redox speciation within minerals such as magnetite and thereby influence the reactivity of these Fe minerals and their role in biogeochemical Fe cycling. Furthermore, such processes are also likely to have an effect on the fate of other elements bound to the surface of Fe minerals.
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http://dx.doi.org/10.1186/s12932-017-0044-1DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5648731PMC
October 2017

Desulfamplus magnetovallimortis gen. nov., sp. nov., a magnetotactic bacterium from a brackish desert spring able to biomineralize greigite and magnetite, that represents a novel lineage in the Desulfobacteraceae.

Syst Appl Microbiol 2017 Jul 31;40(5):280-289. Epub 2017 May 31.

CNRS/CEA/Aix-Marseille Université, UMR7265 Institut de biosciences et biotechnologies, Laboratoire de Bioénergétique Cellulaire, 13108 Saint Paul lez Durance, France. Electronic address:

A magnetotactic bacterium, designated strain BW-1, was isolated from a brackish spring in Death Valley National Park (California, USA) and cultivated in axenic culture. The Gram-negative cells of strain BW-1 are relatively large and rod-shaped and possess a single polar flagellum (monotrichous). This strain is the first magnetotactic bacterium isolated in axenic culture capable of producing greigite and/or magnetite nanocrystals aligned in one or more chains per cell. Strain BW-1 is an obligate anaerobe that grows chemoorganoheterotrophically while reducing sulfate as a terminal electron acceptor. Optimal growth occurred at pH 7.0 and 28°C with fumarate as electron donor and carbon source. Based on its genome sequence, the G+C content is 40.72mol %. Phylogenomic and phylogenetic analyses indicate that strain BW-1 belongs to the Desulfobacteraceae family within the Deltaproteobacteria class. Based on average amino acid identity, strain BW-1 can be considered as a novel species of a new genus, for which the name Desulfamplus magnetovallimortis is proposed. The type strain of D. magnetovallimortis is BW-1 (JCM 18010-DSM 103535).
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http://dx.doi.org/10.1016/j.syapm.2017.05.001DOI Listing
July 2017

Magnetotactic Coccus Strain SHHC-1 Affiliated to Forms Octahedral Magnetite Magnetosomes.

Front Microbiol 2017 30;8:969. Epub 2017 May 30.

Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of SciencesBeijing, China.

Magnetotactic bacteria (MTB) are morphologically and phylogenetically diverse prokaryotes. They can form intracellular chain-assembled magnetite (FeO) or greigite (FeS) nanocrystals each enveloped by a lipid bilayer membrane called a magnetosome. Magnetotactic cocci have been found to be the most abundant morphotypes of MTB in various aquatic environments. However, knowledge on magnetosome biomineralization within magnetotactic cocci remains elusive due to small number of strains that have been cultured. By using a coordinated fluorescence and scanning electron microscopy method, we discovered a unique magnetotactic coccus strain (tentatively named SHHC-1) in brackish sediments collected from the estuary of Shihe River in Qinhuangdao city, eastern China. It phylogenetically belongs to the class. Transmission electron microscopy analyses reveal that SHHC-1 cells formed many magnetite-type magnetosomes organized as two bundles in each cell. Each bundle contains two parallel chains with smaller magnetosomes generally located at the ends of each chain. Unlike most magnetotactic alphaproteobacteria that generally form magnetosomes with uniform crystal morphologies, SHHC-1 magnetosomes display a more diverse variety of crystal morphology even within a single cell. Most particles have rectangular and rhomboidal projections, whilst others are triangular, or irregular. High resolution transmission electron microscopy observations coupled with morphological modeling indicate an idealized model-elongated octahedral crystals, a form composed of eight {111} faces. Furthermore, twins, multiple twins and stack dislocations are frequently observed in the SHHC-1 magnetosomes. This suggests that biomineralization of strain SHHC-1 magnetosome might be less biologically controlled than other magnetotactic alphaproteobacteria. Alternatively, SHHC-1 is more sensitive to the unfavorable environments under which it lives, or a combination of both factors may have controlled the magnetosome biomineralization process within this unique MTB.
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http://dx.doi.org/10.3389/fmicb.2017.00969DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5447723PMC
May 2017

Single-Cell Resolution of Uncultured Magnetotactic Bacteria via Fluorescence-Coupled Electron Microscopy.

Appl Environ Microbiol 2017 06 31;83(12). Epub 2017 May 31.

Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, People's Republic of China.

Magnetotactic bacteria (MTB) form intracellular chain-assembled nanocrystals of magnetite or greigite termed magnetosomes. The characterization of magnetosome crystals requires electron microscopy due to their nanoscopic sizes. However, electron microscopy does not provide phylogenetic information for MTB. We have developed a strategy for the simultaneous and rapid phylogenetic and biomineralogical characterization of uncultured MTB at the single-cell level. It consists of four steps: (i) enrichment of MTB cells from an environmental sample, (ii) 16S rRNA gene sequencing of MTB, and (iii) fluorescence hybridization analyses coordinated with (iv) transmission or scanning electron microscopy of the probe-hybridized cells. The application of this strategy identified a magnetotactic strain, SHHR-1, from brackish sediments collected from the Shihe River estuary in Qinhuangdao City, China. SHHR-1 magnetosomes are elongated prismatic magnetites which can be idealized as hexagonal prisms. Taxonomic groups of uncultured MTB were also identified in freshwater sediments from Lake Miyun in northern Beijing via this novel coordinated fluorescence and scanning electron microscopy method based on four group-specific rRNA-targeted probes. Our analyses revealed that major magnetotactic taxonomic groups can be accurately determined only with coordinated scanning electron microscopy observations on fluorescently labeled single cells due to limited group coverage and specificity for existing group-specific MTB fluorescence hybridization (FISH) probes. Our reported strategy is simple and efficient, offers great promise toward investigating the diversity and biomineralization of MTB, and may also be applied to other functional groups of microorganisms. Magnetotactic bacteria (MTB) are phylogenetically diverse and biomineralize morphologically diverse magnetic nanocrystals of magnetite or greigite in intracellular structures termed magnetosomes. However, many uncultured MTB strains have not been phylogenetically identified or structurally investigated at the single-cell level, which limits our comprehensive understanding of the diversity of MTB and their role in biomineralization. We developed a fluorescence-coupled electron microscopy method for the rapid phylogenetic and biomineralogical characterization of uncultured MTB at the single-cell level. Using this novel method, we successfully identified taxonomic groups of several uncultured MTB and one novel magnetotactic strain, SHHR-1, from natural environments. Our analyses further indicate that strain SHHR-1 forms elongated prismatic magnetites. Our findings provide a promising strategy for the rapid characterization of phylogenetic and biomineralogical properties of uncultured MTB at the single-cell level. Furthermore, due to its simplicity and generalized methodology, this strategy can also be useful in the study of the diversity and biomineralization properties of microbial taxa involved in other mineralization processes.
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http://dx.doi.org/10.1128/AEM.00409-17DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5452806PMC
June 2017
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