Damien Faivre

Bio: Damien Faivre is an academic researcher from Aix-Marseille University. The author has contributed to research in topics: Magnetotactic bacteria & Magnetosome. The author has an hindex of 37, co-authored 137 publications receiving 5176 citations. Previous affiliations of Damien Faivre include Weizmann Institute of Science & Max Planck Society.

Nucleation and growth of magnetite from solution.

Abstract: The formation of crystalline materials from solution is usually described by the nucleation and growth theory, where atoms or molecules are assumed to assemble directly from solution. For numerous systems, the formation of the thermodynamically stable crystalline phase is additionally preceded by metastable intermediates . More complex pathways have recently been proposed, such as aggregational processes of nanoparticle precursors or pre-nucleation clusters, which seem to contradict the classical theory. Here we show by cryogenic transmission electron microscopy that the nucleation and growth of magnetite-a magnetic iron oxide with numerous bio- and nanotechnological applications-proceed through rapid agglomeration of nanometric primary particles and that in contrast to the nucleation of other minerals, no intermediate amorphous bulk precursor phase is involved. We also demonstrate that these observations can be described within the framework of classical nucleation theory.

An acidic protein aligns magnetosomes along a filamentous structure in magnetotactic bacteria

Abstract: Aquatic magnetobacteria are able to navigate along Earth's magnetic field thanks to organelles called magnetosomes. In these, magnetite crystals are enclosed in a membrane and arranged in chains so as to act rather like compass needles. A gene cluster in the magnetobacterium Magnetospirillum gryphiswaldense was recently implicated in magnetosome formation. Now one of its genes, mamJ, is shown to code for a protein similar in structure to those controlling biomineralization in bones. In the absence of this protein, the magnetosomes collapse. MamJ protein seems to act by connecting empty vesicles to the filamentous structure, so that magnetite crystals then grow within the vesicles. Magnetotactic bacteria are widespread aquatic microorganisms that use unique intracellular organelles to navigate along the Earth's magnetic field. These organelles, called magnetosomes, consist of membrane-enclosed magnetite crystals that are thought to help to direct bacterial swimming towards growth-favouring microoxic zones at the bottom of natural waters1. Questions in the study of magnetosome formation include understanding the factors governing the size and redox-controlled synthesis of the nano-sized magnetosomes and their assembly into a regular chain in order to achieve the maximum possible magnetic moment, against the physical tendency of magnetosome agglomeration. A deeper understanding of these mechanisms is expected from studying the genes present in the identified chromosomal ‘magnetosome island’, for which the connection with magnetosome synthesis has become evident2. Here we use gene deletion in Magnetospirillum gryphiswaldense to show that magnetosome alignment is coupled to the presence of the mamJ gene product. MamJ is an acidic protein associated with a novel filamentous structure, as revealed by fluorescence microscopy and cryo-electron tomography. We suggest a mechanism in which MamJ interacts with the magnetosome surface as well as with a cytoskeleton-like structure. According to our hypothesis, magnetosome architecture represents one of the highest structural levels achieved in prokaryotic cells.

Synthesis of magnetite nanoparticles for bio- and nanotechnology: genetic engineering and biomimetics of bacterial magnetosomes.

Abstract: Magnetotactic bacteria (MTB) have the ability to navigate along the Earth's magnetic field. This so-called magnetotaxis is a result of the presence of magnetosomes, organelles which comprise nanometer-sized intracellular crystals of magnetite (Fe(3)O(4)) enveloped by a membrane. Because of their unique characteristics, magnetosomes have a high potential for nano- and biotechnological applications, which require a specifically designed particle surface. The functionalization of magnetosomes is possible either by chemical modification of purified particles or by genetic engineering of magnetosome membrane proteins. The second approach is potentially superior to chemical approaches as a large variety of biological functions such as protein tags, fluorophores, and enzymes may be directly incorporated in a site-specific manner during magnetosome biomineralization. An alternative to the bacterial production of magnetosomes are biomimetic approaches, which aim to mimic the bacterial biomineralization pathway in vitro. In MTB a number of magnetosome proteins with putative functions in the biomineralization of the nanoparticles have been identified by genetic and biochemical approaches. The initial results obtained by several groups indicate that some of these proteins have an impact on nanomagnetite properties in vitro. In this article the key features of magnetosomes are discussed, an overview of their potential applications are given, and different strategies are proposed for the functionalization of magnetosome particles and for the biomimetism of their biomineralization pathway.

Magnetotactic Bacteria Powered Biohybrids Target E. coli Biofilms.

Abstract: Biofilm colonies are typically resistant to general antibiotic treatment and require targeted methods for their removal. One of these methods includes the use of nanoparticles as carriers for antibiotic delivery, where they randomly circulate in fluid until they make contact with the infected areas. However, the required proximity of the particles to the biofilm results in only moderate efficacy. We demonstrate here that the nonpathogenic magnetotactic bacteria Magnetosopirrillum gryphiswalense (MSR-1) can be integrated with drug-loaded mesoporous silica microtubes to build controllable microswimmers (biohybrids) capable of antibiotic delivery to target an infectious biofilm. Applying external magnetic guidance capability and swimming power of the MSR-1 cells, the biohybrids are directed to and forcefully pushed into matured Escherichia coli (E. coli) biofilms. Release of the antibiotic, ciprofloxacin, is triggered by the acidic microenvironment of the biofilm, ensuring an efficient drug delivery system. ...

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

Abstract: 抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

Methods in Enzymology.

Abstract: I read this book the same weekend that the Packers took on the Rams, and the experience of the latter event, obviously, colored my judgment. Although I abhor anything that smacks of being a handbook (like, \"How to Earn a Merit Badge in Neurosurgery\") because too many volumes in biomedical science already evince a boyscout-like approach, I must confess that parts of this volume are fast, scholarly, and significant, with certain reservations. I like parts of this well-illustrated book because Dr. Sj6strand, without so stating, develops certain subjects on technique in relation to the acquisition of judgment and sophistication. And this is important! So, given that the author (like all of us) is somewhat deficient in some areas, and biased in others, the book is still valuable if the uninitiated reader swallows it in a general fashion, realizing full well that what will be required from the reader is a modulation to fit his vision, propreception, adaptation and response, and the kind of problem he is undertaking. A major deficiency of this book is revealed by comparison of its use of physics and of chemistry to provide understanding and background for the application of high resolution electron microscopy to problems in biology. Since the volume is keyed to high resolution electron microscopy, which is a sophisticated form of structural analysis, but really morphology in a modern guise, the physical and mechanical background of The instrument and its ancillary tools are simply and well presented. The potential use of chemical or cytochemical information as it relates to biological fine structure , however, is quite deficient. I wonder when even sophisticated morphol-ogists will consider fixation a reaction and not a technique; only then will the fundamentals become self-evident and predictable and this sine qua flon will become less mystical. Staining reactions (the most inadequate chapter) ought to be something more than a technique to selectively enhance contrast of morphological elements; it ought to give the structural addresses of some of the chemical residents of cell components. Is it pertinent that auto-radiography gets singled out for more complete coverage than other significant aspects of cytochemistry by a high resolution microscopist, when it has a built-in minimal error of 1,000 A in standard practice? I don't mean to blind-side (in strict football terminology) Dr. Sj6strand's efforts for what is \"routinely used in our laboratory\"; what is done is usually well done. It's just that …

Image Processing

Abstract: MUCKE aims to mine a large volume of images, to structure them conceptually and to use this conceptual structuring in order to improve large-scale image retrieval. The last decade witnessed important progress concerning low-level image representations. However, there are a number problems which need to be solved in order to unleash the full potential of image mining in applications. The central problem with low-level representations is the mismatch between them and the human interpretation of image content. This problem can be instantiated, for instance, by the incapability of existing descriptors to capture spatial relationships between the concepts represented or by their incapability to convey an explanation of why two images are similar in a content-based image retrieval framework. We start by assessing existing local descriptors for image classification and by proposing to use co-occurrence matrices to better capture spatial relationships in images. The main focus in MUCKE is on cleaning large scale Web image corpora and on proposing image representations which are closer to the human interpretation of images. Consequently, we introduce methods which tackle these two problems and compare results to state of the art methods. Note: some aspects of this deliverable are withheld at this time as they are pending review. Please contact the authors for a preview.