135 research outputs found
Fonctions des plantes et bacteriennes nécessaires à la différenciation morphologique des bactéroïdes dans le modèle Aeschynomene-Bradyrhizobium
No full textLes légumineuses sont capables de développer des organes symbiotiques, les nodules, qui hébergent des bactéries du sol appelées rhizobia. Au sein des nodules les rhizobia intracellulaires se différencient en bactéroïdes capables de réduire l'azote atmosphérique en ammonium au bénéfice de la plante. En contrepartie, la plante alimente la bactérie en sources de carbone. Des études récentes sur le modèle symbiotique Medicago/Sinorhizobium ont montré dans les nodules la forte présence d'une grande diversité de peptides appelés NCR qui sont similaires aux peptides antimicrobiens (AMP) impliqués dans l'immunité innée. Ces NCR sont responsables du maintien de l'homéostasie entre les cellules hôtes et la forte population bactérienne qu'elles contiennent. Bien que certains NCR sont de vrais AMP, capable de tuer des bactéries in vitro, dans les nodules ils induisent plutôt une différenciation terminale caractérisée par une élongation cellulaire, une amplification du génome, une perméabilité membranaire et une perte des capacités de division de la bactérie. Néanmoins le mode d'action des NCR reste à élucider. Au cours de ma thèse j'ai participé à la caractérisation des processus de différenciation dans le modèle Aeschynomene, une légumineuse tropicale, Bradyrhizobium.Dans un premier temps, une nouvelle classe de NCR a été identifiée chez différentes espèces d'Aeschynomene. Ces NCR sont responsables de la différenciation des Bradyrhizobium via un processus similaire à celui décrit chez Medicago. Ces résultats suggèrent une évolution convergente des processus de différenciation chez les Dalbergioïdes (Aeschynomene) et le clade des IRLC (Medicago).Ensuite, pour identifier les fonctions bactériennes requises lors de la différenciation, j'ai criblé 53 mutants Tn5 d'Aeschynomene indica fix- . Huit gènes bactériens dont la mutation inhibe ou affecte le processus de différenciation ont été identifiés. Parmi eux, je me suis focalisé sur la DD-CPase une enzyme de modification du peptidoglycane et sur 2 gènes impliqués dans l'homéostasie du phosphate.La caractérisation du gène DD-CPase1 a permis de démontrer que le remodelage du peptidoglycane est requis pour une différenciation correcte des bactéroïdes chez les plantes hôtes qui produisent des NCR, en général, et chez Aeschynomene en particulier. Ces résultats suggèrent une interaction possible entre DD-CPase1 et des NCR conduisant à l'endoréplication des bactéroïdes.Enfin, j'ai étudié les propriétés physiologiques et symbiotiques des mutants pstC et pstB. Les mutants Tn5 des gènes pstC et pstB de la souche ORS285 de Bradyrhizobium sont sévèrement affectés par la carence en phosphate en culture pure et leurs propriétés symbiotiques (différenciation, réduction de l'azote) sont fortement réduites. Des analyses fonctionnelles plus approfondies de l'opéron Pst devraient permettre une meilleure compréhension du lien entre l'homéostasie du phosphate et l'efficience symbiotique dans l'interaction Aeschynomene-Bradyrhizobium.Mes travaux ont permis d'élargir nos connaissances sur l'évolution de la symbiose en montrant que le modus operandi impliquant des peptides dérivés de l'immunité innée utilisée par certaines légumineuses pour maintenir leur population bactérienne intracellulaire sous contrôle est plus répandue et ancienne qu'on ne le pensait et a été utilisée par l'évolution à plusieurs reprises. De plus différentes cibles bactériennes pouvant participer au processus de différenciation ont également été identifiées.The legume species are able to form symbiotic organs, the nodules, that house soil bacteria called rhizobia. Within these nodules intracellular rhizobia differentiate into bacteroids, which are able to reduce atmospheric dinitrogen to ammonium for the benefit of the plants. In counterpart, the plants provide carbon sources to the bacteria. Recent studies on symbiotic model Medicago-Sinorhizobium showed that the nodules of M. truncatula produce a massive diversity of peptides called NCRs, which are similar to antimicrobial peptides (AMPs) of innate immune systems. These NCRs are responsible in maintaining the homeostasis between the host cells in the nodules and the large bacterial population they contain. Although many NCRs are genuine AMPs, which kill microbes in vitro, in nodule cells they do not kill the bacteria but induce them into the terminally differentiated bacteroids characterized by cell elongation, genome amplification, membrane permeability and loss of cell division capacity. However, the action mode of NCRs is still an open question. During my PhD thesis I focused on the identification of plant and bacterial functions required for bacteroid differentiation in the Aeschynomene-Bradyrhizobium model.Firstly, a new class of cysteine rich peptides (NCR-like) was identified in tropical aquatic legumes of the Aeschynomene genus, which belong to the Dalbergioid clade. These peptides govern terminal bacteroid differentiation of photosynthetic Bradyrhizobium spp. This mechanism is similar to the one previously described in Medicago suggesting that the endosymbiont differentiation in Dalbergioid and ILRC legumes is convergently evolved.Secondly, in order to identify the bacterial functions involved in bacteroid differentiation, I screened 53 fix- Tn5 mutants of the ORS278 strain on Aeschynomene indica. This screening allowed identify 8 bacterial genes, which inhibit or disorder the bacteroid differentiation. Among these identified genes, I focused on DD-CPase encoding a peptidoglycan-modifying enzyme and two genes pstC and pstB belonging to Pst-system.The characterization of DD-CPase gene demonstrated that the remodeling peptidoglycan enzyme, DD-CPase1, of Bradyrhizobium is required for normal bacteroid differentiation in host legumes that produce NCRs, in general, and in Aeschynomene spp., in particular. This prompts a possibility of direct interaction of DD-CPase1 with NCRs leading to endoreduplication of the bacteroids.Finally, I have investigated the physiological and symbiotic properties of different mutants of pstC and pstB genes. The Tn5 mutants of pstC and pstB genes of Bradyrhizobium sp. strain ORS278 severely affected symbiosis on A. indica and A. evenia. Further functional studies on pst-operon will provide deeper understanding the correlation between phosphate homeostasis and nitrogen fixation efficiency in Aeschynomene-Bradyrhizobium symbiosis.This study broadens our knowledge on the evolution of symbiosis by showing that the modus operandi involving peptides derived from innate immunity used by some legumes to keep their intracellular bacterial population under control is more widespread and ancient than previously thought and has been invented by evolution several times
Correction:Experimental Study of the Impact of Folding Wingtip Devices on Aircraft Flight Mechanics and Handling Qualities (AIAA SciTech Forum and Exposition, 2023)
No full textCorrection Notice 1. One more author needs to be included to the author list: Huaiyuan Gu, Ronald Cheung, Fintan Healy, Djamel Rezgui, Mark Lowenberg, Jonathan Cooper Author(s) Affiliations: Professor of Flight Dynamics, Department of Aerospace Engineering, University of Bristol 2. Figure 9 caption needs to be changed to: Comparison of the drag curves of (a)(b) straight wing and (c)(d) swept wing with various hinge conditions. 3. Figure 11 caption needs to be changed to: Schematic representation of the shift of aerodynamic centre on the (a) straight and (b) swept wings caused by different hinge conditions. 4. Figure 23 caption needs to be changed to: Comparison of the short period damping and frequency measured from (a) straight wing model and (b) swept wing model incorporating various hinge conditions.</p
La thioestérase YbgC, l'Acyl Carrier Protein et le métabolisme des phospholipides chez Escherichia coli
No full textAIX-MARSEILLE2-BU Sci.Luminy (130552106) / SudocSudocFranceF
Unsupervised assignment for dynamic author name disambiguation in bibliographic citations
No full textFil: Gómez García, Carlos Andrés. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina
Unsupervised assignment for dynamic author name disambiguation in bibliographic citations
No full textFil: Gómez García, Carlos Andrés. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina
Rapid application development in the internet of things : a model-based approach
No full textThe Internet of Things (IoT) is a vision in which physical and digital objects are connected and cooperate to achieve particular goals. Unfortunately, the extent of expertise required to incorporate intelligent hardware, software, and computer network still presents a significant challenge. Service-oriented IoT middleware have been proposed quite often to solve this problem. However, they are mostly designed for professional developers with a high degree of flexibility and extensive features. Consequently, tool’s simplicity is often sacrificed, and they present a steep learning curve for entry-level developers. This dissertation aims at addressing this gap by elaborating the state-of-the-art in IoT developments and proposing IoTLink, a rapid IoT software development tool for novice developers. For designing IoTLink, the author reviewed the available IoT architectures. A typical pattern suggests that a physical object must be uniquely identifiable, has physical qualities that partly can be sensed by sensors, and has some capabilities or services that could affect the environment. Virtual entities may act as proxies to execute services and retrieving information about the physical objects. IoTLink is designed for enabling inexperienced developers to develop proxies representing domain objects and abstracting individual sensors and actuators. IoTLink design concept comprises a five layered architecture. The first layer is responsible for abstracting communication with heterogeneous data sources. The second layer deals with sensor fusion components to process and fuse sensor data into useful information. The third layer is concerned with the definitions of domain models and the concrete objects. The fourth layer provides output components, including interfaces to the application logic, distributed applications, and databases to store the information about the virtual objects. The fifth layer abstracts the application logic that access the domain objects. IoTLink employs a model driven approach for wiring these components visually. The visual model is then serialized into XML data and used to generate a Java implementation which can be executed as proxies. In addition, IoTLink offers a discovery broker allowing developers to share and discover IoT resources within the internet. The key advantage of IoTLink discovery is the ability to detect if similar devices are described with synonymous terms. This approach increases the discoverability of similar devices described with diverse terms. The author evaluated the practicability of IoTLink and model-driven approach within three distinct case studies in European research projects. The result shows that it could reduce approximately 2/3 of the development efforts. In addition, the author compared IoTLink’s usability to a Java middleware approach in a controlled experiment performed by 24 participants. The results show that IoTLink could on average reduce 44% of the development time and 48% of mistakes. Moreover, when used by developers with less than five years object-oriented experience, IoTLink was able to reduce up to 57% of mistakes compared to Java development
A proposal for a separative network to evacuate drainage waters and pluvial waters of stagnation in arid zones (Ain Sahra locality, Touggourt, Algeria)
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