Hybrid supracolloidal structures through interface driven assembly

We investigated different strategies for the preparation of armoured polymer particles. Inorganic nanoparticles, such as clay platelets and Ludox colloidal silica grades, were used as solids-stabilisers in processes such as miniemulsion, suspension and/or emulsion polymerisations. These nanoparticles were either assembled at liquid-liquid interfaces for the stabilisation of monomer droplets or adsorbed onto solid surfaces in the case of poly(vinyl acetate) latex particles. Colloidal assembly was promoted by modifying the pH and/or the ionic strength of the dispersion medium, thereby tuning the surface properties of the nanoparticles. When prepared in miniemulsion polymerisation, latexes with controlled particle size distributions were obtained. Their diameter was dictated by the amount of solids-stabiliser (Laponite clay) or by the dimensions of the building blocks (Ludox colloidal silica). We developed a versatile emulsion polymerisation process leading to silicaarmoured poly(vinyl acetate) particles and showed that quantitative disc centrifugation analyses throughout the polymerisation process unravelled mechanistic aspects of particle formation and growth. Stability of the armoured particles was studied in dispersion and after spray-drying the hybrid dispersions. The thickness of the silica shell on the polymer particles had an important role in limiting polymer inter-diffusion upon film formation. The obtained powders were tested as additives in cement-based formulations for tile adhesives. However, desired performance characteristics were not obtained in comparison to standard formulations. Soft polymer composite foams were prepared through freeze-drying a mixture of colloids. ‘Large-soft’ particles of poly(vinyl laurate) reinforced by an armouring layer of ‘small-hard’ nanoparticles of colloidal silica led to the formation of highly porous open-cell foams. Upon addition of a third conducting colloidal component, this newly designed material proved promising results as a gas sensor

Genetic variability in Arbuscular Mycorrhizal Fungi : effect on gene transcription of "Oryza Sativa"

AbstractArbuscular Mycorrhizal Fungi (AMF) form obligate symbioses with the majority of land plants. These fungi influence the diversity and productivity of plants. AMF are unusual organisms, harbouring genetically different nuclei in a common cytoplasm (known as heterokaryosis). Genetic variability has been shown between AMF individuals coming from the same population. Recent findings showed that genetic exchange between genetically different AMF individuals was possible. Additionnaly, segregation was shown to occur at spore formation in AMF. These two processes were shown to increase genetic variability between AMF individuals.Because of the difficulty to study these organisms, almost nothing is known about the effect of intra-specific genetic variability in AMF on the plant transcriptome. The aim of this thesis was to bring insights into the effect of intra-specific genetic variability in AMF on plant gene transcription. We demonstrated that genetic exchange could influence expression of some symbiosis specific plant genes and the timing of the colonization of the fungi in plant roots. We also showed that segregation could have a large impact on plant gene transcription. Taken together, these results demonstrated that AMF intra-specific variability could profoundly affect the life of plants by altering various molecular pathways. Moreover, results obtained on rice open a field of research on AMF genetics in impromvment of growth in agricultural plants and should be taken into account for future experiments.RésuméLes champignons endomycorhiziens arbusculaires (CEA) forment une symbiose obligatoire avec la majorité des plantes sur terre. Ces champignons peuvent influencer la diversité et la productivité des plantes avec lesquelles ils forment la symbiose. Les CEA sont des organismes particuliers de part le fait qu'ils possèdent des noyaux génétiquement différents (appelés hétérocaryosis) dans un cytoplasme commun. Il a été montré qu'il existait de la variabilité génétique intra-specific chez les CEA. De plus, des études recentes ont montré que l'échange génétique chez les CEA était possible entre des individus génétiquement différents tout comme la ségrégation qui a aussi été démontrée au moment de la formation des nouvelles spores chez les CEA. Ces deux processus ont été montrés comme pouvant créer aussi de la variabilité génétique intra-specific.Du fait de la difficulté de travailler avec les CEA et à cause de la nouveauté de ces recherches, très peu de choses sont connues sur l'effet de l'échange génétique et de la ségrégation chez les CEA sur les plantes, et particulièrement au niveau moléculaire. Le but de cette thèse a été d'apporter la lumière sur les effets de la viariabilité génétique intra-specific chez les CEA, sur la transcription des gènes chez la plante. Nous avons pu montrer que l'échange génétique pouvait avoir des effets sur l'expression de gènes spécifiques à cette symbiose mais aussi pouvait influencer le timing de colonisation des racines de plantes par les CEA. Nous avons aussi montré que la ségrégation pouvait grandement influencer le transcriptome complet de la plante, et pas seulement les voies métaboliques spécifiques à la symbiose comme cela avait été montré auparavant.L'ensemble de ces résultats démontre l'importance de la variation intra-specific chez les CEA sur les plantes et leur implication sur leur cycle de vie en changeant l'expression de voies métaboliques. De plus, ces résultats obtenus sur le riz ouvrent un champ de recherches sur les plantes destinées à l'agriculture et devraient être pris en compte pour des expériences futures

The role of community and population ecology in applying mycorrhizal fungi for improved food security.

The global human population is expected to reach ∼9 billion by 2050. Feeding this many people represents a major challenge requiring global crop yield increases of up to 100%. Microbial symbionts of plants such as arbuscular mycorrhizal fungi (AMF) represent a huge, but unrealized resource for improving yields of globally important crops, especially in the tropics. We argue that the application of AMF in agriculture is too simplistic and ignores basic ecological principals. To achieve this challenge, a community and population ecology approach can contribute greatly. First, ecologists could significantly improve our understanding of the determinants of the survival of introduced AMF, the role of adaptability and intraspecific diversity of AMF and whether inoculation has a direct or indirect effect on plant production. Second, we call for extensive metagenomics as well as population genomics studies that are crucial to assess the environmental impact that introduction of non-local AMF may have on native AMF communities and populations. Finally, we plead for an ecologically sound use of AMF in efforts to increase food security at a global scale in a sustainable manner

Face-centered cubic carbon as a fourth basic carbon allotrope with properties of intrinsic semiconductors and ultra-wide bandgap

Carbon is considered to exist in three basic forms: diamond, graphite/graphene/fullerenes, and carbyne, which differ in a type of atomic orbitals hybridization. Since several decades the existence of the fourth basic carbon allotropic form with the face-centered cubic (fcc) crystal lattice has been a matter of discussion despite clear evidence for its laboratory synthesis and presence in nature. Here, we obtain this carbon allotrope in form of epitaxial films on diamond in a quantity sufficient to perform their comprehensive studies. The carbon material has an fcc crystal structure, shows a negative electron affinity, and is characterized by a peculiar hybridization of the valence atomic orbitals. Its bandgap (similar to 6 eV) is typical for insulators, whereas the noticeable electrical conductivity (similar to 0.1 S m(-1)) increases with temperature, which is typical for semiconductors. Ab initio calculations explain this apparent contradiction by noncovalent sharing p-electrons present in the uncommon valence band structure comprising an intraband gap. This carbon allotrope can create a new pathway to 'carbon electronics' as the first intrinsic semiconductor with an ultra-wide bandgap

Population genomics reveals that within-fungus polymorphism is common and maintained in populations of the mycorrhizal fungus Rhizophagus irregularis.

Arbuscular mycorrhizal (AM) fungi are symbionts of most plants, increasing plant growth and diversity. The model AM fungus Rhizophagus irregularis (isolate DAOM 197198) exhibits low within-fungus polymorphism. In contrast, another study reported high within-fungus variability. Experiments with other R. irregularis isolates suggest that within-fungus genetic variation can affect the fungal phenotype and plant growth, highlighting the biological importance of such variation. We investigated whether there is evidence of differing levels of within-fungus polymorphism in an R. irregularis population. We genotyped 20 isolates using restriction site-associated DNA sequencing and developed novel approaches for characterizing polymorphism among haploid nuclei. All isolates exhibited higher within-isolate poly-allelic single-nucleotide polymorphism (SNP) densities than DAOM 197198 in repeated and non-repeated sites mapped to the reference genome. Poly-allelic SNPs were independently confirmed. Allele frequencies within isolates deviated from diploids or tetraploids, or that expected for a strict dikaryote. Phylogeny based on poly-allelic sites was robust and mirrored the standard phylogeny. This indicates that within-fungus genetic variation is maintained in AM fungal populations. Our results predict a heterokaryotic state in the population, considerable differences in copy number variation among isolates and divergence among the copies, or aneuploidy in some isolates. The variation may be a combination of all of these hypotheses. Within-isolate genetic variation in R. irregularis leads to large differences in plant growth. Therefore, characterizing genomic variation within AM fungal populations is of major ecological importance

What place for developmental biology in paleoanthropology?

La connaissance des processus développementaux chez les hominines a connu des avancées significatives dans la période récente. Cela a été permis par l’étude d’un nombre croissant de sujets immatures, le progrès des techniques d’analyse et des modèles comparatifs, mais aussi l’utilisation de concepts et méthodes issus de la biologie du développement. Cette communication propose une réflexion sur l’intégration de la biologie du développement dans la paléoanthropologie, avec un triple objectif : 1) Clarifier les différentes manières de comprendre ce qu’est le développement, en termes de génétique, d’adaptation fonctionnelle, de plasticité phénotypique ou encore d’histoire de vie ; 2) Réfléchir aux spécificités du matériel d’étude disponible pour retracer le développement des hominines : tandis que la biologie du développement se fonde principalement sur le développement in utero, la paléoanthropologie étudie le développement postnatal, documenté par des restes fossiles, souvent incomplets et détériorés. Parce qu’elle travaille à partir d’instantanés dans des trajectoires de développement, mais aussi parce qu’elle s’inscrit dans le temps long de la macroévolution, nous montrerons que la paléoanthropologie apporte une contribution originale à la biologie du développement ; 3) Mettre en évidence les implications de cette connaissance plus fine des processus développementaux sur l’interprétation de la variation phénotypique dans le registre fossile. Nous discuterons la pertinence de réviser le cadre théorique hérité de la synthèse moderne, dans lequel toutes les variations morphologiques pourraient être expliquées par la sélection naturelle. Nous examinerons enfin les apports d’une "synthèse évolutionnaire étendue", accordant une place plus importante aux contraintes et biais développementaux, ainsi qu’à leur rôle dans l’évolution

Face centered cubic carbon as a fourth basic carbon allotrope with properties of intrinsic semiconductors and ultra wide bandgap

Carbon is considered to exist in three basic forms diamond, graphite graphene fullerenes, and carbyne, which differ in a type of atomic orbitals hybridization. Since several decades the existence of the fourth basic carbon allotropic form with the face centered cubic fcc crystal lattice has been a matter of discussion despite clear evidence for its laboratory synthesis and presence in nature. Here, we obtain this carbon allotrope in form of epitaxial films on diamond in a quantity sufficient to perform their comprehensive studies. The carbon material has an fcc crystal structure, shows a negative electron affinity, and is characterized by a peculiar hybridization of the valence atomic orbitals. Its bandgap 6 amp; 8201;eV is typical for insulators, whereas the noticeable electrical conductivity 0.1 amp; 8201;S amp; 8201;m amp; 8722;1 increases with temperature, which is typical for semiconductors. Ab initio calculations explain this apparent contradiction by noncovalent sharing p electrons present in the uncommon valence band structure comprising an intraband gap. This carbon allotrope can create a new pathway to carbon electronics as the first intrinsic semiconductor with an ultra wide bandga

Correction Face centered cubic carbon as a fourth basic carbon allotrope with properties of intrinsic semiconductors and ultra wide bandgap

correctio