Science & Mathematics

La Politique agricole commune est engagée dans un processus continu de réforme, avec le découplage des aides proposé par l’accord de Luxembourg comme étape récente. S’appuyant sur des travaux de modélisation, le programme GENEDEC contribue aux évaluations des impacts de la réforme en ce qui concerne les marges brutes, l’allocation des terres, les coûts d’opportunité des facteurs, et quelques critères environnementaux. Ce document restitue une partie des résultats obtenus à l’aide du modèle AROPAj de l’Unité mixte de recherche « Economie Publique » de Grignon.

Large stone circle with rectangular markers and stelae.

Adaptation to one environment can often generate phenotypic and genotypic changes which impact the future ability of an organism to thrive in other environmental conditions. In the context of host-microbe interactions, biofilm formation can increase survival rates in vivo upon exposure to stresses, like the host's immune system or antibiotic therapy. However, how the generic process of adaptation impacts the ability to form biofilm and how it may change through time has seldomly been studied. To do so, we used a previous evolution experiment with three strains of the Klebsiella pneumoniae species complex, in which we specifically did not select for biofilm formation. We observed that changes in the ability to form biofilm happened very fast at first and afterwards reverted to ancestral levels in many populations. Biofilm changes were associated to changes in population yield and surface polysaccharide production. Genotypically, mutations in the tip adhesin of type III fimbriae (mrkD) or the fim switch of type I fimbriae were shaped by nutrient availability during evolution, and their impact on biofilm formation was dependent on capsule production. Analyses of natural isolates revealed similar mutations in mrkD, suggesting that such mutations also play an important role in adaptation outside the laboratory. Our work reveals that the latent evolution of biofilm formation, and its temporal dynamics, depend on nutrient availability, the genetic background and other intertwined phenotypic and genotypic changes. Ultimately, it suggests that small differences in the environment can alter an organism's fate in more complex niches like the host.

The Nelson-Oppen combination method is ubiquitous in Satisfiability Modulo Theories solvers. However, one of its major drawbacks is to be restricted to disjoint unions of theories. We investigate the problem of extending this combination method to particular non-disjoint unions of theories defined by connecting disjoint theories via bridging functions. A possible application is to solve verification problems expressed in a combination of data structures connected to arithmetic with bridging functions such as the length of lists and the size of trees. We present a sound and complete combination method à la Nelson-Oppen for the theory of absolutely free data structures, including lists and trees. This combination procedure is then refined for standard interpretations. The resulting theory has a nice politeness property, enabling combinations with arbitrary decidable theories of elements. In addition, we have identified a class of polite data structure theories for which the combination method remains sound and complete. This class includes all the subtheories of absolutely free data structures (e.g, the empty theory, injectivity, projection). Again, the politeness property holds for any theory in this class, which can thus be combined with bridging functions and arbitrary decidable theories of elements. This illustrates the significance of politeness in the context of non-disjoint combinations of theories.

La diminution des performances de reproduction chez la vache laitière haute-productrice est un fait incontestable, évoluant depuis de nombreuses années, sous l’influence de la sélection génétique orientée massivement pour la production laitière, en dépit de caractères comme la fertilité. La pression économique que cette diminution fait peser sur les élevages est importante. Des facteurs de risques alimentaires ayant un impact sur la reproduction ont été étudiés. Ainsi, une revue bibliographique a permis de mettre en évidence que le déficit énergétique en début de lactation, une alimentation riche en azote soluble, un déficit en calcium ou en sélénium ainsi que la présence de mycotoxines telles que la zéaralénone provoquait une diminution manifeste de la fertilité. Des solutions de terrain ont alors été explorées. La Note d’État Corporel permet aux éleveurs d’objectiver le déficit énergétique, et d’y parer en ajoutant à la ration des éléments glucoformateurs comme le propylène glycol. Une mesure de l’urée dans le lait de tank permet de mettre en évidence un taux d’azote soluble trop important dans la ration. D’autres mesures comme le pH urinaire permettent enfin d’avoir une idée du statut ionique de l’animal et de corriger d’éventuelles déséquilibres. Enfin, des composés alimentaires tels que le propylène-glycol, le beta-carotène, les acides gras à chaîne longue et insaturés ou encore charbon activé permettent de parer ou de corriger certaines dérives alimentaires nuisibles à la fonction de reproduction. Des moyens sont alors à disposition des professionnels du secteur pour limiter l’impact de l’alimentation sur la reproduction.

This data paper presents a survey conducted in a participatory manner in the territory of Santarém, in the Brazilian Amazon. The aim is to understand how global changes are affecting family farmers. In the study area, family farming has been confronted over the past 20 years with the rapid expansion of large-scale monocultures, especially soybean. As part of the Odyssea socio-environmental observatory, academic researchers and family farming organizations entered into a partnership to co-produce data that could be strategically useful for these organizations. A process of co-construction of the expectations allowed priorities to be established and the data collection strategy to be defined. Three levels of analysis were chosen in order to allow an integrated understanding of the dynamics of change: the Santarem Plateau territory, the rural community level (living place recognized by the farmers) and the farmers’ households. Twenty-one farmers, called community researchers, organized in 3 teams, applied a questionnaire through the KoboCollect smartphone application to 544 families in the municipalities of Santarém, Mojuí dos Campos and Belterra. Meetings were previously held in the rural communities and questionnaires were applied with representatives of 32 communities. Data was collected between April and June 2019. The community researchers and academic researchers then came together for two collective sessions of data analysis and interpretation in July and October 2019. Data was standardized and cleaned using SPSS software, between September and December 2019. The metadata and databases are available on the CIRAD dataverse.

Pseudomonas aeruginosa is a widespread γ-proteobacterium and an important opportunistic pathogen. The genetically diverse P. aeruginosa phylogroup 3 strains are characterized by producing the pore-forming ExlA toxin and by their lack of a type III secretion system. However, like all strains of this species, they produce several virulence-associated traits, such as elastase, rhamnolipids and pyocyanin, which are regulated by quorum sensing (QS). The P. aeruginosa QS response comprises three systems (Las, Rhl and Pqs, respectively) that hierarchically regulate these virulence factors. The Pqs QS system is composed of the PqsR transcriptional factor, which, coupled with the alkyl-quinolones HHQ or PQS, activates the transcription of the pqsABCDE operon. The products of the first four genes of this operon produce HHQ, which is then converted to PQS by PqsH, while PqsE forms a complex with RhlR and stabilizes it. In this study we report that mutations affecting the Pqs system are particularly common in phylogroup 3 strains. To better understand QS in phylogroup 3 strains we studied strain MAZ105 isolated from tomato rhizosphere and showed that it contains mutations in the central QS transcriptional regulator, LasR, and in the gene encoding the PqsA enzyme involved in the synthesis of PQS. However, it can still produce QS-regulated virulence factors and is virulent in Galleria mellonella and mildly pathogenic in the mouse abscess/necrosis model; our results show that this may be due to the expression of pqsE from a different PqsR-independent promoter than the pqsA promoter. Our results indicate that using anti-virulence therapy based on targeting the PQS system will not be effective against infections by P. aeruginosa phylogroup 3 strains.

The regulated secretory pathway in neuroendocrine cells ends with the release of hormones and neurotransmitters following a rise in cytosolic calcium. This process known as regulated exocytosis involves the assembly of soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) proteins, the synaptic vesicle VAMP (synaptobrevin), and the plasma membrane proteins syntaxin and SNAP-25. Although there is much evidence suggesting that SNARE proteins play a key role in the fusion machinery, other cellular elements regulating the kinetics, the extent of fusion, and the preparation of vesicle for release have received less attention. Among those factors, lipids have also been proposed to play important functions both at the level of secretory vesicle recruitment and late membrane fusion steps. Here, we will review the latest evidence supporting the concept of the fusogenic activity of lipids, and also discuss how this may be achieved. These possibilities include the recruitment and sequestration of the components of the exocytotic machinery, regulation of protein function, and direct effects on membrane topology.

Background : Five randomized controlled trials recently appeared in the literature demonstrating that early mechanical thrombectomy in patients with acute ischemic stroke is significantly related to an improved outcome. Stent retrievers are accepted as the most effective devices for intracranial thrombectomy. Objective : To analyze the mechanical properties of stent retrievers, their behavior during retrieval, and interaction with different clots and to identify device features that might correlate with the effectiveness of thrombus removal. Materials and methods : All stent retrievers available in France up to June 2015 were evaluated by mechanical and functional tests aimed at investigating the variation of their radial force and their behavior during retrieval. Devices were also tested during in vitro thrombectomies using white and red experimental thrombi produced with human blood. Functional tests and in vitro thrombectomies were conducted using a rigid 3D printed vascular model. Results : Mechanical tests showed a variation in radial force during retrieval for each stent. A constant radial force during retrieval was related to continuous cohesion over the vessel wall and a higher rate of clot removal efficacy. All stent retrievers failed when interacting with white large thrombi (diameter ≥6 mm). Conclusions : None of the tested devices were effective in removing white clots of large diameter (≥6 mm). Constant radial force during retrieval allows constant cohesion to the vessel wall and pressure over the clot; such features allow for a higher rate of clot removal.

Type 1 and type 2 diabetes are growing public health problems. Despite having different pathophysiologies, both diseases are associated with defects in immune regulation. Invariant natural killer T (iNKT) cells are innate-like T cells that recognize glycolipids presented by CD1d. These cells not only play a key role in the defense against pathogens, but also exert potent immunoregulatory functions. The regulatory role of iNKT cells in the prevention of type 1 diabetes has been demonstrated in murine models and analyzed in diabetic patients. The decreased frequency of iNKT cells in non-obese diabetic mice initially suggested the regulatory role of this cell subset. Increasing the frequency or the activation of iNKT cells with agonists protects non-obese diabetic mice from the development of diabetes. Several mechanisms mediate iNKT regulatory functions. They can rapidly produce immunoregulatory cytokines, interleukin (IL)-4 and IL-10. They induce tolerogenic dendritic cells, thereby inducing the anergy of autoreactive anti-islet T cells and increasing the frequency of T regulatory cells (Treg cells). Synthetic agonists are able to activate iNKT cells and represent potential therapeutic treatment in order to prevent type 1 diabetes. Growing evidence points to a role of immune system in glucose intolerance and type 2 diabetes. iNKT cells are resident cells of adipose tissue and their local and systemic frequencies are reduced in obese patients, suggesting their involvement in local and systemic inflammation during obesity. With the discovery of potential continuity between type 1 and type 2 diabetes in some patients, the role of iNKT cells in these diseases deserves further investigation.

18x24 cm, plaque de verre

Moral entrepreneurs who volunteer to enforce rules by themselves have spread in 2010s Russia. As ‘rule enforcers’ they patrol the streets to catch offenders. Some of these enforcers have conflictual relations with the police, while others operate in cooperation with it. This essay describes the development of vigilante justice in contemporary Russia. Two particularities of the Russian case are striking. First, the activities of several citizen policing initiatives are in fact recorded and posted on YouTube and VKontakte, where they reach a large audience, generating support for their activities and, in particular, for the leaders of such groups. Second, the development of these groups is not the simple outcome of a powerless state failing to maintain order or to fight crime. The essay will reveal how these new forms of policing contribute, paradoxically, to the strengthening of state authority.

The selectivity of L-lysine acylation by lauric acid catalysed by Candida antarctica lipase B (CALB) was investigated combining experimental and theoretical methodologies. Experiments showed the near-exclusive acylation of lysine ε-amino group; only traces of product resulting from the acylation of lysine α-amino group were observed fleetingly. Molecular modelling simulations were performed aiming to understand the molecular rules for selectivity. Flexible docking simulations combined with structural investigations into lysine/CALB binding modes also suggested the preferential acylation of lysine ε-amino group without, however, excluding the acylation of the lysine α-amino group. Electrostatic interaction energy between lysine and the residues covering the catalytic cavity was calculated in order to understand the discrimination between the two lysine amino groups. The results suggests that the proximity of the carboxylate group hinders the binding of the substrate in configurations enabling the N-acylation. Key interactions with the polar region covering the catalytic triad were identified and a plausible explanation for selectivity was proposed.

The massive alcoholization of young people does not seem to weaken in spite of an important number of actions organized to curb this phenomenon. Setting out from this premise, this research aims at identifying better the real-life experience of young people during student nights and their perception of alcohol risk factors. The main result concerns the highlighting of a group effect with its social hierarchy which contributes to strengthen a falsified perception of the incurred risks.