Rôle du monoxyde d'azote dans la symbiose entre Sinorhizobium meliloti et Medicago truncatula

Le monoxyde d'azote (NO) est une molécule gazeuse connue pour participer à de nombreux processus biologiques allant du développement aux réponses aux stress biotiques ou abiotiques chez tous les organismes vivants. Au cours des interactions hôte-pathogène, le NO est utilisé par l'hôte en tant que moyen de défense pour bloquer une éventuelle infection, ce à quoi les pathogènes se sont adaptés en mettant en place des systèmes de réponses au NO et de dégradation du NO. Au cours d'interactions symbiotiques de type mutualiste, du NO a également été mis en évidence et joue un rôle dans la mise en place de l'interaction via une action sur les deux partenaires. Dans la symbiose fixatrice d'azote entre la légumineuse Medicago truncatula et l'alpha-proteobactérie Sinorhizobium meliloti, du NO a été détecté durant toutes les phases de l'interaction. Au cours de cette thèse, nous nous sommes intéressés à déterminer le rôle du NO et de la réponse bactérienne associée sur la symbiose M. truncatula/ S. meliloti. Nous avons pu montrer que la bactérie en développe une réponse au NO via deux régulateurs, le système à deux composants FixLJ et le régulateur spécifique du NO, NnrR. Au cours de cette réponse, nous avons montré que la bactérie exprime une flavohémoglobine, Hmp, capable de dégrader le NO. In planta, nous avons détecté du NO dans les crosses de berger des poils absorbants et au niveau des parois des cordons d'infections. Par l'utilisation de mutants nuls ou surexprimant cette flavohémoglobine et par des traitements pharmacologiques, nous avons fait varier le niveau de NO dans les nodules et suivi le phénotype symbiotique résultant. Ainsi, nous avons montré que le NO est nécessaire à la mise en place de la symbiose. Au cours des étapes tardives, nous avons montré que le NO déclenche la sénescence des nodules et que les bactéries via la flavohémoglobine participent de façon importante au contrôle du niveau de NO dans les nodules et donc au contrôle de la sénescence nodulaire.Nitric oxide (NO) is a little gaseous molecule known to participate in many biological processes from development to responses to biotic and abiotic stress in all living organisms. During host-pathogens interactions, NO is used by the host as a defense mechanism to prevent a possible infection. Pathogens adapt themselves to it by developing response and degradation systems to NO. During symbiotic interactions, NO has also been detected and it has been shown that it plays a role in the establishment of the interaction through an action on both partners. In the nitrogen fixing symbiosis between the legume Medicago truncatula and the ?-proteobacteria Sinorhizobium meliloti, NO has been detected during each step of the interaction. In this thesis, we've been interested in finding the role of NO and of the associated bacterial response on the M. truncatula/ S. meliloti symbiosis. We've shown that bacteria develop a response to NO through two regulators, the two components system FixLJ and the NO specific regulator NnrR. During this response, we've demonstrated that bacteria express a flavohemoglobin, Hmp, able to degrade NO. In planta, we've detected NO in shepherd crosses of root hairs and on infection thread membrane. By using null or overexpressing mutants of Hmp and by pharmacological treatments, we modified the NO level in nodules and follow the resulting symbiotic phenotype. Thus, we've shown that NO is needed to establish the symbiosis. During the late steps of the symbiosis, we've also demonstrated that NO triggers the nodule senescence and that bacteria through the flavohemoglobin are largely involved in the NO level control in nodules and consequently in the control of nodule senescence

Optimization of ethylene glycol production from (d)-xylose via a synthetic pathway implemented in Escherichia coli

BACKGROUND: Ethylene glycol (EG) is a bulk chemical that is mainly used as an anti-freezing agent and a raw material in the synthesis of plastics. Production of commercial EG currently exclusively relies on chemical synthesis using fossil resources. Biochemical production of ethylene glycol from renewable resources may be more sustainable. RESULTS: Herein, a synthetic pathway is described that produces EG in Escherichia coli through the action of (d)-xylose isomerase, (d)-xylulose-1-kinase, (d)-xylulose-1-phosphate aldolase, and glycolaldehyde reductase. These reactions were successively catalyzed by the endogenous xylose isomerase (XylA), the heterologously expressed human hexokinase (Khk-C) and aldolase (Aldo-B), and an endogenous glycolaldehyde reductase activity, respectively, which we showed to be encoded by yqhD. The production strain was optimized by deleting the genes encoding for (d)-xylulose-5 kinase (xylB) and glycolaldehyde dehydrogenase (aldA), and by overexpressing the candidate glycolaldehyde reductases YqhD, GldA, and FucO. The strain overproducing FucO was the best EG producer reaching a molar yield of 0.94 in shake flasks, and accumulating 20 g/L EG with a molar yield and productivity of 0.91 and 0.37 g/(L.h), respectively, in a controlled bioreactor under aerobic conditions. CONCLUSIONS: We have demonstrated the feasibility to produce EG from (d)-xylose via a synthetic pathway in E. coli at approximately 90 % of the theoretical yield. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1186/s12934-015-0312-7) contains supplementary material, which is available to authorized users

High-resolution laser system for the S3-Low Energy Branch

In this paper we present the first high-resolution laser spectroscopy results obtained at the GISELE laser laboratory of the GANIL-SPIRAL2 facility, in preparation for the first experiments with the S$^3$-Low Energy Branch. Studies of neutron-deficient radioactive isotopes of erbium and tin represent the first physics cases to be studied at S$^3$. The measured isotope-shift and hyperfine structure data are presented for stable isotopes of these elements. The erbium isotopes were studied using the $4f^{12}6s^2$ $^3H_6 \rightarrow 4f^{12}(^3 H)6s6p$ $J = 5$ atomic transition (415 nm) and the tin isotopes were studied by the $5s^25p^2 (^3P_0) \rightarrow 5s^25p6s (^3P_1)$ atomic transition (286.4 nm), and are used as a benchmark of the laser setup. Additionally, the tin isotopes were studied by the $5s^25p6s (^3P_1) \rightarrow 5s^25p6p (^3P_2)$ atomic transition (811.6 nm), for which new isotope-shift data was obtained and the corresponding field-shift $F_{812}$ and mass-shift $M_{812}$ factors are presented

The synthetic xylulose-1 phosphate pathway increases production of glycolic acid from xylose-rich sugar mixtures

Background: Glycolic acid (GA) is a two-carbon hydroxyacid with applications in the cosmetic, textile, and medical industry. Microbial GA production from all sugars can be achieved by engineering the natural glyoxylate shunt. The synthetic (D)-xylulose-1 phosphate (X1P) pathway provides a complementary route to produce GA from (D)-xylose. The simultaneous operation of the X1P and glyoxylate pathways increases the theoretical GA yield from xylose by 20 %, which may strongly improve GA production from hemicellulosic hydrolysates. Results: We herein describe the construction of an E. coli strain that produces GA via the glyoxylate pathway at a yield of 0.31, 0.29, and 0.37 g/g from glucose, xylose, or a mixture of glucose and xylose ( mass ratio: 33: 66 %), respectively. When the X1P pathway operates in addition to the glyoxylate pathway, the GA yields on the three substrates are, respectively, 0.39, 0.43, and 0.47 g/g. Upon constitutive expression of the sugar permease GalP, the GA yield of the strain which simultaneously operates the glyoxylate and X1P pathways further increases to 0.63 g/g when growing on the glucose/ xylose mixture. Under these conditions, the GA yield on the xylose fraction of the sugar mixture reaches 0.75 g/g, which is the highest yield reported to date. Conclusions: These results demonstrate that the synthetic X1P pathway has a very strong potential to improve GA production from xylose-rich hemicellulosic hydrolysates

Simultaneous production of glycolic acid via the glyoxylate shunt and the synthetic (D)-xylulose-1 phosphate pathway increases product yield

Glycolic acid (GA) is an alpha-hydroxy acid with a wide range ofchemical and pharmaceutical applications..

The synthetic xylulose-1 phosphate pathway increases production of glycolic acid from xylose-rich sugar mixtures

Background: Glycolic acid (GA) is a two-carbon hydroxyacid with applications in the cosmetic, textile, and medical industry. Microbial GA production from all sugars can be achieved by engineering the natural glyoxylate shunt. The synthetic (D)-xylulose-1 phosphate (X1P) pathway provides a complementary route to produce GA from (D)-xylose. The simultaneous operation of the X1P and glyoxylate pathways increases the theoretical GA yield from xylose by 20 %, which may strongly improve GA production from hemicellulosic hydrolysates. Results: We herein describe the construction of an E. coli strain that produces GA via the glyoxylate pathway at a yield of 0.31, 0.29, and 0.37 g/g from glucose, xylose, or a mixture of glucose and xylose ( mass ratio: 33: 66 %), respectively. When the X1P pathway operates in addition to the glyoxylate pathway, the GA yields on the three substrates are, respectively, 0.39, 0.43, and 0.47 g/g. Upon constitutive expression of the sugar permease GalP, the GA yield of the strain which simultaneously operates the glyoxylate and X1P pathways further increases to 0.63 g/g when growing on the glucose/ xylose mixture. Under these conditions, the GA yield on the xylose fraction of the sugar mixture reaches 0.75 g/g, which is the highest yield reported to date. Conclusions: These results demonstrate that the synthetic X1P pathway has a very strong potential to improve GA production from xylose-rich hemicellulosic hydrolysates

Managing Epilepsy Well: Emerging e-Tools for epilepsy self-management

The Managing Epilepsy Well (MEW) Network was established in 2007 by the Centers for Disease Control and Prevention Epilepsy Program to expand epilepsy self-management research. The network has employed collaborative research strategies to develop, test, and disseminate evidence-based, community-based, and e-Health interventions (e-Tools) for epilepsy self-management for people with epilepsy, caregivers, and health-care providers. Since its inception, MEW Network collaborators have conducted formative studies (n. = 7) investigating the potential of e-Health to support epilepsy self-management and intervention studies evaluating e-Tools (n. = 5). The MEW e-Tools (the MEW website, WebEase, UPLIFT, MINDSET, and PEARLS online training) and affiliated e-Tools (Texting 4 Control) are designed to complement self-management practices in each phase of the epilepsy care continuum. These tools exemplify a concerted research agenda, shared methodological principles and models for epilepsy self-management, and a communal knowledge base for implementing e-Health to improve quality of life for people with epilepsy. © 2013 Elsevier Inc