Comprendre les comportements face à un risque modéré d’inondation. Etude de cas dans le périurbain toulousain (Sud-Ouest de la France)

Les espaces urbanisés soumis à des risques modérés d’inondation pour les vies humaines sont souvent peu considérés dans les études sur la vulnérabilité aux risques naturels en dépit des enjeux qu’ils représentent en termes de gestion de crise. Comment les riverains y font-ils face au danger et quelles sont leurs « bonnes raisons » d’agir? A partir de l’étude socio-géographique de deux inondations récentes (2000 et 2003) dans la périphérie toulousaine (Sud-Ouest de la France), nous montrons que les caractéristiques de l’aléa dans les vallées étudiées influencent les représentations du risque et par conséquent les motivations à se protéger. Face au risque majeur, la vulnérabilité sociale se trouve ainsi augmentée. Pour améliorer la résilience des populations, il convient d’adapter la communication sur les risques: personnaliser l’information, améliorer la compréhension de l’événement vécu et mobiliser de nouvelles formes de médiation entre gestionnaires et riverains

Heterologous Expression of Alteromonas macleodii and Thiocapsa roseopersicina [NiFe] Hydrogenases in Synechococcus elongatus

Oxygen-tolerant [NiFe] hydrogenases may be used in future photobiological hydrogen production systems once the enzymes can be heterologously expressed in host organisms of interest. To achieve heterologous expression of [NiFe] hydrogenases in cyanobacteria, the two hydrogenase structural genes from Alteromonas macleodii Deep ecotype (AltDE), hynS and hynL, along with the surrounding genes in the gene operon of HynSL were cloned in a vector with an IPTG-inducible promoter and introduced into Synechococcus elongatus PCC7942. The hydrogenase protein was expressed at the correct size upon induction with IPTG. The heterologously-expressed HynSL hydrogenase was active when tested by in vitro H2 evolution assay, indicating the correct assembly of the catalytic center in the cyanobacterial host. Using a similar expression system, the hydrogenase structural genes from Thiocapsa roseopersicina (hynSL) and the entire set of known accessory genes were transferred to S. elongatus. A protein of the correct size was expressed but had no activity. However, when the 11 accessory genes from AltDE were co-expressed with hynSL, the T. roseopersicina hydrogenase was found to be active by in vitro assay. This is the first report of active, heterologously-expressed [NiFe] hydrogenases in cyanobacteria

ATP synthase: evolution, energetics, and membrane interactions

The synthesis of ATP, life's 'universal energy currency', is the most prevalent chemical reaction in biological systems, and is responsible for fueling nearly all cellular processes, from nerve impulse propagation to DNA synthesis. ATP synthases, the family of enzymes that carry out this endless task, are nearly as ubiquitous as the energy-laden molecule they are responsible for making. The F-type ATP synthase (F-ATPase) is found in every domain of life, and is believed to predate the divergence of these lineages over 1.5 billion years ago. These enzymes have therefore facilitated the survival of organisms in a wide range of habitats, ranging from the deep-sea thermal vents to the human intestine. In this review, we present an overview of the current knowledge of the structure and function of F-type ATPases, highlighting several adaptations that have been characterized across taxa. We emphasize the importance of studying these features within the context of the enzyme's particular lipid environment: Just as the interactions between an organism and its physical environment shape its evolutionary trajectory, ATPases are impacted by the membranes within which they reside. We argue that a comprehensive understanding of the structure, function, and evolution of membrane proteins -- including ATP synthase -- requires such an integrative approach.Comment: Review article; 29 pages, 6 figures/1 tabl

Use of hupS::lacZ gene fusion to study regulation of hydrogenase expression in Rhodobacter capsulatus: stimulation by H2.

The Escherichia coli beta-galactosidase enzyme was used as a reporter molecule for genetic fusions in Rhodobacter capsulatus. DNA fragments that were from the upstream region of the hydrogenase structural operon hupSLM and contained 5' hupS sequences were fused in frame to a promoterless lacZ gene, yielding fusion proteins comprising the putative signal sequence and the first 22 amino acids of the HupS protein joined to the eight amino acid of beta-galactosidase. We demonstrate the usefulness of the hupS::lacZ fusion in monitoring regulation of hydrogenase gene expression. The activities of plasmid-determined beta-galactosidase and chromosome-encoded hydrogenase changed in parallel in response to various growth conditions (light or dark, aerobiosis or anaerobiosis, and presence or absence of ammonia or of H2), showing that changes in hydrogenase activity were due to changes in enzyme synthesis. Molecular hydrogen stimulated hydrogenase synthesis in dark, aerobic cultures and in illuminated, anaerobic cultures. Analysis of hupS::lacZ expression in various mutants indicated that neither the hydrogenase structural genes nor NifR4 (sigma 54) was essential for hydrogen regulation of hydrogenase synthesis

Transcriptional regulation of the uptake [NiFe]hydrogenase genes in Rhodobacter capsulatus.

International audienceTranscription of the hupSL genes, which encode the uptake [NiFe]hydrogenase of Rhodobacter capsulatus, is specifically activated by H(2). Three proteins are involved, namely the H(2)-sensor HupUV, the histidine kinase HupT and the transcriptional activator HupR. hupT and hupUV mutants have the same phenotype, i.e. an increased level of hupSL expression (assayed by phupS::lacZ fusion) in the absence of H(2); they negatively control hupSL gene expression. HupT can autophosphorylate its conserved His(217), and in vitro phosphotransfer to Asp(54) of its cognate response regulator, HupR, was demonstrated. The non-phosphorylated form of HupR binds to an enhancer site (5'-TTG-N(5)-CAA) of phupS localized at -162/-152 nt and requires integration host factor to activate fully hupSL transcription. HupUV is an O(2)-insensitive [NiFe]hydrogenase, which interacts with HupT to regulate the phosphorylation state of HupT in response to H(2) availability. The N-terminal domain of HupT, encompassing the PAS domain, is required for interaction with HupUV. This interaction with HupT, leading to the formation of a (HupT)(2)-(HupUV)(2) complex, is weakened in the presence of H(2), but incubation of HupUV with H(2) has no effect on the stability of the heterodimer/tetramer, HupUV-(HupUV)(2), equilibrium. HupSL biosynthesis is also under the control of the global two-component regulatory system RegB/RegA, which controls gene expression in response to redox. RegA binds to a site close to the -35 promoter recognition site and to a site overlapping the integration host factor DNA-binding site (5'-TCACACACCATTG, centred at -87 nt) and acts as a repressor