Synthese de ligands opiaces photoactivables et marquage irreversible des recepteurs mu et kappa des opioides

SIGLEAvailable from INIST (FR), Document Supply Service, under shelf-number : TD 80829 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Étude des cinétiques de repliement et d'assemblage de la dihydrofolate réductase R67

PARIS7-Bibliothèque centrale (751132105) / SudocSudocFranceF

A propos de quelques métabolites remarquables de cynobactéries (cyanopeptoline, aéruginosine et anatoxine-a)

Les cyanobactéries sont des organismes procaryotes photosynthétiques capables de produire de nombreux métabolites secondaires. Cette thèse s intéresse à la caractérisation moléculaire de cyanobactéries productrices de neurotoxines (anatoxine-a et homoanatoxine-a) ainsi qu à la mise en évidence d un gène codant pour une activité halogénase dans les clusters de gènes de biosynthèse des métabolites : cyanopeptoline et aéruginosine. De nombreux cas d'intoxications neurotoxiques d'animaux sauvages et domestiques sont régulièrement reportés en France. Nous avons mis en évidence sur deux sites pour lesquels des épisodes mortels ont été rapportés la présence de neurotoxines de cyanobactéries. Les cyanobactéries productrices d anatoxine-a ont été isolées et déposées dans la collection de cyanobactéries de l Institut Pasteur PCC. La caractérisation phénotypique et génétique des souches axéniques obtenues montre qu il s agit de souches du genre Oscillatoria. Sur la base des séquences codant pour les ARNr16S et ITS (Internal Transcribed Spacer) les relations phylogénétiques des nouvelles souches neurotoxiques au sein du genre Oscillatoria ont été étudiées. Une étude du contenu métabolique en cyanopeptoline et aéruginosine et de la présence des leur clusters de gènes de biosynthèse a été entreprise chez une trentaine de souches de Microcystis. Elle a permis de mettre en évidence la présence d halométabolites et d identifier les gènes portant l activité halogénase au sein des clusters aer et mcn. L histoire évolutive des clusters aer et mcn au sein du genre Microcystis a été reconstituée par analyse des séquences ITS. Le gène halogénase semble avoir été acquis par la cyanobactérie probablement d'une protéobactérie ancestrale par transfert horinzontal.PARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

MOTION OF ACTIVE FLUIDS: DIFFUSION DYNAMICS OF CYANOBACTERIA

Cyanobacteria are photosynthetic micro-organisms colonizing all aquatic and terrestrial environments. The motility of such living micro-organisms should make their diffusion distinct from typical Brownian motion. This diffusion can be investigated in terms of global behavior (Fickian or not) and in terms of displacement probabilities, which provide more detail about the motility process. Using cyanobacterium Synechocystis sp. PCC 6803 as the model micro-organism, we carry out time-lapse video microscopy to track and analyze the bacteria\u27s trajectories, from which we compute the mean squared displacement (MSD) and the distribution function of displacement probabilities. We find that the motility of Synechocystis sp. PCC 6803 is intermittent: high-motility run phases are separated by low motility tumble phases corresponding to trapped states. However, this intermittent motility leads to a Fickian diffusive behavior, as shown by the evolution of the MSD with time

Phase diagrams for bloom formation.

<p>A-C: Phase diagrams for bloom formation. Open squares indicate that no bloom were observed within a time window of 24 hour while solid squares show that blooming occurred. The later are color coded with the timescale of bloom formation. For various values of the light intensity (A), initial cell density (B) and nutritional history (i.e relative nutrient concentration in the mother culture -C), 8 values of the salinity (relative BG11 concentration) were tested. D-F: Details of the phase diagrams A-C for fixed values of the salinity. Lowering the light intensity (D) increased the blooming timescale while changing the initial cell density OD₅₈₀ had little effect on this timescale (E). For nutritional history in the range 0.2 − 2X no effect on bloom formation were seen while below 0.2X the blooming timescale increased sharply (F).</p

Aggregation of the biomass during a bloom.

<p>A-B: Microscopic details of the microstructure before (A) and following (B) BG11 addition (final relative concentration of 4X) to a cyanobacterial culture of <i>M. aeruginosa</i> (final OD₅₈₀ = 0.5). C: Time evolution of the viscosity of a cyanobacterial culture before (black circles) and after (green circles) nutrient addition. We first measured the viscosity of a concentrated culture (OD₅₈₀ ∼ 2.4) as a function of the shear rate (see Inset). The bacterial suspension exhibits a shear-thinning behavior in the range 10⁻³ to 1 s⁻¹ where the viscosity falls by 3 orders of magnitude. The apparent divergence of viscosity at low shear is the signature of a yield stress behavior and this can be ascribed to the interactions between EPS, bacterial cells and ions. After a crossover regime (1 to 10 s⁻¹) the viscosity becomes independent of the shear rate in the range 10 to 10³ s⁻¹ and saturate at 1.1±0.1 mPa.s. In this high-shear limit, the viscosity is very close to that of water as expected for a dilute (volume fraction around 2 ⋅ 10⁻³) suspension of weakly motile bacteria. D: A bubble trapped in a cluster of cells (surrounded by a red dashed line) at high magnification. The contours of growing bubbles in B and D have been highlighted by white dashed lines. E: Cells were separated from their EPS using sonication and centrifugation. Without EPS, “naked” <i>M. aeruginosa</i> cells failed to form a bloom. When the “naked” cells were supplemented with the purified EPS, the ability to form a bloom was restored. Pictures were taken 180 minutes following BG11 addition. In the experiment with naked cells supplemented with purified EPS, the threshold for bloom formation remained identical to that of untreated cells (i.e with their EPS). F: Chemical composition of the EPS before and after blooming.</p

Salt and species-dependent concentration thresholds (in mM, except for the BG11 medium) above which irreversible blooms form.

<p>Reference concentration of 1 is that of BG11 specified in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0120906#sec002" target="_blank">Material and Methods</a>. The reported concentrations of BG11 are the final relative values while the concentrations of all other salt are the amount added to the samples and are expressed in mM. For comparison, the BG11 at 1X contains 17.65 mM NaNO₃, ∼ 18 mM Na⁺, ∼ 0.2 mM K⁺, ∼ 0.25 mM Ca²⁺ and ∼ 0.3 mM Mg²⁺</p><p>Salt and species-dependent concentration thresholds (in mM, except for the BG11 medium) above which irreversible blooms form.</p

Quantification by LC/MS-MS of the neurotoxin BMAA in cyanobacteria.

International audienc

A μ-opioid receptor-filter assay: Rapid estimation of binding affinity of ligands and reversibility of long-lasting ligand-receptor complexes

International audienc

EFFECTS OF SHEAR STRESS ON THE GROWTH RATE OF MICRO-ORGANISMS IN AGITATED REACTORS

The effects of hydrodynamic shear stress on the growth rate of cyanobacteria Synechocystis sp. and Chlamydomonas reinhardtii microalgae cells were studied in agitated photobioreactors, since they have different motility rates and sizes. An experimental setup was designed and constructed to monitor the growth rate of the micro-organisms versus the shear rate; experiments were carried out in a well controlled environment, under constant atmospheric pressure and 20 degrees C temperature. Digitally controlled magnetic agitator-photobioreactors were placed inside a closed chamber with air flow for 4 weeks, under a uniform full-time light intensity provided by two 6-watt white fluorescent light sources. To study the effects of shear stress produced by mechanical agitation on the growth rate of a micro-organism, different agitation frequencies were tested. All reactors were filled with 150 ml of culture medium and micro-organism suspension, with initial dilution factors (ml(suspenion)/Ml(total) (volume)) of 1/30 and 1/300 for Synechocystis and C. reinhardtii respectively. The vessels were placed on different agitating systems at the desired agitator rotation speed, and were sealed with a cotton membrane from the top in order to permit air exchange with the external environment. The micro-organisms\u27 growth was monitored daily by measuring the optical density of the suspensions using a spectrophotometer and was\u27 hen correlated with the cellular concentration, which was measured in turn using a microscopic cell counter. Throughout the experiments pH levels and temperature were measured regularly and adjusted to 7 and 20 C respectively in order to maintain the photosynthetic activity of the species. In addition, to measure the shear stress inside the agitated reactors, a mathematical model was derived to determine the global shear stress magnitude. To determine the local shear stress distribution, the velocity field in the reactor was measured for different agitation frequencies using PIV. Different zones of high and low shear stress were identified. The results showed that the growth rate is independent of the shear stress magnitude for Synechocystis; Synechocystis showed strong resistance, unlike C. reinhardtii, which showed linear dependence of growth rate and shear stress