Sheldon Spectrum and the Plankton Paradox: Two Sides of the Same Coin : A trait-based plankton size-spectrum model

The Sheldon spectrum describes a remarkable regularity in aquatic ecosystems: the biomass density as a function of logarithmic body mass is approximately constant over many orders of magnitude. While size-spectrum models have explained this phenomenon for assemblages of multicellular organisms, this paper introduces a species-resolved size-spectrum model to explain the phenomenon in unicellular plankton. A Sheldon spectrum spanning the cell-size range of unicellular plankton necessarily consists of a large number of coexisting species covering a wide range of characteristic sizes. The coexistence of many phytoplankton species feeding on a small number of resources is known as the Paradox of the Plankton. Our model resolves the paradox by showing that coexistence is facilitated by the allometric scaling of four physiological rates. Two of the allometries have empirical support, the remaining two emerge from predator-prey interactions exactly when the abundances follow a Sheldon spectrum. Our plankton model is a scale-invariant trait-based size-spectrum model: it describes the abundance of phyto- and zooplankton cells as a function of both size and species trait (the maximal size before cell division). It incorporates growth due to resource consumption and predation on smaller cells, death due to predation, and a flexible cell division process. We give analytic solutions at steady state for both the within-species size distributions and the relative abundances across species

L-Plastin nanobodies perturb matrix degradation, podosome formation, stability and lifetime in THP-1 macrophages

Podosomes are cellular structures acting as degradation ‘hot-spots’ in monocytic cells. They appear as dot-like structures at the ventral cell surface, enriched in F-actin and actin regulators, including gelsolin and L-plastin. Gelsolin is an ubiquitous severing and capping protein, whereas L-plastin is a leukocyte-specific actin bundling protein. The presence of the capping protein CapG in podosomes has not yet been investigated. We used an innovative approach to investigate the role of these proteins in macrophage podosomes by means of nanobodies or Camelid single domain antibodies. Nanobodies directed against distinct domains of gelsolin, L-plastin or CapG were stably expressed in macrophage-like THP-1 cells. CapG was not enriched in podosomes. Gelsolin nanobodies had no effect on podosome formation or function but proved very effective in tracing distinct gelsolin populations. One gelsolin nanobody specifically targets actin-bound gelsolin and was effectively enriched in podosomes. A gelsolin nanobody that blocks gelsolin-G-actin interaction was not enriched in podosomes demonstrating that the calcium-activated and actin-bound conformation of gelsolin is a constituent of podosomes. THP-1 cells expressing inhibitory L-plastin nanobodies were hampered in their ability to form stable podosomes. Nanobodies did not perturb Ser5 phosphorylation of L-plastin although phosphorylated L-plastin was highly enriched in podosomes. Furthermore, nanobody-induced inhibition of L-plastin function gave rise to an irregular and unstable actin turnover of podosomes, resulting in diminished degradation of the underlying matrix. Altogether these results indicate that L-plastin is indispensable for podosome formation and function in macrophages

Contribution à l'étude du fractionnement isotopique des acides gras par RMN quantitative du deutérium

La RMN quantitative du deutérium en abondance naturelle permet de déterminer le fractionnement isotopique de métabolites. Celui-ci est fonction des effets isotopiques des enzymes du métabolisme et de l'origine des atomes d'hydrogène. Cette thèse est divisée en deux parties. Dans la première partie la teneur en deutérium d'acides gras isolés de l'huile de vernonia et de l'huile de persil a été mesurée par RMN. Les résultats montrent une répartition non statistique de la teneur en deutérium qui est discutée en terme d'origine des hydrogènes et d'effets isotopiques des enzymes impliquées dans la biosynthèse des acides gras. La deuxième partie consistait à authentifier l'adultération de l'huile d'olive par de l'huile de noisette. Deux stratégies ont ainsi été développées et testées sur différents échantillons d'huile d'olive et de noisette. La faible différence de teneur en deutérium entre les huiles d'olive et de noisette ne permet pas de discriminer ces deux huiles.Quantitative 2H-NMR can be used to measure the distribution of deuterium in long-chain fatty acids at natural abundance. This distribution is determined by both enzyme isotopic effects and the origin of the hydrogen atoms. In the first part of this thesis, fatty acids isolated from vernonia oil and parsley oil were isolated and chemically cleaved. The analysis of these products by quantitative 2H-NMR showed a non-statistical distribution in deuterium. This is interpreted and discussed in terms of the origin of hydrogen atoms and kinetic isotopic effects implicit in the action of the enzymes of synthesis and desaturation. In the second part, two methods were developed and tested aimed at determining adulteration of olive oil by hazelnut oil. The difference of deuterium content between hazelnut oil and olive oil was found too low to distinguish olive and hazelnut oils.NANTES-BU Sciences (441092104) / SudocSudocFranceF

Natural Convection of Nanofluids in a Square Enclosure with a Protruding Heater

This paper reports a numerical study on natural convection from a protruding heater located at the bottom of a square cavity filled with a copper-water nanofluid. The vertical walls of the cavity are cooled isothermally; the horizontal ones are adiabatic, and the heater is attached to the bottom wall. The heat source is assumed either to be isothermal or to have a constant heat flux. The effective viscosity and thermal conductivity of the nanofluid are modeled according to Brinkman and Patel, respectively. Numerical solutions of the full-governing equations, based on the lattice Boltzmann method, are obtained for a wide range of the governing parameters: the Rayleigh number, Ra; the Prandtl number, Pr; the geometrical parameters specifying the heater; the volume fraction of nanoparticles, Φ. For a particular geometry, it has been found that, for a given Ra, heat transfer is enhanced with increasing Φ, independently of the thermal boundary condition applied on the heater