Distribution of micro-organisms along a transect in the South-East Pacific Ocean (BIOSOPE cruise) from epifluorescence microscopy

International audienceThe distribution of selected groups of micro-organisms was analyzed along a South-East Pacific Ocean transect sampled during the BIOSOPE cruise in 2004. The transect could be divided into four regions of contrasted trophic status: a high Nutrient Low Chlorophyll (HNLC) region (mesotrophic) near the equator, the South-East Pacific Ocean gyre (hyper-oligotrophic), the transition region between the gyre and the coast of South America (moderately oligotrophic), and the Chile upwelling (eutrophic). The abundance of phycoerythrin containing picocyanobacteria, autotrophic and heterotrophic eukaryotes in different size ranges, dinoflagellates, and ciliates was determined by epifluorescence microscopy after DAPI staining. All populations reached a maximum in the Chile upwelling and a minimum near the centre of the gyre. Picocyanobacteria reached a maximum abundance of 70×10³ cell mL-1. In the HNLC zone, up to 50% of picocyanobacteria formed colonies. Autotrophic eukaryote and dinoflagellate abundance reached 24.5×10³ and 200 cell mL-1, respectively. We observed a shift in the size distribution of autotrophic eukaryotes from 2–5 µm in eutrophic and mesotrophic regions to less than 2 µm in the central region. The contribution of autotrophic eukaryotes to total eukaryotes was the lowest in the central gyre. Maximum concentration of ciliates (18 cell ml-1) also occurred in the Chile upwelling, but, in contrast to the other groups, their abundance was very low in the HNLC zone and near the Marquesas Islands

Distribution of micro-organisms along a transect in the South-East Pacific Ocean (BIOSOPE cruise) using epifluorescence microscopy

International audienceThe distribution of selected groups of micro-organisms was analyzed along a South-East Pacific Ocean transect sampled during the BIOSOPE cruise in 2004. The transect could be divided into four regions of contrasted trophic status: a High Nutrient Low Chlorophyll (HNLC) region (mesotrophic) near the equator, the South-East Pacific Ocean gyre (hyper-oligotrophic), a transition region between the gyre and the coast of South America (moderately oligotrophic), and the Chile upwelling (eutrophic). The abundance of phycoerythrin containing picocyanobacteria (PE picocyanobacteria), autotrophic and heterotrophic eukaryotes (classified into different size ranges), dinoflagellates, and ciliates was determined by epifluorescence microscopy after DAPI staining. Despite some apparent loss of cells due to sample storage, distribution patterns were broadly similar to those obtained by flow cytometry for PE picocyanobacteria and picoeukaryotes. All populations reached a maximum in the Chile upwelling and a minimum near the centre of the gyre. The maximum abundance of PE picocyanobacteria was 70 103 cell mL-1. Abundance of autotrophic eukaryotes and dinoflagellates reached 24.5 103 and 20 cell mL-1, respectively. We observed a shift in the size distribution of autotrophic eukaryotes from 2–5 µm in eutrophic and mesotrophic regions to less than 2 µm in the central region. The contribution of autotrophic eukaryotes to total eukaryotes was the lowest in the central gyre. Maximum concentration of ciliates (18 cell mL-1) also occurred in the Chile upwelling, but, in contrast to the other groups, their abundance was very low in the HNLC zone and near the Marquesas Islands. Two key findings of this work that could not have been observed with other techniques are the high percentage of PE picocyanobacteria forming colonies in the HLNC region and the observation of numerous dinoflagellates with bright green autofluorescence

Introduction to the special section bio-optical and biogeochemical conditions in the South East Pacific in late 2004: the BIOSOPE program

International audienceThe objectives of the BIOSOPE (BIogeochemistry and Optics SOuth Pacific Experiment) project was to study, during the austral summer, the biological, biogeochemical and bio-optical properties of different trophic regimes in the South East Pacific: the eutrophic zone associated with the upwelling regime off the Chilean coast, the mesotrophic area associated with the plume of the Marquises Islands in the HNLC (High Nutrient Low Chlorophyll) waters of this subequatorial area, and the extremely oligotrophic area associated with the central part of the South Pacific Gyre (SPG). At the end of 2004, a 55-day international cruise with 32 scientists on board took place between Tahiti and Chile, crossing the SPG along a North-West South-East transect. This paper describes in detail the objectives of the BIOSOPE project, the implementation plan of the cruise, the main hydrological entities encountered along the ~8000 km South East Pacific transect, and ends with a general overview of the 32 other papers published in this special issue

Bolidomonas: a new genus with two species belonging to a new algal class, the Bolidophyceae (Heterokonta) 1.

International audienceA new algal class, the Bolidophyceae (Heterokonta), is described from one genus, Bolidomonas, gen, nov., and two species, Bolidomonas pacifica, sp, nov and Bolidomonas mediterranea, sp, nov., isolated from the equatorial Pacific Ocean and the Mediterranean Sea, respectively. Both species are approximately 1.2 mu m in diameter and have two unequal flagella; the longer flagellum bears tubular hairs, whereas the shorter is smooth. The flagellar basal apparatus is restricted to two basal bodies, and there is no transitional helix. Cells are naked, devoid of walls or siliceous structures. The internal cellular organization is simple with a single plastid containing a ring genophore and a girdle lamella, one mitochondrion with tubular cristae, and one Golgi apparatus close to the basal bodies. The Mediterranean and the Pacific species differ in the insertion angle between their flagella and their pattern of swimming, these differences possibly being linked to each other. Analyses of the SSU rDNA gene place the two strains as a sister group to the diatoms, Moreover, pigment analyses confirm this position, as fucoxanthin is found as the major carotenoid in both lineages. These data strongly suggest that the ancestral heterokont that gave rise to the diatom lineage was probably a biflagellated unicell

Insights on the synthesis mechanism of green phenolic resin derived porous carbons via a salt-soft templating approach

International audienceA combined salt-soft template approach to synthesize porous carbon materials is reported along with their synthesis mechanism. This consists in the evaporation induced self-assembly (EISA) of aqueous solutions containing green phenolic resins, a triblock copolymer template and a metallic salt, followed by thermal treatment and washing. The increase of pH up to 5 using NaOH, induces significant improvement in the carbon microporosity but in the detrimental of mesoporosity. As suggest by 13 C and 1 H NMR, the mesoporosity lost is caused by the decrease of H-bonding and self-assembly between the phenolic resin and the template due to the strong "salting-out" effect of eOH ions. For higher pH (pH-9), the porosity start to decrease and graphene-sheet like morphology is formed. The microporosity varies with the salt in the following order: KCl > NaCl > LiCl, while the mesoporosity in the opposite way. The structure changes as well from smooth turbostatic (KCl) to defective graphitic one (NaCl, LiCl). These textural and structural modifications are explained in terms of cation hydration enthalpy and cation-p binding energy and by the competition between the metal salt cations and the Na ions (used to regulate the pH) for water or phenolic resin aromatic ring sites

Prochlorococcus and Synechococcus: A comparative study of their optical properties in relation to their size and pigmentation

Three unialgal strains of Prochlorococcus and four of Synechococcus were grown in batch culture at low irradiances. The spectral values of light absorption, scattering and backscattering of intact cells in suspension were determined, together with cell counts, size distribution and pigment composition (via HPLC). The spectral efficiency factors Qa, Qb, Qbb for light absorption, scattering and backscattering respectively, were derived, as well as the corresponding chlorophyll-specific coefficients a*, b* and bb*. The pigment used when normalizing is “true” chlorophyll a for Synechococcus, and divinyl-chlorophyll a for Prochlorococcus. In correspondence with small sizes (0.6 μm, on average) Prochlorococcus exhibits Qb values below those of Synechococcus (size about 0.9 μm, on average). In contrast, Qa is higher for Prochlorococcus than for Synechococcus, in response to high internal divinyl-chlorophyll content. In the blue part of the spectrum the probability for photons of being absorbed by a Prochlorococcus cell exceeds that of being scattered. Such a combination has never been found before for other algal cells, consistently more efficient as scatterers than as absorbers. The magnitude of the three efficiency Q-factors, as well as their spectral variations, can be understood and reconstructed in the frame of the Mie theory. The impact of these small organisms, dominant in oligotrophic environment, upon the optical properties of such waters are discussed on the basis of their chlorophyll-specific optical coefficients. Their absorption capabilities (per unit of chlorophyll) are not far from being maximum, to the extent that the package effect is rather reduced. With respect to scattering, Prochlorococcus cells have a minute signature compared to that of Synechococcus. This point is illustrated using vertical profiles of fluorescence, attenuation coefficient, cell number, Chl a and divinyl-Chl a concentrations, as observed in an oligotrophic tropical situation. Even if the backscattering-to-scattering ratio is, as theoretically expected, higher for Prochlorococcus than for all other algae (including Synechococcus), their light backscattering capacity definitely remains negligible

Direct synthesis of graphitic mesoporous carbon from green phenolic resins exposed to subsequent UV and IR laser irradiations

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Picophytoplankton biomass distribution in the global ocean

The smallest marine phytoplankton, collectively termed picophytoplankton, have been routinely enumerated by flow cytometry since the late 1980s during cruises throughout most of the world ocean. We compiled a database of 40 946 data points, with separate abundance entries for Prochlorococcus, Synechococcus and picoeukaryotes. We use average conversion factors for each of the three groups to convert the abundance data to carbon biomass. After gridding with 1? spacing, the database covers 2.4% of the ocean surface area, with the best data coverage in the North Atlantic, the South Pacific and North Indian basins, and at least some data in all other basins. The average picophytoplankton biomass is 12 ± 22 µg Cl-1 or 1.9 g Cm-2. We estimate a total global picophytoplankton biomass of 0.53–1.32 Pg C (17–39% Prochlorococcus, 12–15% Synechococcus and 49–69% picoeukaryotes), with an intermediate/best estimate of 0.74 Pg C. Future efforts in this area of research should focus on reporting calibrated cell size and collecting data in undersampled regions

Low Metal Loading (Au, Ag, Pt, Pd) Photo‐Catalysts Supported on TiO2 for Renewable Processes

Photo‐catalysts based on titanium dioxide, and modified with highly dispersed metallic nanoparticles of Au, Ag, Pd and Pt, either mono‐ or bi‐metallic, have been analyzed by multiple characterization techniques, including XRD, XPS, SEM, EDX, UV‐Vis and N2 adsorption/desorption. Mono‐metallic photo‐catalysts were prepared by wet impregnation, while bi‐metallic photocatalysts were obtained via deposition‐precipitation (DP). The relationship between the physico‐chemical properties and the catalyst’s behavior for various photo‐synthetic processes, such as carbon dioxide photo‐reduction to liquid products and glucose photo‐reforming to hydrogen have been investigated. Among the tested materials, the catalysts containing platinum alone (i.e., 0.1 mol% Pt/TiO2) or bi‐metallic gold‐containing materials (e.g., 1 wt% (AuxAgy)/TiO2 and 1 wt% (AuxPtz)/TiO2) showed the highest activity, presenting the best results in terms of productivity and conversion for both applications. The textural, structural and morphological properties of the different samples being very similar, the main parameters to improve performance were function of the metal as electron sink, together with optoelectronic properties. The high activity in both applications was related to the low band gap, that allows harvesting more energy from a polychromatic light source with respect to the bare TiO2. Overall, high selectivity and productivity were achieved with respect to most literature data