27 research outputs found
Phospholipid synthesis rates in the eastern subtropical South Pacific Ocean
Membrane lipid molecules are a major component of planktonic organisms and this is particularly true of the microbial picoplankton that dominate the open ocean; with their high surface-area to volume ratios, the synthesis of membrane lipids places a major demand on their overall cell metabolism. Specifically, the synthesis of cell membrane phospholipids creates a demand for the nutrient phosphorus, and we sought to refine our understanding of the role of phospholipids in the upper ocean phosphorus cycle. We measured the rates of phospholipid synthesis in a transect of the eastern subtropical South Pacific from Easter Island to Concepcion, Chile as part of the BIOSOPE program. Our approach combined standard phosphorus radiotracer incubations and lipid extraction methods. We found that phospholipid synthesis rates varied from less than 1 to greater than 200 pmol P Lâ1 hâ1, and that phospholipid synthesis contributed between less than 5% to greater than 22% of the total PO43â incorporation rate. Changes in the percentage that phospholipid synthesis contributed to total PO43â uptake were strongly correlated with the ratio of primary production to bacterial production, which supported our hypothesis that heterotrophic bacteria were the primary agents of phospholipid synthesis. The spatial variation in phospholipid synthesis rates underscored the importance of heterotrophic bacteria in the phosphorus cycle of the eastern subtropical South Pacific, particularly the hyperoligotrophic South Pacific subtropical gyre
Growth and specific P-uptake rates of bacterial and phytoplanktonic communities in the Southeast Pacific (BIOSOPE cruise)
© 2007 Author(s) et al. This is an open-access article distributed under the terms of a Creative Commons License. The definitive version was published in Biogeosciences 4 (2007): 941-956, doi:10.5194/bg-4-941-2007Predicting heterotrophic bacteria and phytoplankton specific growth rates (ÎŒ) is of great scientific interest. Many methods have been developed in order to assess bacterial or phytoplankton ÎŒ. One widely used method is to estimate ÎŒ from data obtained on biomass or cell abundance and rates of biomass or cell production. According to Kirchman (2002), the most appropriate approach for estimating ÎŒ is simply to divide the production rate by the biomass or cell abundance estimate. Most methods using this approach to estimate ÎŒ are based on carbon (C) incorporation rates and C biomass measurements. Nevertheless it is also possible to estimate ÎŒ using phosphate (P) data. We showed that particulate phosphate (PartP) can be used to estimate biomass and that the P uptake rate to PartP ratio can be employed to assess ÎŒ. Contrary to other methods using C, this estimator does not need conversion factors and provides an evaluation of ÎŒ for both autotrophic and heterotrophic organisms. We report values of P-based ÎŒ in three size fractions (0.2â0.6; 0.6â2 and >2 ÎŒm) along a Southeast Pacific transect, over a wide range of P-replete trophic status. P-based ÎŒ values were higher in the 0.6â2 ÎŒm fraction than in the >2 ÎŒm fraction, suggesting that picoplankton-sized cells grew faster than the larger cells, whatever the trophic regime encountered. Picoplankton-sized cells grew significantly faster in the deep chlorophyll maximum layer than in the upper part of the photic zone in the oligotrophic gyre area, suggesting that picoplankton might outcompete >2 ÎŒm cells in this particular high-nutrient, low-light environment. P-based ÎŒ attributed to free-living bacteria (0.2-0.6 ÎŒm) and picoplankton (0.6â2 ÎŒm) size-fractions were relatively low (0.11±0.07 dâ1 and 0.14±0.04 dâ1, respectively) in the Southeast Pacific gyre, suggesting that the microbial community turns over very slowly.This research was funded by the Centre National de
la Recherche Scientifique (CNRS), the Institut des Sciences de
lâUnivers (INSU), the Centre National dâEtudes Spatiales (CNES),
the European Space Agency (ESA), The National Aeronautics
and Space Administration (NASA) and the Natural Sciences and
Engineering Research Council of Canada (NSERC). This work is
funded in part by the French Research and Education council
Phosphate availability and the ultimate control of new nitrogen input by nitrogen fixation in the tropical Pacific Ocean
International audienceDue to the low atmospheric input of phosphate into the open ocean, it is one of the key nutrients that could ultimately control primary production and carbon export into the deep ocean. The observed trend over the last 20 years has shown a decrease in the dissolved inorganic phosphate (DIP) pool in the North Pacific gyre, which has been correlated to the increase in di-nitrogen (N2) fixation rates. Following a NW-SE transect, in the Southeast Pacific during the early austral summer (BIOSOPE cruise), we present data on DIP, dissolved organic phosphate (DOP) and particulate phosphate (PP) pools along with DIP turnover times (TDIP) and N2 fixation rates. We observed a decrease in DIP concentration from the edges to the centre of the gyre. Nevertheless the DIP concentrations remained above 100 nmol L-1 and T DIP was more than 6 months in the centre of the gyre; DIP availability remained largely above the level required for phosphate limitation to occur and the absence of Trichodesmium spp and low nitrogen fixation rates were likely to be controlled by other factors such as temperature or iron availability. This contrasts with recent observations in the North Pacific Ocean at the ALOHA station and in the western Pacific Ocean at the same latitude (DIAPALIS cruises) where lower DIP concentrations (-1) and T DIP 2 fixation rates and possibly carbon dioxide sequestration, if the primary ecophysiological controls, temperature and/or iron availability, were alleviated
Response of coccolithophorid Emiliania huxleyi to elevated partial pressure of CO2 under nitrogen limitation
peer reviewedPrecipitation of calcium carbonate by phytoplankton in the photic oceanic layer is an important process regulating the carbon cycling and the exchange Of CO2 at the ocean-atmosphere interface. Previous experiments have demonstrated that, under nutrient-sufficient conditions, doubling the partial pressure Of CO2 (pCO(2)) in seawater-a likely scenario for the end of the century-can significantly decrease both the rate of calcification by coccolithophorids and the ratio of inorganic to organic carbon production. The present work investigates the effects of high pCO(2) on calcification by the coccolithophore Emiliania huxleyi (Strain TW1) grown under nitrogen-limiting conditions, a situation that can also prevail in the ocean. Nitrogen limitation was achieved in NO3-limited continuous cultures renewed at the rate of 0.5 d(-1) and exposed to a saturating light level. pCO(2) was increased from 400 to 700 ppm and controlled by bubbling CO2-rich or CO2-free air into the cultures. The pCO(2) shift has a rapid effect on cell physiology that occurs within 2 cell divisions subsequent to the perturbation. Net calcification rate (C) decreased by 25% and, in contrast to previous studies with N-replete cultures, gross community production (GCP) and dark community respiration (DCR) also decreased. These results suggest that increasing pCO(2) has no noticeable effect on the calcification/photosynthesis ratio (C/P) when cells of E. huxleyi are NO3-limited
MAREL-Iroise/SOMLIT-Brest : Un outil Ă "fonctions-multiples", pour lâobservation des eaux cĂŽtiĂšres
International audienceDepuis treize ans, lâInstitut Universitaire EuropĂ©en de la mer (IUEM, UniversitĂ© de Bretagne Occidentale), lâIfremer et le CNRS/INSU sont partenaires dans lâ observation rĂ©guliĂšre et Ă long terme de la physico-chimie des eaux cĂŽtiĂšres, Ă lâinterface de la rade de Brest et de la mer dâIroise. Ces observations sont menĂ©es Ă haute frĂ©quence au moyen de la bouĂ©e instrumentĂ©e MAREL-Iroise et Ă basse frĂ©quence au moyen du suivi manuel hebdomadaire SOMLIT-Brest. SituĂ©s sur le mĂȘme point de prĂ©lĂšvement, MAREL-Iroise et SOMLIT-Brest forment un outil dâobservation robuste pour rĂ©pondre aux besoins des chercheurs. Ces besoins sont liĂ©s Ă des questions multiples en lien avec le fonctionnement de lâĂ©cosystĂšme, les cycles biogĂ©ochimiques ou plus rĂ©cemment, lâimpact des phĂ©nomĂšnes grande Ă©chelle. Une revue des principaux rĂ©sultats scientifiques obtenus jusquâĂ prĂ©sent permet dâapprĂ©cier lâimportance de cet outil dâobservation
DielsAlder Reactions of Furans with Itaconic Anhydride: Overcoming Unfavorable Thermodynamics
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Proprotein Convertase Subtilisin/Kexin 9 Levels in Relation to Systemic Immune Activation and Subclinical Coronary Plaque in HIV
Abstract Background: Proprotein convertase subtilisin/kexin 9 (PCSK9) is known to mediate homeostasis of low-density lipoprotein cholesterol (LDL-c), but it may also participate in immune reactivity and atherogenesis. Methods: We compared circulating PCSK9 levels among asymptomatic individuals with and without HIV. Further, within each group, we assessed the relationship between PCSK9 levels, traditional cardiovascular disease risk factors, immune activation, and subclinical coronary atherosclerotic plaque. Results: PCSK9 levels were higher among HIV-infected (n = 149) vs matched non-HIV-infected subjects (n = 69; 332 [272, 412] ng/mL vs 304 [257, 375] ng/mL; P = .047). Among HIV-infected subjects, significant albeit modest positive associations were noted between PCSK9 levels and markers of systemic monocyte activation including sCD14 (rho = 0.22; P = .009) and sCD163 (rho = 0.23; P = .006). In this group, PCSK9 levels related weakly to LDL-c (rho = 0.16; P = .05) and also to Framingham Point Score but did not relate to subclinical coronary atherosclerotic plaque parameters. Conclusions: Among HIV-infected individuals, circulating PCSK9 levels are elevated and related to systemic markers of monocyte activation but not to coronary plaque parameters. Additional studies are needed to determine the effects of PCSK9 on immune activation and atherogenesis in HIV and to assess whether PCSK9 inhibition reduces immune activation and coronary atherosclerotic plaque burden. Clinical Trial Registration NCT00455793