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61.
Andreas Krupke Wiebke Mohr Julie LaRoche Bernhard M Fuchs Rudolf I Amann Marcel MM Kuypers 《The ISME journal》2015,9(7):1635-1647
Symbiotic relationships between phytoplankton and N2-fixing microorganisms play a crucial role in marine ecosystems. The abundant and widespread unicellular cyanobacteria group A (UCYN-A) has recently been found to live symbiotically with a haptophyte. Here, we investigated the effect of nitrogen (N), phosphorus (P), iron (Fe) and Saharan dust additions on nitrogen (N2) fixation and primary production by the UCYN-A–haptophyte association in the subtropical eastern North Atlantic Ocean using nifH expression analysis and stable isotope incubations combined with single-cell measurements. N2 fixation by UCYN-A was stimulated by the addition of Fe and Saharan dust, although this was not reflected in the nifH expression. CO2 fixation by the haptophyte was stimulated by the addition of ammonium nitrate as well as Fe and Saharan dust. Intriguingly, the single-cell analysis using nanometer scale secondary ion mass spectrometry indicates that the increased CO2 fixation by the haptophyte in treatments without added fixed N is likely an indirect result of the positive effect of Fe and/or P on UCYN-A N2 fixation and the transfer of N2-derived N to the haptophyte. Our results reveal a direct linkage between the marine carbon and nitrogen cycles that is fuelled by the atmospheric deposition of dust. The comparison of single-cell rates suggests a tight coupling of nitrogen and carbon transfer that stays balanced even under changing nutrient regimes. However, it appears that the transfer of carbon from the haptophyte to UCYN-A requires a transfer of nitrogen from UCYN-A. This tight coupling indicates an obligate symbiosis of this globally important diazotrophic association. 相似文献
62.
Resumé Les auteurs ont étudié la composition chimique (N, substances humiques, lignine) de copeaux de bois blanc exposés à l'air libre depuis 2 à 10 ans, ainsi que leur type de peuplement fongique. En l'absence de lignivore, le pH, les taux de lignine et d'N s'élèvent et il se forme des quantités modérées d'humus à forte capacité d'échange. Dans le cas contraire, on voit apparaître, en abondance, des substances humiques peu condensées et la matière organique subit une évolution rappelant celle du mor.Avec la collaboration technique de Melle. M. Clet.Kononova, dans sa monographie5, signale de Troussov (1916) une étude que nous n'avons pas eu en mains. 相似文献
63.
Studies of esterase 6 in Drosophila melanogaster. XVIII. Biochemical differences between the slow and fast allozymes 总被引:1,自引:0,他引:1
Most natural populations of Drosophila melanogaster are polymorphic for two
major electrophoretic variants at the esterase-6 locus. The frequency of
the EST 6F allozyme is greatest in populations in warmer latitudes, whereas
the EST 6S allozyme is predominant in colder latitudes. Latitudinal clines
in electromorph frequencies are found on three continents. Purified
preparations of the allozymes have been characterized for their pH optimum,
substrate specificity, organophosphate inhibition, alcohol activation,
thermal stability, and kinetic parameters. These and previous analyses of
the EST 6 allozymes reveal that the two variants have differences in their
physical and kinetic properties that may provide a basis for the selective
maintenance of the polymorphisms and an explanation of the clinal variation
observed in natural populations.
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A fast integrated enzyme-based pretreatment process concept for cotton containing textiles has been developed for operation in the continuous mode. The total processing time for the desizing and scouring operation is 3–10 minutes for fabrics with a weight of 120–300 g/m2. Essential elements in the process are the high starting temperature, the presence of surfactant, application of vacuum technology and a robust rinsing process afterwards to remove the degraded pectin together with hydrophobic compounds. This rinsing procedure is realized with water containing chelator and surfactant and at high operation temperature beyond 80°C. A mixture of enzymes is used, consisting of a temperature stable α-amylase and a pectate lyase, both operating under alkaline conditions. 相似文献
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Bagrey MM Ngwira Phillimon Tambala A Maria Perez Cameron Bowie David H Molyneux 《Filaria journal》2007,6(1):1-7