Nitrogen Fixation in Mesoscale Eddies of the North Pacific Subtropical Gyre: Patterns and Mechanisms

Mesoscale eddies have been shown to support elevated dinitrogen (N2) fixation rates (NFRs) and abundances of N2-fixing microorganisms (diazotrophs), but the mechanisms underlying these observations are not well understood. We sampled two pairs of mesoscale cyclones and anticyclones in the North Pacific Subtropical Gyre in 2017 and 2018 and compared our observations with seasonal patterns from the Hawaii Ocean Time-series (HOT) program. Consistent with previous reports, we found that NFRs were anomalously high for this region (up to 3.7-fold above previous monthly HOT observations) in the centers of both sampled anticyclones. In 2017, these elevated rates coincided with high concentrations of the diazotroph Crocosphaera. We then coupled our field-based observations, together with transcriptomic analyses of nutrient stress marker genes and ecological models, to evaluate the role of biological (via estimates of growth and grazing rates) and physical controls on populations of Crocosphaera, Trichodesmium, and diatom symbionts at the mesoscale. Our results suggest that increased Crocosphaera abundances in the 2017 anticyclone resulted from the alleviation of phosphate limitation, allowing cells to grow at rates exceeding grazing losses. In contrast, distributions of larger, buoyant taxa (Trichodesmium and diatom symbionts) appeared less affected by eddy-driven biological controls. Instead, they appeared driven by physical dynamics along frontal boundaries that separate cyclonic and anticyclonic eddies. No examined controls were able to explain our 2018 findings of higher NFRs in the anticyclone. A generalized explanation of elevated NFRs in mesoscale eddies remains challenging due to the interplay of eddy-driven bottom-up, top-down, and physical control mechanisms.This work was funded by the Simons Foundation (Award # 721252 to DMK, 721256 to AEW, 721223 to EFD, 721221 to MJC, 721244 to EVA, 721225 to STD, 329108 to SJ, and 724220 to JPZ) and expedition funding from the Schmidt Ocean Institute for R/V Falkor Cruise FK180310 in 2018.Peer reviewe

Dose-dependent prednisolone kinetics

Kinetic data for prednisolone and prednisone have been determined following oral administration of prednisolone over a dosage range of 5 to 200 mg in 43 subjects. Intravenous studies have been performed at 20 mg and 100 mg in 3 subjects. At all dosage levels the elimination (t 1 2β for prednisolone remained constant (t 1 2β 3.5 ± 0.2 hr [20 mg], t 1 2 3.7 ± 0.1 hr [100 mg] mean ± SEM). For prednisolone, there was a linear relationship between dose and AUC0 å and Cmax up to a dose of 20 mg, but above this level AUC0 å and Cmax demonstrated a less rapid increase as the dose increased. The prednisone AUCo å remained a constant proportion, 26 ± 2%, of the prednisolone AUCo å at all dosage levels. Bioavailability of prednisolone was 98.5 ± 4%. There was a constant amount of prednisolone bound to cortisol-binding globulin (CBG) (145 ± 16 ng/ml) and as a proportion of the remaining serum prednisolone, the free remained at 14 ± 2% and non-CBG protein-bound prednisolone at 86 ± 2% over the whole dosage range. The intravenous studies demonstrated a significant difference in the volume of distribution of prednisolone as the close changed from 20 mg (Vd 58 ± 4L) to 100 mg (Vd 90 ± 6 L). Since it has been demonstrated that bioavailability, serum protein binding, prednisone-prednisolone interconversion, and t 1 2β remained constant over this dosage range, the altered Vd may account for the nonlinear relationship between AUC and dose

Prednisolone pharmacokinetics in asthmatic patients

Prednisolone serum levels have been measured by radio-immunoassay in 12 steroid-dependent asthmatic patients. Differences in prednisolone pharmacokinetics did not account for the variation in dose of prednisolone required to control asthma

Succession within the prokaryotic communities during the VAHINE mesocosms experiment in the New Caledonia lagoon

N₂ fixation fuels  ∼  50 % of new primary production in the oligotrophic South Pacific Ocean. The VAHINE experiment has been designed to track the fate of diazotroph-derived nitrogen (DDN) and carbon within a coastal lagoon ecosystem in a comprehensive way. For this, large-volume ( ∼  50 m³) mesocosms were deployed in the New Caledonian lagoon and were intentionally fertilized with dissolved inorganic phosphorus (DIP) to stimulate N₂ fixation. This study examined the temporal dynamics of the prokaryotic community together with the evolution of biogeochemical parameters for 23 consecutive days in one of these mesocosms (M1) and in the Nouméa lagoon using MiSeq 16S rRNA gene sequencing and flow cytometry. Combining these methods allowed for inference of absolute cell numbers from 16S data. We observed clear successions within M1, some of which were not mirrored in the lagoon. The dominating classes in M1 were Alpha- and Gammaproteobacteria, Cyanobacteria, eukaryotic microalgae, Marine Group II Euryarchaeota, Flavobacteriia, and Acidimicrobia. Enclosure led to significant changes in the M1 microbial community, probably initiated by the early decay of <i>Synechococcus</i> and diatoms. However, we did not detect a pronounced bottle effect with a copiotroph-dominated community. The fertilization with  ∼  0.8 µM DIP on day 4 did not have directly observable effects on the overall community within M1, as the data samples obtained from before and 4 days after fertilization clustered together, but likely influenced the development of individual populations later on, like <i>Defluviicoccus</i>-related bacteria and UCYN-C-type diazotrophic cyanobacteria (<i>Cyanothece</i>). Growth of UCYN-C led to among the highest N₂-fixation rates ever measured in this region and enhanced growth of nearly all abundant heterotrophic groups in M1. We further show that different <i>Rhodobacteraceae</i> were the most efficient heterotrophs in the investigated system and we observed niche partitioning within the SAR86 clade. Whereas the location in- or outside the mesocosm had a significant effect on community composition, the temporal effect was significantly stronger and similar in both locations, suggesting that overarching abiotic factors were more influential than the enclosure. While temporal community changes were evident, prokaryotic diversity (Shannon index) only declined slightly from  ∼  6.5 to 5.7 or 6.05 in the lagoon and M1, respectively, throughout the experiment, highlighting the importance of multiple and varying sources of organic matter maintaining competition

Flavonoids in monospecific Eucalyptus honeys from Australia

The HPLC analyses of Australian unifloral Eucalyptus honeys have shown that the flavonoids myricetin (3,5,7,3',4',5'-hexahydroxyflavone), tricetin (5,7,3',4',5'-pentahydroxyflavone), quercetin (3;5,7,3',4'-pentahydroxyflavone), luteolin (5,7,3',4'-tetrahydroxyflavone), and kaempferol (3,5,7,4'-tetrahydroxyflavone) are present in all samples. These compounds were previously suggested as floral markers of European Eucalyptus honeys. The present results confirm the use of flavonoid : analysis as an objective method for the botanical origin determination of eucalyptus honey. Honeys from E. camaldulensis (river red gum honey) contain tricetin as the main flavonoid marker, whereas lin honeys from E. pilligaensis (mallee honey), luteolin is the main flavonoid marker, suggesting that species-specific differences can be detected with this analysis. The main difference between the flavonoid profiles of Australian and European Eucalyptus honeys is that in the Australian honeys, the propolis-derived flavonoids (pinobanksin (3,5,7-trihydroxyflavanone), pinocembrin (5,7-dihydroxyflavanone), and chrysin (5,7-dihydroxyflavone)) are seldom found and in much smaller amounts

Protein metabolism in heat-exposed chickens

International audienc

Radiation-induced changes in the glycome of endothelial cells with functional consequences

International audienceAs it is altered by ionizing radiation, the vascular network is considered as a prime target in limiting normal tissue damage and improving tumor control in radiation therapy. Irradiation activates endothelial cells which then participate in the recruitment of circulating cells, especially by overexpressing cell adhesion molecules, but also by other as yet unknown mechanisms. Since protein glycosylation is an important determinant of cell adhesion, we hypothesized that radiation could alter the glycosylation pattern of endothelial cells and thereby impact adhesion of circulating cells. Herein, we show that ionizing radiation increases high mannose-type N-glycans and decreases glycosaminoglycans. These changes stimulate interactions measured under flow conditions between irradiated endothelial cells and monocytes. Targeted transcriptomic approaches in vitro in endothelial cells and in vivo in a radiation enteropathy mouse model confirm that genes involved in N- and O-glycosylation are modulated by radiation, and in silico analyses give insight into the mechanism by which radiation modifies glycosylation. The endothelium glycome may therefore be considered as a key therapeutic target for modulating the chronic inflammatory response observed in healthy tissues or for participating in tumor control by radiation therapy. © 2017 The Author(s)