A Coastal N₂ Fixation Hotspot at the Cape Hatteras Front: Elucidating Spatial Heterogeneity in Diazotroph Activity Via Supervised Machine Learning

In the North Atlantic Ocean, dinitrogen (N2) fixation on the western continental shelf represents a significant fraction of basin‐wide nitrogen (N) inputs. However, the factors regulating coastal N2 fixation remain poorly understood, in part due to sharp physico‐chemical gradients and dynamic water mass interactions that are difficult to constrain via traditional oceanographic approaches. This study sought to characterize the spatial heterogeneity of N2 fixation on the western North Atlantic shelf, at the confluence of Mid‐ and South Atlantic Bight shelf waters and the Gulf Stream, in August 2016. Rates were quantified using the 15N2 bubble release method and used to build empirical models of regional N2 fixation via a random forest machine learning approach. N2 fixation rates were then predicted from high‐resolution CTD and satellite data to infer the variability of its depth and surface distributions, respectively. Our findings suggest that the frontal mixing zone created conditions conducive to exceptionally high N2 fixation rates (\u3e 100 nmol N L−1 d−1), which were likely driven by the haptophyte‐symbiont UCYN‐A. Above and below this hotspot, N2 fixation rates were highest on the shelf due to the high particulate N concentrations there. Conversely, specific N2 uptake rates, a biomass‐independent metric for diazotroph activity, were enhanced in the oligotrophic slope waters. Broadly, these observations suggest that N2 fixation is favored offshore but occurs continuously across the shelf. Nevertheless, our model results indicate that there is a niche for diazotrophs along the coastline as phytoplankton populations begin to decline, likely due to exhaustion of coastal nutrients

Examining Ecological Succession of Diatoms in California Current System Cyclonic Mesoscale Eddies

The California Current System is a diatom-dominated region characterized by seasonal coastal upwelling and additional elevated mesoscale activity. Cyclonic mesoscale eddies in the region trap productive coastal waters with their planktonic communities and transport them offshore with limited interaction with surrounding waters, effectively acting as natural mesocosms, where phytoplankton populations undergo ecological succession as eddies age. This study examines diatom community composition within two mesoscale cyclonic eddies that formed in the same region of the California Current System 2 months apart and in the California Current waters surrounding them. The diatom communities were analyzed in the context of shifting environmental gradients and through a lens of community succession to expand our understanding of biophysical interactions in California Current System cyclonic eddies. Diatom communities within each eddy were different from non-eddy communities and varied in concert with salinity and dissolved iron (Fe) concentrations. The younger, nearshore eddy displayed higher macronutrient and dissolved Fe concentrations, had higher values for diatom Shannon diversity and evenness, and had nutrient ratios indicative of either eventual silicic acid (Si) or Fe limitation or possibly co-limitation. The older, offshore eddy displayed low macronutrient and dissolved Fe concentrations, was likely nitrate-limited, and had lower diatom Shannon diversity and evenness indices. Sequences from the genus Rhizosolenia, some of which form vertically migrating mats to bypass nitrate limitation, dominated in the older eddy. This is of potential significance as the prevalence of Rhizosolenia mats could impact estimates of carbon cycling and export in the wider California coastal area

High rates of N-2 fixation in temperate, western North Atlantic coastal waters expand the realm of marine diazotrophy

© The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Mulholland, M. R., Bernhardt, P. W., Widner, B. N., Selden, C. R., Chappell, P. D., Clayton, S., Mannino, A., & Hyde, K. High rates of N-2 fixation in temperate, western North Atlantic coastal waters expand the realm of marine diazotrophy. Global Biogeochemical Cycles, 33(7), (2019): 826-840, doi:10.1029/2018GB006130.Dinitrogen (N2) fixation can alleviate N limitation of primary productivity by introducing fixed nitrogen (N) to the world's oceans. Although measurements of pelagic marine N2 fixation are predominantly from oligotrophic oceanic regions, where N limitation is thought to favor growth of diazotrophic microbes, here we report high rates of N2 fixation from seven cruises spanning four seasons in temperate, western North Atlantic coastal waters along the North American continental shelf between Cape Hatteras and Nova Scotia, an area representing 6.4% of the North Atlantic continental shelf area. Integrating average areal rates of N2 fixation during each season and for each domain in the study area, the estimated N input from N2 fixation to this temperate shelf system is 0.02 Tmol N/year, an amount equivalent to that previously estimated for the entire North Atlantic continental shelf. Unicellular group A cyanobacteria (UCYN‐A) were most often the dominant diazotrophic group expressing nifH, a gene encoding the nitrogenase enzyme, throughout the study area during all seasons. This expands the domain of these diazotrophs to include coastal waters where dissolved N concentrations are not always depleted. Further, the high rates of N2 fixation and diazotroph diversity along the western North Atlantic continental shelf underscore the need to reexamine the biogeography and the activity of diazotrophs along continental margins. Accounting for this substantial but previously overlooked source of new N to marine systems necessitates revisions to global marine N budgets.Data presented in the body and supporting information of this manuscript have been deposited in the National Aeronautics and Space Administration (NASA) repository, SeaBASS and is publicly available at the following DOI address: 10.5067/SeaBASS/CLIVEC/DATA 001. This work was supported by a grant from NASA Grant Number: NNX09AE45G to M. R. M., A. M., and K. H.; a grant from NSF to P. D. C; and the Jacques S. Zaneveld and Neil and Susan Kelley Endowed Scholarships to C. S. We thank NOAA for ship time and the captain and crew of NOAA vessels Delaware II and Henry Bigelow for assistance during field sampling. Data have been submitted to SeaBASS (https://seabass.gsfc.nasa.gov/), NASA's preferred archival repository

IRGM Is a Common Target of RNA Viruses that Subvert the Autophagy Network

Autophagy is a conserved degradative pathway used as a host defense mechanism against intracellular pathogens. However, several viruses can evade or subvert autophagy to insure their own replication. Nevertheless, the molecular details of viral interaction with autophagy remain largely unknown. We have determined the ability of 83 proteins of several families of RNA viruses (Paramyxoviridae, Flaviviridae, Orthomyxoviridae, Retroviridae and Togaviridae), to interact with 44 human autophagy-associated proteins using yeast two-hybrid and bioinformatic analysis. We found that the autophagy network is highly targeted by RNA viruses. Although central to autophagy, targeted proteins have also a high number of connections with proteins of other cellular functions. Interestingly, immunity-associated GTPase family M (IRGM), the most targeted protein, was found to interact with the autophagy-associated proteins ATG5, ATG10, MAP1CL3C and SH3GLB1. Strikingly, reduction of IRGM expression using small interfering RNA impairs both Measles virus (MeV), Hepatitis C virus (HCV) and human immunodeficiency virus-1 (HIV-1)-induced autophagy and viral particle production. Moreover we found that the expression of IRGM-interacting MeV-C, HCV-NS3 or HIV-NEF proteins per se is sufficient to induce autophagy, through an IRGM dependent pathway. Our work reveals an unexpected role of IRGM in virus-induced autophagy and suggests that several different families of RNA viruses may use common strategies to manipulate autophagy to improve viral infectivity

Ion-pair reversed-phase liquid chromatography–electrospray mass spectrometry for the analysis of underivatized small peptides

International audienc

Role of fetal blood sampling in cases of non-visualization of fetal gallbladder.

The fetal gallbladder is visualized from 14 weeks of gestation as an anechoic structure located below the liver in the right anterosuperior quadrant of the abdomen. Non‐visualization of the gallbladder occurs in only 0.1% of pregnancies1 and has been reported in association with a range of abnormalities, from benign gallbladder agenesis or empty gallbladder, to aneuploidies, cystic fibrosis (CF) and biliary atresia (BA), all of which carry a poor prognosis (Table 1)1-5. Based on two cases, we examined the potential utility of fetal blood sampling when the gallbladder could not be visualized by prenatal imaging. [...

La régulation négative de la concentration sérique de la LH et de la FSH du foetus est associée à une perte de l'expression des kisspeptines et de KISS1R dans l'hypothalamus tubéral en fin de développement

National audienc

The Mn-Carbonate Rich Black Shales of the Bangombe Plateau, Francevillian Basin, Gabon

Eight drill cores cutting through the Mn-carbonate bearing black shales from the Bangombé Plateau were studied. Mn-carbonates (up to 80 m thick) are underlain by laminated pyrite rich shales with organic carbon contents of about 4 wt. % and MnO contents of about 6 wt. %. Mn and Fe, S poor shales are intercalated. Mn-carbonate rich shales (20-29 wt. % MnO) have low contents of phyllosilicates, but are rich in organic carbon (about 7 wt. %) with moderate S contents (about 2 wt. %). All shale facies were deposited in a closed basin through suspension settling and precipitations under anoxic conditions. The Mn-carbonates, towards the top, were formed most likely under suboxic conditions. Pyrite and Mn-carbonates are characterized by bacteriomorphous structures. The latter are composed of micrometric carbonates finely intergrown with clays, quartz and organic matter. They formed around and corroded the dolomite and/or organic matter. Mn-carbonates and pyrite both form also several tenths of micrometer large agglomerates and sub-automorphous grains. The agglomerates can be attributed to evolving diagenesis. Carbonate chemistry varies mainly from rhodochrosite to dolomite. The present results point to primary microbial Mn-carbonate formation. No signs for a Mn-oxide precursor were detected. Slumping and shearing structures, distortion and disruption of thin pyrite beds indicate synsedimentary deformations

Characterization of Reactive and Sensitive Skin Microbiota: Effect of Halymenia durvillei (HD) Extract Treatment

After characterization of the reactive skin microbiota, we investigated whether the active Halymenia durvillei (HD), rich in polysaccharides, could modulate this microbiota after 28 days of treatment, act on neuroinflammation parameters, and calm feelings of discomfort and redness. Skin microbiota was assessed using next-generation sequencing experiments (16S RNA gene fragment sequencing) on samples collected from 30 volunteers suffering from reactive, sensitive skin. To evaluate the effect of the HD extract on neuroinflammation, we used an ex vivo model. Finally, an in vivo study was performed using a clinical assessment (blood microcirculation via videocapillaroscopy) of functional signs employing the Sensitive Scale and the soothing effect was evaluated and compared to a placebo treatment. At the phylum level, the samples were mostly composed of Actinobacteria, Proteobacteria, Firmicutes, and Bacteroidetes, which accounted for more than 97% of the total sequencing read in all samples, with no differences before or after treatment with the HD active ingredient. The Shannon Diversity index indicated lower microbial communities compared to healthy skin. Maintenance of the Shannon Diversity index was reported after 28 days of HD active ingredient treatment, wherein microbial communities continued to decrease in number during treatment with the placebo. The average taxonomic composition of associated skin microbial communities showed that reactive skin is characterized by a low proportion of the Chryseobacterium genus compared to a high proportion of the Corynebacterium genus. At the species level, Actinobacteria are mainly represented by Propionibacterium acnes (72.13%) and Corynebacterium kroppenstedtii (13.23%), representing species typically observed in clinical cases of redness, the main criteria for volunteer inclusion. Corynebacterium kroppenstedtii, with increased levels being associated with skin redness, decreased with HD treatment. This decrease coincided with the clinical improvement observed after 7 weeks of treatment. The ex vivo study revealed that the HD extract induced a significant decrease in the expression of TRPV-1 (−67%; p < 0.001) and NK1-R (−43%; p < 0.01) compared to the control after 6 days of treatment. These data support the use of polysaccharides, found in red alga, in the treatment of reactive and sensitive skin related to the modulation of skin microbiota