Fronts divide diazotroph communities in the Southern Indian Ocean.

Dinitrogen (N2) fixation represents a key source of reactive nitrogen in marine ecosystems. While the process has been rather well-explored in low latitudes of the Atlantic and Pacific Oceans, other higher latitude regions and particularly the Indian Ocean have been chronically overlooked. Here, we characterize N2 fixation and diazotroph community composition across nutrient and trace metals gradients spanning the multifrontal system separating the oligotrophic waters of the Indian Ocean subtropical gyre from the high nutrient low chlorophyll waters of the Southern Ocean.

Recanalization of portal vein thrombosis after pediatric liver transplantation: Efficacy and safety of the transsplenic access.

Background: Endovascular management of portal vein thrombosis (PVT) is challenging. Transsplenic access (TSA) is growing as an access option to the portal system but with higher rates of bleeding complications. The aim of this article is to evaluate the efficacy and safety of transsplenic portal vein recanalization (PVR) using a metallic stent after pediatric liver transplantation.

Hepatic venous reconstruction of the left lateral segment with emphasis on anomalous hepatic vein in pediatric liver transplantation.

Left lateral segment grafts have become a suitable option in pediatric liver transplantation (PLT). The correlation between hepatic vein (HV) reconstruction and outcome is relevant when assessing the safe use of these grafts. We retrospectively reviewed the medical records prospectively collected from a pediatric living donor liver transplantation database and conducted a comparative analysis of the different left lateral segment graft types according to HV reconstruction.

Diazotrophs are overlooked contributors to carbon and nitrogen export to the deep ocean.

Diazotrophs are widespread microorganisms that alleviate nitrogen limitation in 60% of our oceans, thereby regulating marine productivity. Yet, the group-specific contribution of diazotrophs to organic matter export has not been quantified, which so far has impeded an accurate assessment of their impact on the biological carbon pump. Here, we examine the fate of five groups of globally-distributed diazotrophs by using an original combination of mesopelagic particle sampling devices across the subtropical South Pacific Ocean.

Sinking Trichodesmium fixes nitrogen in the dark ocean.

The photosynthetic cyanobacterium Trichodesmium is widely distributed in the surface low latitude ocean where it contributes significantly to N fixation and primary productivity. Previous studies found nifH genes and intact Trichodesmium colonies in the sunlight-deprived meso- and bathypelagic layers of the ocean (200-4000 m depth). Yet, the ability of Trichodesmium to fix N in the dark ocean has not been explored.

Planktonic Aggregates as Hotspots for Heterotrophic Diazotrophy: The Plot Thickens.

Biological dinitrogen (N) fixation is performed solely by specialized bacteria and archaea termed diazotrophs, introducing new reactive nitrogen into aquatic environments. Conventionally, phototrophic cyanobacteria are considered the major diazotrophs in aquatic environments. However, accumulating evidence indicates that diverse non-cyanobacterial diazotrophs (NCDs) inhabit a wide range of aquatic ecosystems, including temperate and polar latitudes, coastal environments and the deep ocean.

Ingestion of Diazotrophs Makes Corals More Resistant to Heat Stress.

Over the past decade, coral bleaching events have continued to recur and intensify. During bleaching, corals expel millions of their symbionts, depriving the host from its main food source. One mechanism used by corals to resist bleaching consists in exploiting food sources other than autotrophy.

Anomalously high abundance of Crocosphaera in the South Pacific Gyre.

The unicellular diazotrophic cyanobacterium Crocosphaera contributes significantly to fixed nitrogen inputs in the oligotrophic ocean. In the western tropical South Pacific Ocean (WTSP), these diazotrophs abound thanks to the phosphorus-rich waters provided by the South Equatorial Current, and iron provided aeolian and subsurface volcanic activity. East of the WTSP, the South Pacific Gyre (SPG) harbors the most oligotrophic and transparent waters of the world's oceans, where only heterotrophic diazotrophs have been reported before.

Fine-scale sampling unveils diazotroph patchiness in the South Pacific Ocean.

Diazotrophs are important contributors to nitrogen availability in the ocean. Oceanographic cruise data accumulated over the past three decades has revealed a heterogeneous distribution of diazotroph species at regional to global scales. However, dynamic fine-scale physical structures likely affect the distribution of diazotrophs at smaller spatiotemporal scales.

Impact of hypoxemia on pediatric liver transplantation for hepatopulmonary syndrome.

Background: The treatment of choice for patients with cirrhosis and HPS is LT. The clinical manifestations associated with hypoxemia result in limitations and a poor health-related quality of life of affected patients. The present report aims to study the differences in outcomes between patients with PaO  < 50 mm Hg and those with PaO  ≥ 50 mm Hg.

Untreated sewage outfalls do not promote Trichodesmium blooms in the coasts of the Canary Islands.

During the summer of 2017, recurrent extensive blooms of the diazotrophic cyanobacterium Trichodesmium invaded the beaches and coastal waters of the Canary Islands, causing great social alarm. Some local media and public sectors ascribed, without any strong scientific evidence, the origin and reactivation of these blooms to untreated sewage outfalls distributed along the coasts. In order to test whether sewage outfalls could have any influence on the metabolic activity of Trichodesmium, we performed C and N uptake experiments with colonies experiencing three different bloom development stages, incubated both with clear seawater and sewage water from an outfall south of Gran Canaria island.

Dissolved organic matter stimulates N2 fixation and nifH gene expression in Trichodesmium.

Mixotrophy, the combination of heterotrophic and autotrophic nutrition modes, is emerging as the rule rather than the exception in marine photosynthetic plankton. Trichodesmium, a prominent diazotroph ubiquitous in the (sub)tropical oceans, is generally considered to obtain energy via autotrophy. While the ability of Trichodesmium to use dissolved organic phosphorus when deprived of inorganic phosphorus sources is well known, the extent to which this important cyanobacterium may benefit from other dissolved organic matter (DOM) resources is unknown.

INT Toxicity over Natural Bacterial Assemblages from Surface Oligotrophic Waters: Implications for the Assessment of Respiratory Activity.

Plankton community respiration (R) is a major component of the carbon flux in aquatic ecosystems. However, current methods to measure actual respiration from oxygen consumption at relevant spatial scales are not sensitive enough in oligotrophic environments where respiration rates are very low. To overcome this drawback, more sensitive indirect enzymatic approaches are commonly used as R proxies.

Bleaching forces coral's heterotrophy on diazotrophs and Synechococcus.

Coral reefs are threatened by global warming, which disrupts the symbiosis between corals and their photosynthetic symbionts (Symbiodiniaceae), leading to mass coral bleaching. Planktonic diazotrophs or dinitrogen (N)-fixing prokaryotes are abundant in coral lagoon waters and could be an alternative nutrient source for corals. Here we incubated untreated and bleached coral colonies of Stylophora pistillata with a N-pre-labelled natural plankton assemblage containing diazotrophs.

Amino acids promote black carbon aggregation and microbial colonization in coastal waters off Vietnam.

The combustion of fossil fuels and biomass produces pyrogenic organic matter usually known as 'black carbon' (BC), which are transported across the atmosphere as particulate aerosol, eventually deposited on land and oceans. Soil studies have investigated the potential microbial colonization and remineralization of BC particles, but this process has been seldom studied in marine waters. BC provides a significant input of organic carbon to the oceans, yet its fate and role in biogeochemical cycling remains unknown.

Long-term outcomes of transmesenteric portal vein recanalization for the treatment of chronic portal vein thrombosis after pediatric liver transplantation.

Portal vein thrombosis (PVT) may occur at any time following liver transplantation. We describe our experience with portal vein recanalization in cases of thrombosis after liver transplantation. Twenty-eight children (5%) out of 566 liver transplant recipients underwent portal vein recanalization using a transmesenteric approach.

Mixotrophic metabolism by natural communities of unicellular cyanobacteria in the western tropical South Pacific Ocean.

Cyanobacteria are major contributors to ocean biogeochemical cycling. However, mixotrophic metabolism and the relative importance of inorganic and organic carbon assimilation within the most abundant cyanobacteria are still poorly understood. We explore the ability of Prochlorococcus and Synechococcus to assimilate organic molecules with variable C:N:P composition and its modulation by light availability and photosynthetic impairment.

Chasing after Non-cyanobacterial Nitrogen Fixation in Marine Pelagic Environments.

Traditionally, cyanobacterial activity in oceanic photic layers was considered responsible for the marine pelagic dinitrogen (N) fixation. Other potentially N-fixing bacteria and archaea have also been detected in the pelagic water column, however, the activity and importance of these non-cyanobacterial diazotrophs (NCDs) remain poorly constrained. In this perspective we summarize the N fixation rates from recently published studies on photic and aphotic layers that have been attributed to NCD activity via parallel molecular measurements, and discuss the status, challenges, and data gaps in estimating non-cyanobacterial N fixation NCNF in the ocean.

Dissolved organic matter uptake by Trichodesmium in the Southwest Pacific.

The globally distributed diazotroph Trichodesmium contributes importantly to nitrogen inputs in the oligotrophic oceans. Sites of dissolved organic matter (DOM) accumulation could promote the mixotrophic nutrition of Trichodesmium when inorganic nutrients are scarce. Nano-scale secondary ion mass spectrometry (nanoSIMS) analyses of individual trichomes sampled in the South Pacific Ocean, showed significant C-enrichments after incubation with either C-labeled carbohydrates or amino acids.

Diazotrophs: a non-negligible source of nitrogen for the tropical coral Stylophora pistillata.

Corals are mixotrophs: they are able to fix inorganic carbon through the activity of their symbiotic dinoflagellates and to gain nitrogen from predation on plankton and uptake of dissolved organic and inorganic nutrients. They also live in close association with diverse diazotrophic communities, inhabiting their skeleton, tissue and mucus layer, which are able to fix dinitrogen (N2). The quantity of fixed N2 transferred to the corals and its distribution within coral compartments as well as the quantity of nitrogen assimilated through the ingestion of planktonic diazotrophs are still unknown.

Mesopelagic N2 Fixation Related to Organic Matter Composition in the Solomon and Bismarck Seas (Southwest Pacific).

Dinitrogen (N2) fixation was investigated together with organic matter composition in the mesopelagic zone of the Bismarck (Transect 1) and Solomon (Transect 2) Seas (Southwest Pacific). Transparent exopolymer particles (TEP) and the presence of compounds sharing molecular formulae with saturated fatty acids and sugars, as well as dissolved organic matter (DOM) compounds containing nitrogen (N) and phosphorus (P) were higher on Transect 1 than on Transect 2, while oxygen concentrations showed an opposite pattern. N2 fixation rates (up to ~1 nmol N L-1 d-1) were higher in Transect 1 than in Transect 2, and correlated positively with TEP, suggesting a dependence of diazotroph activity on organic matter.