The Bunsen gas solubility coefficient of ethylene as a function of temperature and salinity and its importance for nitrogen fixation assays

The acetylene reduction assay is a common method for assessing nitrogen fixation in a variety of marine and freshwater systems. The method measures ethylene, the product of the conversion of the gas acetylene to its reduced form by nitrogenase. Knowledge of the solubility of ethylene in aqueous solution is crucial to the calculation of nitrogen fixation rates and depends on the temperature and salinity of the assay conditions. Despite the increasing interest in marine nitrogen fixation, no gas solubility (Bunsen) coefficients for ethylene in seawater are published to date. Here, we provide a set of equations and present semiempirically derived Bunsen coefficients for ethylene in water (ranging from 0.069 to 0.226) for a range of temperatures and salinities that are relevant for aquatic nitrogen fixation. We apply these data to nitrogen fixation scenarios at different temperatures and salinities and stress the importance of using accurate Bunsen coefficients in nitrogen fixation assays

Symbiotic unicellular cyanobacteria fix nitrogen in the Arctic Ocean.

Biological dinitrogen (N2) fixation is an important source of nitrogen (N) in low-latitude open oceans. The unusual N2-fixing unicellular cyanobacteria (UCYN-A)/haptophyte symbiosis has been found in an increasing number of unexpected environments, including northern waters of the Danish Straight and Bering and Chukchi Seas. We used nanoscale secondary ion mass spectrometry (nanoSIMS) to measure 15N2 uptake into UCYN-A/haptophyte symbiosis and found that UCYN-A strains identical to low-latitude strains are fixing N2 in the Bering and Chukchi Seas, at rates comparable to subtropical waters. These results show definitively that cyanobacterial N2 fixation is not constrained to subtropical waters, challenging paradigms and models of global N2 fixation. The Arctic is particularly sensitive to climate change, and N2 fixation may increase in Arctic waters under future climate scenarios

Effects of Disturbance and Conspecific Negative Density Dependence on Forest Composition and Diversity: A Simulation-Based Approach

Forests provide a wide range of services to humans and create critical habitat for countless species. Tree species composition and diversity, key attributes of forest health and identity, are influenced by both disturbance and conspecific negative density dependence (CNDD). These factors have been thoroughly researched in isolation, but much less is known about how they interact. We present results of a simulation model constructed to investigate the interactions of variable CNDD strengths and disturbance types. We found that while CNDD consistently increased diversity, the magnitude of this effect was heavily influenced by the disturbance regime. The difference between weak and strong CNDD was most pronounced with understory disturbance, and the greatest diversity overall was achieved when strong CNDD was paired with understory disturbance. Empirical studies of CNDD have yielded widely divergent results. Our study suggests a comprehensive understanding of forest ecosystems may require simultaneous consideration of both disturbance and CNDD

Journey to Burning Man

This comic book tells the story of four friends coping from personal trauma and stress as they embark on a journey of self-discovery and healing. The storyline focuses on character development and growth as they travel to the Burning Man festival in the Black Rock Desert of Nevada. This trip, and their desire to go in the first place, reflects open-mindedness and a willingness to engage in alternative forms of medicine beneficial to surviving and thriving after illness or injury

Mechanism for Initiation of Food Allergy: Dependence on skin barrier mutations and environmental allergen co-stimulation

Background Mechanisms for the development of food allergy in neonates are unknown but are clearly linked in patient populations to a genetic predisposition towards skin barrier defects. Whether skin barrier defects functionally contribute to development of food allergy is unknown. Objective The purpose of the study was to determine whether skin barrier mutations, that are primarily heterozygous in patient populations, contribute to the development of food allergy. Methods Mice heterozygous for the Flgft and Tmem79ma mutations were skin sensitized with environmental allergens and food allergens. After sensitization, mice received oral challenge with food allergen and then inflammation, inflammatory mediators, and anaphylaxis were measured. Results We define development of inflammation, inflammatory mediators, and food allergen-induced anaphylaxis in neonatal mice with skin barrier mutations following brief concurrent cutaneous exposure to food and environmental allergens. Moreover, neonates of allergic mothers have elevated responses to suboptimal sensitization with food allergens. Importantly, the responses to food allergens by these neonatal mice were dependent on genetic defects in skin barrier function and on exposure to environmental allergens. Blockade of ST2 during skin sensitization inhibited development of anaphylaxis, antigen-specific IgE and inflammatory mediators. The neonatal anaphylactic responses and antigen-specific IgE were also inhibited by oral pre-exposure to food allergen but, interestingly, this was blunted by concurrent pre-exposure of the skin to environmental allergen. Conclusion These studies uncover mechanisms for food allergy sensitization and anaphylaxis in neonatal mice that are consistent with features of human early life exposures and genetics in clinical food allergy and demonstrate that changes in barrier function drive development of anaphylaxis to food allergen

XUV Frequency Combs via Femtosecond Enhancement Cavities

We review the current state of tabletop extreme ultraviolet (XUV) sources based on high harmonic generation (HHG) in femtosecond enhancement cavities (fsEC). Recent developments have enabled generation of high photon flux (1014 photons/sec) in the XUV, at high repetition rates (>50 MHz) and spanning the spectral region from 40 nm - 120 nm. This level of performance has enabled precision spectroscopy with XUV frequency combs and promises further applications in XUV spectroscopic and photoemission studies. We discuss the theory of operation and experimental details of the fsEC and XUV generation based on HHG, including current technical challenges to increasing the photon flux and maximum photon energy produced by this type of system. Current and future applications for these sources are also discussed.Comment: invited review article, 38 page

Timeliness of Clinic Attendance is a good predictor of Virological Response and Resistance to Antiretroviral drugs in HIV-infected patients

Ensuring long-term adherence to therapy is essential for the success of HIV treatment. As access to viral load monitoring and genotyping is poor in resource-limited settings, a simple tool to monitor adherence is needed. We assessed the relationship between an indicator based on timeliness of clinic attendance and virological response and HIV drug resistance

Phytoplankton transcriptomic and physiological responses to fixed nitrogen in the California current system

Marine phytoplankton are responsible for approximately half of photosynthesis on Earth. However, their ability to drive ocean productivity depends on critical nutrients, especially bioavailable nitrogen (N) which is scarce over vast areas of the ocean. Phytoplankton differ in their preferences for N substrates as well as uptake efficiencies and minimal N requirements relative to other critical nutrients, including iron (Fe) and phosphorus. In this study, we used the MicroTOOLs high-resolution environmental microarray to examine transcriptomic responses of phytoplankton communities in the California Current System (CCS) transition zone to added urea, ammonium, nitrate, and also Fe in the late summer when N depletion is common. Transcript level changes of photosynthetic, carbon fixation, and nutrient stress genes indicated relief of N limitation in many strains of Prochlorococcus, Synechococcus, and eukaryotic phytoplankton. The transcriptomic responses helped explain shifts in physiological and growth responses observed later. All three phytoplankton groups had increased transcript levels of photosynthesis and/or carbon fixation genes in response to all N substrates. However, only Prochlorococcus had decreased transcript levels of N stress genes and grew substantially, specifically after urea and ammonium additions, suggesting that Prochlorococcus outcompeted other community members in these treatments. Diatom transcript levels of carbon fixation genes increased in response to Fe but not to Fe with N which might have favored phytoplankton that were co-limited by N and Fe. Moreover, transcription patterns of closely related strains indicated variability in N utilization, including nitrate utilization by some high-light adapted Prochlorococcus. Finally, up-regulation of urea transporter genes by both Prochlorococcus and Synechococcus in response to filtered deep water suggested a regulatory mechanism other than classic control via the global N regulator NtcA. This study indicated that co-existing phytoplankton strains experience distinct nutrient stresses in the transition zone of the CCS, an understudied region where oligotrophic and coastal communities naturally mix