317 research outputs found
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Using deuterated PAH amendments to validate chemical extraction methods to predict PAH bioavailability in soils
Validating chemical methods to predict bioavailable fractions of polycyclic aromatic hydrocarbons (PAHs) by comparison with accumulation bioassays is problematic. Concentrations accumulated in soil organisms not only depend on the bioavailable fraction but also on contaminant properties. A historically contaminated soil was freshly spiked with deuterated PAHs (dPAHs). dPAHs have a similar fate to their respective undeuterated analogues, so chemical methods that give good indications of bioavailability should extract the fresh more readily available dPAHs and historic more recalcitrant PAHs in similar proportions to those in which they are accumulated in the tissues of test organisms. Cyclodextrin and butanol extractions predicted the bioavailable fraction for earthworms (Eisenia fetida) and plants (Lolium multiflorum) better than the exhaustive extraction. The PAHs accumulated by earthworms had a larger dPAH:PAH ratio than that predicted by chemical methods. The isotope ratio method described here provides an effective way of evaluating other chemical methods to predict bioavailability
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Relative proportions of polycyclic aromatic hydrocarbons differ between accumulation bioassays and chemical methods to predict bioavailability
Chemical methods to predict the bioavailable fraction of organic contaminants are usually validated in the literature by comparison with established bioassays. A soil spiked with polycyclic aromatic hydrocarbons (PAHs) was aged over six months and subjected to butanol, cyclodextrin and tenax extractions as well as an exhaustive extraction to determine total PAH concentrations at several time points. Earthworm (Eisenia fetida) and rye grass root (Lolium multiflorum) accumulation bioassays were conducted in parallel. Butanol extractions gave the best relationship with earthworm accumulation (r2 †0.54, p †0.01); cyclodextrin, butanol and acetoneâhexane extractions all gave good predictions of accumulation in rye grass roots (r2 †0.86, p †0.01). However, the profile of the PAHs extracted by the different chemical methods was significantly different (p < 0.01) to that accumulated in the organisms. Biota accumulated a higher proportion of the heavier 4-ringed PAHs. It is concluded that bioaccumulation is a complex process that cannot be predicted by measuring the bioavailable fraction alone.
The ability of chemical methods to predict PAH accumulation in Eisenia fetida and Lolium multiflorum was hindered by the varied metabolic fate of the different PAHs within the organisms
A spatial investigation of the environmental controls over cryoconite aggregation on Longyearbreen glacier, Svalbard.
A cryoconite granule is a near-spherical aggregation of biota and abiotic
particles found upon glacier surfaces. Recently, microstructural studies
have revealed that photosynthetic microorganisms and extracellular polymeric
substances (EPS) are omnipresent within cryoconite granules and have
suggested their importance as biological "forming factors". To assess these
forming factors, and their biological control over aggregate size and
stability, across a typical Arctic valley glacier surface, a suite of rapid,
spectrophotometric, microplate methods were utilised. Subsequent spatial
mapping of these data revealed distinct patterns. Labile carbohydrates were
found to increase up-glacier, suggestive of EPS production for
cryoprotection and nutrient assimilation. Conversely, pigment concentrations
were found to increase towards the glacier terminus and valley sides,
suggestive of allochthonous input, a general reduction in physical
disturbance and of the build-up of photosynthetic pigments and less labile
cyanobacterial sheath material. Aggregate size was found to increase towards
the glacier edges, linked to the input of particulate matter from the valley
sides, and to broadly increase down-glacier, in the same way as pigment
concentrations. Statistical analyses of transect data revealed that the
photoautotrophic count and carbohydrateâchlorophyll ratio of the cryoconite
sampled could explain 83% of the measured variation in aggregate size and
stability. Considering solely aggregate size, the number and length of
photoautotrophic filaments could explain 92% of the variation in this
parameter. These findings demonstrate the two-dimensional distribution of
key biological controls upon cryoconite aggregation for the first time, and
highlight the importance of filamentous cyanobacteria and EPS production to
the development of stable cryoconite granules
Fineâtuned photochromic sulfonylureas for optical control of beta cell Ca <sup>2+</sup> fluxes
We previously developed, synthesized and tested light-activated sulfonylureas for optical control of KATP channels and pancreatic beta cell activity in vitro and in vivo. Such technology relies on installation of azobenzene photoswitches onto the sulfonylurea backbone, affording light-dependent isomerization, alteration in ligand affinity for SUR1 and hence KATP channel conductance. Inspired by molecular dynamics simulations and to further improve photoswitching characteristics, we set out to develop a novel push-pull closed ring azobenzene unit, before installing this on the sulfonylurea glimepiride as a small molecule recipient. Three fine-tuned, light-activated sulfonylureas were synthesized, encompassing azetidine, pyrrolidine and piperidine closed rings. Azetidine-, pyrrolidine- and piperidine-based sulfonylureas all increased beta cell Ca2+ -spiking activity upon continuous blue light illumination, similarly to first generation JB253. Notably, the pyrrolidine-based sulfonylurea showed superior switch OFF performance to JB253. As such, third generation sulfonylureas afford more precise optical control over primary pancreatic beta cells, and showcase the potential of pyrrolidine-azobenzenes as chemical photoswitches across drug classes
Marked Seasonal Changes in the Microbial Production, Community Composition, and Biogeochemistry of Glacial Snowpack Ecosystems in the Maritime Antarctic
We describe seasonal changes in the biogeochemistry, microbial community and ecosystem production of two glacial snowpacks in the maritime Antarctic during a cold summer. Frequent snowfall and low, intermittent melt on the glaciers suppressed surface photosynthesis and promoted net heterotrophy. Concentrations of autotrophic cells (algae and cyanobacteria) were therefore low (average: 150 - 500 cells mL-1), and short-term estimates of primary production were almost negligible in early summer ( 104 cells mL-1 in basal ice near the penguin colony). The ratio of bacteria to autotrophs also increased throughout the summer, and short-term bacterial production rates (0.2 â 2000 ”g C L-1 d-1) usually exceeded primary production, especially in basal ice (10 â 1400 ”g C L-1 d-1). The basal ice represented the least diverse but most productive habitat, and a striking feature was its low pH (down to 3.3). Furthermore, all of the overlying snow cover became increasingly acidic as the summer season progressed, which is attributed to enhanced emissions from wet guano in the penguin colony. The study demonstrates that active microbial communities can be expected, even when snowmelt is intermittent in the Antarctic summer
Median eminence blood flow influences food intake by regulating ghrelin access to the metabolic brain
Central integration of peripheral appetite-regulating signals ensures maintenance of energy
homeostasis. Thus, plasticity of circulating molecule access to neuronal circuits involved in feeding
behavior plays a key role in the adaptive response to metabolic changes. However, the mechanisms
involved remain poorly understood despite their relevance for therapeutic development. Here, we
investigated the role of median eminence mural cells, including smooth muscle cells and pericytes,
in modulating gut hormone effects on orexigenic/anorexigenic circuits. We found that conditional
activation of median eminence vascular cells impinged on local blood flow velocity and altered
ghrelin-stimulated food intake by delaying ghrelin access to target neurons. Thus, activation of
median eminence vascular cells modulates food intake in response to peripheral ghrelin by reducing
local blood flow velocity and access to the metabolic brain.</p
Enzyme self-label-bound ATTO700 in single-molecule and super-resolution microscopy
Herein, we evaluate near-infrared ATTO700 as an acceptor in SNAP- and Halo-tag protein labelling for Förster Resonance Energy Transfer (FRET) by ensemble and single molecule measurements. Microscopy of cell surface proteins in live cells is perfomed including super-resolution stimulated emission by depletion (STED) nanoscopy
The PTEN Phosphatase Functions Cooperatively with the Fanconi Anemia Proteins in DNA Crosslink Repair
Fanconi anemia (FA) is a genetic disease characterized by bone marrow failure and increased cancer risk. The FA proteins function primarily in DNA interstrand crosslink (ICL) repair. Here, we have examined the role of the PTEN phosphatase in this process. We have established that PTEN-deficient cells, like FA cells, exhibit increased cytotoxicity, chromosome structural aberrations, and error-prone mutagenic DNA repair following exposure to ICL-inducing agents. The increased ICL sensitivity of PTEN-deficient cells is caused, in part, by elevated PLK1 kinase-mediated phosphorylation of FANCM, constitutive FANCM polyubiquitination and degradation, and the consequent inefficient assembly of the FA core complex, FANCD2, and FANCI into DNA repair foci. We also establish that PTEN function in ICL repair is dependent on its protein phosphatase activity and ability to be SUMOylated, yet is independent of its lipid phosphatase activity. Finally, via epistasis analysis, we demonstrate that PTEN and FANCD2 function cooperatively in ICL repair
Quantifying wheat blast disease induced yield and production losses of wheat: A quasi-natural experiment
Applying the difference-in-difference (DID) estimation procedure, this study quantifies the wheat blast (Magnaporthe oryzae pathotype Triticum) induced losses in wheat yield, quantity of wheat sold, consumed, or stored, as well as wheat grain value in Bangladesh in 2016 following a disease outbreak that affected over 15,000 ha. Estimates show that the blast-induced yield loss was 540 kg haâ1 on average for households in blast-affected districts. Estimated total wheat production loss was approximately 8,205 tons worth USD 2.1 million in during the 2016 outbreak. Based on these insights, we discuss the need for long-term assured investment and concerted research efforts in controlling transboundary diseases such as wheat blast, including the importance of weather forecast driven early warning systems and the dissemination of blast-resistant varieties
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