A previously undescribed cyclic heptapeptide hepatotoxin was isolated from a cyanobacteria waterbloom collected in Pakowki Lake, Alberta, Canada (49°20′N and 110°55′W). The compound was characterized ...by amino acid analysis, ESIMS/CID/MS,
1H and
13C NMR, and UV spectroscopy. Structure of the new microcystin was assigned as
d-Leu
1microcystin-LR (
1). The amino acid composition is the same as microcystin-LR (
2) except for
d-Leu and
l-Leu in
1 instead of
d-Ala and
l-Leu in
2. This is the first microcystin identified, among the 64 known microcystins, that has both a
d- and
l-Leu amino acid. Toxicity as measured by the protein phosphatase inhibition activity of
1 is similar to microcystin-LR. The presence of microcystins in waterblooms from this lake is discussed in relation to the almost yearly bird mortalities that have occurred there since 1995.
Abstract
A field survey was conducted to detect signals of atmospheric nitrogen (N) in 11 dune systems along a nitrogen deposition gradient in the United Kingdom. In the mobile and semi-fixed dunes, ...above-ground biomass was positively related to N inputs. This increase was largely due to increased height and cover of AMMOPHILA ARENARIA. In the long term, this increased biomass may lead to increased organic matter accumulation and consequently accelerated soil development. In the fixed dunes, above ground biomass also showed a positive relationship with N inputs as did soil C : N ratio while soil available N was negatively related to N inputs. Plant species richness was negatively related to N inputs. In the dune slacks, while soil and bulk vegetation parameters showed no relationship with N inputs, cover of CAREX ARENARIA and HYPOCHAERIS RADICATA increased. Site mean Ellenberg N numbers showed no relationship with N deposition either within habitats or across the whole dataset. Neither abundance-weighting nor inclusion of the Siebel numbers for bryophytes improved the relationship. The survey reveals that the relationships of soil and vegetation with atmospheric N deposition vary between sand dune habitats but, despite this variability, clear correlations with N inputs exist. While this survey cannot establish causality, on the basis of the relationships observed we suggest a critical load range of 10 - 20 kg N ha
-1
yr
-1
for coastal sand dunes in the UK.
Dune slacks are a species-rich habitat controlled largely by water chemistry and fluctuations in groundwater. Changes in water chemistry and water table level were analysed in 8 piezometers and 15 ...ephemeral surface water locations at a large UK dune system over a 12-month period. Total nitrogen concentrations in groundwater varied from 0.27-8.21 mg N L(-1), where dissolved organic nitrogen was dominant at the low nitrogen locations and nitrate was dominant at the high nitrogen locations. Principal components analysis of the water chemistry suggests at least four chemically distinct groundwater signatures. Water levels showed strong temporal heterogeneity. Comparisons of water levels with antecedent rainfall identified a component of year-round groundwater feed and differing seasonal responses overlain by a complex series of lags. In summer, there were lags of four, six and seven months with an additional rapid peaky response to daily rainfall with a one-day lag. In winter, water levels were strongly influenced by exogenous groundwater supply, but again exhibited multiple lags. This study shows that local variations in water chemistry and in hydrological regime can be more complicated than previously thought, with clear implications for optimum management of these high priority habitats for conservation.
Male factors, including those of autoimmune origin, contribute to approximately 50% of infertility cases in humans. However, the mechanisms underlying autoimmune male infertility are poorly ...understood. Deficiency in autoimmune regulator (AIRE) impairs central immune tolerance because of diminished expression of self-antigens in the thymus. Humans with AIRE mutations and mice with engineered ablation of Aire develop multiorgan autoimmunity and infertility. To determine the immune targets contributing to infertility in male Aire-deficient (−/−) mice, Aire−/− or wild-type (WT) males were paired with WT females. Aire−/− males exhibited dramatically reduced mating frequency and fertility, hypogonadism, and reduced serum testosterone. Approximately 15% of mice exhibited lymphocytic infiltration into the testis, accompanied by atrophy, azoospermia, and reduced numbers of mitotically active germ cells; the remaining mice showed normal testicular morphology, sperm counts, and motility. However, spermatozoa from all Aire−/− mice were defective in their ability to fertilize WT oocytes in vitro. Lymphocytic infiltration into the epididymis, seminal vesicle, and prostate gland was evident. Aire−/− male mice generated autoreactive antibodies in an age-dependent manner against sperm, testis, epididymis, prostate gland, and seminal vesicle. Finally, expression of Aire was evident in the seminiferous epithelium in an age-dependent manner, as well as in the prostate gland. These findings suggest that Aire-dependent central tolerance plays a critical role in maintaining male fertility by stemming autoimmunity against multiple reproductive targets.
V1647 Ori is a low-mass star in the L1630 star-forming region that underwent an outburst in late 2003 and early 2004. We present postoutburst infrared spectra obtained with NIRSPEC (Keck II) and SpeX ...(IRTF) and compare these to spectra taken during the outburst. The results show that the temperature of the hot CO formed in the inner part of the disk has declined by 6800 K, while the water and CO ice and low-J CO gas features remained unchanged, consistent with previous assertions that the latter, low-temperature features arise in the foreground cloud. The P Cygni profiles of the Paschen series that were present in the outburst spectra taken in 2004 March disappeared by late 2004. The equivalent width of the helium absorption line at 1.0830 km decreased from 8.9 to 3.9 Ae between 2004 March and November, evidence that the hot, fast wind has decreased substantially. We discuss the implications for categorizing V1647 Ori among the known classes of outbursting young stars.
Negative Poisson's ratio (NPR) materials—which shrink along one axis when compressed along an orthogonal one—are currently composed of reentrant cells with dimensions greater than 1 mm. The ...fabrication of NPR materials from various materials and in various cell geometries with dimensions in the micrometer range, for example the epoxy NPR material shown in the Figure, is described.
Context. The gas- and dust dissipation processes in disks around young stars remain uncertain despite numerous studies. At the distance of ~99–116 pc, HD 141569A is one of the nearest HerbigAe stars ...that is surrounded by a tenuous disk, probably in transition between a massive primordial disk and a debris disk. Atomic and molecular gases have been found in the structured 5-Myr old HD 141569A disk, making HD 141569A the perfect object within which to directly study the gaseous atomic and molecular component. Aims. We wish to constrain the gas and dust mass in the disk around HD 141569A. Methods. We observed the fine-structure lines of O i at 63 and 145 μm and the C ii line at 157 μm with the PACS instrument onboard the Herschel Space Telescope as part of the open-time large program GASPS. We complemented the atomic line observations with archival Spitzer spectroscopic and photometric continuum data, a ground-based VLT-VISIR image at 8.6 μm, and 12CO fundamental ro-vibrational and pure rotational J = 3–2 observations. We simultaneously modeled the continuum emission and the line fluxes with the Monte Carlo radiative transfer code MCFOST and the thermo-chemical code ProDiMo to derive the disk gas- and dust properties assuming no dust settling. Results. The models suggest that the oxygen lines are emitted from the inner disk around HD 141569A, whereas the C ii line emission is more extended. The CO submillimeter flux is emitted mostly by the outer disk. Simultaneous modeling of the photometric and line data using a realistic disk structure suggests a dust mass derived from grains with a radius smaller than 1 mm of ~2.1 × 10-7M⊙ and from grains with a radius of up to 1 cm of 4.9 × 10-6M⊙. We constrained the polycyclic aromatic hydrocarbons (PAH) mass to be between 2 × 10-11 and 1.4 × 10-10M⊙ assuming circumcircumcoronene (C150H30) as the representative PAH. The associated PAH abundance relative to hydrogen is lower than those found in the interstellar medium (3 × 10-7) by two to three orders of magnitude. The disk around HD 141569A is less massive in gas (2.5 to 4.9 × 10-4M⊙ or 67 to 164 M⊕) and has a flat opening angle (<10%). Conclusions. We constrained simultaneously the silicate dust grain, PAH, and gas mass in a ~5-Myr old Herbig Ae disk. The disk-averaged gas-to-dust-mass is most likely around 100, which is the assumed value at the disk formation despite the uncertainties due to disagreements between the different gas tracers. If the disk was originally massive, the gas and the dust would have dissipated at the same rate.
The Herschel GASPS key program is a survey of the gas phase of protoplanetary discs, targeting 240 objects which cover a large range of ages, spectral types, and disc properties. To interpret this ...large quantity of data and initiate self-consistent analyses of the gas and dust properties of protoplanetary discs, we have combined the capabilities of the radiative transfer code MCFOST with the gas thermal balance and chemistry code ProDiMo to compute a grid of approximate to 300 000 disc models (DENT). We present a comparison of the first Herschel/GASPS line and continuum data with the predictions from the DENT grid of models. Our objective is to test some of the main trends already identified in the DENT grid, as well as to define better empirical diagnostics to estimate the total gas mass of protoplanetary discs. Photospheric UV radiation appears to be the dominant gas-heating mechanism for Herbig stars, whereas UV excess and/or X-rays emission dominates for T Tauri stars. The DENT grid reveals the complexity in the analysis of far-IR lines and the difficulty to invert these observations into physical quantities. The combination of Herschel line observations with continuum data and/or with rotational lines in the (sub-)millimetre regime, in particular CO lines, is required for a detailed characterisation of the physical and chemical properties of circumstellar discs.
Context. Circumstellar discs are ubiquitous around young stars, but rapidly dissipate their gas and dust on timescales of a few Myr. The Herschel Space Observatory allows for the study of the warm ...disc atmosphere, using far-infrared spectroscopy to measure gas content and excitation conditions, and far-IR photometry to constrain the dust distribution.Aims. We aim to detect and characterize the gas content of circumstellar discs in four targets as part of the Herschel science demonstration phase.Methods. We carried out sensitive medium resolution spectroscopy and high sensitivity photometry at gimel similar to 60-190 mu m using the Photodetector Array Camera and Spectrometer instrument on the Herschel Space Observatory.Results. We detect OI 63 mu m emission from the young stars HD 169142, TW Hydrae, and RECX 15, but not HD 181327. No other lines, including CII 158 and OI 145, are significantly detected. All four stars are detected in photometry at 70 and 160 mu m. Extensive models are presented in associated papers.
Unexplained deaths of pond‐grown catfish have occurred for many years. At least some of these mortalities could be from cyanobacteria toxins ingested during feeding on floating diets or passively ...assimilated through gills during breathing. Recently we were able to document algal production and subsequent ingestion of these toxicants by catfish during a mortality event. The causative organism, Microcystis aeruginosa, was the dominant species within the phytoplankton community during the cooler autumn‐winter season. Pond conditions included a drop in water temperature by c. 5 °C during the 10 days preceding the fish mortalities. Microcystin‐LR, a hepatotoxin produced by Microcystis, was detected in water samples and in catfish liver tissue. Fish exposed to pond water containing this toxic bloom were killed within 24 h. Necropsy of fish revealed congested liver and spleen tissues. The combination of clinical signs, detection of microcystin LR in water and in liver, and death of fish exposed to pond water supports the diagnosis of microcystin toxicosis. More research is needed to identify specific environmental conditions initiating toxin production to model and predict occurrence of these toxic algal blooms.
![[ d-Leu 1] microcystin-LR, ...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/0041-0101/small "[ d-Leu 1] microcystin-LR, a new microcystin isolated from waterbloom in a Canadian prairie lake")
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