Arsenate resistance in the ericoid mycorrhizal fungus Hymenoscyphus ericae

• Differential resistance to arsenate (AsO₄ ^3-) is demonstrated here among populations of the ericoid mycorrhizal fungus Hymenoscyphus ericae isolated from Calluna vulgaris in natural heathland soils and soils contaminated with AsO₄ ^3-. • Isolates (c. 25) of the fungus from each of two As and Cu mine sites, and a natural heathland site, were screened for AsO₄ ^3- and Cu²⁺ resistance by growing isolates in media containing a range of AsO₄ ^3- and Cu²⁺ concentrations. • H. ericae populations from the mine sites demonstrated resistance to AsO₄ ^3- compared with the heathland population; the mine-site populations producing significant growth at the highest AsO₄ ^3- concentration (4.67 mol m^-3), whereas growth of the heathland population was almost completely inhibited. EC₅₀ values for mine-site isolates were estimated to be 5-41-times higher than the heathland population. All isolates produced identical responses to increasing Cu²⁺ concentrations, with no differences observed between mine-site and heathland isolates. • Populations of H. ericae on the contaminated mine sites have developed adaptive resistance to AsO₄ ^3-. By contrast, Cu²⁺ resistance appears to be constitutive.

Genetic diversity of root-associated fungal endophytes from Calluna vulgaris at contrasting field sites

A total of 107 putative ericoid mycorrhizal endophytes were isolated from hair roots of Calluna vulgaris from two abandoned arsenic/copper mine sites and a natural heathland site in southwest England. The endophytes were initially grouped as 14 RFLP types, based on the results of ITS-RFLP analysis using the restriction endonucleases Hinf I, Rsa I and Hae III. ITS sequences were obtained for representative isolates from each RFLP type and compared phylogenetically with sequences for known ericoid mycorrhizal endophytes and selected ascomycetes. The majority of endophyte isolates (62-92%) from each site were identified as Hymenoscyphus ericae, but a number of other less common mycorrhizal RFLP types were also identified, all of which appear to have strong affinities with the order Leotiales. None of the less common RFLP types was isolated from C. vulgaris at more than one field site. Neighbour-joining analysis indicated similarities between the endophytes from C. vulgaris and mycorrhizal endophytes isolated from other Ericaceae and Epacridaceae hosts in North America and Australia.

Phosphorus nutrition of arsenate-tolerant and nontolerant phenotypes of velvetgrass

Velvetgrass (Holcus lanatus L.), also known as Yorkshire fog grass, has evolved tolerance to high levels of arsenate, and this adaptation involves reduced accumulation of arsenate through the suppression of the high affinity phosphate-arsenate uptake system. To determine the role of P nutrition in arsenate tolerance, inhibition kinetics of arsenate influx by phosphate were determined. The concentration of inhibitor required to reduce maximum influx (V(max)) by 50%, K₁, of phosphate inhibition of arsenate influx was 0.02 mol m^-3 in both tolerant and nontolerant clones. This was compared with the concentration where influx is 50% of maximum, a K(m), for arsenate influx of 0.6 mol m^-3 for tolerants and 0.025 mol m^-3 for nontolerants and, therefore, phosphate was much more effective at inhibiting arsenate influx in tolerant genotypes. The high affinity phosphate uptake system is inducible under low plant phosphate status, this increasing plant phosphate status should increase tolerance by decreasing arsenate influx. Root extension in arsenate solutions of tolerant and nontolerant tillers grown under differing phosphate nutritional regimes showed that indeed, increased plant P status increased the tolerance to arsenate of both tolerant and nontolerant clones. That plant P status increased tolerance again argues that P nutrition has a critical role in arsenate tolerance. To determine if short term flux and solution culture studies were relevant to As and P accumulation in soils, soil and plant material from a range of As contaminated sites were analyzed. As predicted from the short-term competition studies, P was accumulated preferentially to As in arsenate tolerant clones growing on mine spoil soils even when acid extractable arsenate in the soils was much greater than acid extractable phosphate. Though phosphate was much more efficient at competing with arsenate for uptake, plants growing on arsenate contaminated land still accumulated considerable amounts of As. Plants from the differing habitats showed large variation in plant phosphate status, pasture plants having much higher P levels than plants growing on the most contaminated mine spoil soils. The selectivity of the phosphate-arsenate uptake system for phosphate compared with arsenate, coupled with the suppression of this uptake system enabled tolerant clones of the grass velvetgrass to grow on soils that were highly contaminated with arsenate and deficient in phosphate.

Polymorphism and physiology of arsenate tolerance in Holcus lanatus L. from an uncontaminated site

The polymorphism of arsenate tolerance in a Holcus lanatus L. population from an uncontaminated soil was investigated and a high percentage of tolerant individuals (65%) was found in the population studied. Influx of arsenate was highly correlated to arsenate tolerance within the population, with the most tolerant individuals having the lowest rates of arsenate influx. Isotherms for the high affinity arsenate uptake systems were determined in six tolerant and six non-tolerant genotypes. Tolerant plants had the lowest rates of arsenate influx. This was achieved by adaptation of the V_max of arsenate influx with the V_max of the high affinity uptake system saturating at lower substrate concentrations in the tolerant plants. The polymorphism is discussed with relation to adaptation to the extreme environments to which the plants are subjected on mine-spoil soils. © 1992 Kluwer Academic Publishers.

Spatial and temporal variability of the freshwater reservoir effect (FRE) in lacustrine sediments in a cold climate zone, Northwest Territories (Canada)

Climate variability along the 600 km Tibbitt to Contwyoto Winter Road (TCWR) in central Northwest Territories is poorly understood. With the transportation of goods from Yellowknife to the mines projected to increase significantly as new mines open, it is critical that planners and mine developers have reasonable data on the future viability of the road, as alternative transportation costs (e.g. air transport) are prohibitively high.

The research presented here is part of a paleoclimate study based on the analysis of multiple proxy data derived from freeze cores in lakes along the TCWR.

Type Ia supernovae from exploding oxygen-neon white dwarfs

Context. The progenitor problem of Type Ia supernovae (SNe Ia) is still unsolved. Most of these events are thought to be explosions of carbon-oxygen (CO) white dwarfs (WDs), but for many of the explosion scenarios, particularly those involving the externally triggered detonation of a sub-Chandrasekhar mass WD (sub-M-Ch, WD), there is also a possibility of having an oxygen-neon (ONe) WD as progenitor.

Aims. We simulate detonations of ONe WDs and calculate synthetic observables from these models. The results are compared with detonations in CO WDs of similar mass and observational data of SNe Ia.

Methods. We perform hydrodynamic explosion simulations of detonations in initially hydrostatic ONe WDs for a range of masses below the Chandrasekhar mass (M-Ch), followed by detailed nucleosynthetic postprocessing with a 384-isotope nuclear reaction network. The results are used to calculate synthetic spectra and light curves, which are then compared with observations of SNe Ia. We also perform binary evolution calculations to determine the number of SNe Ia involving ONe WDs relative to the number of other promising progenitor channels.

Results. The ejecta structures of our simulated detonations in sub-M-Ch, ONe WDs are similar to those from CO WDs. There are, however, small systematic deviations in the mass fractions and the ejecta velocities. These lead to spectral features that are systematically less blueshifted. Nevertheless, the synthetic observables of our ONe WD explosions are similar to those obtained from CO models.

Conclusions. Our binary evolution calculations show that a significant fraction (3-10%) of potential progenitor systems should contain an ONe WD. The comparison of our ONe models with our CO models of comparable mass (similar to 1.2 M-circle dot) shows that the less blueshifted spectral features fit the observations better, although they are too bright for normal SNe Ia.

The ejected mass distribution of Type Ia supernovae: a significant rate of non-Chandrasekhar-mass progenitors

The ejected mass distribution of Type Ia supernovae (SNe Ia) directly probes progenitor evolutionary history and explosion mechanisms, with implications for their use as cosmological probes. Although the Chandrasekhar mass is a natural mass scale for the explosion of white dwarfs as SNe Ia, models allowing SNe Ia to explode at other masses have attracted much recent attention. Using an empirical relation between the ejected mass and the light-curve width, we derive ejected masses Mej and 56Ni masses MNi for a sample of 337 SNe Ia with redshifts z <0.7 used in recent cosmological analyses. We use hierarchical Bayesian inference to reconstruct the joint Mej-MNi distribution, accounting for measurement errors. The inferred marginal distribution of Mej has a long tail towards sub-Chandrasekhar masses, but cuts off sharply above 1.4 M⊙. Our results imply that 25-50 per cent of normal SNe Ia are inconsistent with Chandrasekhar-mass explosions, with almost all of these being sub-Chandrasekhar mass; super-Chandrasekhar-mass explosions make up no more than 1 per cent of all spectroscopically normal SNe Ia. We interpret the SN Ia width-luminosity relation as an underlying relation between Mej and MNi, and show that the inferred relation is not naturally explained by the predictions of any single known explosion mechanism.

Locations of peculiar supernovae as a diagnostic of their origins

We put constraints on the properties of the progenitors of peculiar calcium-rich transients using the distribution of locations within their host galaxies. We confirm that this class of transients do not follow the galaxy stellar mass profile and are more likely to be found in remote locations of their apparent hosts. We test the hypothesis that these transients are from low-metallicity progenitors by comparing their spatial distributions with the predictions of self-consistent cosmological simulations that include star formation and chemical enrichment. We find that while metal-poor stars and our transient sample show a consistent preference for large offsets, metallicity alone cannot explain the extreme cases. Invoking a lower age limit on the progenitor helps to improve the match, indicating these events may result from a very old metal-poor population. We also investigate the radial distribution of globular cluster systems, and show that they too are consistent with the class of calcium-rich transients. Because photometric upper limits exist for globular clusters for some members of the class, a production mechanism related to the dense environment of globular clusters is not favoured for the calcium-rich events. However, the methods developed in this paper may be used in the future to constrain the effects of low metallicity on radially distant core-collapse events or help establish a correlation with globular clusters for other classes of peculiar explosions.

A comparative study of Type II-P and II-L supernova rise times as exemplified by the case of LSQ13cuw

We report on our findings based on the analysis of observations of the Type II-L supernova LSQ13cuw within the framework of currently accepted physical predictions of core-collapse supernova explosions. LSQ13cuw was discovered within a day of explosion, hitherto unprecedented for Type II-L supernovae. This motivated a comparative study of Type II-P and II-L supernovae with relatively well-constrained explosion epochs and rise times to maximum (optical) light. From our sample of twenty such events, we find evidence of a positive correlation between the duration of the rise and the peak brightness. On average, SNe II-L tend to have brighter peak magnitudes and longer rise times than SNe II-P. However, this difference is clearest only at the extreme ends of the rise time versus peak brightness relation. Using two different analytical models, we performed a parameter study to investigate the physical parameters that control the rise time behaviour. In general, the models qualitatively reproduce aspects of the observed trends. We find that the brightness of the optical peak increases for larger progenitor radii and explosion energies, and decreases for larger masses. The dependence of the rise time on mass and explosion energy is smaller than the dependence on the progenitor radius. We find no evidence that the progenitors of SNe II-L have significantly smaller radii than those of SNe II-P.

SN 2011dh: DISCOVERY OF A TYPE IIb SUPERNOVA FROM A COMPACT PROGENITOR IN THE NEARBY GALAXY M51

On 2011 May 31 UT a supernova (SN) exploded in the nearby galaxy M51 (the Whirlpool Galaxy). We discovered this event using small telescopes equipped with CCD cameras and also detected it with the Palomar Transient Factory survey, rapidly confirming it to be a Type II SN. Here, we present multi-color ultraviolet through infrared photometry which is used to calculate the bolometric luminosity and a series of spectra. Our early-time observations indicate that SN 2011dh resulted from the explosion of a relatively compact progenitor star. Rapid shock-breakout cooling leads to relatively low temperatures in early-time spectra, compared to explosions of red supergiant stars, as well as a rapid early light curve decline. Optical spectra of SN 2011dh are dominated by H lines out to day 10 after explosion, after which He I lines develop. This SN is likely a member of the cIIb (compact IIb) class, with progenitor radius larger than that of SN 2008ax and smaller than the eIIb (extended IIb) SN 1993J progenitor. Our data imply that the object identified in pre-explosion Hubble Space Telescope images at the SN location is possibly a companion to the progenitor or a blended source, and not the progenitor star itself, as its radius (~1013 cm) would be highly inconsistent with constraints from our post-explosion spectra.

Fast Rule Mining over Multi-dimensional Windows

Association rule mining is an indispensable tool for discovering
insights from large databases and data warehouses.
The data in a warehouse being multi-dimensional, it is often
useful to mine rules over subsets of data defined by selections
over the dimensions. Such interactive rule mining
over multi-dimensional query windows is difficult since rule
mining is computationally expensive. Current methods using
pre-computation of frequent itemsets require counting
of some itemsets by revisiting the transaction database at
query time, which is very expensive. We develop a method
(RMW) that identifies the minimal set of itemsets to compute
and store for each cell, so that rule mining over any
query window may be performed without going back to the
transaction database. We give formal proofs that the set of
itemsets chosen by RMW is sufficient to answer any query
and also prove that it is the optimal set to be computed
for 1 dimensional queries. We demonstrate through an extensive
empirical evaluation that RMW achieves extremely
fast query response time compared to existing methods, with
only moderate overhead in pre-computation and storage

VentBase:Developing a consensus among stakeholders in the deep-sea regarding environmental impact assessment for deep-sea mining-A workshop report

Mining seafloor massive sulfides for metals is an emergent industry faced with environmental management challenges. These revolve largely around limits to our current understanding of biological variability in marine systems, a challenge common to all marine environmental management. VentBase was established as a forum where academic, commercial, governmental, and non-governmental stakeholders can develop a consensus regarding the management of exploitative activities in the deep-sea. Participants advocate a precautionary approach with the incorporation of lessons learned from coastal studies. This workshop report from VentBase encourages the standardization of sampling methodologies for deep-sea environmental impact assessment. VentBase stresses the need for the collation of spatial data and importance of datasets amenable to robust statistical analyses. VentBase supports the identification of set-asides to prevent the local extirpation of vent-endemic communities and for the post-extraction recolonization of mine sites. © 2013.

A biological survey method applied to seafloor massive sulphides (SMS) with contagiously distributed hydrothermal-vent fauna

Strategies for mitigation of seafloor massive sulphide (SMS) extraction in the deep sea include establishment of suitable reference sites that allow for studies of natural environmental variability and that can serve as sources of larvae for re-colonisation of extracted hydrothermal fields. In this study, we characterize deep-sea vent communities in Manus Basin (Bismarck Sea, Papua New Guinea) and use macrofaunal data sets from a proposed reference site (South Su) and a proposed mine site (Solwara 1) to test the hypothesis that there was no difference in macrofaunal community structure between the sites. We used dispersion weighting to adjust taxa-abundance matrices to down-weight the contribution of contagious distributions of numerically abundant taxa. Faunal assemblages of 3 habitat types defined by biogenic taxa (2 provannid snails, Alviniconcha spp. and Ifremeria nautilei; and a sessile barnacle, Eochionelasmus ohtai) were distinct from one another and from the vent peripheral assemblage, but were not differentiable from mound-to-mound within a site or between sites. Mussel and tubeworm populations at South Su but not at Solwara 1 enhance the taxonomic and habitat diversity of the proposed reference site. © Inter-Research 2012.

A primer for use of genetic tools in selecting and testing the suitability of set-aside sites protected from deep-sea seafloor massive sulfide mining activities

Seafloor massive sulfide (SMS) mining will likely occur at hydrothermal systems in the near future. Alongside their mineral wealth, SMS deposits also have considerable biological value. Active SMS deposits host endemic hydrothermal vent communities, whilst inactive deposits support communities of deep water corals and other suspension feeders. Mining activities are expected to remove all large organisms and suitable habitat in the immediate area, making vent endemic organisms particularly at risk from habitat loss and localised extinction. As part of environmental management strategies designed to mitigate the effects of mining, areas of seabed need to be protected to preserve biodiversity that is lost at the mine site and to preserve communities that support connectivity among populations of vent animals in the surrounding region. These "set-aside" areas need to be biologically similar to the mine site and be suitably connected, mostly by transport of larvae, to neighbouring sites to ensure exchange of genetic material among remaining populations. Establishing suitable set-asides can be a formidable task for environmental managers, however the application of genetic approaches can aid set-aside identification, suitability assessment and monitoring. There are many genetic tools available, including analysis of mitochondrial DNA (mtDNA) sequences (e.g. COI or other suitable mtDNA genes) and appropriate nuclear DNA markers (e.g. microsatellites, single nucleotide polymorphisms), environmental DNA (eDNA) techniques and microbial metagenomics. When used in concert with traditional biological survey techniques, these tools can help to identify species, assess the genetic connectivity among populations and assess the diversity of communities. How these techniques can be applied to set-aside decision making is discussed and recommendations are made for the genetic characteristics of set-aside sites. A checklist for environmental regulators forms a guide to aid decision making on the suitability of set-aside design and assessment using genetic tools. This non-technical primer document represents the views of participants in the VentBase 2014 workshop.