The coevolution of toxin and antitoxin genes drives the dynamics of bacterial addiction complexes and intragenomic conflict

Bacterial genomes commonly contain ‘addiction’ gene complexes that code for both a toxin and a corresponding antitoxin. As long as both genes are expressed, cells carrying the complex can remain healthy. However, loss of the complex (including segregational loss in daughter cells) can entail death of the cell. We develop a theoretical model to explore a number of evolutionary puzzles posed by toxin–antitoxin (TA) population biology. We first extend earlier results demonstrating that TA complexes can spread on plasmids, as an adaptation to plasmid competition in spatially structured environments, and highlight the role of kin selection. We then considered the emergence of TA complexes on plasmids from previously unlinked toxin and antitoxin genes. We find that one of these traits must offer at least initially a direct advantage in some but not all environments encountered by the evolving plasmid population. Finally, our study predicts non-transitive ‘rock-paper-scissors’ dynamics to be a feature of intragenomic conflict mediated by TA complexes. Intragenomic conflict could be sufficient to select deleterious genes on chromosomes and helps to explain the previously perplexing observation that many TA genes are found on bacterial chromosomes

Diversity of woody-host infecting Phytophthora species in public parks and botanic gardens as revealed by metabarcoding, and opportunities for mitigation through best practice

The diversity of Phytophthora species in soils collected from 14 highly disturbed sites in northern Britain, including botanic gardens, arboreta, public parks and other amenity woodland sites, was analysed using a molecular technique known as DNA metabarcoding. This technique enables the identification of multiple species present in a single environmental sample based on a DNA ‘barcode’ unique to each species. The genus Phytophthora was targeted in this study due to its increasing impact on Britain’s forests and woodlands over thelast 20 years. The introduction and spread of new Phytophthora species into Britain has been strongly associated with the movement of traded containerised plants, with a number of Phytophthora outbreaks reported on host trees located in public gardens and parks that had recently undergone planting or landscape regeneration schemes. This study was undertaken to assess the extent to which these highly disturbed sites with extensive planting regimes act as harbours for woody-host infecting Phytophthora species. A total of 23 Phytophthora species, the majority of which are known to be pathogens of woody hosts, were detected across the 14 sites sampled. These included four quarantine-regulated pathogens and four species notpreviously recorded in Britain. Also detected were three as-yet undescribed Phytophthora species and nine oomycete sequences with no clear match to any known genus. There was no effect of geographical location, elevation, underlying soil type, host family or host health status on the Phytophthora assemblages at each site, suggesting that the Phytophthora communities detected are likely to comprise introduced species associated with planting programmes. P. austrocedri and P. pseudosyringae were two of the most abundant Phytophthoraspecies detected, both of which cause serious damage to trees and are regarded as fairly recent introductions to Britain. The practical implications of the findings in terms of mitigating Phytophthora introduction, spread and impact at botanic gardens, arboreta and urban parks are discussed

PIM-MOF Composites for Use in Hybrid Hydrogen Storage Tanks

It is well understood that fossil fuels (coal, oil and natural gas) are non-renewable and their combustion is a major driver of anthropogenic climate change, and therefore replacement energy sources and energy vectors must be found. Hydrogen has long been touted as an alternative energy vector, due to its very high gravimetric energy density, and that its full combustion releases only water as a side product. However, hydrogen is a very sparse gas, and as a result its volumetric energy density is very low, making hydrogen storage a difficult technical challenge. The current industrial standard for hydrogen storage in vehicles is compression, in which hydrogen gas is compressed to 70 MPa. This technique has a high energy penalty, and safety concerns due to the high pressure. The tank must also be made out of low weight, high strength carbon fibre composite, which incurs a large economic cost. One alternative solution is adsorption, in which high surface area microporous use the physical bonding between hydrogen molecules and the solid surface area to achieve high hydrogen storage densities at reasonable pressures and temperatures.One potential class of materials for use in such a class are polymers of intrinsic microporosity (PIMs), which are polymeric materials featuring spiro-centres in their molecular chains that cause kinking and thus inefficient packing of the material, which leads to an inherent microporosity. These materials are attractive for a hybrid adsorption-compression tank due to their flexibility and processability. The central material being investigated in this study, PIM-1, is soluble in polar-aprotic solvents such as chloroform and tetrahydrofuran, and forms robust, flexible films upon solvent casting [1]. However, the BET surface area of these films is relatively low (~ 600 m2 g-1) [1], and therefore hydrogen storage capacity must be added for this material to achieve the U.S. Department of Energy targets for hydrogen storage systems [2]. This project aims to achieve this by incorporating crystals of MOF-5, a well understood metal-organic framework (MOF) that has been receiving industrial attention due to its high BET surface area and hydrogen storage capacity [3]. This work aims to synthesise and characterise PIM-1 and MOF-5 independendetly, before combining into a composite-type film material. Characterisation work on these materials is focussed on adsorption isotherms between 0 – 20 MPa at 77 K, using both nitrogen and hydrogen as sorbents. This work is supported through the use of helium pycnometry and thermogravimetric analysis. This characterisation data is compared between the materials, and the relationship between the characteristic properties of the composite and the ratio of materials in its composition is discussed. References:[1] P. M. Budd, E. S. Elabas, B. S. Ghanem, S. Makhseed, N. B. McKeown, K. J. Msayib, C. E. Tattershall & D. Wang, Adv. Mater. 16 (2004) 456-459[2] United States Department of Energy (2009) http://energy.gov/sites/prod/files/2015/01/f19/fcto_myrdd_table_onboard_h2_storage_systems_doe_targets_ldv.pdf [Accessed 13/04/2015][3] M. Veenstra, J. Yang, C. Xu, M. Gaab, L. Arnold, U. Müller, D. Siegel & Y. Ming (2014) http://www.hydrogen.energy.gov/pdfs/review14/st010_veenstra_2014_o.pdf [Accessed 13/04/2015

Re-establishing the ‘outsiders’: English press coverage of the 2015 FIFA Women’s World Cup

In 2015, the England Women’s national football team finished third at the Women’s World Cup in Canada. Alongside the establishment of the Women’s Super League in 2011, the success of the women’s team posed a striking contrast to the recent failures of the England men’s team and in doing so presented a timely opportunity to examine the negotiation of hegemonic discourses on gender, sport and football. Drawing upon an ‘established-outsider’ approach, this article examines how, in newspaper coverage of the England women’s team, gendered constructions revealed processes of alteration, assimilation and resistance. Rather than suggesting that ‘established’ discourses assume a normative connection between masculinity and football, the findings reveal how gendered ‘boundaries’ were both challenged and protected in newspaper coverage. Despite their success, the discursive positioning of the women’s team as ‘outsiders’, served to (re)establish men’s football as superior, culturally salient and ‘better’ than the women’s team/game. Accordingly, we contend that attempts to build and, in many instances, rediscover the history of women’s football, can be used to challenge established cultural representations that draw exclusively from the history of the men’s game. In such instances, the 2015 Women’s World Cup provides a historical moment from which the women’s game can be relocated in a context of popular culture

Metabarcoding reveals a high diversity of woody host-associated Phytophthora spp. in soils at public gardens and amenity woodlands in Britain

This work was supported by Forestry Commission Scotland (grant number SLA-14/15-034), the Living With Environmental Change Phase 3 project ‘Phyto-Threats’ as part of the Tree Health and Plant Biosecurity Initiative (grant number BB/N023463/1) and the European Union’s Horizon 2020 research and innovation programme POnTE (Pest Organisms Threatening Europe) (grant number 635646). David E.L. Cooke, Pete E. Hedley, Leighton Pritchard, Peter Thorpe also received funding from the Scottish GovernmentForests and woodlands worldwide are being severely impacted by invasive Phytophthora species, with initial outbreaks in some cases occurring on host trees located in public parks and gardens. These highly disturbed sites with diverse planting practices may indeed act as harbours for invasive Phytophthora pathogens which are particularly well adapted to surviving in soil. High throughput Illumina sequencing was used to analyse Phytophthora species diversity in soil samples collected from 14 public garden/amenity woodland sites in northern Britain. Bioinformatic analyses revealed some limitations to using internal transcribed spacer as the barcode region; namely reporting of false positives and ambiguous species matches. Taking this into account, 35 distinct sequences were amplified across the sites, corresponding to 23 known Phytophthora species as well as twelve oomycete sequences with no match to any known Phytophthora species. Phytophthora pseudosyringae and P. austrocedri, both of which cause serious damage to trees and are regarded as fairly recent introductions to Britain, were the two most abundant Phytophthora species detected. There was no evidence that any of the detected Phytophthora species were more associated with any one type of host, healthy or otherwise. This study has demonstrated the ubiquity and diversity of Phytophthora species endemic in highly managed, extensively planted soil environments in Britain. Suggested improvements to the methodology and the practical implications of the findings in terms of mitigating Phytophthora spread and impact are discussed.Publisher PDFPeer reviewe

P-type conductivity in Sn-doped Sb2Se3

Antimony selenide (Sb2Se3) is a promising absorber material for thin-film photovoltaics. However, certain areas of fundamental understanding of this material remain incomplete and this presents a barrier to further efficiency gains. In particular, recent studies have highlighted the role of majority carrier type and extrinsic doping in drastically changing the performance of high efficiency devices [1]. Herein, Sndoped Sb2Se3 bulk crystals are shown to exhibit p-type conductivity using Hall effect and hot-probe measurements. The measured conductivities are higher than those achieved through native defects alone, but with a carrier density (up to 7.4 × 1014 cm−3) several orders of magnitude smaller than the quantity of Sn included in the source material. Additionally, a combination of ultraviolet, X-ray and hard X-ray photoemission spectroscopies are employed to obtain a non-destructive depth profile of the valence band maximum, confirming p-type conductivity and indicating a majority carrier type inversion layer at the surface. Finally, these results are supported by density functional theory calculations of the defect formation energies in Sn-doped Sb2Se3, showing a possible limit on the carrier concentration achievable with Sn as a dopant. This study sheds light on the effectiveness of Sn as a p-type dopant in Sb2Se3 and highlights avenues for further optimisation of doped Sb2Se3 for solar energy devices