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The bumblebee Bombus terrestris is commonly infected by a trypanosomatid gut parasite Crithidia bombi. This system shows a striking degree of genetic specificity where host genotypes are susceptible to different genotypes of parasite. To a degree, variation in host gene expression underlies these differences, however, the effects of standing genetic variation has not yet been explored. Here we report on an extensive experiment where workers of twenty colonies of B. terrestris were each infected by one of twenty strains of C. bombi. To elucidate the host’s genetic bases of susceptibility to infection (measured as infection intensity), we used a low-coverage (~2 x) genome-wide association study (GWAS), based on angsd, and a standard high-coverage (~15x) GWAS (with a reduced set from a 8 x 8 interaction matrix, selected from the full set of twenty). The results from the low-coverage approach remained ambiguous. The high-coverage approach suggested potentially relevant genetic variation in cell surface and adhesion processes. In particular, mucin, a surface mucoglycoprotein, potentially affecting parasite binding to the host gut epithelia, emerged as a candidate. Sequencing the gut microbial community of the same bees showed that the abundance of bacterial taxa, such as Gilliamella, Snodgrassella, or Lactobacillus, differed between’susceptible’ and’resistant’ microbiota, in line with earlier studies. Our study suggests that the constitutive microbiota and binding processes at the cell surface are candidates to affect infection intensity after the first response (captured by gene expression) has run its course. We also note that a low-coverage approach may not be powerful enough to analyse such complex traits. Furthermore, testing large interactions matrices (as with the full 20 x 20 combinations) for the effect of interaction terms on infection intensity seems to blur the specific host x parasite interaction effects, likely because the outcome of an infection is a highly non-linear process dominated by variation in individually different pathways of host defence (immune) responses., PLoS ONE, 17 (11), ISSN:1932-6203

This thesis reports on the development, optimization and experimental testing of a solar receiver-reactor for the thermochemical splitting of H2O and CO2 to produce H2 and CO (syngas). The solar reactor allows to apply a temperature and pressure swing redox cycle to pure ceria in the form of a reticulated porous ceramic (RPC). In the first, endothermic step, the ceria RPC is directly heated with concentrated solar radiation to around 1500 °C while under vacuum pressure of less than 100 mbar, thereby releasing oxygen from its crystal lattice. In the subsequent, exothermic step, the reactor is repressurized with H2O and/or CO2 as it cools, and at temperatures typically below 1000 °C, the partially reduced ceria is re-oxidized with a flow of H2O and/or CO2 at atmospheric pressure. The produced syngas can be catalytically processed to conventional liquid hydrocarbon fuels. A reactor prototype at the 4 kW scale has been previously designed and tested using a high-flux solar simulator. In this work, the same reactor technology is realized and optimized at the 50 kW scale and tested under realistic conditions using a solar concentrating facility located in Móstoles, Spain. Initial experiments focused on comparing the cycling performance and the mechanical stability of three different ceria cavities made of an interlocking structure of RPC bricks with different porosities, thicknesses and geometries. The performance of the solar reactor for CO2 splitting was experimentally assessed in a high-flux solar simulator. The mechanical strength and stability of the RPCs was assessed with three-point bend testing after fabrication and visually after testing in the solar reactor. The results indicate that lower porosity and higher thickness, both resulting in a higher ceria mass loading, are generally beneficial for the mechanical integrity of the RPC cavity, but the addition of mass without ensuring effective volumetric absorption of the solar radiation and uniform heating of the ceria does not increase the reactor performance. The maximum power of the solar simulator was limited to 32.2 kW delivered at the 16 cm diameter aperture of the solar reactor, which corresponds to a solar concentration ratio of 1602 suns. As a result of the limited power input, a relatively low maximum solar-to-fuel conversion efficiency, defined as the ratio of the heating value of the fuel produced to the input of solar radiative energy and the energy penalties associated with inert gas separation and vacuum pumping, of 3.48±0.08% was measured. Stable operation over multiple cycles without observable degradation was shown with an extended experiment of five consecutive CO2 splitting cycles. To further analyse the performance of the solar reactor and to gain insight into improved design and operation conditions, a transient heat transfer model of the solar reactor was developed. The numerical model couples the incoming concentrated solar radiation using Monte Carlo ray tracing, incorporates the reduction chemistry by assuming thermodynamic equilibrium, and accounts for internal radiation heat transfer inside the porous ceria by applying effective heat transfer properties. The model was experimentally validated using the data acquired in the high-flux solar simulator. The numerical results highlight the potential of the solar reactor to reach high solar-to-fuel energy conversion efficiencies when operated at high power levels. At a solar radiative power input of 50 kW, an efficiency exceeding 6% is predicted. If the RPC macroporosity could be substantially increased to achieve better volumetric absorption of radiation and uniform heating of the ceria, the model predicts efficiencies exceeding 10%. Based on the experimental results acquired in the high-flux solar simulator and the numerical results of the heat transfer model, a new ceria RPC cavity was designed for the operation of the solar reactor with the solar concentrating facility located in Móstoles, Spain. The facility consists of 169 heliostats which concentrate sunlight onto a tower with an optical height of 15 m. The solar reactor, situated on top of the tower, is facing downwards onto the heliostats and features a self-supporting design of the ceria RPC cavity that is adapted for the inclination angle of 40 degrees. With this adjusted solar reactor, a maximum solar-to-fuel energy conversion efficiency of 5.6±1.0% is experimentally demonstrated for CO2 splitting at a solar radiative power input of 55.8±8.2 kW. Simulating the same experiment using the transient heat transfer model reveals how the performance of the reactor could be further improved. At a power input of 55.8 kW, 21.0% of the total solar energy input is lost by reradiation from the hot cavity, but by far the biggest share of energy is used for sensible heating of the ceria and the bulk reactor components, accounting for 58.4% of the solar energy input in total. This energy is mostly lost when the reactor cools down to the oxidation temperature, which highlights the need for implementing heat recovery in order to increase the efficiency of such reactor technology in the future. For the co-splitting of H2O and CO2 in the solar reactor, different measures to adjust the composition of the produced syngas are discussed. At optimal operating conditions, 62 consecutive redox cycles are performed with the same ceria RPC cavity. The produced syngas is collected and stored in a pressurized gas cylinder. Within the European research consortium SUN-to-LIQUID, the accumulated syngas is further processed via Fischer-Tropsch synthesis to produce liquid hydrocarbon fuels on-site. This work demonstrates the technical feasibility of solar thermochemical H2O and CO2 splitting via ceria redox cycling under real-world conditions and at a relevant scale and as such contributes towards the development of a commercial application for the production of solar hydrocarbon fuels.

Sequencing of pooled samples (Pool-Seq) using next-generation sequencing technologies has become increasingly popular, because it represents a rapid and cost-effective method to determine allele frequencies for single nucleotide polymorphisms (SNPs) in population pools. Validation of allele frequencies determined by Pool-Seq has been attempted using an individual genotyping approach, but these studies tend to use samples from existing model organism databases or DNA stores, and do not validate a realistic setup for sampling natural populations. Here we used pyrosequencing to validate allele frequencies determined by Pool-Seq in three natural populations of Arabidopsis halleri (Brassicaceae). The allele frequency estimates of the pooled population samples (consisting of 20 individual plant DNA samples) were determined after mapping Illumina reads to (i) the publicly available, high-quality reference genome of a closely related species (Arabidopsis thaliana) and (ii) our own de novo draft genome assembly of A. halleri. We then pyrosequenced nine selected SNPs using the same individuals from each population, resulting in a total of 540 samples. Our results show a highly significant and accurate relationship between pooled and individually determined allele frequencies, irrespective of the reference genome used. Allele frequencies differed on average by less than 4%. There was no tendency that either the Pool-Seq or the individual-based approach resulted in higher or lower estimates of allele frequencies. Moreover, the rather high coverage in the mapping to the two reference genomes, ranging from 55 to 284x, had no significant effect on the accuracy of the Pool-Seq. A resampling analysis showed that only very low coverage values (below 10-20x) would substantially reduce the precision of the method. We therefore conclude that a pooled re-sequencing approach is well suited for analyses of genetic variation in natural populations., PLoS ONE, 8 (11), ISSN:1932-6203

Multiple geranylgeranyl diphosphate synthases (GGPPS) for biosynthesis of geranylgeranyl diphosphate (GGPP) exist in plants. GGPP is produced in the isoprenoid pathway and is a central precursor for various primary and specialized plant metabolites. Therefore, its biosynthesis is an essential regulatory point in the isoprenoid pathway. We selected 119 GGPPSs from 48 species representing all major plant lineages, based on stringent homology criteria. After the diversification of land plants, the number of GGPPS paralogs per species increases. Already in the moss Physcomitrella patens, GGPPS appears to be encoded by multiple paralogous genes. In gymnosperms, neofunctionalization of GGPPS may have enabled optimized biosynthesis of primary and specialized metabolites. Notably, lineage-specific expansion of GGPPS occurred in land plants. As a representative species we focused here on Arabidopsis thaliana, which retained the highest number of GGPPS paralogs (twelve) among the 48 species we considered in this study. Our results show that the A. thaliana GGPPS gene family is an example of evolution involving neo- and subfunctionalization as well as pseudogenization. We propose subfunctionalization as one of the main mechanisms allowing the maintenance of multiple GGPPS paralogs in A. thaliana genome. Accordingly, the changes in the expression patterns of the GGPPS paralogs occurring after gene duplication led to developmental and/or condition specific functional evolution., Frontiers in Plant Science, 5, ISSN:1664-462X

Salmonids are of particular interest to evolutionary biologists due to their incredible diversity of life‐history strategies and the speed at which many salmonid species have diversified. In Switzerland alone, over 30 species of Alpine whitefish from the subfamily Coregoninae have evolved since the last glacial maximum, with species exhibiting a diverse range of morphological and behavioural phenotypes. This, combined with the whole genome duplication which occurred in the ancestor of all salmonids, makes the Alpine whitefish radiation a particularly interesting system in which to study the genetic basis of adaptation and speciation and the impacts of ploidy changes and subsequent rediploidization on genome evolution. Although well‐curated genome assemblies exist for many species within Salmonidae, genomic resources for the subfamily Coregoninae are lacking. To assemble a whitefish reference genome, we carried out PacBio sequencing from one wild‐caught Coregonus sp. “Balchen ” from Lake Thun to ~90× coverage. PacBio reads were assembled independently using three different assemblers, falcon , canu and wtdbg2 and subsequently scaffolded with additional Hi‐C data. All three assemblies were highly contiguous, had strong synteny to a previously published Coregonus linkage map, and when mapping additional short‐read data to each of the assemblies, coverage was fairly even across most chromosome‐scale scaffolds. Here, we present the first de novo genome assembly for the Salmonid subfamily Coregoninae. The final 2.2‐Gb wtdbg2 assembly included 40 scaffolds, an N50 of 51.9 Mb and was 93.3% complete for BUSCOs. The assembly consisted of ~52% transposable elements and contained 44,525 genes., Molecular Ecology Resources, 20 (4), ISSN:1755-098X, ISSN:1471-8278, ISSN:1755-0998, ISSN:1471-8286