| 1. |
- Abrego, Nerea, et al.
(författare)
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Airborne DNA reveals predictable spatial and seasonal dynamics of fungi
- 2024
-
Ingår i: Nature. - 0028-0836 .- 1476-4687. ; 631, s. 835-842
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Tidskriftsartikel (refereegranskat)abstract
- Fungi are among the most diverse and ecologically important kingdoms in life. However, the distributional ranges of fungi remain largely unknown as do the ecological mechanisms that shape their distributions1,2. To provide an integrated view of the spatial and seasonal dynamics of fungi, we implemented a globally distributed standardized aerial sampling of fungal spores3. The vast majority of operational taxonomic units were detected within only one climatic zone, and the spatiotemporal patterns of species richness and community composition were mostly explained by annual mean air temperature. Tropical regions hosted the highest fungal diversity except for lichenized, ericoid mycorrhizal and ectomycorrhizal fungi, which reached their peak diversity in temperate regions. The sensitivity in climatic responses was associated with phylogenetic relatedness, suggesting that large-scale distributions of some fungal groups are partially constrained by their ancestral niche. There was a strong phylogenetic signal in seasonal sensitivity, suggesting that some groups of fungi have retained their ancestral trait of sporulating for only a short period. Overall, our results show that the hyperdiverse kingdom of fungi follows globally highly predictable spatial and temporal dynamics, with seasonality in both species richness and community composition increasing with latitude. Our study reports patterns resembling those described for other major groups of organisms, thus making a major contribution to the long-standing debate on whether organisms with a microbial lifestyle follow the global biodiversity paradigms known for macroorganisms4,5.
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| 2. |
- Franc, Niklas, 1972, et al.
(författare)
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Factors and scales potentially important for saproxylic beetles in temperate mixed oak forest
- 2007
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Ingår i: Biological Conservation. - : Elsevier BV. - 0006-3207. ; 135:1, s. 86-98
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Tidskriftsartikel (refereegranskat)abstract
- The influence of environmental factors on species richness and species composition may be manifested at different spatial levels. Exploring these relationships is important to understand at which spatial scales certain species and organism groups become sensitive to fragmentation and changes in habitat quality. At different spatial scales we evaluated the potential influence of 45 factors (multiple regression, PCA) on saproxylic oak beetles in 21 smaller broadleaved Swedish forests of conservation importance (woodland key habitats, WKH). Local amount of dead wood in forests is often assumed to be important, but two landscape variables, area of oak dominated woodland key habitats within 1 km of sites and regional amount of dead oak wood, were the main (and strong) predictors of variation in local species richness of oak beetles. The result was similar for red-listed beetles associated with oak. Species composition of the beetles was also best predicted by area of oak woodland key habitat within 1 km, with canopy closure as the second predictor. Despite suitable local quality of the woodland key habitats, the density of such habitat patches may in many areas be too low for long-term protection of saproxylic beetles associated with broadleaved temperate forests. Landscapes with many clustered woodland key habitats rich in oak should have high priority for conservation of saproxylic oak beetles.
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| 3. |
- Götmark, Frank, et al.
(författare)
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Naturvårdsgallring : vad är det?
- 2009
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Ingår i: Biodiverse. - : Centrum för biologisk mångfald. - 1401-5064. ; 14:1, s. 20-20
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Tidskriftsartikel (populärvet., debatt m.m.)
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| 4. |
- Kurina, Olavi, et al.
(författare)
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Fungus gnats (Diptera: Sciaroidea excl. Sciaridae) in the Swedish boreonemoral forests
- 2004
-
Ingår i: Studia dipterologica. ; 11:2, s. 471-488
-
Tidskriftsartikel (refereegranskat)abstract
- Fungus gnats in boreonemoral forests of south Sweden are studied using material collected with Malaise and window traps from 17 localities in the years 2001 and 2002. 250 species are recorded including 76 species new to Sweden. 14 of these are found in Fennoscandia for the first time: Docosia setosa Landrock, D. spec. (indet. sensu Hutson et al. 1980), Brevicornu cognatum Ostroverkhova, Mycetophila eppingensis Chandler, M. lobulata A. Zaitzev, M. pyrenaica Matile, M. subsigillata A. Zaitzev, Sceptonia cryptocauda Chandler, S. flavipuncta Edwards, S. longisetosa Ševcik, S. pilosa Bukowski, S. pughi Chandler, Sciophila interrupta (Winnertz) and S. plurisetosa Edwards. One new synonym is proposed: Dynatosoma dihaeta Polevoi, 1995 = Dynatosoma schachti Plassmann, 1999 syn. nov.
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| 5. |
- Ovaskainen, O., et al.
(författare)
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Combining high-throughput sequencing with fruit body surveys reveals contrasting life-history strategies in fungi
- 2013
-
Ingår i: Isme Journal. - : Springer Science and Business Media LLC. - 1751-7362 .- 1751-7370. ; 7:9, s. 1696-1709
-
Tidskriftsartikel (refereegranskat)abstract
- Before the recent revolution in molecular biology, field studies on fungal communities were mostly confined to fruit bodies, whereas mycelial interactions were studied in the laboratory. Here we combine high-throughput sequencing with a fruit body inventory to study simultaneously mycelial and fruit body occurrences in a community of fungi inhabiting dead wood of Norway spruce. We studied mycelial occurrence by extracting DNA from wood samples followed by 454-sequencing of the ITS1 and ITS2 regions and an automated procedure for species identification. In total, we detected 198 species as mycelia and 137 species as fruit bodies. The correlation between mycelial and fruit body occurrences was high for the majority of the species, suggesting that high-throughput sequencing can successfully characterize the dominating fungal communities, despite possible biases related to sampling, PCR, sequencing and molecular identification. We used the fruit body and molecular data to test hypothesized links between life history and population dynamic parameters. We show that the species that have on average a high mycelial abundance also have a high fruiting rate and produce large fruit bodies, leading to a positive feedback loop in their population dynamics. Earlier studies have shown that species with specialized resource requirements are rarely seen fruiting, for which reason they are often classified as red-listed. We show with the help of high-throughput sequencing that some of these species are more abundant as mycelium in wood than what could be expected from their occurrence as fruit bodies.
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| 6. |
- Ovaskainen, Otso, et al.
(författare)
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Global Spore Sampling Project: A global, standardized dataset of airborne fungal DNA
- 2024
-
Ingår i: Scientific Data. - 2052-4463. ; 11
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Tidskriftsartikel (refereegranskat)abstract
- Novel methods for sampling and characterizing biodiversity hold great promise for re-evaluating patterns of life across the planet. The sampling of airborne spores with a cyclone sampler, and the sequencing of their DNA, have been suggested as an efficient and well-calibrated tool for surveying fungal diversity across various environments. Here we present data originating from the Global Spore Sampling Project, comprising 2,768 samples collected during two years at 47 outdoor locations across the world. Each sample represents fungal DNA extracted from 24 m3 of air. We applied a conservative bioinformatics pipeline that filtered out sequences that did not show strong evidence of representing a fungal species. The pipeline yielded 27,954 species-level operational taxonomic units (OTUs). Each OTU is accompanied by a probabilistic taxonomic classification, validated through comparison with expert evaluations. To examine the potential of the data for ecological analyses, we partitioned the variation in species distributions into spatial and seasonal components, showing a strong effect of the annual mean temperature on community composition.
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| 7. |
- Økland, Björn, et al.
(författare)
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Oak woodland restoration: testing the effects on biodiversity of mycetophilids in Sweden
- 2008
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Ingår i: Biodiversity and Conservation 17. - : Springer Science and Business Media LLC. - 0960-3115 .- 1572-9710. ; 17:11, s. 2599-2616
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Tidskriftsartikel (refereegranskat)abstract
- The effect of harvesting biofuel and woodland restoration on biodiversity is debated. To evaluate the effects of partial cutting on more organism groups, we used pairwise experimental and undisturbed control stands in a large landscape. On average 26% of the basal area including 50-95% of the understorey was harvested at each of 15 oak-rich forest sites. Our earlier results of partial cutting suggested a positive short-term effect for vascular plants and beetles and no or minor negative effects for fungi. Here we analyse the response of mycetophilids (Diptera: Sciaroidea excl. Sciaridae), a neglected but species-rich insect group that was strongly disfavoured by clear-cutting in previous studies. Increased deadwood (slash) caused increase in the number of individuals of mycetophilids associated with wood or wood fungi. The rarefaction species numbers of mycetophilids declined after the treatment, but the absolute number of species was not affected. Our results indicate that a 25% harvest can be compatible with conservation of vascular plants, fungi, saproxylic and herbivorous beetles and mycetophilids in temperate hardwood stands of the type studied. However, more studies are needed to determine what level(s) of stand thinning can be tolerated by different taxa in landscapes with small fragmented conservation stands.
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| 8. |
- Økland, Bjørn, et al.
(författare)
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Regional diversity of mycetophilids (Diptera : Sciaroidea) in Scandinavian oak-dominated forests
- 2005
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Ingår i: Biological Conservation. - : Elsevier BV. - 0006-3207. ; 121:1, s. 9-20
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Tidskriftsartikel (refereegranskat)abstract
- Mycetophilids is a species-rich insect group for which the ecological requirements in temperate forests are poorly understood. This study of mycetophilids was based on trap samples from 15 oak-dominated sites in the boreonemoral zone of southern Sweden. Species richness and composition were analysed in relation to environmental variables at a local and at larger scales (multiple regression), and compared to results from similar studies in spruce-dominated sites in the boreal zone of Norway (PCA and two-sample t tests). Regressions showing a dominance of regional factors over local in-site variables agree with species-richness models assuming that local communities most often are unsaturated. Precipitation (inter-correlated with elevation) was the strongest factor for explaining the variation in species-richness, which is consistent with previous results indicating that mycetophilids are disfavoured by drought. In addition to precipitation, the area of mixed forest with high biodiversity values (woodland key habitats and protected areas) was a positive factor for species-richness, probably because such habitats combine elements of both coniferous and deciduous forests. PCA ordination revealed a clear separation of the species composition between boreal and boreonemoral forests. Species-richness in boreal forest was significantly higher than in boreonemoral forest, indicating a preference for boreal habitats in many of the species. For mycetophilids and other drought-sensitive insects, it is suggested that (partial) cutting in some dense successional oak stands should be avoided, and that some invading spruces should be tolerated. (C) 2004 Elsevier Ltd. All rights reserved.
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| 9. |
- A, Komonen, et al.
(författare)
-
Insects associated with fruit bodies of the wood-decaying fungus Oak mazegill (Daedalea quercina) in mixed oak forests in southern Sweden
- 2012
-
Ingår i: Entomologisk Tidskrift. - 0013-886X. ; 133:4, s. 173-181
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Tidskriftsartikel (refereegranskat)abstract
- Polypores host species rich insect assemblages, but relatively few polypore species have been studied in detail. We investigated insect assemblages associated with the fruit bodies of Daedalea quercina, a specialist species on oak in southern Sweden. Fruit bodies (n = 228) were collected from 25 nature reserves and woodland key habitats, and were taken into the laboratory to collect emerging insects. A total of 245 insect individuals were recorded, belonging to at least 45 species. The numerically dominant fungivores were the tineid moths Montescardia tessulatella (n = 38 individuals) and Nemapogon fungivorellus (n = 10) and the coleopteran Ennearthron cornutum (Ciidae) (n = 44). Altogether 40 individuals of hymenopteran parasitoids were recorded, belonging to Braconidae (Exothecinae, Microgastrinae and Rogadinae, altogether 6 spp.), Ichneumonidae (Banchinae, Cryptinae and Orthocentrinae, altogether 4 spp.), Torymidae (1 sp.), Perilampidae (1 sp.) and Scelionidae (1 sp.). Most of the remaining insect species are not specifically associated with fruit bodies, but occupy many types of decaying material. In conclusion, D. quercina hosted a low number of insect individuals in general and only a few coleopteran species. The fungus apparently has only one specialist species, N. fungivorellus, which is a near-threatened (NT) species on the Swedish red list; the record from Norra Vi is the first from the Jönköping. The overall low number of insect individuals and the dominance of Lepidoptera among the fungivores is possibly explained by the tough fruit bodies of D. quercina, which only moths are able to utilize; fruit bodies which had already started to rot were devoid of moths.
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| 10. |
- Ahlsson, Fredrik, et al.
(författare)
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Insulin Resistance, a Link between Maternal Overweight and Fetal Macrosomia in Nondiabetic Pregnancies
- 2010
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Ingår i: Hormone research in paediatrics. - : S. Karger AG. - 1663-2818 .- 1663-2826. ; 74:4, s. 267-274
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Tidskriftsartikel (refereegranskat)abstract
- Background/Aims: During the last decades the number of large for gestational age infants delivered by nondiabetic mothers has increased. Our aim was to investigate to what extent fetal growth in nondiabetic pregnant women can be explained by rates of maternal energy substrate production and resting energy expenditure. Methods: Twenty nonsmoking pregnant women without impaired glucose tolerance and with a wide range of fetal weights (0.2-2.7 SDS) were investigated at 36 weeks of gestation. Maternal lipolysis, glucose production, resting energy expenditure, body composition and insulin resistance were assessed.Results: Median (range) glucose production rate was 805 (653-1,337) mumol/min and that of glycerol, reflecting lipolysis, was 214 (110-576) mumol/min. Multiple linear regression analysis showed that maternal fat mass explained 36% of the variation in insulin resistance, accounting for 62% of the variation in glucose production. Further, glucose production explained 31% of the variation in fetal weight. Resting energy expenditure explained 51% of the variation in estimated fetal weight. Conclusion: Fetal weight is dependent on maternal glucose production, which is in turn determined by the degree of insulin resistance, induced in part by the maternal fat mass. The variation in maternal resting energy expenditure is closely related to fetal weight.
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| 11. |
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| 12. |
- Bengtson, Ola, et al.
(författare)
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Ädellövskogar i Lysekils kommun
- 1997
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Föreliggande rapport ingår som en del i ett större projekt som avser att kartera och naturvärdes-bedöma länets ädellövskogar och i vissa fall även andra typer av lövskogar. Inventeringen av Lysekils kommun genomfördes under 1994 av Pro Natura i nära samarbete med Länsstyrelsen i Göteborgs och Bohus län där Katrina Envall haft det övergripande ansvaret.
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| 13. |
- Bergqvist, Björn, 1965, et al.
(författare)
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Effect of microwave radiation on permeability of liposomes. Evidence against non-thermal leakage
- 1994
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Ingår i: Biochimica et Biophysica Acta - General Subjects. - : Elsevier BV. - 1872-8006 .- 0304-4165. ; 1201:1, s. 51-54
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Tidskriftsartikel (refereegranskat)abstract
- The effect of 2.45 GHz microwave radiation on the permeability of unilamellar phosphatidylcholine liposomes has been studied. Leakage of 5(6)-calboxyfluorescein from the liposomes was measured using spectrofluorimetry after exposure to either microwaves or thermal heating for 5-20 min intervals. The exposure temperature, 37.6 +/- 0.5 degrees C, was well above the phase transition temperature of the lipid membrane. The microwave exposure did not result in any non-thermal increase in permeability above that produced by thermal heating. This study refutes the results reported by Saalman et al. [1] in which an increased liposome permeability due to microwave exposure was reported. The refined analysis in the present study shows that this increased liposome permeability was not a non-thermal microwave effect.
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| 14. |
- Bosaeus, Niklas, 1982, et al.
(författare)
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Force-induced melting of DNA-evidence for peeling and internal melting from force spectra on short synthetic duplex sequences
- 2014
-
Ingår i: Nucleic Acids Research. - : Oxford University Press (OUP). - 0305-1048 .- 1362-4962. ; 42:12, s. 8083-8091
-
Tidskriftsartikel (refereegranskat)abstract
- Overstretching of DNA occurs at about 60-70 pN when a torsionally unconstrained double-stranded DNA molecule is stretched by its ends. During the transition, the contour length increases by up to 70% without complete strand dissociation. Three mechanisms are thought to be involved: force-induced melting into single-stranded DNA where either one or both strands carry the tension, or a B-to-S transition into a longer, still base-paired conformation. We stretch sequence-designed oligonucleotides in an effort to isolate the three processes, focusing on force-induced melting. By introducing site-specific inter-strand cross-links in one or both ends of a 64 bp AT-rich duplex we could repeatedly follow the two melting processes at 5 mM and 1 M monovalent salt. We find that when one end is sealed the AT-rich sequence undergoes peeling exhibiting hysteresis at low and high salt. When both ends are sealed the AT sequence instead undergoes internal melting. Thirdly, the peeling melting is studied in a composite oligonucleotide where the same AT-rich sequence is concatenated to a GC-rich sequence known to undergo a B-to-S transition rather than melting. The construct then first melts in the AT-rich part followed at higher forces by a B-to-S transition in the GC-part, indicating that DNA overstretching modes are additive.
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| 15. |
- Bosaeus, Niklas, 1982, et al.
(författare)
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Tension induces a base-paired overstretched DNA conformation
- 2012
-
Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 109:38, s. 15179-15184
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Tidskriftsartikel (refereegranskat)abstract
- Mixed-sequence DNA molecules undergo mechanical overstretching by approximately 70% at 60-70 pN. Since its initial discovery 15 y ago, a debate has arisen as to whether the molecule adopts a new form [Cluzel P, et al. (1996) Science 271: 792-794; Smith SB, Cui Y, Bustamante C (1996) Science 271: 795-799], or simply denatures under tension [van Mameren J, et al. (2009) Proc Natl Acad Sci USA 106: 18231-18236]. Here, we resolve this controversy by using optical tweezers to extend small 60-64 bp single DNA duplex molecules whose base content can be designed at will. We show that when AT content is high (70%), a force-induced denaturation of the DNA helix ensues at 62 pN that is accompanied by an extension of the molecule of approximately 70%. By contrast, GC-rich sequences (60% GC) are found to undergo a reversible overstretching transition into a distinct form that is characterized by a 51% extension and that remains base-paired. For the first time, results proving the existence of a stretched basepaired form of DNA can be presented. The extension observed in the reversible transition coincides with that produced on DNA by binding of bacterial RecA and human Rad51, pointing to its possible relevance in homologous recombination.
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| 16. |
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| 17. |
- Brogaard, Jonathan, et al.
(författare)
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Trading Fast and Slow : Colocation and Liquidity
- 2015
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Ingår i: The Review of financial studies. - : Oxford University Press (OUP). - 0893-9454 .- 1465-7368. ; 28:12, s. 3407-3443
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Tidskriftsartikel (refereegranskat)abstract
- We exploit an optional colocation upgrade at NASDAQ OMX Stockholm to assess how speed affects market liquidity. Liquidity improves for the overall market and even for noncolocated trading entities. We find that the upgrade is pursued mainly by participants who engage in market making. Those that upgrade use their enhanced speed to reduce their exposure to adverse selection and to relax their inventory constraints. In particular, the upgraded trading entities remain competitive at the best bid and offer even when their inventories are in their top decile. Our results suggest that increasing the speed of market making participants benefits market liquidity.
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| 18. |
- Carlsson, Nils, 1978, et al.
(författare)
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DNA hosted and aligned in aqueous interstitia of a lamellar liquid crystal - a membrane-biomacromolecule interaction model system
- 2013
-
Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-6848 .- 1744-683X. ; 9:33, s. 7951-7959
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Tidskriftsartikel (refereegranskat)abstract
- We report that DNA molecules can be intercalated and macroscopically oriented in the aqueous interstitia of a lyotropic lamellar liquid crystal. Using UV-vis linear dichroism and fluorescence spectroscopy we show that double-stranded oligonucleotides (25 base pairs) in the water-octanoate-decanol system remain base-paired in the B conformation and are confined in two dimensions, with the helix axis preferentially parallel to the lipid bilayer surfaces but free to rotate within this plane. The degree of helix confinement and the corresponding 2-D orientation can be improved by decreasing the thickness of the water interstitia via the fraction of water in the ternary mixture. Not surprisingly, the corresponding single-stranded oligonucleotides are not aligned, with their persistence length being short in comparison to the lamellar interstitium thickness. We propose this as a model system for studying interactions of DNA-ligand complexes near a lipid bilayer membrane which we demonstrate by using dye probes that are either covalently attached to one end of the oligonucleotide or reversibly bound by intercalation between the base pairs. Three cationic dyes, all strongly bound by intercalation to DNA when free in solution, are found to not bind to DNA but to prefer the membrane surface. The covalently attached Cy5 also binds to the bilayer while Cy3 tends to end-stack to the oligonucleotide duplex. The orientation of Cy5 parallel to the membrane indicates that electrostatic surface binding predominates over insertion into the hydrophobic interior of the membrane. Anionic and zwitterionic dyes (FAM and ROX) are found to remain randomly oriented in the water between the lipid bilayer surfaces. This journal is © The Royal Society of Chemistry.
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| 19. |
- Coates, C. G., et al.
(författare)
-
Picosecond time-resolved resonance Raman probing of the light-switch states of Ru(Phen)(2)dppz (2+)
- 2001
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 105:50, s. 12653-12664
-
Tidskriftsartikel (refereegranskat)abstract
- Picosecond time-resolved resonance Raman (picosecond-TR3) spectroscopy has been used to conduct an extensive photophysical characterization of the light- switch complex [Ru(phen)(2)dppz](2+) as a function of environment, in which studies have been carried out in aqueous and nonaqueous media and in DNA. The results are considered in rotation to a previous report describing environment-sensitive lowest triplet MLCT states. Vibrational marker features and enhancement patterns were used to determine the rapid progression (< 20 ps) between two triplet MLCT states in aqueous environment, followed by subnanosecond, nonradiative deactivation to the ground state. In nonaqueous environment, the long-lived, emissive triplet MLCT state is spectrally identified as the short-lived first triplet MLCT state observed in water, in agreement with the earlier proposed mechanism. The present data are shown to correlate well with previous nanosecond RR findings for the complex in each environment. Interestingly, a precursor state has been identified upon excitation in both nonaqueous solvent and in DNA, which precedes the triplet MLCT state, and the lifetime of which appears to be environment dependent. Observation of this state is discussed in relation to other recent femtosecond spectroscopic studies on this complex.
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| 20. |
- Dahlberg, Anders, et al.
(författare)
-
786 svampar på 2015 års rödlista
- 2015
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Ingår i: Svensk Mykologisk Tidskrift. - 1653-0357. ; 36, s. 91-97-
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Tidskriftsartikel (populärvet., debatt m.m.)abstract
- A new Swedish Red List was published April 28th 2015 by the Swedish Species Information Centre in which 786 species of fungi are listed. Compared to the previous Red List published in 2010, 11 species have been down-listed, 51 species have been added and 35 species have changed names or taxonomic rank, thus the list has increased by 41. The changes are mainly due to increased knowledge of taxonomy, ecology and distribution, not to changes in the sta-tus of the species. Here, the members of the Species Specialist Group for Fungi 2011 – 2015 summarize the results of the red listing.
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| 21. |
- Dahlberg, Anders, et al.
(författare)
-
Den nya rödlistan har 746 svampar
- 2010
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Ingår i: Svensk mykologisk tidskrift. - 1653-0357. ; 31:2, s. 37-47
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Tidskriftsartikel (refereegranskat)abstract
- The new Red List that was recently presented by the Swedish Species Information Centre (Gärdenfors 2010) includes 746 species of fungi considered to be threatened. Compared to the previous Red List published in 2005, 36 species have been down-listed whereas 150 species have been added, thus the list has increased by 114. The changes are above all due to increased knowledge of taxonomy, ecology and distribution. In the present paper members of the Species Specialist Group for Fungi 2006-2010 summarize the background and results of the red-listing process and present the habitats in which the red-listed species occur.
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| 22. |
- Dahlberg, Anders, et al.
(författare)
-
Svampar – Fungi
- 2010
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Ingår i: Rödlistade arter i Sverige 2010 – The 2010 Red List of Swedish Species. - 9789188506351 ; , s. 231-246
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Bokkapitel (övrigt vetenskapligt/konstnärligt)
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| 23. |
- Dahlberg, Anders, et al.
(författare)
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Svampar Fungi
- 2020
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Ingår i: Rödlistade arter i Sverige 2020. - 9789187853548 ; , s. 67-88
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Bokkapitel (övrigt vetenskapligt/konstnärligt)
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| 24. |
- Dahlberg, Anders, et al.
(författare)
-
Svampar Fungi
- 2015
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Ingår i: Rödlistade arter i Sverige 2015. - 9789187853104 ; , s. 53-71
-
Bokkapitel (övrigt vetenskapligt/konstnärligt)
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| 25. |
- Dahlström, Petter, et al.
(författare)
-
Determinants of Limit Order Cancellations
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- We investigate the economic rationale behind limit order cancellations from the perspective of liquidity suppliers. We predict that an order is cancelled whenever its expected revenue no longer exceeds the expected cost and we model how order profitability variation can be determined from changes in the state of the order book and the order queue position. Our empirical evidence supports the predictions in general and for orders submitted by high-frequency trading firms in particular. Consistent with our model approach, we find that order cancellation patterns are more consistent with market making than with liquidity demand strategies.
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| 26. |
- Dahlström, Petter, et al.
(författare)
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Dr. Jekyll and Mr. Hyde : Market Makers and Toxic Arbitrageurs
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Toxic arbitrage opportunities can arise when the prices of two related securities move sequentially rather than simultaneously. Relatively slow liquidity providers could then incur losses to the arbitrageurs, known as snipers. We investigate arbitrage activity between futures and exchange-traded funds in the Swedish blue-chip index. We find that trading firms that otherwise behave as market makers morph into snipers as toxic arbitrage opportunities emerge. In contrast to common belief, market makers are net beneficiaries of toxic arbitrage. The finding can be rationalized by economies of scope, since both arbitrage and market-making strategies rely on low-latency market monitoring technology.
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| 27. |
- Dahlström, Petter, 1980-
(författare)
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New Insights on Computerized Trading : Implications of Frequently Revised Trading Decisions
- 2019
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Computerized trading may be viewed as an aspect of modernization of financial markets. This dissertation contains four articles that in different ways examine to what extent the modernization influences the economics of the markets.Article 1 investigates transaction costs for large orders which are split up by execution algorithms to be executed in smaller pieces. I find that the costs associated with not being able to execute all pieces are substantial. These costs can be lowered by speeding up the trading pace but at the expense of higher costs for the successfully executed pieces.Article 2 investigates the strategies trading firms pursue in particular cases, known as toxic arbitrage opportunities. We find that trading firms, that otherwise behave as market makers, morph into liquidity takers as toxic arbitrage opportunities emerge. In contrast to common belief, market makers are net beneficiaries of toxic arbitrage, and this finding puts into question whether the amount of toxic arbitrage leads to wider bid-ask spreads.Article 3 investigates the information content of limit orders in an alternative way by studying the price impact implied by the depth in the limit order book. I find that the price impact estimates are slightly lower relative to those from a structural vector auto regressive model, but slightly higher compared to those from a price impact regression. Thus, the limit order book implied price impact estimates match those from benchmark models, and this finding contradicts earlier research.Article 4 investigates the economic rationale behind limit order cancellations. We put forth a model that explains the frequent limit order cancellations seen in today’s markets, and we test its predictions using a unique data set from Nasdaq. Our results points towards that frequent order cancellations is a benign feature of modern market making, as opposed to different types of manipulative behavior.
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| 28. |
- Dahlström, Petter, et al.
(författare)
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The determinants of limit order cancellations
- 2024
-
Ingår i: The Financial Review. - 0732-8516 .- 1540-6288. ; 59:1, s. 181-201
-
Tidskriftsartikel (refereegranskat)abstract
- Almost all limit orders are canceled. We examine two economic channels that can motivate cancellations: reductions in the expected profit at execution, and reductions in the probability of execution. An order-level analysis shows that changes in depth at the best bid and offer prices, as well as changes in the order queue position, influence cancellation in a way consistent with the former channel, that market makers monitor the expected profit at execution of each limit order. Although buy-side investors use passive orders extensively, our findings indicate that limit order cancellations on aggregate are best understood through models of liquidity provision.
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| 29. |
- Götmark, Frank, 1955, et al.
(författare)
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Broadleaved tree species in conifer-dominated forestry: Regeneration and limitation of saplings in southern Sweden
- 2005
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Ingår i: Forest Ecology and Management. - : Elsevier BV. - 0378-1127. ; 214:1-3, s. 142-157
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Tidskriftsartikel (refereegranskat)abstract
- Forests and forestry in Sweden are dominated by conifers. Silviculture using mixed or broadleaved stands is often recommended, but the degree to which broadleaves regenerate naturally needs to be clarified. The Swedish National Forest Inventory is here used for a region-wide study of broadleaved saplings (1.3 m tall to 4.9 cm dbh) regenerated naturally. For 12 species (taxa) in young forests (< 7 m tall) and high forests (> 7 m), sapling densities were related to seven forest types and three productivity classes. Birch had highest densities in all but two broadleaved forest types. Birch, oak, rowan and sallow had 70-85% of their total sapling populations in conifer-dominated forest types, indicating good potential for mixed stands. Beech, lime, hornbeam, ash and elm were mostly restricted to 'noble' (hardwood) forests. The regeneration success (saplings per mature tree) for birch, rowan and oak was highest in conifer-dominated forest; beech was about equally successful in conifer-dominated and broadleaved forests, and ash was very successful in broadleaved forest. Oak regeneration may be problematical in broadleaved forests, but we suggest this is not the case in conifer-dominated forests (where oaks have rarely been studied). Sapling densities of the species in the forest types were not consistently correlated with productivity, but birch and aspen generally regenerated strongest at intermediate and at high productivity, respectively. In noble forests, oak, ash and elm regenerated strongest at low productivity. The role of asexual regeneration (sprouting) remains to clarify. Our results suggest that lime, elm, ash and some other trees currently are limited mainly by poor dispersal, rather than habitat availability. The results are promising for various forms of mixed-species forestry that does not require planting (or little planting) and that would be beneficial for nature conservation. (c) 2005 Elsevier B.V. All rights reserved.
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| 30. |
- Götmark, Frank, 1955, et al.
(författare)
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Evaluating partial cutting in broadleaved temperate forest under strong experimental control: Short-term effects on herbaceous plants
- 2005
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Ingår i: Forest Ecology and Management. - : Elsevier BV. - 0378-1127. ; 214:1-3, s. 124-141
-
Tidskriftsartikel (refereegranskat)abstract
- Partial harvesting of forest for biofuel and other products may be less harmful to biodiversity than clear-cutting, and may even be beneficial for some species or groups of organisms such as herbs. There are, however, few well-controlled experiments evaluating positive and negative effects, such as species losses directly after harvest. In closed canopy mixed oak forest in Sweden, about 25% of the tree basal area and 50-90% of the understory was removed (mainly spruce, birch, aspen, lime, rowan and hazel). In each of six forests, we studied herbs in an experimental (cutting) plot and a control plot (undisturbed) before, and in the first summer, after the harvest (conducted in winter). Losses of species were similar in experimental and control plots (15-16%). The harvest increased species richness by 4-31% (mean 18%); also species diversity (H) increased. Several ruderals increased in experimental plots, but most changes occurred in grassland and forest species; partial cutting led to complex, partly unpredictable early changes in the herb community. A review of early effects of partial cutting (eight experiments) indicated that it increases herb species richness in stands of broadleaves, but apparently not in conifer stands; there was no evidence that partial cutting increases species losses. Thus, with respect to early changes after harvest, we found no negative effects of partial cutting on herbs. We suggest, however, that some proportion of closed-canopy mixed oak forest should not be harvested, to protect rare, potentially sensitive herbs, and to create stand diversity. (c) 2005 Elsevier B.V. All rights reserved.
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| 31. |
- Götmark, Frank, 1955, et al.
(författare)
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Naturvårdsgallring, vad är det?
- 2009
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Ingår i: Biodiverse. - 1401-5064. ; 2009:1
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Fri utveckling, bete och gallring är huvudalternativen för naturvård i värdefulla lövbestånd. Principen är att grundinventera, sätta upp mål, spara gamla träd och lämna död ved.
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| 32. |
- Hagströmer, Björn, et al.
(författare)
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Closing Call Auctions at the Index Futures Market
- 2014
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Ingår i: Journal of futures markets. - : Wiley. - 0270-7314 .- 1096-9934. ; 34:4, s. 299-319
-
Tidskriftsartikel (refereegranskat)abstract
- We investigate the effects from the introduction of a closing call auction (CCA) at the index futures market. Limit order book models, where trader patience determines trading strategies, predict that a CCA increases trader patience and, hence, improves closing price accuracy and end‐of‐day liquidity. We find that the introduction leads to increased trader patience, improved futures closing price accuracy, unaffected tightness and resiliency, and decreased depth. Decreased depth is likely due to less order fishing activity. With the CCA, opportunistic patient traders’ posting of limit orders deep in the order book, to profit from impatient traders, is no longer feasible.
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| 33. |
- Hagströmer, Björn, et al.
(författare)
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Components of the Bid-Ask Spread and Variance : A Unified Approach
- 2016
-
Ingår i: Journal of futures markets. - : Wiley. - 0270-7314 .- 1096-9934. ; 36:6, s. 545-563
-
Tidskriftsartikel (refereegranskat)abstract
- We develop a structural model for the price formation and liquidity supply of an asset. Ourmodel facilitates decompositions of both the bid–ask spread and the return variance intocomponents related to adverse selection, inventory, and order processing costs. Furthermore,the model shows how the fragmentation of trading volume across trading venues influencesinventory pressure and price discovery. We use the model to analyze intraday price formationfor gold futures traded at the Shanghai Futures Exchange. We find that order processing costsexplain about 50% of the futures bid–ask spread, whereas the remaining 50% is equally due toasymmetric information and to inventory costs. About a third of the variance in futures returnsis attributable to microstructure noise. Trading at the spot market has a significant influence onfutures price discovery, but only a limited impact on the futures bid–ask spread.
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| 34. |
- Hagströmer, Björn, 1981-, et al.
(författare)
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How aggressive are high-frequency traders?
- 2014
-
Ingår i: The Financial Review. - : Wiley. - 0732-8516 .- 1540-6288. ; 49:2, s. 395-419
-
Tidskriftsartikel (refereegranskat)abstract
- We study order aggressiveness of market-making high-frequency traders (MM-HFTs), opportunistic HFTs (Opp-HFTs), and non-HFTs. We find that MM-HFTs follow their own group's previous order submissions more than they follow other traders’ orders. Opp-HFTs and non-HFTs tend to split market orders into small portions submitted in sequence. HFTs submit more (less) aggressive orders when the same-side (opposite-side) depth is large, and supply liquidity when the bid–ask spread is wide. Thus, HFTs adhere strongly to the tradeoff between waiting cost and the cost of immediate execution. Non-HFTs care less about this tradeoff, but react somewhat stronger than HFTs to volatility.
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| 35. |
- Hagströmer, Björn, 1981-, et al.
(författare)
-
The diversity of high-frequency traders
- 2013
-
Ingår i: Journal of financial markets. - : Elsevier. - 1386-4181 .- 1878-576X. ; 16:4, s. 741-770
-
Tidskriftsartikel (refereegranskat)abstract
- The regulatory debate concerning high-frequency trading (HFT) emphasizes the importance of distinguishing different HFT strategies and their influence on market quality. Using data from NASDAQ-OMX Stockholm, we compare market-making HFTs to opportunistic HFTs. We find that market makers constitute the lion's share of HFT trading volume (63–72%) and limit order traffic (81–86%). Furthermore, market makers have higher order-to-trade ratios and lower latency than opportunistic HFTs. In a natural experiment based on tick size changes, we find that the activity of market-making HFTs mitigates intraday price volatility.
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| 36. |
- Hallenberg, Nils, 1947, et al.
(författare)
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The Peniophorella praetermissa species complex (Basidiomycota)
- 2007
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Ingår i: Mycological Research. - : Elsevier BV. - 0953-7562. ; 111:12, s. 1366-1376
-
Tidskriftsartikel (refereegranskat)abstract
- The corticioid basidiomycete Peniophorella praetermissa has long been regarded as a morphologically variable species complex. An ITS-based phylogenetic study based on a worldwide sampling was carried out using parsimony and Bayesian inference. The resulting trees feature three major clades, further divided into well-supported subclades. These could be considered as distinct species, a contention that is further supported by crossing test data. Only two out of the eight phylogenetic lineages identified can be distinctly morphologically characterized: P. odontiaeformis and P. subpraetermissa. P. odontiaeformis is an odontioid species with a paleotropical distribution whereas the taxa in the remaining subclades have smooth basidiomata and are distributed in temperate areas. P. subpraetermissa is known only from the type collection and is distinguished microscopically by its reddish brown apically encrustated cystidia. Taxa in the remaining subclades are impossible to distinguish from each other morphologically, and therefore, are viewed as a species complex, P. praetermissa s. lat. One of the subclades, which is widely distributed but restricted to the Northern hemisphere, is proposed to represent P. praetermissa s. str. An epitype is selected from the same area as the holotype, among the specimens studied here. However, the geographically most widespread clade with many representatives from both hemispheres is here referred to as P. pertenuis, a taxon that was previously considered a synonym to P. praetermissa.
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| 37. |
- Hanczyc, Piotr, 1985, et al.
(författare)
-
DNA in a polyvinyl alcohol matrix and interactions with three intercalating cyanine dyes
- 2011
-
Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 115:42, s. 12192-12201
-
Tidskriftsartikel (refereegranskat)abstract
- We investigate how DNA interacts with drugs in humid polyvinyl alcohol (PVA) films by using a homologous set of cyanine dyes (YO(+), YO-PRO(2+), and YOYO(4+)) known to intercalate into DNA with increasing affinity with increasing charge. UV-vis spectroscopy shows that the PVA matrix destabilizes all three DNA-dye complexes compared to aqueous solution but to a lesser degree as the dye charge increases. The monovalent YO is fully dissociated from DNA within minutes, whereas the dissociation of the divalent YO-PRO takes about one hour and occurs by a two-step mechanism. The tetravalent homodimer YOYO is even less affected by the PVA environment and remains intercalated in the B-form DNA also in the PVA films. The reduced stability of the DNA-dye complexes is discussed in terms of steric and dielectric properties of the PVA matrix. After being kept in dry PVA films for 48 h the DNA-YOYO complexes can be reformed reversibly by rehumidifying the films for 30 min. The ability to store aligned and confined DNA intercalated with ligand complexes may be useful in studies on structural properties of nucleic acids.
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| 38. |
- Hanczyc, Piotr, 1985, et al.
(författare)
-
Short Oligonucleotides Aligned in Stretched Humid Matrix – Secondary DNA structure in Poly(Vinyl Alcohol) Environment
- 2012
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 1520-5827 .- 0743-7463. ; 28:16, s. 6662-6669
-
Tidskriftsartikel (refereegranskat)abstract
- We report that short, synthetic, double- as well as single-stranded DNA can be aligned in stretched humid poly(vinyl alcohol) (PVA) matrix, and the secondary structure (nucleobase orientation) can be characterized with linear dichroism (LD) spectroscopy. Oligonucleotides of lengths varying between 10 (3.4 nm) and 60 bases (20.4 nm) were investigated with respect to structural properties in the gel-like polymer environment. The DNA conformation as a function of relative humidity reveals a strong dependence of helical structure of DNA on PVA hydration level, results of relevance for nanotechnical studies of DNA-based supramolecular systems. Also, the PVA gel could provide possibilities to test models for nucleic acid interactions and distribution in cell contexts, including structural stability of genetic material in the cell and PVA-packaging for gene delivery. A method by which duplex oligonucleotides, with sequences designed to provide specific binding sites, become amenable to polarized-light spectroscopy opens up new possibilities for studying structure in DNA complexes with small adduct molecules as well as proteins.
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| 39. |
- Heintz, Fredrik, 1975-, et al.
(författare)
-
Introducing Programming and Digital Competence in Swedish K-9 Education
- 2017
-
Ingår i: Informatics in Schools. - Cham : Springer. - 1611-3349 .- 0302-9743. - 9783319714820 - 9783319714837 ; , s. 117-128
-
Konferensbidrag (refereegranskat)abstract
- The role of computer science and IT in Swedish schools has varied throughout the years. In fall 2014, the Swedish government gave the National Agency for Education (Skolverket) the task of preparing a proposal for K–9 education on how to better address the competences required in a digitalized society. In June 2016, Skolverket handed over a proposal introducing digital competence and programming as interdisciplinary traits, also providing explicit formulations in subjects such as mathematics (programming, algorithms and problem-solving), technology (controlling physical artifacts) and social sciences (fostering aware and critical citizens in a digital society). In March 2017, the government approved the new curriculum, which needs to be implemented by fall 2018 at the latest. We present the new K–9 curriculum and put it in a historical context. We also describe and analyze the process of developing the revised curriculum, and discuss some initiatives for how to implement the changes.
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| 40. |
- Holmqvist, Jacob, et al.
(författare)
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Cardiac dysfunction and mortality in critically ill patients with COVID-19: A Swedish multicentre observational study
- 2022
-
Ingår i: Acta Anaesthesiologica Scandinavica. - : Wiley. - 0001-5172 .- 1399-6576. ; 66:5, s. 606-614
-
Tidskriftsartikel (refereegranskat)abstract
- Background The prevalence and importance of cardiac dysfunction in critically ill patients with COVID-19 in Sweden is not yet established. The aim of the study was to assess the prevalence of cardiac dysfunction and elevated pulmonary artery pressure (PAP), and its influence on mortality in patients with COVID-19 in intensive care in Sweden. Methods This was a multicentre observational study performed in five intensive care units (ICUs) in Sweden. Patients admitted to participating ICU with COVID-19 were examined with echocardiography within 72 h from admission and again after 4 to 7 days. Cardiac dysfunction was defined as left ventricular (LV) dysfunction (ejection fraction <50% and/or regional hypokinesia) or right ventricular (RV) dysfunction (defined as TAPSE <17 mm or visually assessed moderate/severe RV dysfunction). Results We included 132 patients, of whom 127 (96%) were intubated. Cardiac dysfunction was found in 42 (32%) patients. Most patients had cardiac dysfunction at the first assessment (n = 35) while a few developed cardiac dysfunction later (n = 7) and some changed type of dysfunction (n = 3). LV dysfunction was found in 21 and RV dysfunction in 19 patients, while 5 patients had combined dysfunction. Elevated PAP was found in 34 patients (26%) and was more common in patients with RV dysfunction. RV dysfunction and elevated PAP were independently associated with an increased risk of death (OR 3.98, p = .013 and OR 3.88, p = .007, respectively). Conclusions Cardiac dysfunction occurs commonly in critically ill patients with COVID-19 in Sweden. RV dysfunction and elevated PAP are associated with an increased risk of death.
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| 41. |
- Johansson, Johan, 1980, et al.
(författare)
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Covalent functionalization of carbon nanotube forests grown in situ on a metal-silicon chip
- 2012
-
Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. - 9780819490018 ; 8344
-
Konferensbidrag (refereegranskat)abstract
- We report on the successful covalent functionalization of carbon nanotube (CNT) forests, in situ grown on a silicon chip with thin metal contact film as the buffer layer between the CNT forests and the substrate. The CNT forests were successfully functionalized with active amine and azide groups, which can be used for further chemical reactions. The morphology of the CNT forests was maintained after the functionalization. We thus provide a promising foundation for a miniaturized biosensor arrays system that can be easily integrated with Complementary Metal-Oxide Semiconductor (CMOS) technology.
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| 42. |
- Jonsson, Mattias, et al.
(författare)
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Cost-effectiveness of silvicultural measures to increase substrate availability for red-listed wood-living organisms in Norway spruce forests
- 2006
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Ingår i: Biological Conservation. - : Elsevier. - 0006-3207 .- 1873-2917. ; 127:4, s. 443-467
-
Tidskriftsartikel (refereegranskat)abstract
- It is important that measures to maintain biodiversity are taken in a way that is cost-effective for the landowner. We analyzed the cost-effectiveness of silvicultural measures that aim at increasing the substrate availability for red-listed (species that are threatened, near threatened or where species probably are threatened but data is deficient) saproxylic (wood-inhabiting) organisms. We modelled stands of Norway spruce (Picea abies) in three regions of Sweden by using computer simulations and a database with substrate requirements of saproxylic beetles and cryptogams on the Swedish Red-List. Conclusions concerning cost-effectiveness of silvicultural measures depend on the extinction thresholds of the species they are intended to conserve; measures that generate only small amounts of coarse woody debris (CWD) may provide too little substrate to be useful for species with high extinction thresholds. In northern Sweden, forestland is relatively inexpensive, so a cost-effective strategy to increase the amount of spruce CWD was to set aside more forests as reserves. In central and southern Sweden, more emphasis should instead be given to increasing the amount of CWD in the managed forest. The regulations by the Forest Stewardship Council (FSC) could be made more cost-effective by prescribing creation of more high stumps and retention of larger amounts of naturally dying trees. Large-sized CWD, CWD from slow-growing trees, and CWD in late decay stages are substrate types that were particularly rare in managed forest in relation to unmanaged forests. Manual soil scarification and retention of living trees are measures that can increase the proportion of these underrepresented CWD types.
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| 43. |
- Jonsson, Mats, 1939, et al.
(författare)
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Orientation of DNA during gel electrophoresis studied with linear dichroism spectroscopy
- 1988
-
Ingår i: Biopolymers. - : Wiley. - 0006-3525 .- 1097-0282. ; 27:3, s. 381-414
-
Tidskriftsartikel (refereegranskat)abstract
- A method for in situ study of orientation of DNA during gel electrophoresis has been developed. Linear dichroism spectra measured by this phase-modulation technique can sensitively and selectively detect orientation of DNA during electrophoretic migration in gel. [Measurement of “electrophoretic orientation” was first reported in 1985 by B. Åkerman, M. Jonsson, and B. Nordén (1985) (J. Chem. Soc. Chem. Commun. 422–423)]. Restriction fragments of duplex DNA of lengths in the ranges of 300–2319 base pairs (bp) and 4361–23130 bp have been studied in 5% polyacrylamide and 1% agarose gels, respectively. The fragments become preferentially oriented with the DNA helix axis parallel to the migration direction. In agarose the orientation is found to increase sigmoidally, and in polyacrylamide, linearly, with the electric field strength, within the field ranges accessible to measurement (0–40 and 5–40 V/cm, respectively). In both types of gels a considerable increase in orientation with length of DNA was observed. Compared to dipole orientation in electric fields, the electrophoretic orientation is high: orientation factor S = 0.027 in agarose for 23130 bp at 10 V/cm and S = 0.004 in polyacrylamide for 2319 bp at 10 V/cm. In addition to orientation of DNA, the electrophoresis also leads to orientation effects in the gel structure owing to Joule heating. In agarose there is also an effect that is associated with the migrating DNA zones and that produces different orientations of the gel at the front and rear parts of a zone. Evidence is presented that this effect is due to a DNA-induced electroosmotic flow causing a contraction of the gel in the front of the zone and an expansion in the rear. The experimental results on DNA orientation are compared with the reptation theories for gel electrophoresis. The theory of Lumpkin et al. [O. J. Lumpkin, P. Dejardin, and B. H. Zimm (1985) Biopolymers24, 1573–1593] predicts no orientation length dependence, but it does predict a shape of the field dependence that resembles the shape observed in agarose. The theory of Slater and Noolandi [G. W. Slater and J. Noolandi (1986) Biopolymers25, 431–454] predicts an orientational length dependence that is an order of magnitude less than the experimental one, and a field dependence that agrees neither with the sigmoidal shape observed in agarose nor with the linear dependence in polyacrylamide.
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| 44. |
- Klos, Ryk, et al.
(författare)
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Potential for high transient doses due to accumulation and chemical zonation of long-lived radionuclides across the geosphere-biosphere interface
- 2011
-
Ingår i: Radioprotection - Revue de la Societé Francaise de Radioprotection. - : EDP Sciences. - 0033-8451 .- 1769-700X. ; 46:6, s. S453-S459
-
Tidskriftsartikel (refereegranskat)abstract
- Planning for the disposal of spent nuclear fuel is at an advanced stage in several nations around the world. Licensing of the disposal facility requires correspondingly detailed assessment of the future performance of the facility. With increased site-specific detail available to the assessment, local characteristics play an increasingly important role in determining the potential radiological risk posed by releases to the biosphere. In this paper we go beyond existing reference biosphere models and investigate the potential for specific accumulation mechanisms. The implications for the modelling carried out in long timescale performance assessment are discussed.
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| 45. |
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| 46. |
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| 47. |
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| 48. |
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| 49. |
- Luo, Z. L., et al.
(författare)
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Structures of self-assembled amphiphilic peptide-heterodimers: effects of concentration, pH, temperature and ionic strength
- 2010
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Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-6848 .- 1744-683X. ; 6:10, s. 2260-2270
-
Tidskriftsartikel (refereegranskat)abstract
- The amphiphilic double-tail peptides AXG were studied regarding secondary structure and self-assembly in aqueous solution. The two tails A = Ala6 and G = Gly(6) are connected by a central pair X of hydrophilic residues, X being two aspartic acids in ADG, two lysines in AKG and two arginines in ARG. The peptide AD (Ala(6)Asp) served as a single-tail reference. The secondary structure of the four peptides was characterized by circular dichroism spectroscopy under a wide range of peptide concentrations (0.01-0.8 mM), temperatures (20-98 degrees C), pHs (4-9.5) and ionic strengths. In salt-free water both ADG and AD form a beta-sheet type of structure at high concentration, low pH and low temperature, in a peptide-peptide driven assembly of individual peptides. The transition has a two-state character for ADG but not for AD, which indicates that the added tail in ADG makes the assembly more cooperative. By comparison the secondary structures of AKG and ARG are comparatively stable over the large range of conditions covered. According to dynamic light scattering the two-tail peptides form supra-molecular aggregates in water, but high-resolution AFM-imaging indicate that ordered (self-assembled) structures are only formed when salt (0.1 M NaCl) is added. Since the CD-studies indicate that the NaCl has only a minor effect on the peptide secondary structure we propose that the main role of the added salt is to screen the electrostatic repulsion between the peptide building blocks. According to the AFM images ADG and AKG support a correlation between nanofibers and a beta-sheet or unordered secondary structure, whereas ARG forms fibers in spite of lacking beta-sheet structure. Since the AKG and ARG double-tail peptides self-assemble into distinct nanostructures while their secondary structures are resistant to environment factors, these new peptides show potential as robust building blocks for nano-materials in various medical and nanobiotechnical applications.
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| 50. |
- Nilsson, R. Henrik, 1976, et al.
(författare)
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Phylogeography of Hyphoderma setigerum (Basidiomycota) in the Northern Hemisphere
- 2003
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Ingår i: Mycological Research. ; 107:6, s. 645-652
-
Tidskriftsartikel (refereegranskat)abstract
- Previous studies of morphological variation in the homobasidiomycete Hyphoderma setigerum have lead to suspicions of a species complex. This study explores variation in DNA sequences from the nuclear ribosomal ITS region of 45 specimens from America, Asia, and Europe in a phylogeographic context. Based on molecular analysis, morphological studies, and crossing tests, nine preliminary taxa are shown to exist inside the species complex, and the two previously described segregate species H. subsetigerum and H. nudicephalum are confirmed. The molecular analysis shows evidence of allopatric differentiation over intercontinental distances. Only one of the nine well-supported clades has a geographic distribution spanning more than one continent, probably indicating the importance of vicariance in the evolution of this species complex. The basionym of H. setigerum, Thelephora setigera, is neotypified to fix the application of that name.
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