Technical University of Denmark

About: Technical University of Denmark is a education organization based out in Kongens Lyngby, Hovedstaden, Denmark. It is known for research contribution in the topics: Population & Catalysis. The organization has 24126 authors who have published 66394 publications receiving 2443649 citations. The organization is also known as: Danmarks Tekniske Universitet & DTU.

Mucoid conversion of Pseudomonas aeruginosa by hydrogen peroxide: a mechanism for virulence activation in the cystic fibrosis lung.

Abstract: The leading cause of mortality in patients with cystic fibrosis (CF) is respiratoy failure due in large part to chronic lung infection with Pseudomonas aeruginosa strains that undergo mucoid conversion, display a biofilm mode of growth in vivo and resist the infiltration of polymorphonuclear leukocytes (PMNs), which release free oxygen radicals such as H2O2. The mucoid phenotype among the strains infecting CF patients indicates overproduction of a linear polysaccharide called alginate. To mimic the inflammatory environment of the CF lung, P. aeruginosa PAO1, a typical non-mucoid strain, was grown in a biofilm. This was treated with low levels of H2O2, as if released by the PMNs, and the formation of mucoid variants was observed. These mucoid variants had mutations in mucA, which encodes an anti-σ factor; this leads to the deregulation of an alternative σ factor (σ22, AlgT or AlgU) required for expression of the alginate biosynthetic operon. All of the mucoid variants tested showed the same mutation, the mucA22 allele, a common allele seen in CF isolates. The mucoid mucA22 variants, when compared to the smooth parent strain PA01, produced 2--6-fold higher levels of alginate|ii) exhibited no detectable differences in growth rate|iii) showed an unaltered LPS profile|iv) were ~72% reduced in the amount of inducible-β-lactamase and (v) secreted little no LasA protease and only showed 44% elastase activity. A characteristic ~54 kDa protein associated with alginate overproducing strains was identified as AlgE (Alg76) by N-terminal sequence analysis. Thus, the common phenotype of the mucoid variants, which included a genetically engineered mucA22 mutant, suggested that the only mutation incurred as a result of H2O2 treatment was in mucA. When a P. aeruginosa biofilm was repeatedly expose to activated PMNs in vitro, mucoid variants were also observed, mimicking in vivo observations. Thus, PMNs and their oxygen by-products may cause P. aeruginosa to undergo the typical adaptation to the intractable mu- coid form in the CF lung. These findings indicate that gene activation in bacteria by toxic oxygen radicals, similar to that found in plants and mammalian cells, may serve as a defence mechanism for the bacteria. This suggests that mucoid conversion is a response to oxygen radical exposure and that this response is mechanism of defence by the bacteria. This is the first report to show that PMNs and their oxygen radicals can cause this phenotypic and genotypic change which is so typical of the intractable form of P. aeruginosa in the CF lung. These findings may provide a basis for the development of anti-oxidant and anti-inflammatory therapy for the early stages of infection in CF patients

Evolution of species interactions in a biofilm community

Abstract: Biofilms are specialized environments where communities of microorganisms are insulated from the outside world by an extracellular polymer matrix that they themselves secrete The resulting microbial mats have been compared to tropical rainforests in terms of complexity and biodiversity Selective pressures on such biofilms are likely to demand intense interactions between the individual bacteria, and an experiment with a simple community of two species (soil dwellers Pseudomonas putida and Acinetobacter sp) shows just how close that relationship is The physical structure of the community altered, to the mutual benefit of both species, as a result of a simple mutation in the genome of one of the species In the absence of a partner the mutation (in P putida) would have been deleterious This system demonstrates the importance of interspecies interactions, and may be useful in work on the evolution of these interactions Biofilms are specialized environments where one might predict that evolution demands intense interactions between bacteria However, by using two species, this paper demonstrates that genomic changes occur to favour species working together to enhance fitness Biofilms are spatially structured communities of microbes whose function is dependent on a complex web of symbiotic interactions1,2 Localized interactions within these assemblages are predicted to affect the coexistence of the component species3,4,5, community structure6 and function7,8,9,10, but there have been few explicit empirical analyses of the evolution of interactions11 Here we show, with the use of a two-species community, that selection in a spatially structured environment leads to the evolution of an exploitative interaction Simple mutations in the genome of one species caused it to adapt to the presence of the other, forming an intimate and specialized association The derived community was more stable and more productive than the ancestral community Our results show that evolution in a spatially structured environment can stabilize interactions between species, provoke marked changes in their symbiotic nature and affect community function

Quantifying the promotion of Cu catalysts by ZnO for methanol synthesis

Abstract: Promoter elements enhance the activity and selectivity of heterogeneous catalysts. Here, we show how methanol synthesis from synthesis gas over copper (Cu) nanoparticles is boosted by zinc oxide (ZnO) nanoparticles. By combining surface area titration, electron microscopy, activity measurement, density functional theory calculations, and modeling, we show that the promotion is related to Zn atoms migrating in the Cu surface. The Zn coverage is quantitatively described as a function of the methanol synthesis conditions and of the size-dependent thermodynamic activities of the Cu and ZnO nanoparticles. Moreover, experimental data reveal a strong interdependency of the methanol synthesis activity and the Zn coverage. These results demonstrate the size-dependent activities of nanoparticles as a general means to design synergetic functionality in binary nanoparticle systems.

From probabilistic forecasts to statistical scenarios of short-term wind power production

Abstract: Short-term (up to 2-3 days ahead) probabilistic forecasts of wind power provide forecast users with a highly valuable information on the uncertainty of expected wind generation. Whatever the type of these probabilistic forecasts, they are produced on a per horizon basis, and hence do not inform on the development of the forecast uncertainty through forecast series. However, this additional information may be paramount for a large class of time-dependent and multi-stage decision-making problems e.g. optimal operation of combined wind-storage systems or multiple-market trading with different gate closures. This issue is addressed here by describing a method that permits the generation of statistical scenarios of short-term wind generation that accounts for both the interdependence structure of prediction errors and the predictive distributions of wind power production. The method is based on the conversion of series of prediction errors to a multivariate Gaussian random variable, the interdependence structure of which can then be summarized by a unique covariance matrix. Such matrix is recursively estimated in order to accommodate long-term variations in the prediction error characteristics. The quality and interest of the methodology are demonstrated with an application to the test case of a multi-MW wind farm over a period of more than two years.