University of Marburg

About: University of Marburg is a education organization based out in Marburg, Germany. It is known for research contribution in the topics: Population & Gene. The organization has 23195 authors who have published 42907 publications receiving 1506069 citations. The organization is also known as: Philipps University of Marburg & Philipps-Universität.

IL-4 instructs TH1 responses and resistance to Leishmania major in susceptible BALB/c mice.

Abstract: Immunity to infection with intracellular pathogens is regulated by interleukin 12 (IL-12), which mediates protective T helper type 1 (TH1) responses, or IL-4, which induces TH2 cells and susceptibility. Paradoxically, we show here that when present during the initial activation of dendritic cells (DCs) by infectious agents, IL-4 instructed DCs to produce IL-12 and promote TH1 development. This TH1 response established resistance to Leishmania major in susceptible BALB/c mice. When present later, during the period of T cell priming, IL-4 induced TH2 differentiation and progressive leishmaniasis in resistant mice. Because immune responses developed via the consecutive activation of DCs and then T cells, the contrasting effects of IL-4 on DC development and T cell differentiation led to immune responses that had opposing functional phenotypes.

Tree Diversity, Forest Structure and Productivity along Altitudinal and Topographical Gradients in a Species‐Rich Ecuadorian Montane Rain Forest

Abstract: We studied the spatial heterogeneity of tree diversity, and of forest structure and productivity in a highly diverse tropical mountain area in southern Ecuador with the aim of understanding the causes of the large variation in these parameters. Two major environmental gradients, elevation and topography, representing a broad range of climatic and edaphic site conditions, were analyzed. We found the highest species richness of trees in valleys <2100 m. Valleys showed highest values of basal area, leaf area index and tree basal area increment as well. Tree diversity also increased from ridges to valleys, while canopy openness decreased. Significant relationships existed between tree diversity and soil parameters (pH, total contents of Mg, K, Ca, N and P), and between diversity and the spatial variability of pH and Ca and Mg contents suggesting a dependence of tree diversity on both absolute levels and on the small-scale heterogeneity of soil nutrient availability. Tree diversity and basal area increment were positively correlated, partly because both are similarly affected by soil conditions. We conclude that the extraordinarily high tree species richness in the area is primarily caused by three factors: (1) the existence of steep altitudinal and topographic gradients in a rather limited area creating a small-scale mosaic of edaphically different habitats; (2) the intermingling of Amazonian lowland plant species, that reach their upper distribution limits, and of montane forest species; and (3) the geographical position of the study area between the humid eastern Andean slope and the dry interandean forests of South Ecuador.

Crystal structure of DhbE, an archetype for aryl acid activating domains of modular nonribosomal peptide synthetases.

Abstract: The synthesis of the catecholic siderophore bacillibactin is accomplished by the nonribosomal peptide synthetase (NRPS) encoded by the dhb operon. DhbE is responsible for the initial step in bacillibactin synthesis, the activation of the aryl acid 2,3-dihydroxybenzoate (DHB). The stand-alone adenylation (A) domain DhbE, the structure of which is presented here, exhibits greatest homology to other NRPS A-domains, acyl-CoA ligases and luciferases. It's structure is solved in three different states, without the ligands ATP and DHB (native state), with the product DHB-AMP (adenylate state) and with the hydrolyzed product AMP and DHB (hydrolyzed state). The 59.9-kDa protein folds into two domains, with the active site at the interface between them. In contrast to previous proposals of a major reorientation of the large and small domains on substrate binding, we observe only local structural rearrangements. The structure of the phosphate binding loop could be determined, a motif common to many adenylate-forming enzymes, as well as with bound DHB-adenylate and the hydrolyzed product DHB*AMP. Based on the structure and amino acid sequence alignments, an adapted specificity conferring code for aryl acid activating domains is proposed, allowing assignment of substrate specificity to gene products of previously unknown function.

Observations on vegetative reproduction and sexual life cycles of two freshwater dinoflagellates, Gymondinium pseudopalustre Schiller and Woloszynskia apiculata sp. nov.

Abstract: In unialgal culture, Gymnodinium pseudopalustre Schiller (G.p.) and Woloszynskia apiculata sp. nov. (W.a.) multiply respectively by binary fission in the motile state and by motionless zoosporangia, releasing 2, 4 or 8 zoospores. Both species are isogamous, but G.p. is homothallic, W.a. heterothallic. Fusion of the planogametes leads to long-lived planozygotes, which retain two posterior flagella and, while enlarging, assume specific morphologies. The motile stage of the zygotes is terminated by formation of hypnozygotes (resting spores), globular and spiny in G.p., grossly fusiform (‘horned’) and tubercled in W.a. The composition of the hypnozygote walls is described. After their dormancy has been broken by a cold treatment of several weeks in the dark, hypnozygotes of both species germinate when brought back to higher temperature and light. In so doing, those of G.p. excyst one posteriorly biflagellate swarmer as a meiocyte, which, after a stage of nuclear cyclosis or, in karyological terms, zygotene th...

Semiconductor excitons in new light

Abstract: Excitons are quasi-particles that form when Coulomb-interacting electrons and holes in semiconductors are bound into pair states. They have many features analogous to those of atomic hydrogen. Because of this, researchers are interested in exploring excitonic phenomena, from optical, quantum-optical and thermodynamic transitions to the possible condensation of excitons into a quantum-degenerate state. Excitonic signatures commonly appear in the optical absorption and emission of direct-gap semiconductor systems. However, the precise properties of incoherent exciton populations in such systems are difficult to determine and are the subject of intense debate. We review recent contributions to this discussion, and argue that to obtain detailed information about exciton populations, conventional experimental techniques should be supplemented by direct quasi-particle spectroscopy using the relatively newly available terahertz light sources. Finally, we propose a scheme of quantum-optical excitation to generate quantum-degenerate exciton states directly.