Dialkyl phosphate-related ionic liquids as selective solvents for xylan

Herein we describe a possibility of selective dissolution of xylan, the most important type of hemicellulose, from Eucalyptus globulus kraft pulp using ionic liquids (ILs). On the basis of the IL 1-butyl-3-methylimidazolium dimethyl phosphate, which is well-known to dissolve pulp, the phosphate anion was modified by substituting one oxygen atom for sulfur and selenium, respectively. This alteration reduces the hydrogen bond basicity of the IL and therefore prevents dissolution of cellulose fibers, whereas the less ordered xylan is still dissolved. (1)H NMR spectra of model solutions and Kamlet-Taft parameters were used to quantify the solvent polarity and hydrogen bond acceptor properties of the ILs. These parameters have been correlated to their ability to dissolve xylan and cellulose, which was monitored by (13)C NMR spectroscopy. It was found that the selectivity for xylan dissolution increases to a certain extent with decreasing hydrogen-bond-accepting ability of anions of the ILs.     

Effects of predation and dispersal on Mastomys natalensis population dynamics in Tanzanian maize fields

1. We investigate the effects of different levels of predation pressure and rodent dispersal on the population dynamics of the African pest rodent Mastomys natalensis in maize fields in Tanzania. 2. Three levels of predation risk were used in an experimental set-up: natural level (control), excluding predators by nets and attracting avian predators by nest boxes and perch poles. Because dispersal of the rodents could mask the predation pressure treatment effects, control and predator exclusion treatments were repeated with enclosed rodent populations. 3. Population growth during the annual population rise period was faster in the absence of predators and peak population size was higher, but otherwise dynamics patterns were similar for populations where predators had access or were attracted, indicating that compensatory mechanisms operate when rodents are exposed to high levels of predation risk. Reducing dispersal of rodents removed the effect of predation on population growth and peak size, suggesting that local predators may play a role in driving rodent dispersal, but have otherwise little direct effect on population dynamics.     

Successfully Recovered Grassland: A Promising Example from Romanian Old-Fields

In this study, I analyzed the natural recovery of grasslands on abandoned agricultural fields in the Transylvanian Lowland (Câmpia Transilvaniei), Romania. I examined fields that were abandoned 1–40 years ago and considered how successful they have been in recovering spontaneously as compared to reference grassland, especially in relation to species composition and dominance structure. Diverse, nondegraded seminatural grasslands from the surroundings were chosen as targets for the recovery. Five such grasslands were analyzed in order to have multiple references that accounted for site heterogeneity and different land use history. This study found that the number of natural and seminatural habitat species increased, whereas the number of weeds and aliens decreased with age. Old-fields had become very similar in species composition and dominance structure to reference grasslands over a 14- to 20-year time interval, with the only failure being the unsuccessful or slow colonization of a few grassland species. Because spontaneous succession is efficient, human interventions are not needed to restore target communities on the old-fields. Propagule pressure expressed by the area of potential seed source in a 500-m-radius buffer was found to have a strong influence on recovery success of old-fields. The success of grassland species in colonizing postagricultural fields was not affected by their dispersal mode but by their frequency in the landscape, this being another evidence for the importance of propagule availability in the course of recovery. In order to maintain the potential for recovery of this landscape, we need to protect those close to natural habitats that contain a high amount of native flora.     

The effect of species diversity on lipid production by micro-algal communities

Current research investigating the importance of diversity for biofuel lipid production remains limited. In contrast, the relationship between diversity and productivity within terrestrial and algal primary producers has been well documented in ecology. Hence, we set out to investigate, experimentally, whether diversity may also affect lipid production in micro-algae. We investigated the growth and lipid production of micro-algae using species from all major algal groups. Algae were grown in a large number of treatments differing in their diversity level. Additionally, we compared the growth and lipid production of laboratory communities to natural lake and pond phytoplankton communities of different diversity. Our results show that lipid production increased with increasing diversity in both natural and laboratory micro-algal communities. The underlying reason for the observed ‘diversity–productivity’ relationship seems to be resource use complementarity. We observed higher lipid production of highly diverse algal communities under the same growth and resource supply conditions compared to monocultures. Hence, the incorporation of the ecological advantages of diversity-related resource-use dynamics into algal biomass production may provide a powerful and cost effective way to improve biofuel production.     

Prediction in the face of uncertainty: a Monte Carlo-based approach for systems biology of cancer treatment

Cancer is known to be a complex disease and its therapy is difficult. Much information is available on molecules and pathways involved in cancer onset and progression and this data provides a valuable resource for the development of predictive computer models that can help to identify new potential drug targets or to improve therapies. Modeling cancer treatment has to take into account many cellular pathways usually leading to the construction of large mathematical models. The development of such models is complicated by the fact that relevant parameters are either completely unknown, or can at best be measured under highly artificial conditions. Here we propose an approach for constructing predictive models of such complex biological networks in the absence of accurate knowledge on parameter values, and apply this strategy to predict the effects of perturbations induced by anti-cancer drug target inhibitions on an epidermal growth factor (EGF) signaling network. The strategy is based on a Monte Carlo approach, in which the kinetic parameters are repeatedly sampled from specific probability distributions and used for multiple parallel simulations. Simulation results from different forms of the model (e.g., a model that expresses a certain mutation or mutation pattern or the treatment by a certain drug or drug combination) can be compared with the unperturbed control model and used for the prediction of the perturbation effects. This framework opens the way to experiment with complex biological networks in the computer, likely to save costs in drug development and to improve patient therapy.     

Complex cell rearrangements during intersegmental vessel sprouting and vessel fusion in the zebrafish embryo

The formation of intersegmental blood vessels (ISVs) in the zebrafish embryo serves as a paradigm to study angiogenesis in vivo. ISV formation is thought to occur in discrete steps. First, endothelial cells of the dorsal aorta migrate out and align along the dorsoventral axis. The dorsal-most cell, also called tip cell, then joins with its anterior and posterior neighbours, thus establishing a simple vascular network. The vascular lumen is then established via formation of vacuoles, which eventually fuse with those of adjacent endothelial cells to generate a seamless tube with an intracellular lumen. To investigate the cellular architecture and the development of ISVs in detail, we have analysed the arrangement of endothelial cell junctions and have performed single cell live imaging. In contrast to previous reports, we find that endothelial cells are not arranged in a linear head-to-tail configuration but overlap extensively and form a multicellular tube, which contains an extracellular lumen. Our studies demonstrate that a number of cellular behaviours, such as cell divisions, cell rearrangements and dynamic alterations in cell-cell contacts, have to be considered when studying the morphological and molecular processes involved in ISV and endothelial lumen formation in vivo.     

Effect of testosterone on long-term organ cultures of canine prostate

Summary Organ cultures of rodent and human prostate glands have shown marked differences in their morphological response to testosterone. In this study, explants from 19 canine prostate glands were cultivated for a minimum of 9 days in Trowell’s T-8 medium. Groups of explants were exposed to media containing from 0.05 to 100 μm testosterone. While the higher testosterone levels (50 and 100 μm) markedly decreased explant viability, explants cultivated at lower levels (0.05 to 5 μm) appeared similar to control explants in testosterone-free Trowell’s T-8 medium. Atmospheric mixtures containing either 95% or 50% oxygen were equally effective. Shortly after the cultures were initiated, large amounts of secretory product were liberated into the lumen. After 9 or more days in vitro, glandular epithelium appeared cuboidal and never revealed the acid phosphatase-rich secretory granules seen in the preculture control. However, the epithelium exhibited an increase in alkaline phosphatase and lipid content following cultivation. This project was supported by contract N01-CP-33331, Carcinogenesis Program, Division of Cancer Cause and Prevention, National Cancer Institute, Bethesda, Maryland.