Phylogeography of the common vampire bat (Desmodus rotundus): Marked population structure, Neotropical Pleistocene vicariance and incongruence between nuclear and mtDNA markers

Background  

The common vampire bat Desmodus rotundus is an excellent model organism for studying ecological vicariance in the Neotropics due to its broad geographic range and its preference for forested areas as roosting sites. With the objective of testing for Pleistocene ecological vicariance, we sequenced a mitocondrial DNA (mtDNA) marker and two nuclear markers (RAG2 and DRB) to try to understand how Pleistocene glaciations affected the distribution of intraspecific lineages in this bat.     

Purification of reversibly oxidized proteins (PROP) reveals a redox switch controlling p38 MAP kinase activity

Oxidation of cysteine residues of proteins is emerging as an important means of regulation of signal transduction, particularly of protein kinase function. Tools to detect and quantify cysteine oxidation of proteins have been a limiting factor in understanding the role of cysteine oxidation in signal transduction. As an example, the p38 MAP kinase is activated by several stress-related stimuli that are often accompanied by in vitro generation of hydrogen peroxide. We noted that hydrogen peroxide inhibited p38 activity despite paradoxically increasing the activating phosphorylation of p38. To address the possibility that cysteine oxidation may provide a negative regulatory effect on p38 activity, we developed a biochemical assay to detect reversible cysteine oxidation in intact cells. This procedure, PROP, demonstrated in vivo oxidation of p38 in response to hydrogen peroxide and also to the natural inflammatory lipid prostaglandin J2. Mutagenesis of the potential target cysteines showed that oxidation occurred preferentially on residues near the surface of the p38 molecule. Cysteine oxidation thus controls a functional redox switch regulating the intensity or duration of p38 activity that would not be revealed by immunodetection of phosphoprotein commonly interpreted as reflective of p38 activity.     

Focus on Water: Biodesalination: A Case Study for Applications of Photosynthetic Bacteria in Water Treatment

Shortage of freshwater is a serious problem in many regions worldwide, and is expected to become even more urgent over the next decades as a result of increased demand for food production and adverse effects of climate change. Vast water resources in the oceans can only be tapped into if sustainable, energy-efficient technologies for desalination are developed. Energization of desalination by sunlight through photosynthetic organisms offers a potential opportunity to exploit biological processes for this purpose. Cyanobacterial cultures in particular can generate a large biomass in brackish and seawater, thereby forming a low-salt reservoir within the saline water. The latter could be used as an ion exchanger through manipulation of transport proteins in the cell membrane. In this article, we use the example of biodesalination as a vehicle to review the availability of tools and methods for the exploitation of cyanobacteria in water biotechnology. Issues discussed relate to strain selection, environmental factors, genetic manipulation, ion transport, cell-water separation, process design, safety, and public acceptance.Bacteria are commonly employed for the purification of municipal and industrial wastewater but until now, established water treatment technologies have not taken advantage of photosynthetic bacteria (i.e. cyanobacteria). The ability of cyanobacterial cultures to grow at high cell densities with minimal nutritional requirements (e.g. sunlight, carbon dioxide, and minerals) opens up many future avenues for sustainable water treatment applications.Water security is an urgent global issue, especially because many regions of the world are experiencing, or are predicted to experience, water shortage conditions: More than one in six people globally are water stressed, in that they do not have access to safe drinking water (United Nations, 2006). Ninety-seven percent of the Earth’s water is in the oceans; consequently, there are many efforts to develop efficient methods for converting saltwater into freshwater. Various processes using synthetic membranes, such as reverse osmosis, are successfully used for large-scale desalination. However, the high energy consumption of these technologies has limited their application predominantly to countries with both relatively limited freshwater resources and high availability of energy, for example, in the form of oil reserves.The development of an innovative, low-energy biological desalination process, using biological membranes of cyanobacteria, would thus be both attractive and pertinent. The core of the proposed biodesalination process (Fig. 1) is a low-salt biological reservoir within seawater that can serve as an ion exchanger. Its development can be separated into several complementary steps. The first step comprises the selection of a cyanobacterial strain that can be grown to high cell densities in seawater with minimal requirement for energy sources other than those that are naturally available. The environmental conditions during growth can be manipulated to enhance natural extrusion of sodium (Na⁺) by cyanobacteria. In the second step, cyanobacterial ion transport mechanisms must be manipulated to generate cells in which sodium export is replaced with intracellular sodium accumulation. This will involve inhibition of endogenous Na⁺ export and expression of synthetic molecular units that facilitate light-driven sodium flux into the cells. A robust control system built from biological switches will be required to achieve precisely timed expression of the salt-accumulating molecular units. The third step consists of engineering efficient separation of the cyanobacterial cells from the desalinated water, using knowledge of physicochemical properties of the cell surface and their natural ability to produce extracellular polymeric substances (EPSs), which aid cell separation while preserving cell integrity. The fourth step integrates the first three steps into a manageable and scalable engineering process. The fifth and final step assesses potential risks and public acceptance issues linked to the new technology.Open in a separate windowFigure 1.Proposed usage of cyanobacterial cultures for water treatment. A, Hypothetical water treatment station. Situated in basins next to the water source, sun-powered cell cultures remove unwanted elements from the water. The clean water is separated from the cells for human uses. The produced biomass is available for other industries. The proposed biodesalination process is based on the following steps. B, Photoautotrophic cells divide to generate high-density cultures. C, The combined cell volume is low in salt as a result of transport proteins in the cell membrane that export sodium using photosynthetically generated energy. D, Through environmental and genetic manipulation, salt export is inhibited and replaced with transport modules that accumulate salt inside the cells. This process is again fueled by light energy. E, Manipulation of cell surface properties separates the salt-enriched cells from the desalinated water.In this review, we outline the state of knowledge and available technology for each of the steps, as well as summarize the current knowledge gaps and technical limitations in employing a large-scale water treatment process using cyanobacteria. Before discussing these issues, we provide some background information on the usage of cyanobacteria in biotechnology and the impact of sodium on cellular functions of cyanobacteria. The example of biodesalination provides a good vehicle to discuss the suitability of photosynthetic bacteria for water treatment more generally. The issues addressed in this review are relevant for a wide range of biotechnological applications of cyanobacteria, including bioremediation and biodegradation as well as the generation of biofuels, natural medicines, or cosmetics.     

The hydrophobin EAS is largely unstructured in solution and functions by forming amyloid-like structures

BACKGROUND: Fungal hydrophobin proteins have the remarkable ability to self-assemble into polymeric, amphipathic monolayers on the surface of aerial structures such as spores and fruiting bodies. These monolayers are extremely resistant to degradation and as such offer the possibility of a range of biotechnological applications involving the reversal of surface polarity. The molecular details underlying the formation of these monolayers, however, have been elusive. We have studied EAS, the hydrophobin from the ascomycete Neurospora crassa, in an effort to understand the structural aspects of hydrophobin polymerization. RESULTS: We have purified both wild-type and uniformly 15N-labeled EAS from N. crassa conidia, and used a range of physical methods including multidimensional NMR spectroscopy to provide the first high resolution structural information on a member of the hydrophobin family. We have found that EAS is monomeric but mostly unstructured in solution, except for a small region of antiparallel beta sheet that is probably stabilized by four intramolecular disulfide bonds. Polymerised EAS appears to contain substantially higher amounts of beta sheet structure, and shares many properties with amyloid fibers, including a characteristic gold-green birefringence under polarized light in the presence of the dye Congo Red. CONCLUSIONS: EAS joins an increasing number of proteins that undergo a disorder-->order transition in carrying out their normal function. This report is one of the few examples where an amyloid-like state represents the wild-type functional form. Thus the mechanism of amyloid formation, now thought to be a general property of polypeptide chains, has actually been applied in nature to form these remarkable structures.     

A Murine Inhalation Model to Characterize Pulmonary Exposure to Dry Aspergillus fumigatus Conidia

Most murine models of fungal exposure are based on the delivery of uncharacterized extracts or liquid conidia suspensions using aspiration or intranasal approaches. Studies that model exposure to dry fungal aerosols using whole body inhalation have only recently been described. In this study, we aimed to characterize pulmonary immune responses following repeated inhalation of conidia utilizing an acoustical generator to deliver dry fungal aerosols to mice housed in a nose only exposure chamber. Immunocompetent female BALB/cJ mice were exposed to conidia derived from Aspergillus fumigatus wild-type (WT) or a melanin-deficient (Δalb1) strain. Conidia were aerosolized and delivered to mice at an estimated deposition dose of 1×10⁵ twice a week for 4 weeks (8 total). Histopathological and immunological endpoints were assessed 4, 24, 48, and 72 hours after the final exposure. Histopathological analysis showed that conidia derived from both strains induced lung inflammation, especially at 24 and 48 hour time points. Immunological endpoints evaluated in bronchoalveolar lavage fluid (BALF) and the mediastinal lymph nodes showed that exposure to WT conidia led to elevated numbers of macrophages, granulocytes, and lymphocytes. Importantly, CD8⁺ IL17⁺ (Tc17) cells were significantly higher in BALF and positively correlated with germination of A. fumigatus WT spores. Germination was associated with specific IgG to intracellular proteins while Δalb1 spores elicited antibodies to cell wall hydrophobin. These data suggest that inhalation exposures may provide a more representative analysis of immune responses following exposures to environmentally and occupationally prevalent fungal contaminants.     

Landscape influences on dispersal behaviour: a theoretical model and empirical test using the fire salamander,Salamandra infraimmaculata

When populations reside within a heterogeneous landscape, isolation by distance may not be a good predictor of genetic divergence if dispersal behaviour and therefore gene flow depend on landscape features. Commonly used approaches linking landscape features to gene flow include the least cost path (LCP), random walk (RW), and isolation by resistance (IBR) models. However, none of these models is likely to be the most appropriate for all species and in all environments. We compared the performance of LCP, RW and IBR models of dispersal with the aid of simulations conducted on artificially generated landscapes. We also applied each model to empirical data on the landscape genetics of the endangered fire salamander, Salamandra infraimmaculata, in northern Israel, where conservation planning requires an understanding of the dispersal corridors. Our simulations demonstrate that wide dispersal corridors of the low-cost environment facilitate dispersal in the IBR model, but inhibit dispersal in the RW model. In our empirical study, IBR explained the genetic divergence better than the LCP and RW models (partial Mantel correlation 0.413 for IBR, compared to 0.212 for LCP, and 0.340 for RW). Overall dispersal cost in salamanders was also well predicted by landscape feature slope steepness (76 %), and elevation (24 %). We conclude that fire salamander dispersal is well characterised by IBR predictions. Together with our simulation findings, these results indicate that wide dispersal corridors facilitate, rather than hinder, salamander dispersal. Comparison of genetic data to dispersal model outputs can be a useful technique in inferring dispersal behaviour from population genetic data.     

Population sizes and within-deme movement of Trimerotropis saxatilis (Acrididae), a grasshopper with a fragmented distribution

Capture-mark-recapture studies were initiated in 1990 on four Missouri populations of the lichen grasshopper, Trimerotropis saxatilis. This grasshopper lives only on glade habitat, predominantly in the Ozark Mountains. Genetic data suggest that no gene flow occurs among T. saxatilis populations. Lichen grasshopper population size (both present and historical), and the likelihood of movement within and between glades, are the subjects of this study. Population sizes on all glades were found to be small (<280 individuals) and to vary from year to year. Inbreeding effective sizes were found to be much larger than census sizes. On one of the sites, Graham Cave Glade, population size was calculated for 5 years; in 3 of those years (1991, 1993 and 1994) our studies of this population also tested for movement of T. saxatilis individuals among different regions of the moderately subdivided glade. Maintenance of Graham Cave Glade (burning and clearing) was initiated after the 1991 capture-mark-recapture season. Comparisons of before-and after-burning intraglade movement probabilities did not show a significant difference. Grasshoppers more frequently remained in the part of the glade where they were previously captured, but were able to move about the moderately subdivided glade. The presence of a closed-canopy forest, rather than distance, appears to be an effective dispersal barrier.