Continental-scale effects of nutrient pollution on stream ecosystem functioning

Excessive nutrient loading is a major threat to aquatic ecosystems worldwide that leads to profound changes in aquatic biodiversity and biogeochemical processes. Systematic quantitative assessment of functional ecosystem measures for river networks is, however, lacking, especially at continental scales. Here, we narrow this gap by means of a pan-European field experiment on a fundamental ecosystem process--leaf-litter breakdown--in 100 streams across a greater than 1000-fold nutrient gradient. Dramatically slowed breakdown at both extremes of the gradient indicated strong nutrient limitation in unaffected systems, potential for strong stimulation in moderately altered systems, and inhibition in highly polluted streams. This large-scale response pattern emphasizes the need to complement established structural approaches (such as water chemistry, hydrogeomorphology, and biological diversity metrics) with functional measures (such as litter-breakdown rate, whole-system metabolism, and nutrient spiraling) for assessing ecosystem health.     

The innate immune response against Brucella in humans

Pathogens have developed different strategies to survive and multiply within their host. Among them is the ability to control phagocyte apoptosis while another is to affect the expression of cytokines which is necessary for a normal protective function of the immune response. To establish themselves and cause chronic disease in humans and animals, Brucella spp. invade and proliferate within monocytic phagocytes. We have established that in humans, Brucella suis impairs the apoptosis of monocytes and macrophages, thus preventing its host cell elimination. In mice, which are not naturally colonized by the bacteria, Brucella infection results in Type1 (Th1) cellular immune response which promotes a clearance of the bacterial organism. The development of this response is under the control of major cytokines like TNF-alpha, IFN-gamma and IL-12 produced at the onset of infection. We have observed that in humans, B. suis-infected macrophages which produce IL-1, IL-6, IL-10 and several chemokines including IL-8, do not secrete TNF-alpha. By constructing null mutants, we demonstrated that this inhibition involves the outer membrane protein Omp25 of Brucella, however the mechanism regulating the inhibition has not yet been clearly defined. It is likely that the Omp25-induced effect on TNF-alpha production assists bacterial evasion of antimicrobial defences at different levels. Firstly, by preventing the autocrine activation of macrophages thus inhibiting innate immunity and secondly by impairing the production of IL-12 and the development of a Th1 type specific immunity. In addition to the central role of the macrophage in Brucella infection, others cells of the innate immune response are recruited and influenced by the interactions between bacteria and host. For instance, human Vgamma9Vdelta2 T-cells play an important role in the early response to infection with intracellular pathogens. Evidence has been presented that their number dramatically increased in the peripheral blood of patients with acute brucellosis. We have shown that human Vgamma9Vdelta2 T-cells can be specifically activated by non-peptidic low molecular weight compound(s) from B. suis lysate or by soluble factors produced by B. suis-infected macrophages. Under these conditions, they produce TNF-alpha and IFN-gamma and reduce the bacterial multiplication inside infected autologous macrophages. This impairment of B. suis multiplication is due to both soluble factors released from activated gammadeltaT-cells (including TNF-alpha and IFN-gamma) and to a contact-dependent cytotoxicity directed against the infected cells. The interactions between the bacteria and these cells can counteract the intramacrophagic development of the bacteria and finally influence the further development of the host defense. We hypothesize that the chronicity or the elimination of the infection will depend on the balance between contradictory effects induced by the bacteria which favor either the host or the pathogen. Moreover, the interrelationship between the different cells must be taken into account in the analysis of the virulence of the bacteria and in the development of in vitro models of human macrophage infection.     

Progressive myelopathy due to a spontaneous intramedullary hematoma in a dog: pre- and postoperative clinical and magnetic resonance imaging follow-up

A 4-year-old, male Jack Russell terrier was presented for a 6-month history of progressive right hemiparesis with episodic cervical hyperesthesia. The neurological examination showed a right-sided, upper motoneuron syndrome and partial Horner's syndrome. Two magnetic resonance imaging (MRI) examinations were performed 3 months apart and revealed a persistent cervical intramedullary hematoma. A dorsal myelotomy was performed. A subacute hematoma was confirmed histologically without underlying lesions. Eighteen months later, the dog's clinical signs were minimal. Two MRI examinations were performed 2 weeks and 5 months after surgery and revealed regressing signal abnormalities at the surgical site, consistent with a surgical scar.     

Assessment of genetic diversity of Highland bananas from the National Banana Germplasm Collection at Rubona,Rwanda using RAPD markers

The genetic similarities of 49 accessions of bananas from The National Banana Collection at Rubona were investigated using random amplified polymorphic DNA markers. A total of 120 primers were screened for their usefulness in amplifying DNA fragments of four cultivars belonging to the subgroup Mutika–Lujugira. Fifteen random primers were selected for more detailed analysis, on the basis of providing reproducible amplification and revealing a high level of variation between the four cultivars. The genetic similarity was estimated using a simple matching coefficient which showed the lowest value of 0.46 between ‘Ingumba’ and ‘Ishika’ and the highest value of 0.85 between ‘Kirayenda’ and ‘Inyabukuwe’. The data of matrix of coefficient of similarity was subjected to cluster analysis using the unweighted pair group method with arithmetic average (UPGMA). Each accession was clearly separated. The results of this study are important for the curation of the banana germplasm collection in Eastern Central Africa and for future breeding of this crop.     

Interpreting ecological patterns generated through simple stochastic processes

The analysis of spatial patterns is fundamental to understanding ecological processes across geographic scales. Through an analysis of two simple, one-dimensional stochastic models, we develop a framework for identifying the scale of processes producing pattern. We show that for some simple model systems spectral analysis identifies exactly the scale of pattern formation. In other, more complicated systems, autocorrelation analysis appears to yield greater insight into the scale of the dynamics producing pattern; in these, the relative importance of processes at different scales can be determined directly from the change in slope of the autocorrelation function.In general, it is not possible to state which technique will be most useful in the analysis of pattern. Spectral analysis and autocorrelation analysis represent duals that can be extended and applied to more complex systems, potentially yielding insight into the nature of a wide variety of spatially determined ecological processes.     

Synthesis of carbenes through substitution reactions at a carbene center

An (amino)(phosphino) carbene can be transformed into (amino)(phosphonio) carbenes, which undergo nucleophilic intermolecular as well as intramolecular substitution reactions at the carbene center. A variety of carbenes can be synthesized starting from a single carbene precursor. The resulting gamut of electronic and steric effects possible should open the way not only to a detailed study of the mechanism, but also to the subsequent improvement of catalytic reactions that involve carbene-transition metal complexes.     

The PIDDosome, a protein complex implicated in activation of caspase-2 in response to genotoxic stress

Apoptosis is triggered by activation of initiator caspases upon complex-mediated clustering of the inactive zymogen, as occurs in the caspase-9-activating apoptosome complex. Likewise, caspase-2, which is involved in stress-induced apoptosis, is recruited into a large protein complex, the molecular composition of which remains elusive. We show that activation of caspase-2 occurs in a complex that contains the death domain-containing protein PIDD, whose expression is induced by p53, and the adaptor protein RAIDD. Increased PIDD expression resulted in spontaneous activation of caspase-2 and sensitization to apoptosis by genotoxic stimuli. Because PIDD functions in p53-mediated apoptosis, the complex assembled by PIDD and caspase-2 is likely to regulate apoptosis induced by genotoxins.     

Gas chromatographic analysis of histamine in mahi-mahi (Coryphaena hippurus)

Several authors have studied histamine using gas chromatography (GC) as a tool for quantitation, but the methods used were not always suitable depending on the kind of food. Problems frequently cited include incomplete histamine elution from the columns and peak tailing. Histamine is of interest because it is the factor common to all cases of scombroid poisoning, it has physiological and biological activity, and it is a chemical indicator of fish quality. In this study a modified GC method was used to quantify histamine in mahi-mahi (Coryphaena hippurus). Mean recovery was 67% for the GC method, compared with 90% for the AOAC fluorometric method. There was a 0.96 correlation of the GC histamine values with those of the AOAC fluorometric method. A temperature program, splitless/split injection, and analyte cleanup were essential for GC properties. Histamine retention time was 8.2 min. The method allowed peak height to be used for quantitation and simultaneous analysis of cadaverine and putrescine.