Improved diagnosis of virulent ovine footrot using the intA gene

Footrot is a mixed bacterial infection of the hooves of sheep. The Gram-negative anaerobic bacterium 'Dichelobacter nodosus' is the principal causative agent, with different strains causing diseases of different severity, ranging from benign to virulent. In Australia, in the state of New South Wales (NSW), only virulent footrot is subject to regulatory action, including quarantine. However, it is often difficult to distinguish benign footrot from virulent footrot in the initial stages of infection, or under adverse climatic conditions. The gelatin gel test, which measures the thermostability of secreted bacterial proteases, is the laboratory test most widely used in Australia to aid in the differential diagnosis of footrot. The proteases of virulent strains are, in general, more thermostable than the proteases of benign strains. However, there are some false positives in the gelatin gel test, which may lead to unnecessary quarantine procedures. We used Southern blot analysis on 595 isolates of 'D. nodosus' from 124 farms on which sheep had benign or virulent footrot to test for the presence of the intA gene. We found that for 'D. nodosus' strains which are stable in the gelatin gel test, there is a high correlation between the presence of the intA gene and the ability of the strain to cause virulent footrot. We also developed a PCR-based assay for the rapid detection of intA, which can be used to test DNA extracted from colonies grown on plates, or DNA extracted from cotton swabs of culture plates

A pulse of mid-Pleistocene rift volcanism in Ethiopia at the dawn of modern humans

The Ethiopian Rift Valley hosts the longest record of human co-existence with volcanoes on Earth, however, current understanding of the magnitude and timing of large explosive eruptions in this region is poor. Detailed records of volcanism are essential for interpreting the palaeoenvironments occupied by our hominin ancestors; and also for evaluating the volcanic hazards posed to the 10 million people currently living within this active rift zone. Here we use new geochronological evidence to suggest that a 200 km-long segment of rift experienced a major pulse of explosive volcanic activity between 320 and 170 ka. During this period, at least four distinct volcanic centres underwent large-volume (>10 km3) caldera-forming eruptions, and eruptive fluxes were elevated five times above the average eruption rate for the past 700 ka. We propose that such pulses of episodic silicic volcanism would have drastically remodelled landscapes and ecosystems occupied by early hominin populations

Lifetime and size of shallow magma bodies controlled by crustal-scale magmatism

ISSN:1752-0908ISSN:1752-089

A Framework for Validation and Benchmarking of Pyroclastic Current Models

Numerical models of pyroclastic currents are widely used for fundamental research and for hazard and risk modeling that supports decision-making and crisis management. Because of their potential high impact, the credibility and adequacy of models and simulations needs to be assessed by means of an established, consensual validation process. To define a general validation framework for pyroclastic current models, we propose to follow a similar terminology and the same methodology that was put forward by Oberkampf and Trucano (Prog Aerosp Sci, 38, 2002) for the validation of computational fluid dynamics (CFD) codes designed to simulate complex engineering systems. In this framework, the term validation is distinguished from verification (i.e., the assessment of numerical solution quality), and it is used to indicate a continuous process, in which the credibility of a model with respect to its intended use(s) is progressively improved by comparisons with a suite of ad hoc experiments. The methodology is based on a hierarchical process of comparing computational solutions with experimental datasets at different levels of complexity, from unit problems (well-known, simple CFD problems), through benchmark cases (complex setups having well constrained initial and boundary conditions) and subsystems (decoupled processes at the full scale), up to the fully coupled natural system. Among validation tests, we also further distinguish between confirmation (comparison of model results with a single, well-constrained dataset) and benchmarking (inter-comparison among different models of complex experimental cases). The latter is of particular interest in volcanology, where different modeling approaches and approximations can be adopted to deal with the large epistemic uncertainty of the natural system

Quaternary bimodal volcanism in the Niğde Volcanic Complex (Cappadocia, central Anatolia, Turkey): age, petrogenesis and geodynamic implications

The late Neogene to Quaternary Cappadocian Volcanic Province (CVP) in central Anatolia is one of the most impressive volcanic fields of Turkey because of its extent and spectacular erosionally sculptured landscape. The late Neogene evolution of the CVP started with the eruption of extensive andesitic-dacitic lavas and ignimbrites with minor basaltic lavas. This stage was followed by Quaternary bimodal volcanism. Here, we present geochemical, isotopic (Sr-Nd-Pb and delta O-18 isotopes) and geochronological (U-Pb zircon and Ar-Ar amphibole and whole-rock ages) data for bimodal volcanic rocks of the Ni g de Volcanic Complex (NVC) in the western part of the CVP to determine mantle melting dynamics and magmatic processes within the overlying continental crust during the Quaternary. Geochronological data suggest that the bimodal volcanic activity in the study area occurred between ca. 1.1 and ca. 0.2 Ma (Pleistocene) and comprises (1) mafic lavas consisting of basalts, trachybasalts, basaltic andesites and scoria lapilli fallout deposits with mainly basaltic composition, (2) felsic lavas consisting of mostly rhyolites and pumice lapilli fall-out and surge deposits with dacitic to rhyolitic composition. The most mafic sample is basalt from a monogenetic cone, which is characterized by Sr-87/Sr-86 = 0.7038, Nd-143/Nd-144 = 0.5128, Pb-206/Pb-204 = 18.80, Pb-207/Pb-204 = 15.60 and Pb-208/Pb-204 = 38.68, suggesting a moderately depleted signature of the mantle source. Felsic volcanic rocks define a narrow range of Nd-143/Nd-144 isotope ratios (0.5126-0.5128) and are homogeneous in Pb isotope composition (Pb-206/Pb-204 = 18.84-18.87, Pb-207/Pb-204 = 15.64-15.67 and Pb-208/Pb-204 = 38.93-38.99). Sr-87/Sr-86 isotopic compositions of mafic (0.7038-0.7053) and felsic (0.7040-0.7052) samples are similar, reflecting a common mantle source. The felsic rocks have relatively low zircon delta O-18 values (5.6 +/- 0.6 %) overlapping mantle values (5.3 +/- 0.3 %), consistent with an origin by fractional crystallization from a mafic melt with very minor continental crustal contamination. The geochronological and geochemical data suggest that mafic and felsic volcanic rocks of the NVC are genetically closely related to each other. Mafic rocks show a positive trend between Sr-87/Sr-86 and Th, suggesting simultaneous assimilation and fractional crystallization, whereas the felsic rocks are characterized by a flat or slightly negative variation. High Sr-87/Sr-86 gneisses are a potential crustal contaminant of the mafic magmas, but the comparatively low and invariant Sr-87/Sr-86 in the felsic volcanics suggests that these evolved dominantly by fractional crystallization. Mantle-derived basaltic melts, which experienced low degree of crustal assimilation, are proposed to be the parent melt of the felsic volcanics. Geochronological and geochemical results combined with regional geological and geophysical data suggest that bimodal volcanism of the NVC and the CVP, in general, developed in a post-collisional extensional tectonic regime that is caused by ascending asthenosphere, which played a key role during magma genesis