Sensitivity of African biomes to changes in the precipitation regime

Aim Africa is identified by the Inter‐governmental Panel on Climate Change (IPCC) as the least studied continent in terms of ecosystem dynamics and climate variability. The aim of this study was (1) to adapt the Lund‐Postdam‐Jena‐GUESS (LPJ‐GUESS) ecological modelling framework to Africa by providing new parameter values for tropical plant functional types (PFT), and (2) to assess the sensitivity of some African biomes to changes in precipitation regime. Location The study area was a representative transect (0–22° N and 7–18° E) through the transition from equatorial evergreen forests to savannas, steppes and desert northwards. The transect showed large latitudinal variation in precipitation (mean rainfall ranged from 50 to 2300 mm year^?1). Methods New PFT parameters used to calibrate LPJ‐GUESS were based on modern pollen PFTs and remote sensed leaf area index (LAI). The model was validated using independent modern pollen assemblages, LAI and through comparison with White's modern potential vegetation map. Several scenarios were developed by combining changes in total rainfall amount with variation in the length of the dry season in order to test the sensitivity of African biomes. Results Simulated vegetation compared well to observed data at local and regional scales, in terms of ecosystem functioning (LAI), and composition (pollen and White's vegetation map). The assessment of the sensitivity of biomes to changes in precipitation showed that none of the ecosystems would shift towards a new type under the range of precipitation increases suggested by the IPCC (increases from 5 to 20%). However, deciduous and semi‐deciduous forests may be very sensitive to small reductions in both the amount and seasonality of precipitation. Main conclusions This version of LPJ‐GUESS parameterized for Africa simulated correctly the vegetation present over a wide precipitation gradient. The biome sensitivity assessment showed that, compared with savannas and grasslands, closed canopy forests may be more sensitive to change in precipitation regime due to the synergetic effects of changed rainfall amounts and seasonality on vegetation functioning.     

Anaerobic co-digestion of dairy manure with mulched switchgrass for improvement of the methane yield

The owners of farm-scale anaerobic digesters are relying on off-farm wastes or energy crops as a co-digestion feedstock with animal manure in order to increase their production of methane and thus revenues. Switchgrass represents an interesting feedstock for Canadian digesters owners as it is a high-yielding low-maintenance perennial crop, well adapted to northern climate. Methane potential assays in batch tests showed methane production of 19.4 ± 3.6, 28.3 ± 1.7, 37.3 ± 7.1 and 45.7 ± 0.8 L kg⁻¹, for raw manure, blended manure, manure and mulched switchgrass, manure and pretreated switchgrass, respectively. Two 6-L lab-scale anaerobic digesters were operated for 130 days in order to assess the benefit of co-digesting switchgrass with bovine manure (digester #2), at a 20% wet mass fraction, compared with a manure-only operation (digester #1) The digesters were operated at an hydraulic retention time of 37 ± 6 days and at loads of 2.4 ± 0.6 and 2.6 ± 0.6 kg total volatile solids (TVS) L⁻¹ day⁻¹ for digesters #1 (D1) and #2 (D2), respectively. The TVS degradation reached 25 and 39%, which resulted in a methane production of 1.18 ± 0.18 and 2.19 ± 0.31 L day⁻¹ for D1 and D2, respectively. The addition of 20% on a wet mass ratio of switchgrass to a manure digester increased its methane production by 86%. The co-digestion of switchgrass in a 500 m³ manure digester could yield up to 10.2 GJ day⁻¹ of purified methane or 1.1 MWh day⁻¹ of electricity.     

The performance of a thermophilic microbial fuel cell fed with synthesis gas

This study demonstrated electricity generation in a thermophilic microbial fuel cell (MFC) operated on synthesis gas (syngas) as the sole electron donor. At 50°C, a volumetric power output of 30-35 mWL(R)(-1) and a syngas conversion efficiency of 87-98% was achieved. The observed pathway of syngas conversion to electricity primarily consisted of a two-step process, where the carbon monoxide and hydrogen were first converted to acetate, which was then consumed by the anodophilic bacteria to produce electricity. A denaturing gradient gel electrophoresis (DGGE) analysis of the 16S rDNA revealed the presence of Geobacter species, Acetobacter, methanogens and several uncultured bacteria and archaea in the anodic chamber.     

PDE4 Control on cAMP/PKA Compartmentation Revealed by Biosensor Imaging in Neurons

Electrophysiological recordings (using the slow-AHP potassium current) together with novel biosensor imaging methods (with AKAR and Epac sensors) were used in preparations of rodent brain slices to record PKA activation in real time and in individual neurons. The experiments revealed the propagation of the PKA signal from the membrane to the cytosol and eventually to the nucleus. The experiments show how the geometry of the neurons combined with phosphodiesterase activities (mostly rolipram-sensitive PDE4) contributes to a functional compartmentation of the cAMP in subcellular domains.     

Genomic Analysis of Carbon Monoxide Utilization and Butanol Production by Clostridium carboxidivorans Strain P7T

Increasing demand for the production of renewable fuels has recently generated a particular interest in microbial production of butanol. Anaerobic bacteria, such as Clostridium spp., can naturally convert carbohydrates into a variety of primary products, including alcohols like butanol. The genetics of microorganisms like Clostridium acetobutylicum have been well studied and their solvent-producing metabolic pathways characterized. In contrast, less is known about the genetics of Clostridium spp. capable of converting syngas or its individual components into solvents. In this study, the type of strain of a new solventogenic Clostridium species, C. carboxidivorans, was genetically characterized by genome sequencing. C. carboxidivorans strain P7^T possessed a complete Wood-Ljungdahl pathway gene cluster, involving CO and CO₂ fixation and conversion to acetyl-CoA. Moreover, with the exception of an acetone production pathway, all the genetic determinants of canonical ABE metabolic pathways for acetate, butyrate, ethanol and butanol production were present in the P7^T chromosome. The functionality of these pathways was also confirmed by growth of P7^T on CO and production of CO₂ as well as volatile fatty acids (acetate and butyrate) and solvents (ethanol and butanol). P7^T was also found to harbour a 19 Kbp plasmid, which did not include essential or butanol production related genes. This study has generated in depth knowledge of the P7^T genome, which will be helpful in developing metabolic engineering strategies to improve C. carboxidivorans''s natural capacity to produce potential biofuels from syngas.     

Definition of grassland biomes from phytoliths in West Africa

Aim In order to enhance the effectiveness of comparisons between modelled and empirical data for present and past vegetation, it is important to improve the characterization of tropical grass‐dominated biomes reconstructed from fossil tracers. This study presents a method for assigning phytolith assemblages to tropical grass‐dominated biomes, with the objective of offering a new tool for combining pollen and phytolith data in the reconstruction of tropical biomes. Location The West African latitudinal transect studied here extends from 12° N (southern Senegal) to 23° N (southern Mauritania), passing through the Guinean, Sudanian, Sahelian and Saharan bioclimatic zones. Methods Modern phytolith assemblages were extracted from 59 soil surface samples taken throughout the study area and allocated, a priori, to three current biomes: (1) desert C₄ grassland, (2) short grass savanna, and (3) tall grass savanna. Five out of nine phytolith types identified were used as predictors in a discriminant analysis (with calibration and validation steps) for assigning phytolith assemblages to biomes. In addition, 74 modern pollen spectra from the West African transect, acquired from the African Pollen Database ( http://medias.obs‐mip.fr/apd ), were processed by the biomization method. This mathematical procedure involves assigning palynological taxa to one or more plant functional types, which represent broad classes of plants. The plant functional types, in turn, are combined to define biomes following a specific set of algorithms and rules. The resulting maps of the phytolith biomes thus derived were compared with maps of pollen biomes and of contemporary ecosystem classes. Results In the calibration and validation steps, 91.5% and up to 83%, respectively, of the phytolith samples were assigned to the correct biome. The short grass savanna and tall grass savanna biomes were assigned with similar accuracy by both the phytolith and pollen biomization methods, but the phytolith method gave substantially superior results for the desert C₄ grassland biome, providing seven out of seven correct assignments, compared with just one out of four by pollen biomization. Comparisons between an existing ecosystem map and the maps created from phytolith estimation showed close correspondence for desert C₄ grassland, short grass savanna and tall grass savanna, the latter providing correct assignments in 88, 62 and 91% of cases, respectively. Main conclusions The phytolith discriminant analysis method presented here accurately estimates three C₄ grass‐dominated biomes that are widespread in West Africa. Complementarities between the phytolith method and pollen biomization are highlighted. Combining complementary phytolith and pollen data would provide more accurate assignments of C₄ grass‐dominated biomes than pollen biomization alone.     

Sentinel node biopsy should be supplemented by axillary sampling in patients with small breast cancers

Axillary clearance provides important prognostic information but is associated with significant morbidity. Sentinel node biopsy can provide staging .141 patients with node negative early breast cancers-tumour size less than 1.5 cm measured clinically or by imaging had guided axillary sampling (sentinel lymph node biopsy in combination with axillary sampling). Four node axillary sampling improved the detection rate of axillary node metastases by 13.6% as compared to blue dye sentinel node biopsy alone. Positive sampled nodes strongly indicated the likelihood of further metastatic being revealed by axillary dissection (67%). Negative sampled nodes in combination with a positive sentinel node biopsy were associated with a much lower rate of further nodal involvement in the axillary clearance (8%).     

Use of silicone membranes to enhance gas transfer during microbial fuel cell operation on carbon monoxide

Electricity generation in a microbial fuel cell (MFC) using carbon monoxide (CO) or synthesis gas (syngas) as a carbon source has been demonstrated recently. A major challenge associated with CO or syngas utilization is the mass transfer limitation of these sparingly soluble gases in the aqueous phase. This study evaluated the applicability of a dense polymer silicone membrane and thin wall silicone tubing for CO mass transfer in MFCs. Replacing the sparger used in our previous study with the membrane systems for CO delivery resulted in improved MFC performance and CO transformation efficiency. A power output and CO transformation efficiency of up to 18 mW (normalized to anode compartment volume) and 98%, respectively, was obtained. The use of membrane systems offers the advantage of improved mass transfer and reduced reactor volume, thus increasing the volumetric power output of MFCs operating on a gaseous substrate such as CO.     

Optimizing the electrode size and arrangement in a microbial electrolysis cell

This study investigates the influence of anode and cathode size and arrangement on hydrogen production in a membrane-less flat-plate microbial electrolysis cell (MEC). Protein measurements were used to evaluate microbial density in the carbon felt anode. The protein concentration was observed to significantly decrease with the increase in distance from the anode-cathode interface. Cathode placement on both sides of the carbon felt anode was found to increase the current, but also led to increased losses of hydrogen to hydrogenotrophic activity leading to methane production. Overall, the best performance was obtained in the flat-plate MEC with a two-layer 10 mm thick carbon felt anode and a single gas-diffusion cathode sandwiched between the anode and the hydrogen collection compartments.     

Characterization of a novel mutation in the cardiac ryanodine receptor that results in catecholaminergic polymorphic ventricular tachycardia

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is an arrhythmogenic disease that manifests as syncope or sudden death during high adrenergic tone in the absence of structural heart defects. It is primarily caused by mutations in the cardiac ryanodine receptor (RyR2). The mechanism by which these mutations cause arrhythmia remains controversial, with discrepant findings related to the role of the RyR2 binding protein FKBP12.6. The purpose of this study was to characterize a novel RyR2 mutation identified in a kindred with clinically diagnosed CPVT.Single-strand conformational polymorphism analysis and direct DNA sequencing were used to screen the RyR2 gene for mutations. Site-directed mutagenesis was employed to introduce the mutation into the mouse RyR2 cDNA. The impact of the mutation on the interaction between RyR2 and a 12.6 kDa FK506 binding protein (FKBP12.6) was determined by immunoprecipitation and immunoblotting and its effect on RyR2 function was characterized by single cell Ca²⁺ imaging and [³H]ryanodine binding.A novel CPVT mutation, E189D, was identified. The E189D mutation does not alter the affinity of the channel for FKBP12.6, but it increases the propensity for store-overload-induced Ca²⁺ release (SOICR). Furthermore, the E189D mutation enhances the basal channel activity of RyR2 and its sensitivity to activation by caffeine.The E189D RyR2 mutation is causative for CPVT and functionally increases the propensity for SOICR without altering the affinity for FKBP12.6. These observations strengthen the notion that enhanced SOICR, but not altered FKBP12.6 binding, is a common mechanism by which RyR2 mutations cause arrhythmias.Key words: arrhythmia, calcium, death sudden, genetics, ion channels