Genome-wide RNAi screen for host factors required for intracellular bacterial infection

Most studies of host-pathogen interactions have focused on pathogen-specific virulence determinants. Here, we report a genome-wide RNA interference screen to identify host factors required for intracellular bacterial pathogenesis. Using Drosophila cells and the cytosolic pathogen Listeria monocytogenes, we identified 305 double-stranded RNAs targeting a wide range of cellular functions that altered L. monocytogenes infection. Comparison to a similar screen with Mycobacterium fortuitum, a vacuolar pathogen, identified host factors that may play a general role in intracellular pathogenesis and factors that specifically affect access to the cytosol by L. monocytogenes.     

Phosphorus uptake of maize as affected by ammonium and nitrate nitrogen - Measurements and model calculations -

Phosphorus uptake is often enhanced by ammonium compared to nitrate nitrogen nutrition of plants. A decrease of pH at the soil-root interface is generally assumed as the cause. However, an alteration of root growth and the mobilization of P by processes other than net release of protons induced by the source of nitrogen may also be considered. To study these alternatives a pot experiment was conducted with maize using a fossil Oxisol high in Fe/Al-P with low soil solution P concentration. Three levels of phosphate (0, 50, 200 mg P kg^?1) in combination with either ammonium or nitrate nitrogen (100 mg N kg^?1) were applied. Plants were harvested 7 and 21 d after sowing, P uptake measured and root and shoot growth determined. To assess the importance of factors involved in the P transfer from soil into plants, calculations were made using a model of Barber and Claassen. In the treatments with no and low P supply NH₄-N compared to NO₃-N nutrition increased the growth of the plants by 25 % and their shoot P content by 38 % while their root growth increased by 6 % only. The rhizosphere pH decreased in the NH₄-N treatments by 0.1 to 0.6 units as compared to the bulk soil while in the NO₃-N treatments it increased by 0.1 to 0.5 units. These pH changes had a minor influence on P uptake only, as was demonstrated by artificially altering the soil pH to 4.7 and 6.3 respectively. At the same rhizosphere pH, however, P influx was doubled by the application of NH₄-compared to NO₃-N. It is concluded that in this soil the enhancement of P uptake of maize plants after ammonium application cannot be attributed to the acidification of the rhizosphere but to effects mobilizing soil phosphate or increasing P uptake efficiency of roots. Model calculation showed that these effects accounted for 53 % of the P influx per unit root length in the NO₃-N and 72 % in the NH₄-N supplied plants if no P was applied. With high P application the respective figures were only 18 and 19%.     

“Preferential flow”: Eine Übersicht über den heutigen Kenntnisstand

Preferential flow: A review of current knowledge Despite intensive research neither suitable methods of measurement, nor complete theoretical statements give an adequate account of preferential flow due to the exceptional complexity and variability of the soil system. In particular it is not possible to make predictions of preferential flow for a given soil due to observations and measurements. In this work we describe theoretical and technical problems of preferential flow and initiate ideas for future work in this field.     

Flavor release in the presence of melanoidins prepared from L-(+)-ascorbic acid and amino acids

High-molecular-weight (HMW) water-soluble melanoidins were prepared from model systems of L-(+)-ascorbic acid-glycine, L-(+)-ascorbic acid-lysine, L-(+)-ascorbic acid-glutamic acid, and glucose-glycine using a very recently approved standard protocol. The amount of HMW water-soluble melanoidins prepared from L-(+)-ascorbic acid was over 5-15 times higher than the amount obtained from glucose. The study of the release of a model flavor compound, namely isoamyl acetate, from melanoidins by solid-phase microextraction (SPME) showed that SPME is a suitable technique for the analysis of flavor release from melanoidin-containing solutions. From the studies on the retention capacity of the melanoidins toward isoamyl acetate, an increased release of the flavor compound was observed from the melanoidins prepared from the L-(+)-ascorbic acid-glycine model system, whereas the opposite effect was observed from the melanoidins prepared from the L-(+)-ascorbic acid-lysine/glutamic acid model systems. The melanoidins prepared from the glucose-glycine model system had the same effect as the melanoidins prepared from the L-(+)-ascorbic acid-glycine model system.     

Insect repellent/antifeedant activity of 2,4-methanoproline and derivatives against a leaf- and seed-feeding pest insect

2,4-methanoproline is a natural product isolated from the seeds of Ateleia herbert smithii Pittier that was formerly suggested to have insect repellent/antifeedant activity; however, this was not tested quantitatively. In this study the insect repellent/antifeedant potency of methanoproline was measured against larvae of the cotton leafworm, Spodoptera littoralis (Boisd.), and adults of the cowpea weevil, Callosobruchus maculatus (F.). In addition, several N-alkyl, amino, and nitrile derivatives of methanoproline with varying stereodemanding substituents were synthesized and also tested. It was shown that in S. littoralis methanoproline itself did not show any significant activity but that derivatives 5, 7, 8, and 10 did show a reasonable repulsive/antifeedant activity that was comparable to the commercial repellent DEET. A significant repellent activity was scored for methanoproline in adults of C. maculatus that was similar to DEET.     

Retention of Staphylococci and Total Coliforms During Wastewater Percolation Through Equatorial Soil in Central Africa: The Role of the Soil Column Near Soil Surface and that Closely Above Groundwater Table

Groundwater protection from pollutants depends mostly on retention potentials of soil above groundwater table. Soil separating soil surface from groundwater table is made up of several layers and can be divided into different columns along its vertical transect. Wastewater percolation tests were carried out through one soil column CA, in contact with soil surface and through another CB, closely above groundwater table. The aim of the study was to assess the importance of soil columns CA and CB, in total coliforms and staphylococci retention during wastewater infiltration or groundwater recharge, in equatorial soils in Central African region. The results showed that, the fraction of total coliforms retained through soil column CA varied with respect to wastewater loads applied on top of soil column, from 69.22% to 99.95%, relative to the total coliforms concentration deposited on top. The fraction of total coliforms retained through CB varied with respect to wastewater loads applied, from 96.98 to 99.89% relative to the total coliforms deposited on top. Through both soil columns, fractions of staphylococci retained was in the order of 99.99% relative to the total staphylococci concentration deposited on top. For the whole bacteriological analysis, the fractions of total coliforms retained seems to be greater through deeper soil column than that of upper soil column. The bacterial contaminants retained relative to their concentrations in wastewater poured on soil column surfaces, varied from 6.17 log units to 9.73 log units. An applied load of 100 ml seemed to lead to the bacterial pollutants transported through both soil columns studied. NH₄ ⁺ was retained by fractions varying from 97.37 to 98.74%. Concentrations of various contaminants found in groundwater would be a tiny part, relative to quantities deposited on soil surface. Bacterial retention potentials of soil column separating soil surface from groundwater table during wastewater percolation, varies along its transect. It would be due to numerous and variable physical, chemical and structural properties of soil layers and bacteria on the one hand, and to results of various interactions between soil layer particles and cell bacteria, on the other hand.     

Pflanzenverfügbarkeit der Phosphatvorräte ackerbaulich genutzter Böden. -Langfristige Feldversuche zur Nutzbarkeit des Bodenphosphors und zur Bewertung der Bodenuntersuchung -

Availability of Phosphate Reserves in Arable Soils - Long Term Field Experiments for Assessing Soil P Reserves and Critical Soil Test Values - The objective of this work is to quantify the plant availability of soil P reserves accumulated by former fertilizer applications, the possibility of utilizing them by arable field crops and to determine critical soil test values. For this purpose several long term field experiments with large plots without replicates were initiated in 1977 on luvisols from loess (pH 6.8 – 7.4) in Lower Saxony with a sugar beet - winter wheat - winter barley/winter wheat crop rotation. Annual P applications were 0, 45, 90, 135 and 180 kg P₂O₅/ha as triple phosphate. Application of other fertilizers and plot management were according to farmer's practice. Despite of high yield levels phosphate response of plants was only 2 % at its maximum in the average of all crops in 15 years. This was confirmed by small plot experiments with four replicates placed into the large plots after 9 years, when soil P levels had been differentiated under the influence of plant P removal and P application. Herewith in agreement, shoot P concentration was found within the range generally regarded sufficient. It is therefore concluded that plant P demand has been fully satisfied by soil P reserves. Soil P test values, monitored by the P(H₂O) method of Sissingh, decreased markedly in 15 years, when no P was applied, they remained approximately constant when P application was equal to P removal and they increased when P addition was higher than P removal. Plants on a site with 4 mg P(H₂O)/L initially had severe P deficiency. Maximum yield was obtained when the soil P level was raised to 11 mg P(H₂O)/L. It is concluded that P reserves, which are often high in German arable soils, can be utilized by field crops and thus be lowered to about 10 mg P(H₂O)/L by reducing or omitting P dressings. For practical purposes it is suggested to restrict P application, if necessary at all, to the sugar beet crop in the rotation because they often respond more than small grain.     

Arsenic speciation in farmed Hungarian freshwater fish

Arsenic speciation analysis was carried out on freshwater farmed fish collected from an area with elevated groundwater arsenic concentrations in Hungary as well as from outside of the area (control samples). The arsenic species were determined by high-performance liquid chromatography-inductively coupled plasma mass spectrometry on methanol extracts of the muscle tissue from the fish. Catfish (Claries gariepinus) were raised in geothermal water where the average total arsenic concentrations were 167 (contaminated sites) and 15.1 ng As mL(-1) (control); they were all fed an artificial diet containing 2880 microg As kg(-1) total arsenic, mostly present as arsenobetaine. In the catfish, the accumulated total arsenic (2510-4720 microg As kg(-1)) was found mostly in the form of arsenobetaine suggesting that uptake of arsenic was dominated by their diet. Carp (Cyprinus carpio) were cultured in surface lakes with no significant arsenic pollution and had total arsenic concentrations ranging from 62 to 363 microg As kg(-1). The arsenic species found in the carp extracts differed markedly from those in the catfish in that no arsenobetaine was detected. Most samples of carp from the investigated sites contained low concentrations of As(III) (arsenite), As(V) (arsenate), MA (methylarsonate), and DMA (dimethylarsinate), and no other compounds were detected. The four individuals from the control site, however, all contained appreciable levels of oxo-arsenosugar-glycerol and oxo-arsenosugar-phosphate. Indeed, the oxo-arsenosugar-phosphate dominated the speciation pattern for these carp contributing about 75% of the sum of species. The contrast between these two freshwater aquaculture species regarding total arsenic and arsenic species has relevant toxicological aspects in terms of food safety.     

Manganese uptake and Mn efficiency of wheat cultivars are related to Mn‐uptake kinetics and root growth

Wheat cultivars differ widely in manganese (Mn) efficiency. To investigate the reasons for different Mn efficiencies, a pot experiment with soil, a solution‐culture experiment, and model calculations were carried out. The pot experiment was conducted with wheat (Triticum aestivum L. cvs. PBW 373, PBW 154, PBW 343, PBW 138, and Triticum durum L. cvs. PBW 34 and PDW 233) grown in a screen house in India. The soil was a loamy sand with pH 8.1, DTPA‐extractable Mn 1.62 mg (kg soil)^–1, and initial soil solution Mn concentration (C_Li) of 0.19 μM. When fertilized with 50 mg Mn (kg soil)^–1, C_Li increased to 0.32 μM. At C_Li 0.19 μM, wheat cv. PBW 373 produced 74% of its maximum shoot dry weight (SDW) with 64% of its maximum root length (RL), while cv. PDW 233 produced only 25% of its maximum SDW with 11% of its maximum RL. The other wheat cultivars were between these extremes. Manganese deficiency caused a reduction in shoot growth, but more strongly reduced root growth. The low Mn efficiency of T. durum cv. PDW 233 was related to a strong depression of its root growth. Manganese influx was similar for all cultivars. In solution culture below 1 μM Mn, under controlled climate‐chamber conditions, Mn influx was linearly related to Mn concentration. Both the efficient cv. PBW 343 and the inefficient cv. PDW 233 had a similar influx. Uptake kinetic parameters from the solution experiment together with soil and plant parameters from the pot experiment were used in a mechanistic nutrient‐uptake model. Calculated values of Mn influx for wheat grown in soil were 55% to 74% of measured values. A sensitivity analysis showed that increasing C_Li or the slope of the uptake isotherm by about 30% would be enough to reach the observed influx. The results of this research indicate that an increase of Mn solubility by microbial or chemical mobilization would increase Mn uptake. But on the other hand, no chemical mobilization would be required to increase Mn uptake if the plant improved its uptake kinetics. Low Mn efficiency of some wheat cultivars was related to their reduced root growth at low soil Mn supply.     

Evolution of clinical, haematological and biochemical findings in young dogs naturally infected by vector-borne pathogens

Longitudinal studies evaluating the evolution of clinical, haematological, biochemical findings in young dogs exposed for the first time to multiple vector-borne pathogens have not been reported. With the objective of assessing the evolution of clinical, haematological and biochemical findings, these parameters were serially monitored in naturally infected dogs throughout a 1-year follow-up period. Young dogs, infected by vector-borne pathogens based on cytology or polymerase chain reaction, were examined clinically and blood samples were obtained at seven different follow-up time points. Dogs were randomized to group A (17 dogs treated with a spot-on formulation of imidacloprid 10% and permethrin 50%) or to group B (17 dogs untreated). In addition, 10 4-month-old beagles were enrolled in each group and used as sentinel dogs. At baseline, Anaplasma platys was the most frequently detected pathogen, followed by Babesia vogeli, Bartonella spp., Ehrlichia canis and Hepatozoon canis. Co-infections with A. platys and B. vogeli, followed by E. canis and B. vogeli, A. platys and H. canis and A. platys and Bartonella spp. were also diagnosed. In dogs from group B, abnormal clinical signs were recorded at different time points throughout the study. No abnormal clinical signs were recorded in group A dogs. Thrombocytopenia was the most frequent haematological alteration recorded in A. platys-infected dogs, B. vogeli-infected dogs and in dogs co-infected with A. platys and B. vogeli or A. platys and Bartonella spp. Lymphocytosis was frequently detected among dogs infected with B. vogeli or co-infected with A. platys and B. vogeli. Beagles were often infected with a single pathogen rather than with multiple canine vector-borne pathogens. There was a significant association (p<0.01) between tick infestation and A. platys or B. vogeli, as single infections, and A. platys and B. vogeli or A. platys and Bartonella spp. co-infections. This study emphasizes the clinical difficulties associated with assigning a specific clinical sign or haematological abnormality to a particular canine vector-borne disease.