Effect of nutrient enrichment on the distribution and sedimentation of polychlorinated biphenyls (PCBs) in seawater

The effect of nutrient enrichment on the distribution of polychlorinated biphenyl's (PCBs) in the microbial food web and the residence time of PCBs in seawater was studied in an experimental mesocosm system. Two 5 m high temperature and light controlled mesocosm tubes (⊘ = 0,5 m) were filled with seawater from the northern Baltic Sea. Inorganic phosphorus and nitrogen were added daily to one mesocosm, while the other served as a control. Experiments were conducted at 5, 10 and 20°>C. Three ¹⁴C-labelled PCBs of different degree of chlorination were added to subsamples of the mesocosms: 4 chlorobiphenyl (MCB), IUPAC # 3; 2,2′,5,5′-tetrachlorobiphenyl (TCB), IUPAC # 52 and 2,2′, 4,4′,5,5′-hexachlorobiphenyl (HCB) IUPAC # 153. The biomasses and growth rates of the microorganisms as well as the sedimentation rate of particulate organic material increased with nutrient enrichment. The size distribution of the microorganisms changed with nutrient status, from dominance of picoplankton (< 2 μm) in the control towards increased importance of micro (> 10 μm) and nanoplankton (2– 10 μm) in nutrient enrichment. The specific growth rate of the bacterial community was found to be more temperature dependent than that of the phytoplankton community. The relative proportion of PCBs in the >2 μm fraction was observed to be in the order MCB < TCB < HCB, while the opposite distribution prevailed in the < 2 μm fraction. We hypothesize that this is due to the combined effect of the different Kow values of the PCBs and a different composition of the particulate organic carbon in the > 2 μm and < 2 μm fractions (e.g. different lipid composition). The residence time of the PCBs in the mesocosm generally decreased with nutrient enrichment, but was dependent on the degree of chlorination of the PCB. Our results indicate that the transport of organic pollutants up through the food web is more important in nutrient poor than in nutrient rich waters and that the importance of sedimentation is higher in eutrophic ecosystems. This revised version was published online in July 2006 with corrections to the Cover Date.     

Evidence for a nutritional disorder of Oxalis acetosella L. on acid forest soils; II. Diagnostic field experiments and nutrient solution studies

Different field experiments were performed to discover the main factor(s) responsible for the poor leaf growth, moderate propagation and leaf chlorosis of Oxalis acetosella in an old Norway spruce stand with acid soil (Höglwald Forest). A previous study had suggested, that Ca (or Mg) deficiency or Mn toxicity could be involved.In a Main Diagnostic Field Experiment with an intact population, Ca and Mg were either applied as sulphate or carbonate to distinguish between nutritional and pH effects. Mn and Si were also applied to aggravate or overcome possible effects of Mn toxicity. Enhancement experiments with different amounts of CaSO₄ were conducted to investigate the Ca dose-effect relationship under field conditions. Additional trials with SrCO₃, BaCO₃ and NaHCO₃ had the goal to raise the soil pH without supply of nutrients.Greenhouse experiments with Oxalis acetosella supplemented the field studies by investigating the Ca and Mn dose-effect relationships under controlled conditions. Growth, vitality and nutrition of Oxalis were studied in a nutrient solution culture at pH 4.0 over a range of concentrations of Ca (20 to 5000 mol L_-1) and Mn (5 to 1000 mol L_-1) respectively. Furthermore, the effects of two contrasting ammonium/nitrate ratios were tested. The nutritional composition of the basal nutrient solution and the microclimate in the greenhouse were as far as possible adjusted to the environmental conditions of the plant in the Höglwald Forest.All these studies led to the conclusion, that the moderate growth and vitality of Oxalis in the Höglwald Forest was mainly due to an insufficient Ca supply, rather than an effect of Mg deficiency, low soil pH or Mn toxicity. The application of CaSO₄ caused a similar stimulation of the growth as CaCO₃. A clearly positive, close CaSO₄ dose-effect relationship was detected in field experiments as well as in the nutrient solution study. The same type of leaf chloroses as in the field was reproduced through low Ca nutrient solutions. Predominant ammonium nutrition may significantly impair Ca uptake.Oxalis acetosella displayed a relatively high leaf tissue tolerance of excessive Mn. There was no indication for a Mn-induced Ca deficiency in the Höglwald Forest. Enhanced Si uptake led to a partial vitalization of Oxalis; the reason for that remained unclear.     

Sequential resonance assignment of medium-sized15 N/13C-labeled proteins with projected 4D triple resonance NMR experiments

We recently introduced a new line of reduced-dimensionality experiments making constructive use of axial peak magnetization, which has so far been suppressed as an undesirable artifact in multidimensional NMR spectra [Szyperski, T., Braun, D., Banecki, B. and Wüthrich, K. (1996) J. Am. Chem. Soc., 118, 8146–8147]. The peaks arising from the axial magnetization are located at the center of the doublets resulting from projection. Here we describe the use of such projected four-dimensional (4D) triple resonance experiments for the efficient sequential resonance assignment of ¹⁵N/¹³C-labeled proteins. A 3D ^{/ /}(CO)NHN experiment is recorded either in conjunction with 3D HNN< > or with the newly presented 3D HNN scheme. The first combination yields sequential assignments based on the measurement of¹³ C chemical shifts and provides a complete ¹H, ¹³C and ¹⁵N resonance assignment of polypeptide backbone and CH_n moieties. When employing the second combination, ¹³C=O chemical shifts are not measured, but the sequential assignment relies on both ¹³C and¹ H chemical shifts. The assignment is performed in a semi-automatic fashion using the program XEASY in conjunction with the newly implemented program SPSCAN. This program package offers routines for the facile mutual interconversion of single-quantum and zero/double-quantum frequencies detected in conventional and reduced-dimensionality spectra, respectively. In particular, SPSCAN comprises a peak picking routine tailored to cope with the distinct peak patterns of projected NMR experiments performed with simultaneous acquisition of central peaks. Data were acquired at 13 °C for the N-terminal 63-residue polypeptide fragment of the 434 repressor. Analysis of these spectra, which are representative for proteins of about 15 kDa when working at commonly used temperatures around 30 °C , demonstrates the efficiency of our approach for the assignment of medium-sized¹⁵ N/¹³C doubly labeled proteins.     

Transgenic Melon and Squash Expressing Coat Protein Genes of Aphid-borne Viruses do not Assist the Spread of an Aphid Non- transmissible Strain of Cucumber Mosaic Virus in the Field

Transgenic melon and squash containing the coat protein (CP) gene of the aphid transmissible strain WL of cucumber mosaic cucumovirus (CMV) were grown under field conditions to determine if they would assist the spread of the aphid non-transmissible strain C of CMV, possibly through heterologous encapsidation and recombination. Transgenic melon were susceptible to CMV strain C whereas transgenic squash were resistant although the latter occasionally developed chlorotic blotches on lower leaves. Transgenic squash line ZW-20, one of the parents of commercialized cultivar Freedom II, which expresses the CP genes of the aphid transmissible strains FL of zucchini yellow mosaic (ZYMV) and watermelon mosaic virus 2 (WMV 2) potyviruses was also tested. Line ZW-20 is resistant to ZYMV and WMV 2 but is susceptible to CMV. Field experiments conducted over two consecutive years showed that aphid-vectored spread of CMV strain C did not occur from any of the CMV strain C-challenge inoculated transgenic plants to any of the uninoculated CMV-susceptible non- transgenic plants. Although CMV was detected in 3% (22/764) of the uninoculated plants, several assays including ELISA, RT- PCR-RFLP, identification of CP amino acid at position 168, and aphid transmission tests demonstrated that these CMV isolates were distinct from strain C. Instead, they were non-targeted CMV isolates that came from outside the field plots. This is the first report on field experiments designed to determine the potential of transgenic plants expressing CP genes for triggering changes in virus-vector specificity. Our results indicate that transgenic plants expressing CP genes of aphid transmissible strains of CMV, ZYMV, and WMV 2 are unlikely to mediate the spread of aphid non-transmissible strains of CMV. This finding is of practical relevance because transgenic crops expressing the three CP genes are targeted for commercial release, and because CMV is economically important, has a wide host range, and is widespread worldwide.     

Daily and seasonal CO2 exchange in Scots pine grown under elevated O3 and CO2: experiment and simulation

Starting in early spring of 1994, naturally regenerated, 30-year-old Scots pine (Pinus sylvestris L.) trees were grown in open-top chambers and exposed in situ to doubled ambient O₃,doubled ambient CO₂ and a combination of O₃ and CO₂ from 15 April to 15 September. To investigate daily and seasonal responses of CO₂ exchange to elevated O₃ and CO₂, the CO₂ exchange of shoots was measured continuously by an automatic system for measuring gas exchange during the course of one year (from 1 Januray to 31 December 1996). A process-based model of shoot photosynthesis was constructed to quantify modifications in the intrinsic capacity of photosynthesis and stomatal conductance by simulating the daily CO₂ exchange data from the field. Results showed that on most days of the year the model simulated well the daily course of shoot photosynthesis. Elevated O₃ significantly decreased photosynthetic capacity and stomatal conductance during the whole photosynthetic period. Elevated O₃ also led to a delay in onset of photosynthetic recovery in early spring and an increase in the sensitivity of photosynthesis to environmental stress conditions. The combination of elevated O₃ and CO₂ had an effect on photosynthesis and stomatal conductance similar to that of elevated O₃ alone, but significantly reduced the O₃-induced depression of photosynthesis. Elevated CO₂ significantly increased the photosynthetic capacity of Scots pine during the main growing season but slightly decreased it in early spring and late autumn. The model calculation showed that, compared to the control treatment, elevated O₃ alone and the combination of elevated O₃ and CO₂ decreased the annual total of net photosynthesis per unit leaf area by 55% and 38%, respectively. Elevated CO₂ increased the annual total of net photosynthesis by 13%.     

EVIDENCE FOR IMPACTS OF NONINDIGENOUS MACROALGAE: A META‐ANALYSIS OF EXPERIMENTAL FIELD STUDIES1

Invasions by nonindigenous macroalgal species (NIMS) potentially cause severe impacts on native species. We conducted a meta‐analysis of 18 field‐based manipulative experiments to quantify the direction and magnitude of impacts (Hedges effect size d, hereafter ES). We found significant small‐to‐medium negative effects on “macrophyte abundance” (cover, biomass of native taxa; ES_cumulative = ?0.30) and medium‐to‐large negative effects on “macrophyte assemblages” (richness, diversity, total abundance; ES_cumulative = ?0.70). In contrast, ES_cumulative were not significant for “macrophyte processes” (growth, mortality; ES_cumulative = ?0.39), “animal abundance” (densities; ES_cumulative = ?0.13), or “animal assemblages” (richness, diversity; ES_cumulative = 0.75). The nonsignificant effect sizes were characterized by low sample sizes and should be interpreted with caution. Three study‐specific effect sizes were particularly large (cumulative are likely biased toward larger effects because only the most conspicuous NIMS have been tested and because nonsignificant results are less likely to be published. To better understand the impacts of NIMS, more manipulative experiments are needed, testing more species and under contrasting environmental conditions. Future studies should include procedural control treatments and report the abundance of the NIMS to avoid ambiguous interpretations. In conclusion, current experimental evidence shows that NIMS have, on average, small‐to‐large negative impacts on native plant species and assemblages. It is possible that these effects can result in severe consequences when accumulated over long time periods and large spatial scales.     

Sampling of intracellular metabolites for stationary and non-stationary C metabolic flux analysis in Escherichia coli

The analysis of metabolic intermediates is a rich source of isotopic information for ¹³C metabolic flux analysis (¹³C-MFA) and extends the range of its applications. The sampling of labeled metabolic intermediates is particularly important to obtain reliable isotopic information. The assessment of the different sampling procedures commonly used to generate such data, therefore, is crucial. In this work, we thoroughly evaluated several sampling procedures for stationary and non-stationary ¹³C-MFA using Escherichia coli. We first analyzed the efficiency of these procedures for quenching metabolism and found that procedures based on cold or boiling solvents are reliable, in contrast to fast filtration, which is not. We also showed that separating the cells from the broth is not necessary in isotopic stationary state conditions. On the other hand, we demonstrated that the presence of metabolic intermediates outside the cells strongly affects the transient isotopic data monitored during non-stationary ¹³C-labeling experiments. Meaningful isotopic data can be obtained by recovering intracellular labeled metabolites from pellets of cells centrifuged in cold solvent. We showed that if the intracellular pools are not separated from the extracellular ones, accurate flux maps can be established provided that the contribution of exogenous compounds is taken into account in the metabolic flux model.     

Developments from analysis of variance through to generalized linear models and beyond

The collaborations between statisticians and biologists during the 100 years since AAB was founded have led to a very impressive list of statistical techniques, whose use now goes well beyond agriculture and biology. One example is the maximum likelihood methodology for probit analysis, arising from the collaboration between Sir Ronald Fisher and Chester Bliss. Others include analysis of variance, design of experiments, generalized linear models and the residual, or restricted, maximum likelihood (REML) algorithm for fitting unbalanced linear mixed models.     

HYBRIDIZATION,NATURAL SELECTION,AND EVOLUTION OF REPRODUCTIVE ISOLATION: A 25‐YEARS SURVEY OF AN ARTIFICIAL SYMPATRIC AREA BETWEEN TWO MOSQUITO SIBLING SPECIES OF THE Aedes mariae COMPLEX

Natural selection can act against maladaptive hybridization between co‐occurring divergent populations leading to evolution of reproductive isolation among them. A critical unanswered question about this process that provides a basis for the theory of speciation by reinforcement, is whether natural selection can cause hybridization rates to evolve to zero. Here, we investigated this issue in two sibling mosquitoes species, Aedes mariae and Aedes zammitii, that show postmating reproductive isolation (F1 males sterile) and partial premating isolation (different height of mating swarms) that could be reinforced by natural selection against hybridization. In 1986, we created an artificial sympatric area between the two species and sampled about 20,000 individuals over the following 25 years. Between 1986 and 2011, the composition of mating swarms and the hybridization rate between the two species were investigated across time in the sympatric area. Our results showed that A. mariae and A. zammitii have not completed reproductive isolation since their first contact in the artificial sympatric area. We have discussed the relative role of factors such as time of contact, gene flow, strength of natural selection, and biological mechanisms causing prezygotic isolation to explain the observed results.     

Preanalytical standardization for reactive oxygen species derived oxysterol analysis in human plasma by liquid chromatography–tandem mass spectrometry

The analysis of the oxysterols 7-keto-, 7-α/β-hydroxy-, 5α,6α-epoxy-, 5β,6β-epoxycholesterol and cholestane-3β,5α,6β-triol derived from reactive oxygen species (ROS) is of interest as biomarkers in the field of atherosclerosis. Preanalytical validation is a crucial point to minimize the susceptibility of oxysterols to in vitro autoxidation. The aim of this study was to standardize a preanalytical protocol for ROS-derived oxysterol analysis by liquid chromatography–tandem mass spectrometry in human plasma.