Large 13C/12C and small 15N/14N isotope fractionation in an experimental detrital foodweb (litter–fungi–collembolans)

Correctly estimating the trophic fractionation factors (Δ¹⁵N and Δ¹³C) in controlled laboratory conditions is essential for the application of stable isotope analysis in studies on the trophic structure of soil communities. Laboratory experiments usually suggest large ¹⁵N/¹⁴N and small ¹³C/¹²C trophic fractionation, but in field studies litter-dwelling microarthropods and other invertebrates are consistently enriched in ¹³C relative to plant litter. In the present study, we report data from two laboratory experiments investigating both fungi–collembolans and litter–fungi–collembolans systems. In the fungi–collembolans system, Δ¹⁵N and Δ¹³C averaged 1.4 ± 0.1 and 1.0 ± 0.2 ‰, respectively. In microcosms with fungi-inoculated litter, the difference in δ¹⁵N between collembolans and plant litter averaged 1.5 ± 0.2 ‰, confirming the relatively small ¹⁵N/¹⁴N trophic fractionation at the basal level of detrital foodwebs reported in numerous field studies. In full agreement with field observations, the difference in δ¹³C between bulk litter and collembolans in laboratory microcosms averaged 3.6 ± 0.1 ‰ and only little depended on collembolan species identities or the presence of water-soluble compounds in the litter. We conclude that increased δ¹³C values typical of litter-dwelling decomposers are largely determined by an increased ¹³C content in saprotrophic microorganisms.     

Improvement of collisionless particle confinement in a non-quasi-symmetric stellarator vacuum magnetic field

A non-quasi-symmetric stellarator vacuum magnetic field with an aspect ratio of about 11 is found in which collisionless particles are confined up to about 2/5 of the minor radius.     

High-CO2 tolerance in microalgae: possible mechanisms and implications for biotechnology and bioremediation

Recent developments in the field of microalgal biotechnology, including CO₂ biomitigation and the discovery of new species of microalgae that are tolerant to extremely high CO₂ levels (40–100 vol%), have renewed interest in the physiological effects and mechanisms of high-CO₂ tolerance in photoautotrophs. Photosynthetic apparatus state transitions that increase ATP generation, upregulation of H⁺-ATPases pumping protons out of the cell, rapid shutdown of CO₂-concentrating mechanisms, and adjustment of membranes’ fatty acid composition are currently believed to be the key mechanisms governing cellular pH homeostasis and hence microalgae’s tolerance to high CO₂ levels, which is especially characteristic of extremophile and symbiotic species. The mechanisms governing acclimation to high CO₂ comprise the subject of this review and are discussed in view of the use of CO₂ enrichment to increase the productivity of microalgal cultures, as well as the practice of carbon capture from flue gases.     

Epitope specificity of two anti‐morphine monoclonal antibodies: In vitro and in silico studies

Monoclonal antibodies (mAbs) against morphine are important in the development of immunotherapeutic and diagnostic methods for the treatment and prevention of drug addiction. By the surface plasmon resonance (SPR) and enzyme immunoassay techniques, we characterized two previously obtained mAbs 3K11 and 6G1 and showed their ability to recognize free morphine and morphine‐containing antigens in different ways because of the epitope specificity thereof. Using the defined amino acid sequences, we obtained three‐dimensional models of the variable regions of Fab fragments of these antibodies and compared them with the known sequence and spatial structure of the anti‐morphine antibody 9B1. Docking simulations are performed to obtain models of the antibodies complexes with morphine. Differences in the models of 3K11 and 6G1 complexes with morphine correlate with their experimentally detected epitope specificity. The results, in particular, can be used for the structure‐based design of the corresponding humanized antibodies. According to our modeling and docking results, the very different modes of morphine binding to mAbs 3K11 and 6G1 are qualitatively similar to those previously reported for cocaine and two anti‐cocaine antibodies. Thus, the obtained structural information brings more insight into the hapten recognition diversity.     

Artificial selection for increased dispersal results in lower fitness

Dispersal often covaries with other traits, and this covariation was shown to have a genetic basis. Here, we wanted to explore to what extent genetic constraints and correlational selection can explain patterns of covariation between dispersal and key life‐history traits—lifespan and reproduction. A prediction from the fitness‐associated dispersal hypothesis was that lower genetic quality is associated with higher dispersal propensity as driven by the benefits of genetic mixing. We wanted to contrast it with a prediction from a different model that individuals putting more emphasis on current rather than future reproduction disperse more, as they are expected to be more risk‐prone and exploratory. However, if dispersal has inherent costs, this will also result in a negative genetic correlation between higher rates of dispersal and some aspects of performance. To explore this issue, we used the dioecious nematode Caenorhabditis remanei and selected for increased and decreased dispersal propensity for 10 generations, followed by five generations of relaxed selection. Dispersal propensity responded to selection, and females from high‐dispersal lines dispersed more than females from low‐dispersal lines. Females selected for increased dispersal propensity produced fewer offspring and were more likely to die from matricide, which is associated with a low physiological condition in Caenorhabditis nematodes. There was no evidence for differences in age‐specific reproductive effort between high‐ and low‐dispersal females. Rather, reproductive output of high‐dispersal females was consistently reduced. We argue that our data provide support for the fitness‐associated dispersal hypothesis.     

Analysis of the time-resolved FTIR spectra produced by the photolysis of alkyl phenylglyoxylates.

The photochemistry of alkyl phenylglyoxylates (APG) was further investigated using time-resolved infrared spectroscopy. The primary focus was on the analysis of weak transient bands around 1828 and 1730 cm(-1) in the time-resolved FTIR spectra of glyoxylates. The observed transients were assigned to benzoyl and alkyl mandelate ester radicals, respectively. The formation of benzoyl radical was fast and attributed to the Norrish Type I process. In addition, the intensities of the strong FTIR bands around 1680 and 2100 cm(-1) were used to analyze the yields of the triplet state and ketene, respectively. These new and previous data on APG photochemistry are discussed in relation to the acrylate polymerization photoinitiation by alkyl phenylglyoxylates.     

Within-population variation in cytoplasmic genes affects female life span and aging in Drosophila melanogaster

It has been suggested that mitochondrial DNA (mtDNA) may play an important role in aging. Yet, few empirical studies have tested this hypothesis, partly because the degree of sequence polymorphism in mtDNA is assumed to be low. However, low sequence variation may not necessarily translate into low phenotypic variation. Here, we report an experiment that tests whether there is within-population variation in cytoplasmic genes for female longevity and senescence. To achieve this, we randomly selected 25 "mitochondrial founders" from a single, panmictic population of Drosophila melanogaster and used these founders to generate distinct "mt" lines in which we controlled for the nuclear background by successive backcrossing. Potential confounding effects of cytoplasmically transmitted bacteria were eliminated by tetracycline treatment. The mt lines were then assayed for differences in longevity, Gompertz intercept (frailty), and demographic rate of change in mortality with age (rate-of-senescence) in females. We found significant cytoplasmic effects on all three variables. This provides evidence that genetic variation in cytoplasmic genes, presumably mtDNA, contributes to variation in female mortality and aging.     

A unifying model for activity-dependent and activity-independent mechanisms predicts complete structure of topographic maps in ephrin-A deficient mice

Axons of retinal ganglion cells establish orderly projections to the superior colliculus of the midbrain. Axons of neighboring cells terminate proximally in the superior colliculus thus forming a topographically precise representation of the visual world. Coordinate axes are encoded in retina and in the target through graded expression of chemical labels. Additional sharpening of projections is provided by electric activity, which is correlated between neighboring axons. Here we propose a quantitative model, which allows combining the effects of chemical labels and correlated activity in a single approach. Using this model we study a complete structure of two-dimensional topographic maps in mutant mice, in which the label encoding the horizontal retinal coordinate ephrin-A is reduced/eliminated. We show that topographic maps in ephrin-A deficient mice display a granular structure, with the regions of smooth mapping separated by linear discontinuities reminiscent of fractures observed in the maps of preferred orientation. Action Editor: Jonathan D. Victor     

Activation of redox-systems of monocytes by hydrogen peroxide

In this work the influence of H2O2 on the ability of human blood monocytes to generate ROS upon stimulation of cells by adhesion to glass surface and fMLP was studied using the luminol-dependent chemiluminescence (LDCL) method. Pretreatment of cells with H2O2 increased the adhesiveness of monocytes and ROS generation. Superoxide generation by cells in response to fMLP depended on the duration of pretreatment and the concentration of H2O2. The stimulatory effect on fMLP-induced LDCL of cells further depended on the Ca2+ concentration in the medium and on the activities of phospholipase A2, cyclooxygenases, and Mek1/2.