Transport at the nanoscale: temperature dependence of ion conductance

Temperature dependent ion conductance in nanopores is measured in a wide range of electrolyte concentrations and compared with molecular modeling. Single outer membrane protein F (OmpF) channels from E. coli are reconstituted into planar lipid bilayers. In qualitative agreement with the experimental data, applied-field molecular dynamics unraveled atomistic details of the ion transport. Comparing the temperature dependence of the channel conductance with that of the bulk conductivity in the range from 0 to 90°C revealed that at low salt concentrations the transport is mainly driven along the pore surface. Increasing the salt concentration saturates the surface charge transport and induces ion transport in the center of the nanopore. The confinement of the nanopore then favors the formation of ion pairs. Stepping up the temperature reduces the life time of the ion pairs and increases the channel conductance more than expected from the bulk behavior.     

The effect of strain rate on the mechanical properties of human cortical bone

Bone mechanical properties are typically evaluated at relatively low strain rates. However, the strain rate related to traumatic failure is likely to be orders of magnitude higher and this higher strain rate is likely to affect the mechanical properties. Previous work reporting on the effect of strain rate on the mechanical properties of bone predominantly used nonhuman bone. In the work reported here, the effect of strain rate on the tensile and compressive properties of human bone was investigated. Human femoral cortical bone was tested longitudinally at strain rates ranging between 0.14-29.1 s(-1) in compression and 0.08-17 s(-1) in tension. Young's modulus generally increased, across this strain rate range, for both tension and compression. Strength and strain (at maximum load) increased slightly in compression and decreased (for strain rates beyond 1 s(-1)) in tension. Stress and strain at yield decreased (for strain rates beyond 1 s(-1)) for both tension and compression. In general, there seemed to be a relatively simple linear relationship between yield properties and strain rate, but the relationships between postyield properties and strain rate were more complicated and indicated that strain rate has a stronger effect on postyield deformation than on initiation of yielding. The behavior seen in compression is broadly in agreement with past literature, while the behavior observed in tension may be explained by a ductile to brittle transition of bone at moderate to high strain rates.     

<Emphasis Type="Italic">Paenibacillus</Emphasis>—a predominant endophytic bacterium colonising tissue cultures of woody plants

High densities of endophytic bacteria were found in plant material from poplar, larch and spruce that had been micropropagated for at least 5 years. The majority of these bacteria were assigned to the genus Paenibacillus based on the sequencing of the 16S rRNA genes. Other endophytic bacteria such as Methylobacterium, Stenotrophomonas or Bacillus could also be found but only in some tissue cultures. Certain species or strains of Paenibacillus, especially those with a close relationship to P. humicus, seemed to accumulate under in vitro conditions without visible negative influences on the plant’s development. Poplar microcuttings inoculated with the endophytic Paenibacillus isolate 22 showed significantly more roots per cutting and higher root length in comparison to the control plants after 3 weeks.     

Pigs’ preferences for rooting materials measured in a three-choice maze-test

The aim of this experiment was to investigate pigs’ preferences for rooting materials. Eighteen materials were allocated to six categories each of which consisted of three similar materials based on characteristics such as structure, size of particles, complexity, destructibility and digestibility. Twelve pairs of pigs chose among the three materials of each of the six categories in a balanced design. Within each category each pair was given four instantaneous choices among the three materials in a three-armed maze. ‘No choice’ was scored if the pigs did not enter one of the maze-arms within 90 s. Thus there were four options in each choice situation. The results were analysed using a random utility model incorporating random intercepts to account for the repeated testing of the same animals. The pigs expressed clear preferences within the category EARTH, where compost and peat were preferred to wood-shavings and no choice. In the category CHIP the most probable rank-order was spruce chip, willow chip, fir chip and no choice, while in the category ROUGH the most probable rank-order was maize-silage, grass silage, sugar beets and no choice. However, in these two categories none of the probabilities were sufficiently large to signify a preference for any of the three materials although the probabilities of the ‘no choice’ option were low. The pigs expressed no preferences among any of the four options including ‘no choice’ in the categories TOY (sisal robe, Bite-Rite, wooden beam), HAY (alfalfa hay mixed with straw, seed grass hay, barley straw with under-seed), and STRAW (long straw, chopped straw and straw pellets).     

Comparative analysis of selenocysteine machinery and selenoproteome gene expression in mouse brain identifies neurons as key functional sites of selenium in mammals

Although dietary selenium (Se) deficiency results in phenotypes associated with selenoprotein depletion in various organs, the brain is protected from Se loss. To address the basis for the critical role of Se in brain function, we carried out comparative gene expression analyses for the complete selenoproteome and associated biosynthetic factors. Using the Allen Brain Atlas, we evaluated 159 regions of adult mouse brain and provided experimental analyses of selected selenoproteins. All 24 selenoprotein mRNAs were expressed in the mouse brain. Most strikingly, neurons in olfactory bulb, hippocampus, cerebral cortex, and cerebellar cortex were exceptionally rich in selenoprotein gene expression, in particular in GPx4, SelK, SelM, SelW, and Sep15. Over half of the selenoprotein genes were also expressed in the choroid plexus. A unique expression pattern was observed for one of the highly expressed selenoprotein genes, SelP, which we suggest to provide neurons with Se. Cluster analysis of the expression data linked certain selenoproteins and selenocysteine machinery genes and suggested functional linkages among selenoproteins, such as that between SelM and Sep15. Overall, this study suggests that the main functions of selenium in mammals are confined to certain neurons in the brain.     

The role of nonhomologous end joining and homologous recombination in the clonogenic bystander effects of mammalian cells after exposure to counted 10 MeV protons and 4.5 MeV α-particles of the PTB microbeam

We have studied the dependence of clonogenic bystander effects on defects in the pathways of DNA double-strand break (DSB) repair and on linear energy transfer (LET). The single-ion microbeam of the Physikalisch-Technische Bundesanstalt (PTB) was used to irradiate parental Chinese hamster ovary cells or derivatives deficient in nonhomologous end joining (NHEJ) or homologous recombination (HR) in the G1-phase of the cell cycle. Cell nuclei were targeted with 10 MeV protons (LET = 4.7 keV/μm) or 4.5 MeV α-particles (LET = 100 keV/μm). During exposure, the cells were confluent, allowing signal transfer through both gap junctions and diffusion. When all cell nuclei were targeted with 10 MeV protons, approximately exponential survival curves were obtained for all three cell lines. When only 10% of all cell nuclei were targeted, a significant bystander effect was observed for parental and HR-deficient cells, but not for NHEJ-deficient cells. For all three cell lines, the survival data after exposure of all cell nuclei to 4.5 MeV α-particles could be fitted by exponential curves. When only 10% of all cell nuclei were targeted, significant bystander effects were obtained for parental and HR-deficient cells, whereas for NHEJ-deficient cells a small, but significant, bystander effect was observed only at higher doses. The data suggest that bystander cell killing is a consequence of un- or misrejoined DSB which occur in bystander cells during the S-phase as a result of the processing of oxidative bistranded DNA lesions. The relative contributions of NHEJ and HR to the repairing of DSB in the late S/G2-phase may affect clonogenic bystander effects.