Frequency, timing, extent, and size of winter thaw-refreeze events in Alaska 2001–2008 detected by remotely sensed microwave backscatter data

Creation of ice layers in snow due to thaw-refreeze events can lock away winter forage, preventing access by large mammals and causing population declines. Data are limited, however, on the frequency, timing, extent, and size of thaw-refreeze events in northern latitudes given the area’s remoteness and paucity of weather stations. We used a remote sensing approach to detect thaw-refreeze events in Alaska during winter between 2001 and 2008. We also compared these results to a regional climate reanalysis dataset that identified rain events (freezing and non-freezing rain). All areas of the state, except high elevation sites, had ≥1 thaw-refreeze event during the study period. Southwestern Alaska had the highest frequency of thaw-refreeze events with an average of >4 events each winter, whereas northern Alaska had the lowest frequency with an average of <2 events. We observed substantial inter-annual variation in the distribution and frequency of thaw-refreeze events. For most of the state, thaw-refreeze occurred at similar rates each winter month, except in northern Alaska where thaw-refreeze events were most frequent in early and later winter. The median extent of individual thaw-refreeze events was 469 km², however, events in the interior of the state tended to be larger. Remotely sensed thaw-refreeze detections generally had low correspondence with observations from the climate reanalysis dataset. Our results support the use of remotely sensed data to identify thaw-refreeze events.     

New insights into the membrane-binding and activation mechanism of pyruvate oxidase from Escherichia coli

Pyruvate oxidase from Escherichia coli (EcPOX) is a thiamin diphosphate- (ThDP) and FAD-dependent peripheral membrane protein that carries out the irreversible oxidative decarboxylation of pyruvate to acetate and carbon dioxide. Concomitant two-electron reduction of the flavin cofactor was suggested to induce a structural rearrangement of the C-terminus triggering recruitment of the protein from the cytosol to the cell membrane, where the electrons are eventually transferred to final electron acceptor ubiquinone 8. Binding to the membrane, or alternatively, mild proteolytic digestion leads to a multifold enhancement of both the catalytic activity and substrate affinity. Recent X-ray crystallographic studies on EcPOX in the resting state and on a C-terminal truncation variant mimicking the membrane-bound activated form have fueled our understanding of the membrane-binding mechanism and concomitant catalytic activation. In the resting state, the auto-inhibitory C-terminal membrane anchor adopts a half-barrel/helix fold that occludes the active site. Upon activation, the C-terminus is expelled and becomes structurally flexible thereby freeing the active site. Circular dichroism spectroscopic analysis revealed the isolated C-terminus to be disordered, however, formation of a helical structure was observed in the presence of micelles. Limited proteolysis experiments indicate that activation of EcPOX involves at least two sequential structural transitions: the first occurring after binding of pyruvate to ThDP and the second after two-electron reduction of the flavin.     

The Temperature Gradient-Forming Device,an Accessory Unit for Normal Light Microscopes To Study the Biology of Hyperthermophilic Microorganisms

To date, the behavior of hyperthermophilic microorganisms in their biotope has been studied only to a limited degree; this is especially true for motility. One reason for this lack of knowledge is the requirement for high-temperature microscopy—combined, in most cases, with the need for observations under strictly anaerobic conditions—for such studies. We have developed a custom-made, low-budget device that, for the first time, allows analyses in temperature gradients up to 40°C over a distance of just 2 cm (a biotope-relevant distance) with heating rates up to ∼5°C/s. Our temperature gradient-forming device can convert any upright light microscope into one that works at temperatures as high as 110°C. Data obtained by use of this apparatus show how very well hyperthermophiles are adapted to their biotope: they can react within seconds to elevated temperatures by starting motility—even after 9 months of storage in the cold. Using the temperature gradient-forming device, we determined the temperature ranges for swimming, and the swimming speeds, of 15 selected species of the genus Thermococcus within a few months, related these findings to the presence of cell surface appendages, and obtained the first evidence for thermotaxis in Archaea.     

Evidence of free fatty acid interdigitation in stratum corneum model membranes based on ceramide [AP] by deuterium labelling

This research paper provides direct evidence concerning the localisation of free fatty acids in stratum corneum lipid model membranes. We employed partially deuterated free fatty acids to gain further information about the assembly of a stratum corneum lipid model membrane based on a ceramide of the phytosphingosine-type (ceramide [AP]) with particular respect to the position of the deuterated groups of the free fatty acids. The application of behenic-22,22,22-d₃-acid and cerotic-12,12,13,13-d₄-acid confirmed that the short-chain ceramide [AP] forces the longer-chained free fatty acids to incorporate into the bilayer created by ceramide [AP]. The ceramide [AP] molecules determine the structural assembly of this model membrane and obligate the long-chain free fatty acids to either arrange inside this formation or to separate as a fatty acid rich phase.