Production of molecular hydrogen with immobilized cells ofRhodospirillum rubrum

Summary Cells ofRhodospirillum rubrum have been immobilized in various gels and tested for photobiological hydrogen production. Agar proved to be the best immobilizing agent with respect to production rates as well as stability. Agar immobilized cells were also superior compared to liquid suspension cultures. Growth conditions of the cells prior to immobilization, e.g. cell age, light intensity or nutrient composition, were of primary importance for the activity in the later immobilized state. A reactor with agar immobilized cells has been operated successfully over 3000 h with a loss of the activity of about 60%. Mean rates for hydrogen production for immobilized cells in this work during the first 60 to 70 hours after immobilization were in the range of 18 to 34 μl H₂ mg⁻¹ d.w. h⁻¹ and thus by a factor of up to 2 higher than liquid cultures under the same conditions. Maximal rates of hydrogen production (57 μl H₂ ml⁻¹ immobilized cell suspension) were reached in agar gel beads with cells immobilized after 70 h growth in liquid culture in the light and a cell density of 1.0 mg ml⁻¹, 70 h after immobilization.     

Quantification of ortholog losses in insects and vertebrates

Background  

The increasing number of sequenced insect and vertebrate genomes of variable divergence enables refined comparative analyses to quantify the major modes of animal genome evolution and allows tracing of gene genealogy (orthology) and pinpointing of gene extinctions (losses), which can reveal lineage-specific traits.     

Changes in temperature sensitivity of spring phenology with recent climate warming in Switzerland are related to shifts of the preseason

The spring phenology of plants in temperate regions strongly responds to spring temperatures. Climate warming has caused substantial phenological advances in the past, but trends to be expected in the future are uncertain. A simple indicator is temperature sensitivity, the phenological advance statistically associated with a 1°C warmer mean temperature during the “preseason”, defined as the most temperature‐sensitive period preceding the phenological event. Recent analyses of phenological records have shown a decline in temperature sensitivity of leaf unfolding, but underlying mechanisms were not clear. Here, we propose that climate warming can reduce temperature sensitivity simply by reducing the length of the preseason due to faster bud development during this time period, unless the entire preseason shifts forward so that its temperature does not change. We derive these predictions theoretically from the widely used “thermal time model” for bud development and test them using data for 19 phenological events recorded in 1970–2012 at 108 stations spanning a 1600 m altitudinal range in Switzerland. We consider how temperature sensitivity, preseason start, preseason length and preseason temperature change (i) with altitude, (ii) between the periods 1970–1987 and 1995–2012, which differed mainly in spring temperatures, and (iii) between two non‐consecutive sets of 18 years that differed mainly in winter temperatures. On average, temperature sensitivity increased with altitude (colder climate) and was reduced in years with warmer springs, but not in years with warmer winters. These trends also varied among species. Decreasing temperature sensitivity in warmer springs was associated with a limited forward shift of preseason start, higher temperatures during the preseason and reduced preseason length, but not with reduced winter chilling. Our results imply that declining temperature sensitivity can result directly from spring warming and does not necessarily indicate altered physiological responses or stronger constraints such as reduced winter chilling.     

A focal adhesion factor directly linking intracellularly motile Listeria monocytogenes and Listeria ivanovii to the actin-based cytoskeleton of mammalian cells.

The surface-bound ActA polypeptide of the intracellular bacterial pathogen Listeria monocytogenes is the sole listerial factor needed for recruitment of host actin filaments by intracellularly motile bacteria. Here we report that following Listeria infection the host vasodilator-stimulated phosphoprotein (VASP), a microfilament- and focal adhesion-associated substrate of both the cAMP- and cGMP-dependent protein kinases, accumulates on the surface of intracytoplasmic bacteria prior to the detection of F-actin 'clouds'. VASP remains associated with the surface of highly motile bacteria, where it is polarly located, juxtaposed between one extremity of the bacterial surface and the front of the actin comet tail. Since actin filament polymerization occurs only at the very front of the tail, VASP exhibits properties of a host protein required to promote actin polymerization. Purified VASP binds directly to the ActA polypeptide in vitro. A ligand-overlay blot using purified radiolabelled VASP enabled us to identify the ActA homologue of the related intracellular motile pathogen, Listeria ivanovii, as a protein with a molecular mass of approximately 150 kDa. VASP also associates with actin filaments recruited by another intracellularly motile bacterial pathogen, Shigella flexneri. Hence, by the simple expedient of expressing surface-bound attractor molecules, bacterial pathogens effectively harness cytoskeletal components to achieve intracellular movement.     

Full-length prion protein aggregates to amyloid fibrils and spherical particles by distinct pathways

As limited structural information is available on prion protein (PrP) misfolding and aggregation, a causative link between the specific (supra)molecular structure of PrP and transmissible spongiform encephalopathies remains to be elucidated. In this study, high pressure was utilized, as an approach to perturb protein structure, to characterize different morphological and structural PrP aggregates. It was shown that full-length recombinant PrP undergoes beta-sheet aggregation on high-pressure-induced destabilization. By tuning the physicochemical conditions, the assembly process evolves through two distinct pathways leading to the irreversible formation of spherical particles or amyloid fibrils, respectively. When the PrP aggregation propensity is enhanced, high pressure induces the formation of a partially unfolded aggregated protein, Agg(HP), which relaxes at ambient pressure to form amorphous aggregates. The latter largely retain the native secondary structure. On prolonged incubation at high pressure, followed by depressurization, Agg(HP) transforms to a monodisperse population of spherical particles of about 20 nm in diameter, characterized by an essentially beta-sheet secondary structure. When the PrP aggregation propensity is decreased, an oligomeric reaction intermediate, I(HP), is formed under high pressure. After pressure release, I(HP) relaxes to the original native structure. However, on prolonged incubation at high pressure and subsequent depressurization, it transforms to amyloid fibrils. Structural evaluation, using optical spectroscopic methods, demonstrates that the conformation adopted by the subfibrillar oligomeric intermediate, I(HP), constitutes a necessary prerequisite for the formation of amyloids. The use of high-pressure perturbation thus provides an insight into the molecular mechanism of the first stages of PrP misfolding into amyloids.     

Loss of Kindlin-1 Causes Skin Atrophy and Lethal Neonatal Intestinal Epithelial Dysfunction

Kindler Syndrome (KS), characterized by transient skin blistering followed by abnormal pigmentation, skin atrophy, and skin cancer, is caused by mutations in the FERMT1 gene. Although a few KS patients have been reported to also develop ulcerative colitis (UC), a causal link to the FERMT1 gene mutation is unknown. The FERMT1 gene product belongs to a family of focal adhesion proteins (Kindlin-1, -2, -3) that bind several β integrin cytoplasmic domains. Here, we show that deleting Kindlin-1 in mice gives rise to skin atrophy and an intestinal epithelial dysfunction with similarities to human UC. This intestinal dysfunction results in perinatal lethality and is triggered by defective intestinal epithelial cell integrin activation, leading to detachment of this barrier followed by a destructive inflammatory response.