Publications

Biofilms are aggregates of cells that form on surfaces or at the air-water interface. Cells in a biofilm are encased in a self-secreted extracellular matrix (ECM) that provides them with mechanical stability and protects them from antibiotic treatment. From a soft matter perspective, biofilms are regarded as colloidal hydrogels, with the cells playing the role of colloids and the ECM compared with a cross-linked hydrogel. Here, we examined whole biofilms of the soil bacterium Bacillus subtilis utilizing methods that are commonly used to characterize hydrogels in order to evaluate the uptake of water and the water properties in the biofilms. Specifically, we studied wild-type as well ECM mutants, lacking the protein TasA and the exopolysaccharide (EPS). We characterized the morphology and mesh size of biofilms using electron microscopy, studied the state of water in the biofilms using differential scanning calorimetry, and finally, we tested the biofilms' swelling properties. Our study revealed that Bacillus subtilis biofilms resemble cross-linked hydrogels is their morphology and swelling properties. Strikingly, we discovered that all the water in biofilms was bound water and there was no free water in the biofilms. Water binding was mostly related with the presence of solutes and much less so with the major ECM components, the protein TasA and the polysaccharide EPS. This study sheds light on water uptake and water binding in biofilms and it is therefore important for the understanding of solute transport and enzymatic function inside biofilms.

Shared attention experiments examine the potential differences in function or behavior when stimuli are experienced alone or in the presence of others, and when simultaneous attention of the participants to the same stimulus or set is involved. Previous work has found enhanced reactions to emotional stimuli in social situations, yet these changes might represent enhanced communicative or motivational purposes. This study examines whether viewing emotional stimuli in the presence of another person influences attention to or memory for the stimulus. Participants passively viewed emotionally-valenced stimuli while completing another task (counting flowers). Each participant performed this task both alone and in a shared attention condition (simultaneously with another person in the same room) while EEG signals were measured. Recognition of the emotional pictures was later measured. A significant shared attention behavioral effect was found in the attention task but not in the recognition task. Compared to event-related potential responses for neutral pictures, we found higher P3b response for task relevant stimuli (flowers), and higher Late Positive Potential (LPP) responses for emotional stimuli. However, no main effect was found for shared attention between presence conditions. To conclude, shared attention may therefore have a more limited effect on cognitive processes than previously suggested.

Simulations and experiments of nanorods (NRs) show that co-assembly with block copolymer (BCP) melts leads to the formation of a superstructure of side-to-side NRs perpendicular to the lamellar axis. A mesoscopic model is validated against scanning electron microscopy (SEM) images of CdSe NRs mixed with polystyrene-block-poly(methyl methacrylate). It is then used to study the co-assembly of anisotropic nanoparticles (NPs) with a length in the same order of magnitude as the lamellar spacing. The phase diagram of BCP/NP is explored as well as the time evolution of the NR. NRs that are slightly larger than the lamellar spacing are found to rotate and organize side-to-side with a tilted orientation with respect to the interface. Strongly interacting NPs are found to dominate the co-assembly, while weakly interacting nanoparticles are less prone to form aggregates and tend to form well-ordered configurations.

Evolutionary transitions to a social lifestyle in insects are associated with lineage-specific changes in gene expression, but the key nodes that drive these regulatory changes are unknown. We examined the relationship between social organization and lineage-specific microRNAs (miRNAs). Genome scans across 12 bee species showed that miRNA copy-number is mostly conserved and not associated with sociality. However, deep sequencing of small RNAs in six bee species revealed a substantial proportion (20-35%) of detected miRNAs had lineage-specific expression in the brain, 24-72% of which did not have homologs in other species. Lineage-specific miRNAs disproportionately target lineage-specific genes, and have lower expression levels than shared miRNAs. The predicted targets of lineage-specific miRNAs are not enriched for genes with caste-biased expression or genes under positive selection in social species. Together, these results suggest that novel miRNAs may coevolve with novel genes, and thus contribute to lineage-specific patterns of evolution in bees, but do not appear to have significant influence on social evolution. Our analyses also support the hypothesis that many new miRNAs are purged by selection due to deleterious effects on mRNA targets, and suggest genome structure is not as influential in regulating bee miRNA evolution as has been shown for mammalian miRNAs.

Photocleavage from polystyrene beads is a pivotal reaction for solid phase synthesis that relies on photolabile linkers. Photocleavage from intact porous polystyrene beads is not optimal because light cannot penetrate into the beads and the surface area exposed to irradiation is limited. Thus, hazardous, technically challenging and expensive setups are used for photocleavage from intact beads. We developed a new concept in which grinding the beads during or prior to irradiation is employed as an essential part of the photocleavage process. By grinding the beads we are exposing more surface area to the light source, hence, photocleavage can be performed even using a simple benchtop LED setup. This approach proved very efficient for photocleavage of various model compounds including fully protected oligosaccharides.

What role do Brazil, Russia, India, China, and South Africa (BRICS) play in the global investment regime and what policies do they espouse? How can we account for similarities among and differences across these countries with respect to their approach to international investment agreements (IIAs) and investment arbitration? What are their implications for the future of this regime? This study addresses these questions by situating emerging market economies in the persistent North-South divide, that is endemic to the global politics of foreign direct investment (FDI). Surveying the policies of the five countries since the 1980s, it shows that all were initially motivated to provide foreign investors with protection against political risk in order to attract FDI. As their own position in the global economy has changed and the rules of the regime itself have evolved, the investment policies of the BRICS countries have transformed, albeit in distinct ways. China and, to a lesser extent, Russia appear broadly content with the current state of affairs. Brazil, India, and South Africa, on the other hand, seem to object to current rules, which they view as overly protective of foreign investors at the expense of host state regulatory space. I argue and show that two factors – the amount of FDI outflows and regime type – usefully account for the observed variation across BRICS' international investment policies, but that more research is needed to fully understand this matter. Regardless its sources, the diversity between the BRICS countries suggests that the prospects of them shaping the rules of the global investment regime, either individually or collectively, are rather bleak.  

The interaction between lipid membranes and ions is associated with a range of key physiological processes. Most earlier studies have focused on the interaction of lipids with cations, while the specific effects of the anions have been largely overlooked. Owing to dissolved atmospheric carbon dioxide, bicarbonate is an important ubiquitous anion in aqueous media. In this paper, we examined the effect of bicarbonate anions on the interactions between dipolar lipid membranes in the presence of previously adsorbed calcium cations. Using a combination of solution X-ray scattering, osmotic stress, and molecular dynamic simulations, we followed the interactions between 1,2-didodecanoyl-sn-glycero-3-phosphocholine (DLPC) lipid membranes that were dialyzed against CaCl₂ solutions in the presence and absence of bicarbonate anions. Calcium cations adsorbed onto DLPC membranes charge them and lead to their swelling. In the presence of bicarbonate anions, however, the calcium cations can tightly couple one dipolar DLPC membrane to the other and form a highly condensed and dehydrated lamellar phase with a repeat distance of 3.45±0.02 nm. Similar tight condensation and dehydration has only been observed between charged membranes in the presence of multivalent counterions. Bridging between bilayers by calcium bicarbonate complexes induced this arrangement. Furthermore, in this condensed phase the lipid molecules and the adsorbed ions were arranged in a 2D oblique lattice.

ABC importers are membrane proteins responsible for the transport of nutrients into the cells of prokaryotes. Although the structures of ABC importers vary, all contain four conserved domains: two nucleotide-binding domains (NBDs), which bind and hydrolyze ATP, and two transmembrane domains (TMDs), which help translocate the substrate. ABC importers are also dependent on an additional protein component, a high-affinity substrate-binding protein (SBP) that specifically binds the target ligand for delivery to the appropriate ABC transporter. AbnE is a SBP belonging to the ABC importer for arabino-oligosaccharides in the Gram-positive thermophilic bacterium Geobacillus stearothermophilus. Using isothermal titration calorimetry (ITC), purified AbnE was shown to bind medium-sized arabino-oligosaccharides, in the range of arabino-triose (A3) to arabino-octaose (A8), all with Kd values in the nanomolar range. We describe herein the 3D structure of AbnE in its closed conformation in complex with a wide range of arabino-oligosaccharide substrates (A2-A8). These structures provide the basis for the detailed structural analysis of the AbnE-sugar complexes, and together with complementary quantum chemical calculations, site-specific mutagenesis, and isothermal titration calorimetry (ITC) experiments, provide detailed insights into the AbnE-substrate interactions involved. Small-angle X-ray scattering (SAXS) experiments and normal mode analysis (NMA) are used to study the conformational changes of AbnE, and these data, taken together, suggest clues regarding its binding mode to the full ABC importer.

This paper introduces the Special Issue on Cascading Effects in Disaster Risk Management. It reviews the contributions and highlights their multi-disciplinary interpretations of cascades. It proceeds to discuss whether the on-going unfolding of the COVID-19 pandemic illustrates the cascades metaphor.

We present an economic definition of cascading effects of a disaster on the labor market over the medium to long term. Cascading effects are considered events that alter local amenities. In the context of the labor market, the standard conception of a cascade as a sequence of events that alter the capital stock, may not be very instructive as the immediate time horizon is not the relevant economic timeframe. We outline some of the theoretical implications arising from this definition and give them some intuition based on an agent based simulation model. The model is used to simulate two cascade-type scenarios following an earthquake in the city of Jerusalem. Results indicate that a strong cascading effect in the labor market depends on serious functional change in the physical environment i.e. land-use change. Flow-related changes in labor and population movement are less likely to create effects that cascade into other sub-markets. Implications of these findings point to the key role of labor mobility as workers seek solutions outside the area struck by disaster.

This paper examines reciprocal connections between the discussions on causation in philosophy and in linguistics. Philosophers occasionally seek insights from the linguistic literature on certain expressions, and linguists often rely on philosophers' analyses of causation, and assume that the relevant linguistic expressions denote philosophical concepts related to causation. Through the study of various semantic aspects of causative constructions, mainly targeting the nature of the dependency encoded in various linguistic constructions and the nature of the relata, this paper explores interfaces between the discussions in the two disciplines, and at the same time points to significant differences in their objects of investigation, in their methods and in their goals. Finally, the paper attempts to observe whether the disciplinary line is maintained, i.e. whether or not it is the case that metaphysical questions are examined as linguistic ones and vice versa.

Circadian rhythms of about a day are ubiquitous in animals and considered functionally significant. Honey bees show remarkable circadian plasticity that is related to the complex social organization of their societies. Forager bees show robust circadian rhythms that support time-compensated sun-compass navigation, dance communication and timing visits to flowers. Nest-dwelling nurse bees care for the young brood around the clock. Here, we review our current understanding of the molecular and neuroanatomical mechanisms underlying this remarkable natural plasticity in circadian rhythms.