Water is critical for the survival of most cells and organisms. Remarkably, a small number of multicellular animals are able to survive nearly complete drying. The phenomenon of anhydrobiosis, or ...life without water, has been of interest to researchers for over 300 years. In this review we discuss advances in our understanding of protectants and mechanisms of desiccation tolerance that have emerged from research in three anhydrobiotic invertebrates: brine shrimp (Artemia), roundworms (nematodes), and tardigrades (water bears). Discovery of molecular protectants that allow each of these three animals to survive drying diversifies our understanding of desiccation tolerance, and convergent themes suggest mechanisms that may offer a general model for engineering desiccation tolerance in other contexts.
We revisit the method of cumulants for analysing dynamic light scattering data in particle sizing applications. Here the data, in the form of the time correlation function of scattered light, is ...written as a series involving the first few cumulants (or moments) of the distribution of particle diffusion constants. Frisken (2001 Appl. Opt. 40 4087) has pointed out that, despite greater computational complexity, a non-linear, iterative, analysis of the data has advantages over the linear least-squares analysis used originally. In order to explore further the potential and limitations of cumulant methods we analyse, by both linear and non-linear methods, computer-generated data with realistic 'noise', where the parameters of the distribution can be set explicitly. We find that, with modern computers, non-linear analysis is straightforward and robust. The mean and variance of the distribution of diffusion constants can be obtained quite accurately for distributions of width (standard deviation/mean) up to about 0.6, but there appears to be little prospect of obtaining meaningful higher moments.
Colloidal PMMA particles and an interfacially assembled, pH-switchable lipid film (tetradecylammonium hydrogen phosphate, TAHP) were combined to form emulsion droplets with composite interfaces. Two ...time scales govern the interfacial structure and droplet size of the system: the rate of particle adsorption and the rate of film assembly. We tune these two time scales by varying the particle size (in the case of the particles) and aqueous pH (in the case of the lipid film). Three rates of film assembly are studied: rapid (pH 5), slow (pH 7), and inactive (pH 9). At pH 5, small droplets coated with a mixed interfacial structure are formed, and increasing particle volume fraction does not change the droplet size. At pH 7, the slowed kinetics of TAHP film assembly results in the particle size having a systematic effect upon droplet size: the smaller the particles, the smaller the droplets. At pH 9, TAHP plays no role in the system, and more familiar Pickering emulsions are observed. Finally, we show that at pH 5 both the interfacial particle density and droplet size can be readily tuned in our system. This suggests potential applications in the rational design of capsules and emulsion droplets with tunable interfacial structure.
Recent large-scale computer simulations suggest that it may be possible to create a new class of soft solids, called 'bijels', by stabilizing and arresting the bicontinuous interface in a binary ...liquid demixing via spinodal decomposition using particles that are neutrally wetted by both liquids. The interfacial layer of particles is expected to be semi-permeable; hence, if realized, these new materials would have many potential applications, for example, as micro-reaction media. However, the creation of bijels in the laboratory faces serious obstacles. In general, fast quench rates are necessary to bypass nucleation, so that only samples with limited thickness can be produced, which destroys the three-dimensionality of the putative bicontinuous network. Moreover, even a small degree of unequal wettability of the particles by the two liquids can lead to ill-characterized, 'lumpy' interfacial layers and therefore irreproducible material properties. Here, we report a reproducible protocol for creating three-dimensional samples of bijel in which the interfaces are stabilized by essentially a single layer of particles. We demonstrate how to tune the mean interfacial separation in these bijels, and show that mechanically, they indeed behave as soft solids. These characteristics and their tunability will be of great value for microfluidic applications.
Encysted embryos (cysts) of the primitive crustacean, Artemia franciscana, are among the most resistant of all animal life history stages to extremes of environmental stress. These embryos, ...extremophiles of the animal kingdom, are the main focus of this paper. Previous work has revealed the importance of biochemical and biophysical adaptations that provide a significant part of the basis of their resistance, and I consider some of these here. In the present paper the critical role played by the outer layer of the shell in desiccation tolerance will be one focus. Another involves studies on the response of dried cysts to high temperatures that, among other things, implicate one or more volatile factors released from the cysts that determines the extent of thermotolerance under a given heating regime. A hypothetical scheme is given to account for these peculiar results. Based on western immunoblotting analysis, and data from the literature, the scheme also implicates the heat-induced translocation of the stress protein p26 to nuclei as a potential cause of the reduction in hatching level.
Brine shrimp Artemia have an unequalled ability to endure extreme salinity and complete anoxia. This study aims to elucidate its strategies to cope with these stressors. Here, we present the genome ...of an inbred A. franciscana Kellogg, 1906. We identified 21,828 genes of which, under high salinity, 674 genes and under anoxia, 900 genes were differentially expressed (42%, respectively 30% were annotated). Under high salinity, relevant stress genes and pathways included several Heat Shock Protein and Leaf Embryogenesis Abundant genes, as well as the trehalose metabolism. In addition, based on differential gene expression analysis, it can be hypothesized that a high oxidative stress response and endocytosis/exocytosis are potential salt management strategies, in addition to the expression of major facilitator superfamily genes responsible for transmembrane ion transport. Under anoxia, genes involved in mitochondrial function, mTOR signalling and autophagy were differentially expressed. Both high salt and anoxia enhanced degradation of erroneous proteins and protein chaperoning. Compared with other branchiopod genomes, Artemia had 0.03% contracted and 6% expanded orthogroups, in which 14% of the genes were differentially expressed under high salinity or anoxia. One phospholipase D gene family, shown to be important in plant stress response, was uniquely present in both extremophiles Artemia and the tardigrade Hypsibius dujardini, yet not differentially expressed under the described experimental conditions. A relatively complete genome of Artemia was assembled, annotated and analysed, facilitating research on its extremophile features, and providing a reference sequence for crustacean research.
We study the response of a film of colloidal spherocylinders to compression by combining pressure-area isotherm measurements, microscopy, and computer simulations. We find that the behavior of the ...film depends strongly on the geometry of the particles. For a small aspect ratio, a uniform monolayer forms and then buckles. For a higher aspect ratio, particles flip to orient perpendicular to the interface; we show that flipping occurs in locations where the nematic ordering is low. Our experiments and simulations further demonstrate that the longest particles rearrange to self-assemble a colloidal bilayer, which is stable due to the unique geometry of spherocylinders at an interface.
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