Inorganic ions in cold-hardiness

Cold exposure and freezing may affect ion distribution in several ways and reduce physiologically important ionic gradients. Both freeze-avoiding and freeze-tolerant organisms have developed mechanisms to handle this stress. Supercooled insects seem to be able to maintain their ionic gradients even at temperatures far below zero. When freeze-tolerant insects freeze, ions diffuse down their concentration gradients across the cell membranes and reach electrochemical equilibrium. They quickly reverse this transmembrane diffusion when they are thawed. Trace metals may affect mechanisms for cold-hardening in different ways and reduce cold-hardiness. Freezing may give rise to toxic concentrations of metal ions, and freeze-tolerant organisms probably need to inactivate toxic trace metals. Ice nucleating agents may be important in this context.     

Sensitivity of human embryonic stem cells to different conditions during cryopreservation

Low cell recovery rate of human embryonic stem cells (hESCs) resulting from cryopreservation damages leads to the difficulty in their successful commercialization of clinical applications. Hence in this study, sensitivity of human embryonic stem cells (hESCs) to different cooling rates, ice seeding and cryoprotective agent (CPA) types was compared and cell viability and recovery after cryopreservation under different cooling conditions were assessed. Both extracellular and intracellular ice formation were observed. Reactive oxidative species (ROS) accumulation of hESCs was determined. Cryopreservation of hESCs at 1 °C/min with the ice seeding and at the theoretically predicted optimal cooling rate (TPOCR) led to lower level of intracellular ROS, and prevented irregular and big ice clump formation compared with cryopreservation at 1 °C/min. This strategy further resulted in a significant increase in the hESC recovery when glycerol and 1,2-propanediol were used as the CPAs, but no increase for Me₂SO. hESCs after cryopreservation under all the tested conditions still maintained their pluripotency. Our results provide guidance for improving the hESC cryopreservation recovery through the combination of CPA type, cooling rate and ice seeding.     

The distribution,structure, and composition of freshwater ice deposits in Bolivian salt lakes

Freshwater ice deposits are described from seven, high elevation (4117–4730 m), shallow (mean depth <30 cm), saline (10–103 g l^-1) lakes in the southwestern corner of Bolivia. The ice deposits range to several hundred meters in length and to 7 m in height above the lake or playa surface. They are located near the lake or salar margins; some are completely surrounded by water, others by playa deposits or salt crusts. Upper surfaces and sides of the ice deposits usually are covered by 20–40 cm of white to light brown, dry sedimentary materials. Calcite is the dominant crystalline mineral in these, and amorphous materials such as diatom frustules and volcanic glass are also often abundant.Beneath the dry overburden the ice occurs primarily as horizontal lenses 1–1000 mm thick, irregularly alternating with strata of frozen sedimentary materials. Ice represents from 10 to 87% of the volume of the deposits and yields freshwater (TFR <3 g l^-1) when melted. Oxygen isotope ratios for ice are similar to those for regional precipitation and shoreline seeps but much lower than those for the lakewaters. Geothermal flux is high in the region as evidenced by numerous hot springs and deep (3.0–3.5 m) sediment temperatures of 5–10°C. This flux is one cause of the present gradual wasting away of these deposits. Mean annual air temperatures for the different lakes probably are all in the range of -2 to 4°C, and mean midwinter temperatures about 5°C lower. These deposits apparently formed during colder climatic conditions by the freezing of low salinity porewaters and the building up of segregation ice lenses.     

Ice-shell purification of ice-binding proteins

Ice-affinity purification is a simple and efficient method of purifying to homogeneity both natural and recombinant ice-binding proteins. The purification involves the incorporation of ice-binding proteins into slowly-growing ice and the exclusion of other proteins and solutes. In previous approaches, the ice was grown around a hollow brass finger through which coolant was circulated. We describe here an easily-constructed apparatus that employs ice affinity purification that not only shortens the time for purification from 1–2 days to 1–2 h, but also enhances yield and purity. In this apparatus, the surface area for the separation was increased by extracting the ice-binding proteins into an ice-shell formed inside a rotating round-bottom flask partially submerged in a sub-zero bath. In principle, any ice-binding compound can be recovered from liquid solution, and the method is readily scalable.     

Perturbation of bacterial ice nucleation activity by a grass antifreeze protein

Certain plant-associating bacteria produce ice nucleation proteins (INPs) which allow the crystallization of water at high subzero temperatures. Many of these microbes are considered plant pathogens since the formed ice can damage tissues, allowing access to nutrients. Intriguingly, certain plants that host these bacteria synthesize antifreeze proteins (AFPs). Once freezing has occurred, plant AFPs likely function to inhibit the growth of large damaging ice crystals. However, we postulated that such AFPs might also serve as defensive mechanisms against bacterial-mediated ice nucleation. Recombinant AFP derived from the perennial ryegrass Lolium perenne (LpAFP) was combined with INP preparations originating from the grass epiphyte, Pseudomonas syringae. The presence of INPs had no effect on AFP activity, including thermal hysteresis and ice recrystallization inhibition. Strikingly, the ice nucleation point of the INP was depressed up to 1.9 °C in the presence of LpAFP, but a recombinant fish AFP did not lower the INP-imposed freezing point. Assays with mutant LpAFPs and the visualization of bacterially-displayed fluorescent plant AFP suggest that INP and LpAFP can interact. Thus, we postulate that in addition to controlling ice growth, plant AFPs may also function as a defensive strategy against the damaging effects of ice-nucleating bacteria.     

Thermodynamic aspects of vitrification

Vitrification is a process in which a liquid begins to behave as a solid during cooling without any substantial change in molecular arrangement or thermodynamic state variables. The physical phenomenon of vitrification is relevant to both cryopreservation by freezing, in which cells survive in glass between ice crystals, and cryopreservation by vitrification in which a whole sample is vitrified. The change from liquid to solid behavior is called the glass transition. It is coincident with liquid viscosity reaching 10¹³ Poise during cooling, which corresponds to a shear stress relaxation time of several minutes. The glass transition can be understood on a molecular level as a loss of rotational and translational degrees of freedom over a particular measurement timescale, leaving only bond vibration within a fixed molecular structure. Reduced freedom of molecular movement results in decreased heat capacity and thermal expansivity in glass relative to the liquid state. In cryoprotectant solutions, the change from liquid to solid properties happens over a ∼10 °C temperature interval centered on a glass transition temperature, typically near −120 °C (±10 °C) for solutions used for vitrification. Loss of freedom to quickly rearrange molecular position causes liquids to depart from thermodynamic equilibrium as they turn into a glass during vitrification. Residual molecular mobility below the glass transition temperature allows glass to very slowly contract, release heat, and decrease entropy during relaxation toward equilibrium. Although diffusion is practically non-existent below the glass transition temperature, small local movements of molecules related to relaxation have consequences for cryobiology. In particular, ice nucleation in supercooled vitrification solutions occurs at remarkable speed until at least 15 °C below the glass transition temperature.     

Carbon burial over the last four millennia is regulated by both climatic and land use change

Carbon sequestration by sediments and vegetated marine systems contributes to atmospheric carbon drawdown, but little empirical evidence is available to help separate the effects of climate change and other anthropogenic activities on carbon burial over centennial timescales. We used marine sediment organic carbon to determine the role of historic climate variability and human habitation in carbon burial over the past 5,071 years. There was centennial‐scale sensitivity of carbon supply and burial to climatic variability, with Little Ice Age cooling causing an abrupt ecosystem shift and an increase in marine carbon contributions compared to terrestrial carbon. Although land use changes during the late 1800s did not cause marked alteration in average carbon burial, they did lead to marked increases in the spatial variability of carbon burial. Thus, while carbon burial by vegetated systems is expected to increase with projected climate warming over the coming century, ecosystem restructuring caused by abrupt climate change may produce unexpected change in carbon burial whose variability is also modulated by land use change.     

Effects of harvest dates on microbial communities of ice grape skins from Xinjiang of China

Ice wine is a sweet dessert wine made from pressing grapes naturally frozen on the vines. The structure and metabolic characteristics of native microbial community dominated by organics and nutrients transformation in fermenting process of ice wine on the grape skin are likely to change due to climate events. Our objective was to evaluate the influence of harvest time on structure and metabolic characteristics of bacterial and fungal communities on Vidal ice grape surface. Vidal grape samples were picked between October and December in 2018; Harvest 1 (VG1): 14 October; Harvest 2 (VG2): 16 November; Harvest 3 (VG3): 18 December. Vishniacozyma, Alternaria, Cladosporium, Stenotrophomonas, unidentified_Cyanobacteria and Sphingomonas existed in all harvest dates and were the main genera widespread in most grape samples from the three harvest periods. Saprotrophic fungi and bacteria involved in metabolism were also dominant. For fungi, wood saprotrophs and unidentified saprotrophs were detected comprising Phoma, Didymella, Filobasidium and Clavaria. Delayed harvest of ice grapes has a distinct advantage for pathogen reduction compared with that of normally harvested grapes. Among bacteria, the most frequently occurring types in the metabolism category were energy metabolism, carbohydrate metabolism and lipid metabolism. In short, the harvest period can positively regulate the function of Vidal ice grape epidermal microorganisms.     

Genome wide gene-expression analysis of facultative reproductive diapause in the two-spotted spider mite Tetranychus urticae

Background

Diapause or developmental arrest, is one of the major adaptations that allows mites and insects to survive unfavorable conditions. Diapause evokes a number of physiological, morphological and molecular modifications. In general, diapause is characterized by a suppression of the metabolism, change in behavior, increased stress tolerance and often by the synthesis of cryoprotectants. At the molecular level, diapause is less studied but characterized by a complex and regulated change in gene-expression. The spider mite Tetranychus urticae is a serious polyphagous pest that exhibits a reproductive facultative diapause, which allows it to survive winter conditions. Diapausing mites turn deeply orange in color, stop feeding and do not lay eggs.

Results

We investigated essential physiological processes in diapausing mites by studying genome-wide expression changes, using a custom built microarray. Analysis of this dataset showed that a remarkable number, 11% of the total number of predicted T. urticae genes, were differentially expressed. Gene Ontology analysis revealed that many metabolic pathways were affected in diapausing females. Genes related to digestion and detoxification, cryoprotection, carotenoid synthesis and the organization of the cytoskeleton were profoundly influenced by the state of diapause. Furthermore, we identified and analyzed an unique class of putative antifreeze proteins that were highly upregulated in diapausing females. We also further confirmed the involvement of horizontally transferred carotenoid synthesis genes in diapause and different color morphs of T. urticae.

Conclusions

This study offers the first in-depth analysis of genome-wide gene-expression patterns related to diapause in a member of the Chelicerata, and further adds to our understanding of the overall strategies of diapause in arthropods.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-14-815) contains supplementary material, which is available to authorized users.     

THE COMPETITIVE DEMANDS OF ELITE MALE RINK HOCKEY

The aim of this study was to simulate the activity pattern of rink hockey by designing a specific skate test (ST) to study the energy expenditure and metabolic responses to this intermittent high-intensity exercise and extrapolate the results from the test to competition. Six rink hockey players performed, in three phases, the 20-metre multi-stage shuttle roller skate test, a tournament match and the ST. Heart rate was monitored in all three phases. Blood lactate, oxygen consumption, ventilation and respiratory exchange ratio were also recorded during the ST. Peak HR was 190.7±7.2 beats · min⁻¹. There were no differences in peak HR between the three tests. Mean HR was similar between the ST and the match (86% and 87% of HR_max, respectively). Peak and mean ventilation averaged 111.0±8.8 L · min⁻¹ and 70.3±14.0 L ^· min⁻¹ (60% of V_Emax), respectively. VO_2max was 56.3±8.4 mL · kg⁻¹ · min⁻¹, and mean oxygen consumption was 40.9±7.9 mL · kg^{−1 ·} min⁻¹ (70% of VO_2max). Maximum blood lactate concentration was 7.2±1.3 mmol · L-1. ST yielded an energy expenditure of 899.1±232.9 kJ, and energy power was 59.9±15.5 kJ · min⁻¹. These findings suggest that the ST is suitable for estimating the physiological demands of competitive rink hockey, which places a heavy demand on the aerobic and anaerobic systems, and requires high energy consumption.