Nucleating agents in the haemolymph of an intertidal mollusc tolerant to freezing

Ice in the intertidal: patterns and processes of freeze tolerance in intertidal invertebrates

Many intertidal invertebrates are freeze tolerant, meaning that they can survive ice formation within their body cavity. Freeze tolerance is a fascinating trait, and understanding its mechanisms is important for predicting the survival of intertidal animals during extreme cold weather events. In this Review, we bring together current research on the ecology, biochemistry and physiology of this group of freeze-tolerant organisms. We first introduce the ecology of the intertidal zone, then highlight the strong geographic and taxonomic biases within the current body of literature on this topic. Next, we detail current knowledge on the mechanisms of freeze tolerance used by intertidal invertebrates. Although the mechanisms of freeze tolerance in terrestrial arthropods have been well-explored, marine invertebrate freeze tolerance is less well understood and does not appear to work similarly because of the osmotic differences that come with living in seawater. Freeze tolerance mechanisms thought to be utilized by intertidal invertebrates include: (1) low molecular weight cryoprotectants, such as compatible osmolytes and anaerobic by-products; (2) high molecular weight cryoprotectants, such as ice-binding proteins; as well as (3) other molecular mechanisms involving heat shock proteins and aquaporins. Lastly, we describe untested hypotheses, methods and approaches that researchers can use to fill current knowledge gaps. Understanding the mechanisms and consequences of freeze tolerance in the intertidal zone has many important ecological implications, but also provides an opportunity to broaden our understanding of the mechanisms of freeze tolerance more generally.

Cellulose Nanocrystals Facilitate Needle-like Ice Crystal Growth and Modulate Molecular Targeted Ice Crystal Nucleation

Ice nucleators are of crucial and important implications in various fields including chemistry, climate, agriculture, and cryobiology. However, the complicated extract and biocompatibility of ice nucleators remain unresolved, and the mechanism of ice nucleation remains largely unknown. Herein, we show that natural nanocrystalline cellulose materials possess special properties to enhance ice nucleation and facilitate needle-like ice crystal growth. We reveal the molecular level mechanism that the efficient exposure of cellulose hydroxyl groups on (-110) surface leads to faster nucleation of water. We further design chitosan-decorated cellulose nanocrystals to accomplish molecular cryoablation in CD 44 high-expression cells; the cell viability shows more than ∼10 times decrease compared to cryoablation alone and does not show evident systematic toxicity. Collectively, our findings also offer improved knowledge in molecular level ice nucleation, which may benefit multiple research communities and disciplines.

Bio-inspired design of ice-retardant devices based on benthic marine invertebrates: the effect of surface texture

Growth of ice on surfaces poses a challenge for both organisms and for devices that come into contact with liquids below the freezing point. Resistance of some organisms to ice formation and growth, either in subtidal environments (e.g., Antarctic anchor ice), or in environments with moisture and cold air (e.g., plants, intertidal) begs examination of how this is accomplished. Several factors may be important in promoting or mitigating ice formation. As a start, here we examine the effect of surface texture alone. We tested four candidate surfaces, inspired by hard-shelled marine invertebrates and constructed using a three-dimensional printing process. We examined sub-polar marine organisms to develop sample textures and screened them for ice formation and accretion in submerged conditions using previous methods for comparison to data for Antarctic organisms. The sub-polar organisms tested were all found to form ice readily. We also screened artificial 3-D printed samples using the same previous methods, and developed a new test to examine ice formation from surface droplets as might be encountered in environments with moist, cold air. Despite limitations inherent to our techniques, it appears surface texture plays only a small role in delaying the onset of ice formation: a stripe feature (corresponding to patterning found on valves of blue mussels, Mytilus edulis, or on the spines of the Antarctic sea urchin Sterechinus neumayeri) slowed ice formation an average of 25% compared to a grid feature (corresponding to patterning found on sub-polar butterclams, Saxidomas nuttalli). The geometric dimensions of the features have only a small (∼6%) effect on ice formation. Surface texture affects ice formation, but does not explain by itself the large variation in ice formation and species-specific ice resistance observed in other work. This suggests future examination of other factors, such as material elastic properties and surface coatings, and their interaction with surface pattern.

Do ice nucleating lipoproteins protect frozen insects against toxic chemical agents?

As the body fluid of freeze-tolerant organisms freezes, solutes become concentrated in the gradually smaller unfrozen fluid fraction, and dissolved trace metals may reach toxic levels. A dialysis technique was used to investigate the metal binding capacity of the low density fraction of the hemolymph from the freeze tolerant beetle Phyto depressus. The low density fraction, assumed to contain the ice nucleating lipoproteins, showed approximately 100 times greater capacity to bind metals (Cd (2+), Cu (2+) and Zn (2+)) than the proteins albumin, hemoglobin and similar to metallothionein. The high metal binding capacity in the low density fraction raises the question if the ice nucleating lipoproteins might assist in detoxification of potentially toxic concentrations of metals that may occur when a large fraction of the bodyfluids of freeze tolerant insects freeze. This hypotheis is consistent with the fact that the lipoprotein ice nucleators are present in far greater amounts than required for ice nucleation, and also with the fact that the lipoprotein ice nucleators have a remarkably high content of amino acids with negatively charged residues that may act as metal binding sites.

Physiological and ecological significance of biological ice nucleators

When a pure water sample is cooled it can remain in the liquid state at temperatures well below its melting point (0 degrees C). The initiation of the transition from the liquid state to ice is called nucleation. Substances that facilitate this transition so that it takes place at a relatively high sub-zero temperature are called ice nucleators. Many living organisms produce ice nucleators. In some cases, plausible reasons for their production have been suggested. In bacteria, they could induce frost damage to their hosts, giving the bacteria access to nutrients. In freeze-tolerant animals, it has been suggested that ice nucleators help to control the ice formation so that it is tolerable to the animal. Such ice nucleators can be called adaptive ice nucleators. There are, however, also examples of ice nucleators in living organisms where the adaptive value is difficult to understand. These ice nucleators might be structures with functions other than facilitating ice formation. These structures might be called incidental ice nucleators.

Isolation and identification of an ice-nucleating bacterium from the gills of the intertidal bivalve mollusc Geukensia demissa

In the fall, freeze tolerant intertidal invertebrates usually produce ice-nucleating proteins that are secreted into the hemolymph. These proteins help protect against freeze damage by insuring that ice formation is limited to extracellular spaces. Geukensia demissa, a freeze tolerant, salt marsh bivalve mollusc was examined for the presence of ice nucleating proteins. The ice-nucleating temperature (INT) of the hemolymph was not significantly different from artificial seawater of the same salinity indicating the lack of an ice nucleating protein in the hemolymph. The palial fluid did have an elevated INT, indicating the presence of an ice nucleator. The INT of the palial fluid was significantly reduced by boiling and filtration through a 0.45-&mgr;m filter. High INT was also observed in the seawater associated with the bivalves, and was demonstrated in water samples collected from salt marshes but not sand and pebble beaches. Moreover, the INT of water samples collected from a salt marsh decreased in the summer. All of these data suggest that the ice-nucleating agents in the hemolymph and the seawater are ice-nucleating bacteria. One species of ice-nucleating bacteria, Pseudomonas fulva was isolated from the gills of Geukensia. These bacteria could perform the same function as hemolymph ice-nucleating proteins by limiting ice formation to extracellular compartments.

Ice nucleation and antinucleation in nature

Plants and ectothermic animals use a variety of substances and mechanisms to survive exposure to subfreezing temperatures. Proteinaceous ice nucleators trigger freezing at high subzero temperatures, either to provide cold protection from released heat of fusion or to establish a protective extracellular freezing in freeze-tolerant species. Freeze-avoiding species increase their supercooling potential by removing ice nucleators and accumulating polyols. Terrestrial invertebrates and polar marine fish stabilize their supercooled state by means of noncolligatively acting antifreeze proteins. Some organisms also depress their body fluid melting point to ambient temperature by evaporation and/or solute accumulation.

Biochemical modification of plasma ice nucleating activity in a freeze-tolerant frog

Recently, we reported the presence of ice nucleating activity, apparently proteinaceous, in the plasma of a freeze-tolerant frog, Rana sylvatica, collected in autumn and spring. Although this protein has not been purified, its ice nucleating behavior can act as an internal reference for tests that attempt to modify its ability to nucleate ice formation. If the addition of a chemical reagent alters the temperature of ice crystallization compared with the control, it can be assumed that protein modification may have occurred. The ice nucleating protein in R. sylvatica showed resistance to proteolysis with four different proteases although there was a significant reduction in the temperatures of nucleation with these treatments (ANOVA P less than 0.001). However, ice nucleating activity was lost when plasma was treated with the addition of urea or N-bromosuccinimide. Modification of protein sulphydryl groups with iodoacetamide did not affect the crystallization temperature (Tc) but treatment with iodoacetic acid resulted in a significant increase in Tc of plasma. An abrupt loss of ice nucleating ability was observed in plasma samples after heating above 87 degrees C. Anomalous potentiation of ice nucleating activity occurred when the plasma was heated to and held at temperatures between 67-75 degrees C.

Ice nucleating activity in the blood of the freeze-tolerant frog, Rana sylvatica

Although the presence of antifreeze and ice nucleating agents in the hemolymph of insects has been well documented, there have been no reports of either of these types of agent in vertebrates. The technique of differential scanning calorimetry was used to examine the blood, serum, and plasma of a freeze-tolerant frog, Rana sylvatica, for the presence of antifreeze protein activity. Results demonstrate the absence of antifreeze protein but the presence of an ice nucleating agent that may serve as a functional component of the overwintering strategy of this species. Ice nucleating activity was detected in samples of cell-free blood, serum, and plasma, suggesting that the agent is a soluble component and possibly plasma protein. To our knowledge, the identification of ice nucleating activity in this freeze-tolerant vertebrate is novel.

Cold adaptation in marine organisms

Animals from polar seas exhibit numerous so called resistance adaptations that serve to maintain homeostasis at low temperature and prevent lethal freezing injury. Specialization to temperatures at or below 0 degrees C is associated with an inability to survive at temperatures above 3-8 degrees C. Polar fish synthesize various types of glycoproteins or peptides to lower the freezing point of most extracellular fluid compartments in a non-colligative manner. Antifreeze production is seasonal in boreal species and is often initiated by environmental cues other than low temperature, particularly short day lengths. Most of the adaptations that enable intertidal invertebrates to survive freezing are associated with their ability to withstand ariel exposure. Unique adaptations for freezing avoidance include the synthesis of low molecular mass ice-nucleating proteins that control and induce extracellular ice-formation. Marine poikilotherms also exhibit a range of capacity adaptations that increase the rate of some physiological processes so as to partially compensate for the effects of low temperature. However, the rate of embryonic development in a diverse range of marine organisms shows no evidence of temperature compensation. This results in a significant lengthening of the time from fertilization to hatching in polar, relative to temperate, species. Some aspects of the physiology of polar marine species, such as low metabolic and slow growth rates, probably result from a combination of low temperature and other factors such as the highly seasonal nature of food supplies. Although neuromuscular function shows a partial capacity adaptation in Antarctic fish, maximum swimming speeds are lower than for temperate and tropical species, particularly for early stages in the life history.