Ice-active proteins from the Antarctic nematode Panagrolaimus davidi

A mutation to a fish ice-binding protein synthesized in transgenic Caenorhabditis elegans modulate its cold tolerance

A cryoprotectant known as ice-binding protein (IBP) is thought to facilitate the cold survival of plants, insects, and fungi. Here, we prepared a genetically modified Caenorhabditis elegans strain to synthesize fish-derived IBPs in its body wall muscles and examined whether the antifreeze activity modification of this IBP by point mutation affects the cold tolerance of this worm. We chose a 65-residue IBP identified from notched-fin eelpout, for which the replacement of the 20th alanine residue (A20) modifies its antifreeze activity. These mutant proteins are denoted A20L, A20G, A20T, A20V, and A20I along with the wild-type (WT) protein. We evaluated the survival rate (%) of the transgenic C. elegans that synthesized each IBP mutant following 24 h of preservation at -5, +2, and +5 °C. Significantly, a dramatic improvement in the survival rate was detected for the worms synthesizing the activity-enhanced mutants (A20T and A20I), especially at +2 °C. In contrast, the rate was not improved by the expression of the defective mutants (A20L, A20G, WT and A20V). The survival rate (%) probably correlates with the antifreeze activity of the IBP. These data suggest that IBP protects the cell membrane by employing its ice-binding mechanism, which ultimately improves the cold tolerance of an IBP-containing animal.

Antifreeze Proteins: A Tale of Evolution From Origin to Energy Applications

Icing and formation of ice crystals is a major obstacle against applications ranging from energy systems to transportation and aviation. Icing not only introduces excess thermal resistance, but it also reduces the safety in operating systems. Many organisms living under harsh climate and subzero temperature conditions have developed extraordinary survival strategies to avoid or delay ice crystal formation. There are several types of antifreeze glycoproteins with ice-binding ability to hamper ice growth, ice nucleation, and recrystallization. Scientists adopted similar approaches to utilize a new generation of engineered antifreeze and ice-binding proteins as bio cryoprotective agents for preservation and industrial applications. There are numerous types of antifreeze proteins (AFPs) categorized according to their structures and functions. The main challenge in employing such biomolecules on industrial surfaces is the stabilization/coating with high efficiency. In this review, we discuss various classes of antifreeze proteins. Our particular focus is on the elaboration of potential industrial applications of anti-freeze polypeptides.

Bioinspired materials and technology for advanced cryopreservation

Cryopreservation can help to meet the demand for biosamples of high medical value. However, it remains difficult to effectively cryopreserve some sensitive cells, tissues, and reproductive organs. A coordinated effort from the perspective of the whole frozen biological system is necessary to advance cryopreservation technology. Animals that survive in cold temperatures, such as hibernators and cold-tolerant insects, offer excellent natural models. Their anti-cold strategies, such as programmed suppression of metabolism and the synthesis of cryoprotectants (CPAs), warrant systematic study. Furthermore, the discovery and synthesis of metabolism-regulating and cryoprotective biomaterials, combined with biotechnological breakthroughs, can also promote the development of cryopreservation. Further advances in the quality and duration of biosample storage inspired by nature will promote the application of cryopreserved biosamples in clinical therapy.

Proteomics of intracellular freezing survival

Panagrolaimus sp. DAW1, a nematode cultured from the Antarctic, has the extraordinary physiological ability to survive total intracellular freezing throughout all of its compartments. While a few other organisms, all nematodes, have subsequently also been found to survive freezing in this manner, P. sp. DAW1 has so far shown the highest survival rates. In addition, P. sp. DAW1 is also, depending on the rate or extent of freezing, able to undergo cryoprotective dehydration. In this study, the proteome of P. sp DAW1 is explored, highlighting a number of differentially expressed proteins and pathways that occur when the nematodes undergo intracellular freezing. Among the strongest signals after being frozen is an upregulation of proteases and the downregulation of cytoskeletal and antioxidant activity, the latter possibly accumulated before freezing much in the way the sugar trehalose has been shown to be stored during acclimation.

Transcriptome analyses of Ditylenchus destructor in responses to cold and desiccation stress

The objective of this study was to identify molecular responses in Ditylenchus destructor to cold and desiccation by means of transcriptomes analyses. A total of 102,517 unigenes were obtained, with an average length of 1,076 bp, in which 58,453 (57%) had a functional annotation. A total of 1154 simple sequence repeats (SSRs) distributed over 1078 unigenes were detected. Gene expression profiles in response to cold and desiccation stress and the expression of specific stress-related genes were compared. Gene ontology analysis and pathway-based analysis were used to further investigate the functions of the differentially expressed genes. The reliability of the sequencing data was verified through quantitative real-time PCR analysis of 19 stress-related genes. RNA interference used to further assess the functions of the cold-related unigenes 15628 and 15596 showed that the knockdown of each of these genes led to decreased cold tolerance of D. destructor. Hence, this study revealed molecular processes and pathways active in cold- or dessication-treated nematodes. The transcriptome profiles presented in this study provide insight into the transcriptome complexity and will contribute to further understand stress tolerance in D. destructor.

Effect of freezing on the metabolic status of L3 larvae of Anisakis simplex s. s

The fish-borne parasite, Anisakis simplex s. s., triggers a disease called anisakiasis, that is associated with a gastrointestinal infection. The Anisakis is also associated with allergic response which may lead to anaphylactic shock. The A. simplex s. s. L3 larvae may be freeze tolerant despite when the nematodes will be cooled rapidly to -20 °C according to the sanitary authorities of the USA and the EU. The aim of this work was to study the metabolic status of A. simplex s. s. L3 larvae when frozen in terms of viability, expression of genes involved in the nematodes' survival of freezing, as well content of carbohydrates which play a cryoprotective role in thermal stress and are the main source of energy. The levels of trehalose were significantly higher after slow freezing treatment (p < .0001), than the fast freezing (p < .002). The lower temperatures induce changes, especially in trehalose synthesis gene expression, genes responsible for oxidative metabolism, and chaperone proteins, but we cannot state clearly whether these changes occur during freezing, or because they are already prevalent during cold acclimation. The induction of mentioned genes seems to be a common trait of both cold- and dehydration tolerance.

A comparison of low temperature biology of Pieris rapae from Ontario, Canada, and Yakutia, Far Eastern Russia

Low temperatures limit the distribution and abundance of ectotherms. However, many insects can survive low temperatures by employing one of two cold tolerance strategies: freeze avoidance or freeze tolerance. Very few species can employ both strategies, but those that do provide a rare opportunity to study the mechanisms that differentiate freeze tolerance and freeze avoidance. We showed that overwintering pupae of the cabbage white butterfly Pieris rapae can be freeze tolerant or freeze avoidant. Pupae from a population of P. rapae in northeastern Russia (Yakutsk) froze at c. -9.3 °C and were freeze-tolerant in 2002-2003 when overwintered outside. However, P. rapae from both Yakutsk and southern Canada (London) acclimated to milder laboratory conditions in 2014 and 2017 froze at lower temperatures (< -20 °C) and were freeze-avoidant. Summer-collected P. rapae larvae (collected in Yakutsk in 2016) were partially freeze-tolerant, and decreased the temperature at which they froze in response to starvation at mild low temperatures (4 °C) and repeated partial freezing events. By comparing similarly-acclimated P. rapae pupae from both populations, we identified molecules that may facilitate low temperature tolerance, including the hemolymph ice-binding molecules and several potential low molecular weight cryoprotectants. Pieris rapae from Yakutsk exhibited high physiological plasticity, accumulating cryoprotectants and almost doubling their hemolymph osmolality when supercooled to -15 °C for two weeks, while the London P. rapae population exhibited minimal plasticity. We hypothesize that physiological plasticity is an important adaptation to extreme low temperatures (i.e. in Yakutsk) and may facilitate the transition between freeze avoidance and freeze tolerance.

Expression of Ice-Binding Proteins in Caenorhabditis elegans Improves the Survival Rate upon Cold Shock and during Freezing

Ice-binding proteins (IBPs) are capable of binding ice crystals and inhibiting their growth at freezing temperatures. IBPs are also thought to stabilize the cell membrane at non-freezing temperatures near 0 °C. These two effects have been assumed to reduce cold- and freezing-induced damage to cells and tissues. However, knowledge regarding the effects of IBP on the living animals is limited. Here, we characterized the relationship between the IBP effects and the physiological role by using the nematode Caenorhabditis elegans. The expression of fish (NfeIBPs)- and fungus-derived IBPs (AnpIBPs and TisIBP8) in C. elegans improved its survival rate during exposure to 0 and −2 °C (cold shock) and −5 °C (freezing). The observed cold tolerance of C. elegans after cold shock is attributable to the stabilization of cell-membrane lipids with IBPs, and the freezing tolerance at −5 °C can be attributed to the inhibition of ice-crystal growth by the IBPs. Significantly, the survival rate of C. elegans at −5 °C was improved by expression of wild-type AnpIBP and maximized by that of TisIBP8, whereas it was lowered when a defective AnpIBP mutant was expressed. These results suggest that the ice-binding ability of IBP has a good correlation with the survival rate of C. elegans during freezing.

Laboratory acclimation to autumn-like conditions induces freeze tolerance in the spring field cricket Gryllus veletis (Orthoptera: Gryllidae)

Many temperate insects encounter temperatures low enough to freeze their body fluids. Remarkably, some insects are freeze-tolerant, surviving this internal ice formation. However, the mechanisms underlying freeze tolerance are not well-understood, in part due to a lack of tractable model organisms. We describe a novel laboratory model to study insect freeze tolerance, the spring field cricket Gryllus veletis (Orthopera: Gryllidae). Following acclimation to six weeks of decreasing temperature and photoperiod, G. veletis become freeze-tolerant, similar to those exposed to natural autumn conditions in London, Ontario, Canada. Acclimated crickets suppress their metabolic rate by c. 33%, and survive freezing for up to one week at -8 °C, and to temperatures as low as -12 °C. Freeze-tolerant G. veletis protect fat body cells from freeze injury in vivo, and fat body tissue from freeze-tolerant cricket survives brief freeze treatments when frozen ex vivo. Freeze-tolerant crickets freeze at c. -6 °C, which may be initiated by accumulation of ice-nucleating agents in hemolymph or gut tissue. Although we hypothesize that control of ice formation facilitates freeze tolerance, initiating ice formation at high subzero temperatures does not confer freeze tolerance on freeze-intolerant nymphs. Acclimation increases hemolymph osmolality from c. 400 to c. 650 mOsm, which may facilitate freeze tolerance by reducing ice content. Hemolymph ion concentrations do not change with acclimation, and we therefore predict that freeze-tolerant G. veletis elevate hemolymph osmolality by accumulating other molecules. Gryllus veletis is easily reared and manipulated in a controlled laboratory environment, and is therefore a suitable candidate for further investigating the mechanisms underlying freeze tolerance.

Investigating trehalose synthesis genes after cold acclimation in the Antarctic nematode Panagrolaimus sp. DAW1

Panagrolaimus sp. DAW1 is a freeze-tolerant Antarctic nematode which survives extensive intracellular ice formation. The molecular mechanisms of this extreme adaptation are still poorly understood. We recently showed that desiccation-enhanced RNA interference (RNAi) soaking can be used in conjunction with quantitative polymerase chain reaction (qPCR) to screen for phenotypes associated with reduced expression of candidate genes in Panagrolaimus sp. DAW1. Here, we present the use of this approach to investigate the role of trehalose synthesis genes in this remarkable organism. Previous studies have shown that acclimating Panagrolaimus sp. DAW1 at 5°C before freezing or desiccation substantially enhances survival. In this study, the expression of tps-2 and other genes associated with trehalose metabolism, as well as lea-1, hsp-70 and gpx-1, in cold-acclimated and non-acclimated nematodes was analyzed using qPCR. Pd-tps-2 and Pd-lea-1 were significantly upregulated after cold acclimation, indicating an inducible expression in the cold adaptation of Panagrolaimus sp. DAW1. The role of trehalose synthesis genes in Panagrolaimus sp. DAW1 was further investigated by RNAi. Compared to the controls, Pd-tps-2a(RNAi)-treated and cold-acclimated nematodes showed a significant decrease in mRNA, but no change in trehalose content or freezing survival. The involvement of two other trehalose synthesis genes (tps-2b and gob-1) was also investigated. These findings provide the first functional genomic investigation of trehalose synthesis genes in the non-model organism Panagrolaimus sp. DAW1. The presence of several trehalose synthesis genes with different RNAi sensitivities suggests the existence of multiple backup systems in Panagrolaimus sp. DAW1, underlining the importance of this sugar in preparation for freezing.

Summary: Functional genomics was used to investigate trehalose synthesis genes after cold acclimation in Panagrolaimus sp. DAW1, an Antarctic nematode with the ability to survive intracellular freezing.

Molecular snapshot of an intracellular freezing event in an Antarctic nematode

The Antarctic nematode, Panagrolaimus sp. DAW1 (formerly called Panagrolaimus davidi), is the best documented example of an organism able to survive intracellular ice formation in all of its compartments. Not only is it able to survive such extreme physiological disruption, but it is able to produce progeny once thawed from such a state. In addition, under slower rates, or less extreme degrees, of cooling, its body remains unfrozen and the vapour pressure difference between the supercooled body fluids and the surrounding ice leads to a process termed cryoprotective dehydration. In contrast to a fairly large body of work in building up our molecular understanding of cryoprotective dehydration, no comparable work has been undertaken on intracellular freezing. This paper describes an experiment subjecting cultures of Panagrolaimus sp. DAW1 to a range of temperatures including a rapid descent to -10 °C, in a medium just prior to, and after, freezing. Through deep sequencing of RNA libraries we have gained a snapshot of which genes are highly abundant when P. sp. DAW1 is undergoing an intracellular freezing event. The onset of freezing correlated with a high production of genes involved in cuticle formation and subsequently, after 24 h in a frozen state, protease production. In addition to the mapping of RNA sequencing, we have focused on a select set of genes arising both from the expression profiles, as well as implicated from other cold tolerance studies, to undertake qPCR. Among the most abundantly represented transcripts in the RNA mapping is the zinc-metalloenzyme, neprilysin, which also shows a particularly strong upregulated signal through qPCR once the nematodes have frozen.

Establishing RNAi in a Non-Model Organism: The Antarctic Nematode Panagrolaimus sp. DAW1

The Antarctic nematode Panagrolaimus sp. DAW1 is one of the only organisms known to survive extensive intracellular freezing throughout its tissues. Although the physiological mechanisms of this extreme adaptation are partly understood, the molecular mechanisms remain largely unknown. RNAi is a method that allows the examination of gene function in a direct, targeted manner, by knocking out specific mRNAs and revealing the effects on the phenotype. In this study we have explored the viability of RNAi in Panagrolaimus sp. DAW1. In the first trial, nematodes were fed E. coli expressing Panagrolaimus sp. DAW1 dsRNA of the embryonic lethal genes rps-2 and dhc, and the blister gene duox. Pd-rps-2(RNAi)-treated nematodes showed a significant decrease in larval hatching. However, qPCR showed no significant decrease in the amount of rps-2 mRNA in Pd-rps-2(RNAi)-treated animals. Several soaking protocols for dsRNA uptake were investigated using the fluorescent dye FITC. Desiccation-enhanced soaking showed the strongest uptake of FITC and resulted in a significant and consistent decrease of mRNA levels of two of the four tested genes (rps-2 and tps-2a), suggesting effective uptake of dsRNA-containing solution by the nematode. These findings suggest that RNAi by desiccation-enhanced soaking is viable in Panagrolaimus sp. DAW1 and provide the first functional genomic approach to investigate freezing tolerance in this non-model organism. RNAi, in conjunction with qPCR, can be used to screen for candidate genes involved in intracellular freezing tolerance in Panagrolaimus sp. DAW1.

Ice-Active Substances from the Infective Juveniles of the Freeze Tolerant Entomopathogenic Nematode, Steinernema feltiae

Steinernema feltiae is a moderately freezing tolerant nematode, that can withstand intracellular ice formation. We investigated recrystallization inhibition, thermal hysteresis and ice nucleation activities in the infective juveniles of S. feltiae. Both the splat cooling assay and optical recrystallometry indicate the presence of ice active substances that inhibit recrystallization in the nematode extract. The substance is relatively heat stable and largely retains the recrystallization inhibition activity after heating. No thermal hysteresis activity was detected but the extract had a typical hexagonal crystal shape when grown from a single seed crystal and weak ice nucleation activity. An ice active substance is present in a low concentration, which may be involved in the freezing survival of this species by inhibiting ice recrystallization.

Infective Juveniles of the Entomopathogenic Nematode, Steinernema feltiae Produce Cryoprotectants in Response to Freezing and Cold Acclimation

Steinernema feltiae is a moderately freeze-tolerant entomopathogenic nematode which survives intracellular freezing. We have detected by gas chromatography that infective juveniles of S. feltiae produce cryoprotectants in response to cold acclimation and to freezing. Since the survival of this nematode varies with temperature, we analyzed their cryoprotectant profiles under different acclimation and freezing regimes. The principal cryoprotectants detected were trehalose and glycerol with glucose being the minor component. The amount of cryoprotectants varied with the temperature and duration of exposure. Trehalose was accumulated in higher concentrations when nematodes were acclimated at 5°C for two weeks whereas glycerol level decreased from that of the non-acclimated controls. Nematodes were seeded with a small ice crystal and held at -1°C, a regime that does not produce freezing of the nematodes but their bodies lose water to the surrounding ice (cryoprotective dehydration). This increased the levels of both trehalose and glycerol, with glycerol reaching a higher concentration than trehalose. Nematodes frozen at -3°C, a regime that produces freezing of the nematodes and results in intracellular ice formation, had elevated glycerol levels while trehalose levels did not change. Steinernema feltiae thus has two strategies of cryoprotectant accumulation: one is an acclimation response to low temperature when the body fluids are in a cooled or supercooled state and the infective juveniles produce trehalose before freezing. During this process a portion of the glycerol is converted to trehalose. The second strategy is a rapid response to freezing which induces the production of glycerol but trehalose levels do not change. These low molecular weight compounds are surmised to act as cryoprotectants for this species and to play an important role in its freezing tolerance.

Animal ice-binding (antifreeze) proteins and glycolipids: an overview with emphasis on physiological function

Ice-binding proteins (IBPs) assist in subzero tolerance of multiple cold-tolerant organisms: animals, plants, fungi, bacteria etc. IBPs include: (1) antifreeze proteins (AFPs) with high thermal hysteresis antifreeze activity; (2) low thermal hysteresis IBPs; and (3) ice-nucleating proteins (INPs). Several structurally different IBPs have evolved, even within related taxa. Proteins that produce thermal hysteresis inhibit freezing by a non-colligative mechanism, whereby they adsorb onto ice crystals or ice-nucleating surfaces and prevent further growth. This lowers the so-called hysteretic freezing point below the normal equilibrium freezing/melting point, producing a difference between the two, termed thermal hysteresis. True AFPs with high thermal hysteresis are found in freeze-avoiding animals (those that must prevent freezing, as they die if frozen) especially marine fish, insects and other terrestrial arthropods where they function to prevent freezing at temperatures below those commonly experienced by the organism. Low thermal hysteresis IBPs are found in freeze-tolerant organisms (those able to survive extracellular freezing), and function to inhibit recrystallization – a potentially damaging process whereby larger ice crystals grow at the expense of smaller ones – and in some cases, prevent lethal propagation of extracellular ice into the cytoplasm. Ice-nucleator proteins inhibit supercooling and induce freezing in the extracellular fluid at high subzero temperatures in many freeze-tolerant species, thereby allowing them to control the location and temperature of ice nucleation, and the rate of ice growth. Numerous nuances to these functions have evolved. Antifreeze glycolipids with significant thermal hysteresis activity were recently identified in insects, frogs and plants.

Anhydrobiosis and freezing-tolerance: adaptations that facilitate the establishment of Panagrolaimus nematodes in polar habitats

Anhydrobiotic animals can survive the loss of both free and bound water from their cells. While in this state they are also resistant to freezing. This physiology adapts anhydrobiotes to harsh environments and it aids their dispersal. Panagrolaimus davidi, a bacterial feeding anhydrobiotic nematode isolated from Ross Island Antarctica, can survive intracellular ice formation when fully hydrated. A capacity to survive freezing while fully hydrated has also been observed in some other Antarctic nematodes. We experimentally determined the anhydrobiotic and freezing-tolerance phenotypes of 24 Panagrolaimus strains from tropical, temperate, continental and polar habitats and we analysed their phylogenetic relationships. We found that several other Panagrolaimus isolates can also survive freezing when fully hydrated and that tissue extracts from these freezing-tolerant nematodes can inhibit the growth of ice crystals. We show that P. davidi belongs to a clade of anhydrobiotic and freezing-tolerant panagrolaimids containing strains from temperate and continental regions and that P. superbus, an early colonizer at Surtsey island, Iceland after its volcanic formation, is closely related to a species from Pennsylvania, USA. Ancestral state reconstructions show that anhydrobiosis evolved deep in the phylogeny of Panagrolaimus. The early-diverging Panagrolaimus lineages are strongly anhydrobiotic but weakly freezing-tolerant, suggesting that freezing tolerance is most likely a derived trait. The common ancestors of the davidi and the superbus clades were anhydrobiotic and also possessed robust freezing tolerance, along with a capacity to inhibit the growth and recrystallization of ice crystals. Unlike other endemic Antarctic nematodes, the life history traits of P. davidi do not show evidence of an evolved response to polar conditions. Thus we suggest that the colonization of Antarctica by P. davidi and of Surtsey by P. superbus may be examples of recent “ecological fitting” of freezing-tolerant anhydrobiotic propagules to the respective abiotic conditions in Ross Island and Surtsey.

Cold tolerance of the Antarctic nematodes Plectus murrayi and Scottnema lindsayae

The cold tolerance of the Antarctic nematodes Scottnema lindsayae and Plectus murrayi was determined using material freshly isolated from the field. Both species could survive low temperatures but the survival of S. lindsayae was greater than that of P. murrayi. Field soil temperatures in late spring-early summer indicated a minimum temperature of -19.5 °C and a maximum cooling rate of 0.71 °C min(-1). In P. murrayi grown in culture, there was no significant effect of acclimation, nor of the two culture media used, on survival after freezing but survival was greater if freezing was seeded at -1 °C than at lower temperatures. The freezing survival ability of P. murrayi is much less than that of Panagrolaimus davidi CB1, another Antarctic nematode. Cryomicroscopy indicates that P. murrayi can survive low temperatures by either cryoprotective dehydration or freezing tolerance, but that freezing tolerance is the dominant strategy. Measurable thermal hysteresis was detected only in highly concentrated extracts of the nematodes, indicating the presence of an antifreeze protein, but at the concentrations likely to be found in vivo, the major function of the ice active protein involved is probably recrystallization inhibition.

Molecular analysis of the cold tolerant Antarctic nematode, Panagrolaimus davidi

Isolated and established in culture from the Antarctic in 1988, the nematode Panagrolaimus davidi has proven to be an ideal model for the study of adaptation to the cold. Not only is it the best-documented example of an organism surviving intracellular freezing but it is also able to undergo cryoprotective dehydration. As part of an ongoing effort to develop a molecular understanding of this remarkable organism, we have assembled both a transcriptome and a set of genomic scaffolds. We provide an overview of the transcriptome and a survey of genes involved in temperature stress. We also explore, in silico, the possibility that P. davidi will be susceptible to an environmental RNAi response, important for further functional studies.

Intracellular freezing in the infective juveniles of Steinernema feltiae: an entomopathogenic nematode

Taking advantage of their optical transparency, we clearly observed the third stage infective juveniles (IJs) of Steinernema feltiae freezing under a cryo-stage microscope. The IJs froze when the water surrounding them froze at -2°C and below. However, they avoid inoculative freezing at -1°C, suggesting cryoprotective dehydration. Freezing was evident as a sudden darkening and cessation of IJs' movement. Freeze substitution and transmission electron microscopy confirmed that the IJs of S. feltiae freeze intracellularly. Ice crystals were found in every compartment of the body. IJs frozen at high sub-zero temperatures (-1 and -3°C) survived and had small ice crystals. Those frozen at -10°C had large ice crystals and did not survive. However, the pattern of ice formation was not well-controlled and individual nematodes frozen at -3°C had both small and large ice crystals. IJs frozen by plunging directly into liquid nitrogen had small ice crystals, but did not survive. This study thus presents the evidence that S. feltiae is only the second freeze tolerant animal, after the Antarctic nematode Panagrolaimus davidi, shown to withstand extensive intracellular freezing.

Ice recrystallization inhibition mediated by a nuclear-expressed and -secreted recombinant ice-binding protein in the microalga Chlamydomonas reinhardtii

A Lolium perenne ice-binding protein (LpIBP) demonstrates superior ice recrystallization inhibition (IRI) activity and has proposed applications in cryopreservation, food texturing, as well as in being a "green" gas hydrate inhibitor. Recombinant production of LpIBP has been previously conducted in bacterial and yeast systems for studies of protein characterization, but large-scale applications have been hitherto limited due to high production costs. In this work, a codon-optimized LpIBP was recombinantly expressed and secreted in a novel one-step vector system from the nuclear genome of the green microalga Chlamydomonas reinhardtii. Both mixotrophic and photoautotrophic growth regimes supported LpIBP expression, indicating the feasibility of low-cost production using minimal medium, carbon dioxide, and light energy as input. In addition, multiple growth and bioproduct extraction cycles were performed by repetitive batch cultivation trials, demonstrating the potential for semi-continuous production and biomass harvesting. Concentrations of recombinant protein reached in this proof of concept approach were sufficient to demonstrate IRI activity in culture media without additional purification or concentration, with activity further verified by thermal hysteresis and morphology assays. The incorporation of the recombinant LpIBP into a model gas hydrate offers the promise that algal production may eventually find application as a "green" hydrate inhibitor.

Cold tolerance of New Zealand alpine insects

New Zealand has extensive alpine and subalpine habitats where, together with some lowland sites, insects are exposed to subzero temperatures. Studies of cold tolerance in New Zealand insects have centred on an alpine weta (Hemideina maori), which is the world's largest freezing tolerant insect, and an alpine cockroach (Celatoblatta quinquemaculata). Both of these insects are moderately freezing tolerant and have ice nucleating agents in their haemolymph and guts. There is some evidence for the survival of intracellular ice formation in the isolated gut tissue of C. quinquemaculata. Trehalose is a suggested cryoprotectant in both H. maori and C. quinquemaculata whilst proline also provides this role in H. maori. Cells and tissues of both insects maintain viability and physiological function during freezing to moderately low temperatures but viability declines at lower temperatures, the most vulnerable tissue presumably setting the limit to the survival of the animal. Antifreeze proteins are found in the gut tissue of C. quinquemaculata and may protect this tissue when freezing occurs in the gut. Several other New Zealand insects are also moderately freezing tolerant and the apparent dominance of this cold tolerance strategy in the New Zealand fauna may reflect the relatively mild climate but unpredictable exposure to subzero temperatures that is typical of many Southern Hemisphere environments.

Effect of slow desiccation and freezing on gene transcription and stress survival of an Antarctic nematode

Nematodes are the dominant soil animals of the Antarctic Dry Valleys and are capable of surviving desiccation and freezing in an anhydrobiotic state. Genes induced by desiccation stress have been successfully enumerated in nematodes; however, little is known about gene regulation by Antarctic nematodes that can survive multiple types and incidences of environmental stress. In order to reveal the molecular response of anhydrobiotic survival, we investigated the genetic response of an Antarctic nematode, Plectus murrayi, which can survive desiccation and freezing. Using molecular approaches, we provide insight into the regulation of desiccation-induced transcripts during different stages of stress survival under conditions characteristic of the Antarctic Dry Valley environment. Our study revealed that exposure to slow desiccation and freezing plays an important role in the transcription of stress, metabolism and signal transduction-related genes and improves desiccation and freezing survival compared with nematodes exposed to fast desiccation and freezing. Temporal analyses of gene expression showed that pre-exposure to mild stress promotes survival of harsher stress. Our results further show that exposure to slow dehydration not only improves extreme desiccation survival but also promotes enhanced cold tolerance. We also provide evidence that slow dehydration can enhance freeze tolerance in an Antarctic nematode. Expression profiling of P. murrayi transcripts is an important step in understanding the genome-level response of this nematode to different environmental stressors.

Expression of two self-enhancing antifreeze proteins from the beetle Dendroides canadensis in Drosophila melanogaster

Antifreeze proteins (AFPs) lower the freezing point of water without affecting the melting point. This difference between melting point and freezing point has been termed thermal hysteresis. Antifreeze protein genes, dafp-1 and/or dafp-4, from the freeze-avoiding insect, Dendroides canadensis, were transferred to Drosophila melanogaster via P-element-mediated transformation. The Northern and Western blots showed expression of DAFP(s) at both transcript and protein levels. The highest thermal hysteresis activity of 6.78+/-0.12 degrees C was detected in 5-day adult flies containing two copies of each of the dafp-1 and dafp-4 genes, while flies with two copies of either dafp-1 or dafp-4 had less activity, 5.52 and 3.24 degrees C, respectively (measured by nanoliter osmometer). This suggests synergistic enhancement of thermal hysteresis activity between DAFP-1 and DAFP-4 in transgenic D. melanogaster containing both DAFPs. Supercooling points without ice in contact with the insects were lowered in all 5 transgenic lines compared with controls, however, when ice was in contact with the flies, supercooling points were lowered only in the heterozygous <DAFP-1>+<DAFP-4> transgenic line. Also, transgenic D. melanogaster exhibited higher survivorship compared with controls when placed at low non-freezing temperatures (0 and 4 degrees C), however, DAFP-1 and DAFP-4 did not display any synergistic enhancement in these non-freezing survival experiments.

Thermal stability properties of an antifreeze protein from the desert beetle Microdera punctipennis

An insect antifreeze protein gene Mpafp698 was cloned by the RT-PCR approach from the desert beetle Microdera punctipennis. The gene was constructed and heterogeneously expressed in Escherichia coli as fusion proteins, His-MpAFP698, glutathione S-transferase (GST)-MpAFP698, and maltose-binding protein (MBP)-MpAFP698. The thermostability and thermal hysteresis activity of these proteins were determined, with the aim of elucidating the biological characteristics of this protein. The approximate thermal hysteresis (TH) value of the purified His-MpAFP698 was 0.37 degrees C at 0.84 mg/ml, and maintained approximately 95.7% of the TH activity at 100 degrees C for 5 min. Furthermore, heat incubation showed that MBP-MpAFP698 was 10 degrees C more thermostable than MBP protein, indicating that MpAFP698 could, to some extent, improve the thermal stability of the fused partner MBP protein. This study suggests that MpAFP698 has a high thermal stability and could be used to improve the thermal stability of the less stable proteins by producing fusion proteins, which could be used for biotechnological purposes.

Desiccation survival in an Antarctic nematode: molecular analysis using expressed sequenced tags

Background

Nematodes are the dominant soil animals in Antarctic Dry Valleys and are capable of surviving desiccation and freezing in an anhydrobiotic state. Genes induced by desiccation stress have been successfully enumerated in nematodes; however we have little knowledge of gene regulation by Antarctic nematodes which can survive multiple environmental stresses. To address this problem we investigated the genetic responses of a nematode species, Plectus murrayi, that is capable of tolerating Antarctic environmental extremes, in particular desiccation and freezing. In this study, we provide the first insight into the desiccation induced transcriptome of an Antarctic nematode through cDNA library construction and suppressive subtractive hybridization.

Results

We obtained 2,486 expressed sequence tags (ESTs) from 2,586 clones derived from the cDNA library of desiccated P. murrayi. The 2,486 ESTs formed 1,387 putative unique transcripts of which 523 (38%) had matches in the model-nematode Caenorhabditis elegans, 107 (7%) in nematodes other than C. elegans, 153 (11%) in non-nematode organisms and 605 (44%) had no significant match to any sequences in the current databases. The 1,387 unique transcripts were functionally classified by using Gene Ontology (GO) hierarchy and the Kyoto Encyclopedia of Genes and Genomes (KEGG) database. The results indicate that the transcriptome contains a group of transcripts from diverse functional areas. The subtractive library of desiccated nematodes showed 80 transcripts differentially expressed during desiccation stress, of which 28% were metabolism related, 19% were involved in environmental information processing, 28% involved in genetic information processing and 21% were novel transcripts. Expression profiling of 14 selected genes by quantitative Real-time PCR showed 9 genes significantly up-regulated, 3 down-regulated and 2 continuously expressed in response to desiccation.

Conclusion

The establishment of a desiccation EST collection for Plectus murrayi, a useful model in assessing the structural, physiological, biochemical and genetic aspects of multiple stress tolerance, is an important step in understanding the genome level response of this nematode to desiccation stress. The type of transcript analysis performed in this study sets the foundation for more detailed functional and genome level analyses of the genes involved in desiccation tolerance in nematodes.

Molecular evolution in Panagrolaimus nematodes: origins of parthenogenesis, hermaphroditism and the Antarctic species P. davidi

BACKGROUND

As exemplified by the famously successful model organism Caenorhabditis elegans, nematodes offer outstanding animal systems for investigating diverse biological phenomena due to their small genome sizes, short generation times and ease of laboratory maintenance. Nematodes in the genus Panagrolaimus have served in comparative development and anhydrobiosis studies, and the Antarctic species P. davidi offers a powerful paradigm for understanding the biological mechanisms of extreme cold tolerance. Panagrolaimus nematodes are also unique in that examples of gonochoristic, hermaphroditic and parthenogenetic reproductive modes have been reported for members of this genus. The evolutionary origins of these varying reproductive modes and the Antarctic species P. davidi, however, remain enigmatic.

RESULTS

We collected nuclear ribosomal RNA gene and mitochondrial protein-coding gene sequences from diverse Panagrolaimus species and strains, including newly discovered isolates from Oregon, to investigate phylogenetic relationships in this nematode genus. Nuclear phylogenies showed that the species and strains historically identified as members of Panagrolaimus constitute a paraphyletic group, suggesting that taxonomic revision is required for Panagrolaimus and related nematode lineages. Strain-specific reproductive modes were mapped onto the molecular phylogeny to show a single origin of parthenogenesis from a presumably gonochoristic ancestor. The hermaphroditic strains were all placed outside a major monophyletic clade that contained the majority of other Panagrolaimus nematodes. Phylogenetic analyses of mitochondrial sequences showed that substantial molecular and geographic diversity exists within the clade of parthenogenetic strains. The Antarctic species P. davidi was found to be very closely related to two Panagrolaimus strains from southern California. Phylogenetic and molecular clock analyses suggested that P. davidi and the California strain PS1579 shared a common ancestor in the very recent evolutionary past.

CONCLUSION

Our study provides a phylogenetic framework for understanding the evolutionary origins and diversification patterns of varying reproductive modes within Panagrolaimus and important insights into the origin of the Antarctic species P. davidi. Panagrolaimus offers a powerful nematode model for understanding diverse evolutionary phenomena including the evolution of asexuality and the adaptive evolution of extreme cold tolerance.

Ice-active proteins and cryoprotectants from the New Zealand alpine cockroach, Celatoblatta quinquemaculata

Celatoblatta quinquemaculata is moderately freezing tolerant. We have investigated low and high molecular weight compounds that may be associated with its survival. Glycerol and trehalose were identified as potential cryoprotectants, with trehalose at the higher concentration. Trehalose was at its highest concentration in late autumn, during the periods sampled. Water contents declined with time and were significantly lower in late autumn than in late summer. No thermal hysteresis activity was detected in haemolymph or in extracts of the head, muscles and the fat body. Extracts of the Malpighian tubules showed an hexagonal crystal growth form, as did those of the gut tissue and gut contents. The gut tissue had high levels of thermal hysteresis (approximately 2 degrees C) and the gut contents somewhat lower levels (approximately 0.6 degrees C). Recrystallization inhibition activity mirrored that of thermal hysteresis, with activity absent in the haemolymph or fat body cells but present in the gut tissues and contents. Activity was reduced by heating and was associated with a molecule >14kDa in size. These findings suggest an antifreeze protein is involved. In fed animals, ice nucleation is likely to start in the gut. Gut cells have a much greater resistance to freezing than do fat body or Malpighian tubule cells. The antifreeze protein may enable this tissue to survive freezing stress by inhibiting recrystallization.

Characterization of a family of ice-active proteins from the Ryegrass, Lolium perenne

Five genes coding for ice-active proteins were identified from an expressed sequence tag database of Lolium perenne cDNA libraries. Each of the five genes were characterized by the presence of an N-terminal signal peptide, a region enriched in hydrophilic amino acids and a leucine-rich region in four of the five genes that is homologous with the receptor domain of receptor-like protein kinases of plants. The C-terminal region of all five genes contains sequence homologous with Lolium and Triticum ice-active proteins. Of the four ice-active proteins (IAP1, IAP2, IAP3 and IAP5) cloned, three could be expressed in Escherichia coli and recovered in a functional form in order to study their ice activity. All three ice-active proteins had recrystallization inhibition activity but showed no detectable antifreeze or ice nucleation activity at the concentration tested. IAP2 and IAP5 formed distinct hexagonal-shaped crystals in the nanolitre osmometer as compared to the weakly hexagonal crystals produced by IAP3.

Cold tolerance of an Antarctic nematode that survives intracellular freezing: comparisons with other nematode species

Panagrolaimus davidi is an Antarctic nematode with very high levels of cold tolerance. Its survival was compared with that of some other nematodes (P. rigidus, Rhabditophanes sp., Steinernema carpocapsae, Panagrellus redivivus and Ditylenchus dipsaci) in both unacclimated samples and those acclimated at 5 degrees C. Levels of recrystallization inhibition in homogenates were also compared, using the splat-cooling assay. The survival of P. davidi after the freezing of samples was notably higher than that of the other species tested, suggesting that its survival ability is atypical compared to other nematodes. In general, acclimation improved survival. Levels of recrystallization inhibition were not associated with survival but such a relationship may exist for those species that are freezing tolerant.

Cold-loving microbes, plants, and animals--fundamental and applied aspects

Microorganisms, plants, and animals have successfully colonized cold environments, which represent the majority of the biosphere on Earth. They have evolved special mechanisms to overcome the life-endangering influence of low temperature and to survive freezing. Cold adaptation includes a complex range of structural and functional adaptations at the level of all cellular constituents, such as membranes, proteins, metabolic activity, and mechanisms to avoid the destructive effect of intracellular ice formation. These strategies offer multiple biotechnological applications of cold-adapted organisms and/or their products in various fields. In this review, we describe the mechanisms of microorganisms, plants, and animals to cope with the cold and the resulting biotechnological perspectives.