Physiological and ecological significance of biological ice nucleators

Measurement of Ice Nucleation Activity of Biological Samples

Experimentation with ice-nucleating biomolecules is needed to advance the fundamental understanding of biotic heterogeneous ice nucleation. Standard experimental procedures vary with sample type. Here we describe a generalized primary purification and analysis process to measure ice nucleation activity of biological samples using an advanced freezing droplet assay.

Problems of human spermatozoa cryopreservation: research methods, solutions

Cryopreservation of male gametes is one of the most important methods of assisted reproductive technologies, which allows preserving gametes for research or further use. However, the fertilizing ability of spermatozoa after cryopreservation decreases by 30-70%, which makes it urgent to search for new substances with cryoprotective properties. The review considers the main causes of cell damage during cryopreservation. The relevance of methods for assessing the formation of crystals and the physicochemical properties of cryoprotective media depending on various compositions is discussed. The problem of stabilization of the spermatozoa membrane during cryopreservation is considered. A possible solution to the problem of membrane integrity may consist in modification of the basic cryoprotective media with yolk emulsion or development of methods for saturation of the membrane phospholipid layer with cholesterol.

Lichen species across Alaska produce highly active and stable ice nucleators

Forty years ago, lichens were identified as extraordinary biological ice nucleators (INs) that enable ice formation at temperatures close to 0°C. By employing INs, lichens thrive in freezing environments that surpass the physiological limits of other vegetation, thus making them the majority of vegetative biomass in northern ecosystems. Aerosolized lichen INs might further impact cloud glaciation and have the potential to alter atmospheric processes in a warming Arctic. Despite the ecological importance and formidable ice nucleation activities, the abundance, diversity, sources, and role of ice nucleation in lichens remain poorly understood. Here, we investigate the ice nucleation capabilities of lichens collected from various ecosystems across Alaska. We find ice-nucleating activity in lichen to be widespread, particularly in the coastal rainforest of Southeast Alaska. Across 29 investigated lichen, all species show ice nucleation temperatures above -15 °C and ~30% initiate freezing at temperatures above -6 °C. Concentration series of lichen ice nucleation assays in combination with statistical analysis reveal that the lichens contain two subpopulations of INs, similar to previous observations in bacteria. However, unlike the bacterial INs, the lichen INs appear as independent subpopulations resistant to freeze-thaw cycles and against temperature treatment. The ubiquity and high stability of the lichen INs suggest that they can impact local atmospheric processes and that ice nucleation activity is an essential trait for their survival in cold environments.

Biochemical response of two earthworm taxa exposed to freezing

Several earthworm species are known to be able to withstand freezing. At the biochemical level, this ability is based on cryoprotectant accumulation as well as several other mechanisms. In this study, we used ¹H NMR to investigate metabolomic changes in two freeze-tolerant earthworm taxa, Dendrobaena octaedra and one of the genetic lineages of Eisenia sp. aff. nordenskioldi f. pallida. A total of 45 metabolites were quantified. High concentrations of glucose were present in frozen tissues of both taxa. No other putative cryoprotectants were found. We detected high levels of glycolysis end products and succinate in frozen animals, indicating the activation of glycolysis. Concentrations of many other substances also significantly increased. On the whole, metabolic change in response to freezing was much more pronounced in the specimens of Eisenia sp. aff. nordenskioldi f. pallida, including signs of nucleotide degradation.

History of Discovery and Environmental Role of Ice Nucleating Bacteria

The phenomenon of biological ice nucleation that is exhibited by a variety of bacteria is a fascinating phenotype, which has been shown to incite frost damage to frost-sensitive plants and has been proposed to contribute to atmospheric processes that affect the water cycle and earth's radiation balance. This review explores the several possible drivers for the evolutionary origin of the ice nucleation phenotype. These bacteria and the gene required for this phenotype have also been exploited in processes as diverse as reporter gene assays to assess environmentally responsive gene expression in various plant pathogenic and environmental bacteria and in the detection of foodborne human pathogens when coupled with host-specific bacteriophage, whereas ice nucleating bacteria themselves have been exploited in the production of artificial snow for recreation and oil exploration and in the process of freezing of various food products. This review also examines the historical development of our understanding of ice nucleating bacteria, details of the genetic determinants of ice nucleation, and features of the aggregates of membrane-bound ice nucleation protein necessary for catalyzing ice. Lastly, this review also explores the role of these bacteria in limiting the supercooling ability of plants and the strategies and limitations of avoiding plant frost damage by managing these bacterial populations by bactericides, antagonistic bacteria, or cultural control strategies.

Insect Freeze-Tolerance Downunder: The Microbial Connection

Insects that are freeze-tolerant start freezing at high sub-zero temperatures and produce small ice crystals. They do this using ice-nucleating agents that facilitate intercellular ice growth and prevent formation of large crystals where they can damage tissues. In Aotearoa/New Zealand the majority of cold adapted invertebrates studied survive freezing at any time of year, with ice formation beginning in the rich microbiome of the gut. Some freeze-tolerant insects are known to host symbiotic bacteria and/or fungi that produce ice-nucleating agents and we speculate that gut microbes of many New Zealand insects may provide ice-nucleating active compounds that moderate freezing. We consider too the possibility that evolutionary disparate freeze-tolerant insect species share gut microbes that are a source of ice-nucleating agents and so we describe potential transmission pathways of shared gut fauna. Despite more than 30 years of research into the freeze-tolerant mechanisms of Southern Hemisphere insects, the role of exogenous ice-nucleating agents has been neglected. Key traits of three New Zealand freeze-tolerant lineages are considered in light of the supercooling point (temperature of ice crystal formation) of microbial ice-nucleating particles, the initiation site of freezing, and the implications for invertebrate parasites. We outline approaches that could be used to investigate potential sources of ice-nucleating agents in freeze-tolerant insects and the tools employed to study insect microbiomes.

Epigenetic underpinnings of freeze avoidance in the goldenrod gall moth, Epiblema scudderiana

The goldenrod gall moth (Epiblema scudderiana) is a cold hardy insect that survives subzero temperatures during the winter by supercooling bodily fluids to approximately -40 °C, allowing the insect to remain unfrozen despite the freezing temperatures. This is characterized by a drastic increase of cryoprotectant glycerol along with widespread downregulation of non-essential genes and processes to conserve cellular energy. This study examined the role of epigenetic enzymes in regulating this freeze-avoidant process across a range of freezing temperatures experienced in nature. Cold and subzero temperature exposure in E. scudderiana resulted in upregulation of select DNA methyltransferase (DNMT) enzymes with concurrent decreases in DNMT activity and no change in activity of the Ten-Eleven Translocation (TET) demethylation enzyme activities. Levels of histone acetyltransferase (HAT) and histone deacetylase (HDAC) activity decreased during cold exposures. The increase in DNMT expression and concurrent decrease in HAT activity suggests a role for DNA methylation to assist with transcriptional suppression. These findings propose that epigenetic regulation of genes and histones underpin the winter survival strategies of this insect.

Winter is coming: the future of cryopreservation

The preservative effects of low temperature on biological materials have been long recognised, and cryopreservation is now widely used in biomedicine, including in organ transplantation, regenerative medicine and drug discovery. The lack of organs for transplantation constitutes a major medical challenge, stemming largely from the inability to preserve donated organs until a suitable recipient is found. Here, we review the latest cryopreservation methods and applications. We describe the main challenges-scaling up to large volumes and complex tissues, preventing ice formation and mitigating cryoprotectant toxicity-discuss advantages and disadvantages of current methods and outline prospects for the future of the field.

Cryoprotectant role of exopolysaccharide of Pseudomonas sp. ID1 in the vitrification of IVM cow oocytes

Biological molecules isolated from organisms that live under subzero conditions could be used to protect oocytes from cryoinjuries suffered during cryopreservation. This study examined the cryoprotectant role of exopolysaccharides of Pseudomonas sp. ID1 (EPS ID1) in the vitrification of prepubertal and adult cow oocytes. IVM oocytes were vitrified and warmed in media supplemented with 0, 1, 10, 100 or 1000µgmL-1 EPS ID1. After warming, oocytes were fertilised and embryo development, spindle morphology and the expression of several genes in Day 8 blastocysts were assessed. Vitrification led to significantly lower proportion of prepubertal oocytes exhibiting a normal spindle configuration. In fresh control oocytes and most groups of vitrified adult oocytes, similar percentages of oocytes with a normal spindle configuration were observed. Percentages of Day 8 blastocysts were similar for prepubertal oocytes vitrified in the absence or presence of 1 or 10µgmL-1 EPS ID1 and for adult oocytes vitrified in the presence of 10µgmL-1 EPS ID1 compared with non-vitrified oocytes. EPS ID1 supplementation had no effect on solute carrier family 2 member 3 (SLC2A3), ubiquitin-conjugating enzyme E2A (UBE2A) and histone deacetylase 1 (HDAC1) expression in Day 8 blastocysts form adult oocytes. However, supplementation with 10 and 100µgmL-1 EPS ID1 led to increased expression of genes involved in epigenetic modifications (DNA methyltransferase 3 alpha (DNMT3A) and K (lysine) acetyltransferase 2A (KAT2A)) and apoptosis (BCL2 associated X apoptosis regulator (BAX) and BCL2-like 1 (BCL2L1)). The lowest BAX:BCL2L1 ratio was found in the 10µgmL-1 EPS ID1-supplemented group. The results suggest that 10µgmL-1 EPS ID1 added to vitrification and warming media may help protect bovine oocytes against cryodamage.

Energy balance and metabolic changes in an overwintering wolf spider, Schizocosa stridulans

Winter provides many challenges for terrestrial arthropods, including low temperatures and decreased food availability. Most arthropods are dormant in the winter and resume activity when conditions are favorable, but a select few species remain active during winter. Winter activity is thought to provide a head start on spring growth and reproduction, but few studies have explicitly tested this idea or investigated tradeoffs associated with winter activity. Here, we detail biochemical changes in overwintering winter-active wolf spiders, Schizocosa stridulans, to test the hypothesis that winter activity promotes growth and energy balance. We also quantified levels of putative cryoprotectants throughout winter to test the prediction that winter activity is incompatible with biochemical adaptations for coping with extreme cold. Body mass of juveniles increased 3.5-fold across winter, providing empirical evidence that winter activity promotes growth and therefore advancement of spring reproduction. While spiders maintained protein content throughout most of the winter, lipid content decreased steadily, suggesting either a lack of available prey to maintain lipids, or more likely, an allometric shift in body composition as spiders grew larger. Carbohydrate content showed no clear seasonal trend but also tended to be higher at the beginning of the winter. Finally, we tested the hypothesis that winter activity is incompatible with cryoprotectant accumulation. However, we observed accumulation of glycerol, myo-inositol, and several other cryoprotectants, although levels were lower than those typically observed in overwintering arthropods. Together, our results indicate that winter-active wolf spiders grow during the winter, and while cryoprotectant accumulation was observed in the winter, the modest levels relative to other species could make them susceptible to extreme winter events.

AFM imaging of extracellular ice nucleators

Ice nucleators are substances that can initiate nucleation of pure water at and above -10 °C. Some plant pathogens possess a gene which encodes for a protein that acts as an ice nucleator, activity of which is enhanced when it is combined with the sugar and lipid components from the cell membrane. This matter retains its ice nucleation activity even after it is detached from the cell wall, and is termed extracellular ice nucleator (ECIN). In this paper, surface morphology of ECINs was investigated using atomic force microscopy (AFM) in tapping mode. ECINs were immobilized onto polyelectrolyte multilayers using the layer by layer deposition method. Effect of layer build-up, method of ECIN production, and polyelectrolytes used for multilayer fabrication were investigated. Globular and rod-like structures were observed on the AFM images of the nano-thin ECIN layers. Activity of ECINs, tested in food solutions in earlier studies, was retained when applied as a nano-thin layer onto a silicon wafer surface. Protein aggregate sizes decreased when higher centrifugation speeds were applied, and ice nucleation activity also decreased. Nucleation occurred faster and at higher temperatures when substrates were immersed in solutions of higher ECIN concentration, whereas number of bilayers formed did not have a significant effect. Higher concentration ECIN dipping solutions also led to the formation of thicker and denser ECIN layers as observed via AFM imaging. PRACTICAL APPLICATION: This study demonstrates the properties of nano-thin ECIN layers, which can crystallize pure water into ice at higher temperatures and in shorter time. Accelerating ice nucleation can potentially be utilized to freeze liquids in shorter time hence using less energy, or improve frozen foods' stability against the risk of cold chain breakage.

Freezing from the inside: Ice nucleation in Escherichia coli and Escherichia coli ghosts by inner membrane bound ice nucleation protein InaZ

Ice nucleation (IN) active bacteria such as Pseudomonas syringae promote the growth of ice crystals more effectively than any material known. Using the specialized ice nucleation protein (INP) InaZ, P. syringae-the well studied epiphytic plant pathogen-attacks plants by frost damage and, likewise fascinating, drives ice nucleation within clouds when airborne in the atmosphere by linkage to the Earth's water cycle. While ice nucleation proteins play a tremendous role for life on the planet, the molecular details of their activity on the bacterial membrane surface are largely unknown. Bacterial ghosts (BGs) derived from Escherichia coli can be used as simplified model systems to study the mode of action of InaZ. In this work, the authors used BGs to study the role of InaZ localization on the luminal side of the bacterial inner membrane. Naturally, P. syringae INPs are displayed on the surface of the outer membrane; so in contrast, the authors engineered an N-terminal truncated form of inaZ lacking the transport sequence for anchoring of InaZ on the outer membrane. This construct was fused to N- and C-terminal inner membrane anchors and expressed in Escherichia coli C41. The IN activity of the corresponding living recombinant E. coli catalyzing interfacial ice formation of supercooled water at high subzero temperatures was tested by a droplet-freezing assay and surface spectroscopy. The median freezing temperature (T₅₀) of the parental living E. coli C41 cells without INP was detected at -20.1 °C and with inner membrane anchored INPs at a T₅₀ value between -7 and -9 °C, demonstrating that the induction of IN from the inside of the bacterium by inner membrane anchored INPs facing the luminal inner membrane side is very similar to IN induced by bacterial INPs located at the outer membrane. Bacterial ghosts derived from these different constructs showed first droplet freezing values between -6 and -8 °C, whereas E. coli C41 BGs alone without carrying inner membrane anchored INPs exhibit a T₅₀ of -18.9 °C. Sum frequency generation spectroscopy showed structural ordered water at the BG/water interface, which increased close to the water melting point. Together, this indicates that the more efficient IN of INP-BGs compared to their living parental strains can be explained by the free access of inner membrane anchored INP constructs to ultrapure water filling the inner space of the BGs.

Cold acclimation increases cold tolerance independently of diapause programing in the bean bug, Riptortus pedestris

The bean bug (Riptortus pedestris) is a pest of soybeans and other legumes in Japan and other Asian countries. It enters a facultative adult diapause on exposure to short days. While photoperiodism and diapause are well understood in R. pedestris, knowledge of cold tolerance is very limited, as is information on the effect of diapause on cold tolerance. We examined the effect of photoperiod, cold acclimation, and feeding status on cold tolerance in R. pedestris. We found that cold acclimation significantly increased survival at -10°C in both long- and short-day adult R. pedestris. Since the difference in cold survival between long- and short-day cold-acclimated groups was only marginal, we conclude that entering diapause is not crucial for R. pedestris to successfully pass through cold acclimation and become cold tolerant. We observed similar effects in 5th instar nymphs, with both long- and short-day cold-acclimated groups surviving longer cold exposures compared with non-acclimated groups. Starvation, which was tested only in adult bugs, had only a negligible and negative impact on cold survival. Although cold tolerance significantly increased with cold acclimation in adult bugs, supercooling capacity unexpectedly decreased. Our results suggest that changes in supercooling capacity as well as in water content are unrelated to cold tolerance in R. pedestris. An analysis of metabolites revealed differences between the treatments, and while several metabolites markedly increased with cold acclimation, their concentrations were too low to have a significant effect on cold tolerance.

Boreal pollen contain ice-nucleating as well as ice-binding 'antifreeze' polysaccharides

Ice nucleation and growth is an important and widespread environmental process. Accordingly, nature has developed means to either promote or inhibit ice crystal formation, for example ice-nucleating proteins in bacteria or ice-binding antifreeze proteins in polar fish. Recently, it was found that birch pollen release ice-nucleating macromolecules when suspended in water. Here we show that birch pollen washing water exhibits also ice-binding properties such as ice shaping and ice recrystallization inhibition, similar to antifreeze proteins. We present spectroscopic evidence that both the ice-nucleating as well as the ice-binding molecules are polysaccharides bearing carboxylate groups. The spectra suggest that both polysaccharides consist of very similar chemical moieties, but centrifugal filtration indicates differences in molecular size: ice nucleation occurs only in the supernatant of a 100 kDa filter, while ice shaping is strongly enhanced in the filtrate. This finding may suggest that the larger ice-nucleating polysaccharides consist of clusters of the smaller ice-binding polysaccharides, or that the latter are fragments of the ice-nucleating polysaccharides. Finally, similar polysaccharides released from pine and alder pollen also display both ice-nucleating as well as ice-binding ability, suggesting a common mechanism of interaction with ice among several boreal pollen with implications for atmospheric processes and antifreeze protection.

Annual Cycles of Two Cyanobacterial Mat Communities in Hydro-Terrestrial Habitats of the High Arctic

Cyanobacteria form extensive macroscopic mats in shallow freshwater environments in the High Arctic and Antarctic. In these habitats, the communities are exposed to seasonal freezing and desiccation as well as to freeze-thawing and drying-rewetting cycles. Here, we characterized the annual cycles of two Phormidium communities in very shallow seepages located in central Svalbard. We observed the structure of the communities and the morphology, ultrastructure, metabolic activity, and viability of filaments and single cells. The communities overwintered as frozen mats, which were formed by long filaments enclosed in thick multilayered polysaccharide sheaths. No morphologically and/or ultrastructurally distinct spore-like cells were produced for surviving the winter, and the winter survival of the communities was not provided by a few resistant cells, which did not undergo visible morphological and ultrastructural transformations. Instead, a high proportion of cells in samples (85%) remained viable after prolonged freezing. The sheaths were the only morphological adaption, which seemed to protect the trichomes from damage due to freezing and freeze-associated dehydration. The cells in the overwintering communities were not dormant, as all viable cells rapidly resumed respiration after thawing, and their nucleoids were not condensed. During the whole vegetative season, defined by the presence of water in a liquid state, the communities were constantly metabolically active and contained <1% of dead and injured cells. The morphology and ultrastructure of the cells remained unaltered during observations throughout the year, except for light-induced changes in thylakoids. The dissemination events are likely to occur in spring as most of the trichomes were split into short fragments (hormogonia), a substantial proportion of which were released into the environment by gliding out of their sheaths, as well as by cracking and dissolving their sheaths. The short fragments subsequently grew longer and gradually produced new polysaccharide sheaths.

Forest tree pollen dispersal via the water cycle

PREMISE OF THE STUDY

Pine pollen (Pinus spp.), along with other atmospheric particles, is dispersed by the water cycle, but this mode of dispersal requires cloud-pollen interactions that depend on taxon-specific biological properties. In the simplest form of this dispersal, pine pollen ascends vertically to altitudes of 2 to 6 km, where a fraction is captured by mixed-phase cloud formation. Captured pollen accretes into frozen droplets, which ultimately descend as rain, snow, or hail. Whether Pinus pollen can still germinate after its exposure to high-altitude freezing is pertinent to (1) how forests adapt to climate change and (2) potential gene flow between genetically modified plantation species and their conspecific relatives. •

METHODS

To address this question, pollen from four Old World and two New World Pinus species were subjected to immersion freezing, a common cloud formation mode, under laboratory conditions. •

KEY RESULTS

Some pollen grains immersed at -20°C for 15, 60, or 120 min in either a dehydrated or a water-saturated state were still capable of germination. After exposure, dehydrated pine pollen had higher germination (43.3%) than water-saturated pollen (7.6%). •

CONCLUSIONS

Pine pollen exposed to freezing during cloud formation can still germinate, raising the question of whether rain-delivered live pollen might be linked to rain-facilitated pollination. Dispersal of live pine pollen via cloud formation and the water cycle itself deserves closer study.

Engineering functional nanothin multilayers on food packaging: ice-nucleating polyethylene films

Polyethylene is the most prevalent plastic and is commonly used as a packaging material. Despite its common use, there are not many studies on imparting functionalities to those films which can make them more desirable for frozen food packaging. Here, commercial low-density polyethylene (LDPE) films were oxidized by UV-ozone (UVO) treatment to obtain a negatively charged hydrophilic surface to allow fabrication of functional multilayers. An increase in hydrophilicity was observed when films were exposed to UVO for 4 min and longer. Thin multilayers were formed by dipping the UVO-treated films into biopolymer solutions, and extracellular ice nucleators (ECINs) were immobilized onto the film surface to form a functional top layer. Polyelectrolyte adsorption was studied and confirmed on silicon wafers by measuring the water contact angles of the layers and investigating the surface morphology via atomic force microscopy. An up to 4-5 °C increase in ice nucleation temperatures and an up to 10 min decrease in freezing times were observed with high-purity deionized water samples frozen in ECIN-coated LDPE films. Films retained their ice nucleation activity up to 50 freeze-thaw cycles. Our results demonstrate the potential of using ECIN-coated polymer films for frozen food application.

Ice nucleation by particles immersed in supercooled cloud droplets

The formation of ice particles in the Earth's atmosphere strongly affects the properties of clouds and their impact on climate. Despite the importance of ice formation in determining the properties of clouds, the Intergovernmental Panel on Climate Change (IPCC, 2007) was unable to assess the impact of atmospheric ice formation in their most recent report because our basic knowledge is insufficient. Part of the problem is the paucity of quantitative information on the ability of various atmospheric aerosol species to initiate ice formation. Here we review and assess the existing quantitative knowledge of ice nucleation by particles immersed within supercooled water droplets. We introduce aerosol species which have been identified in the past as potentially important ice nuclei and address their ice-nucleating ability when immersed in a supercooled droplet. We focus on mineral dusts, biological species (pollen, bacteria, fungal spores and plankton), carbonaceous combustion products and volcanic ash. In order to make a quantitative comparison we first introduce several ways of describing ice nucleation and then summarise the existing information according to the time-independent (singular) approximation. Using this approximation in combination with typical atmospheric loadings, we estimate the importance of ice nucleation by different aerosol types. According to these estimates we find that ice nucleation below about -15 °C is dominated by soot and mineral dusts. Above this temperature the only materials known to nucleate ice are biological, with quantitative data for other materials absent from the literature. We conclude with a summary of the challenges our community faces.

Selection of low-temperature resistance in bacteria and potential applications

Microbial consortia may harbour an array of resistance mechanisms that facilitate survival under harsh conditions, including antifreeze and ice-nucleation proteins. Antifreeze proteins lower freezing points as well as inhibit the growth of large, potentially damaging ice crystals from small ice embryos. In contrast, ice-nucleation proteins prevent supercooling and allow ice formation at high, sub-zero temperatures. Psychrophiles and psychrotolerant microbes are typically sought in extremely cold environments. However, given that geography is unlikely to present an insurmountable barrier to microbial dispersal, we reasoned that species with low-temperature adaptations should also be present, although rare, in more temperate environments. In consequence, the challenge then becomes one of selecting for rare microbes present in a larger community. Following the introductory commentary, we demonstrate that both freeze-thaw survival and ice-affinity selection can be used to identify microbes, which demonstrate low-temperature resistance, from enrichments derived from temperate environments. Selection resulted in a drastic decrease in cell abundance and diversity, allowing the isolation of a subset of resistant microbes. Depending on the origin of the consortia, these resistant microbes demonstrated cross-tolerance to osmotic stress, or a high proportion of antifreeze and/or ice-nucleation protein activities. Both types of ice-associating proteins presumably facilitate microbial survival at low temperatures. These proteins, as well as molecules that maintain osmotic balance, are also of commercial interest, with applications in the food, energy and medical industries. In addition, the resistant phenotypes described here provide a glimpse into the breadth of strategies microbes use to survive and thrive at low temperatures.

Geographic, seasonal, and precipitation chemistry influence on the abundance and activity of biological ice nucleators in rain and snow

Biological ice nucleators (IN) function as catalysts for freezing at relatively warm temperatures (warmer than -10 degrees C). We examined the concentration (per volume of liquid) and nature of IN in precipitation collected from Montana and Louisiana, the Alps and Pyrenees (France), Ross Island (Antarctica), and Yukon (Canada). The temperature of detectable ice-nucleating activity for more than half of the samples was > or = -5 degrees C based on immersion freezing testing. Digestion of the samples with lysozyme (i.e., to hydrolyze bacterial cell walls) led to reductions in the frequency of freezing (0-100%); heat treatment greatly reduced (95% average) or completely eliminated ice nucleation at the measured conditions in every sample. These behaviors were consistent with the activity being bacterial and/or proteinaceous in origin. Statistical analysis revealed seasonal similarities between warm-temperature ice-nucleating activities in snow samples collected over 7 months in Montana. Multiple regression was used to construct models with biogeochemical data [major ions, total organic carbon (TOC), particle, and cell concentration] that were accurate in predicting the concentration of microbial cells and biological IN in precipitation based on the concentration of TOC, Ca(2+), and NH(4)(+), or TOC, cells, Ca(2+), NH(4)(+), K(+), PO(4)(3-), SO(4)(2-), Cl(-), and HCO(3)(-). Our results indicate that biological IN are ubiquitous in precipitation and that for some geographic locations the activity and concentration of these particles is related to the season and precipitation chemistry. Thus, our research suggests that biological IN are widespread in the atmosphere and may affect meteorological processes that lead to precipitation.

Improvement of the cryopreservation of the fungal starter Geotrichum candidum by artificial nucleation and temperature downshift control

Food industry tends towards the use of controlled microorganisms in order to improve its technologies including frozen starter production. The fungus Geotrichum candidum, which is currently found in various environments, is widely used as ripening agent in some specific cheese making process. In order to optimize the cryopreservation of this microorganism, freezing experiments were carried out using a Peltier cooler-heater incubator, which permits to control the temperature downshift from +20 to -10 degrees C in time period ranges from 20 to 40min depending on the experiments. Concomitantly, study of the effect of an industrial ice nucleator protein derived from Pseudomonas syringae (SNOMAX) on the dynamic of freezing of G. candidum was carried out. Our results showed that the addition of this protein in the microbiological suspension has different complementary effects: (i) the synchronization of the different samples nucleation, leading to an homogeneous and earlier freezing, (ii) the increase of the freezing point temperature from -8.6 to -2.6 degrees C, (iii) a significant decrease of the lethality of G. candidum cells subjected to a freezing-thawing cycles challenge.

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.

Supercooling ability in two populations of the land snail Helix pomatia (Gastropoda: Helicidae) and ice-nucleating activity of gut bacteria

The land snail Helix pomatia (Gastropoda: Helicidae) is widely distributed in Northern and Central Europe where it may experience subzero temperatures during winter months. Its supercooling ability was studied in two populations of H. pomatia. One population originated from Southern Sweden (Gotaland) and the other from Central France (Auvergne). In the experimental design, they were acclimated, over 2 weeks, to artificial winter conditions (hibernation, T=5 degrees C). The Swedish snails showed a rather limited supercooling ability (temperature of crystallization, T(c)=-6.4+/-0.8 degrees C), significantly greater, however, than the supercooling capacity of the population from France (T(c)=-4.6+/-1.4 degrees C). In artificial spring conditions (3 months of hibernation followed by a progressive acclimation, over 2 weeks, to activity at T=20 degrees C), both populations exhibited a similar high T(c) (-2.0+/-1.0 degrees C). The lower T(c) of hibernating Swedish snails could be due to a greater loss of body water, accompanied by a higher concentration of solutes in the hemolymph. In both populations, the variation in hemolymph osmolality measured between hibernating (250-270 mOsm kg(-1)) and active (165-215 mOsm kg(-1)) snails may be explained by the variation in body water mass and did not suggest the production of colligative cryoprotectants. Moreover, the three bacterial strains, Buttiauxella sp., Kluyvera sp., and Tatumella sp. (Enterobacteriaceae) which were isolated from fed snails, but absent in starved snails, did not show any ice-nucleating activity at temperatures higher than -9 degrees C. Only the strain Kluyvera sp. initiated nucleation at -9 degrees C. This strain, therefore, is a weak, also termed a Type III or Class C ice-nucleating active bacterium, but with no influence on the supercooling ability of individual snails. In summary, fluctuations in body water mass of hibernating snail populations, triggering changes in osmolyte concentration, rather than the presence of endogenous ice-nucleating-active bacteria, accounts for fluctuations in their T(c).

The calculative nature of microbe-mineral interactions

Microorganisms continually redefine themselves at many levels, including the molecule, cell, and community. Although it was initially assumed that this resulted from the genesis of information within DNA alone, it has since been shown that innovation originates at multiple levels. This occurs through calculative units, each unit consisting of two proliferating structures, one nested within the other and each undergoing changes in structural geometry that affect the proliferation rate of the other. For example, the recombination of genetic structures affects the proliferation of community structures, and the recombination of community structures affects the proliferation of genetic structures. The proliferation of a nested series of structures (e.g., genes proliferating within cells, cells proliferating within communities, communities proliferating within ecosystems) results in a logic circuit that calculates the form and function of each structural element in the series. In this situation each element functions as both a habitat and an inhabitant (environment and organism), and it is this dichotomy that determines the balance of nature. Nested geological structures, such as minerals and continents, also proliferate and redefine themselves in much the same way. Microbe-mineral interactions thus link nested biological calculations to an analogous set of nested geological calculations. Examples include the microorganisms involved in the nucleation (proliferation) of ferric hydroxides, carbonates, silicates, and ice crystals.

Bacterial cold shock responses

As a measure for molecular motion, temperature is one of the most important environmental factors for life as it directly influences structural and hence functional properties of cellular components. After a sudden increase in ambient temperature, which is termed heat shock, bacteria respond by expressing a specific set of genes whose protein products are designed to mainly cope with heat-induced alterations of protein conformation. This heat shock response comprises the expression of protein chaperones and proteases, and is under central control of an alternative sigma factor (sigma 32) which acts as a master regulator that specifically directs RNA polymerase to transcribe from the heat shock promotors. In a similar manner, bacteria express a well-defined set of proteins after a rapid decrease in temperature, which is termed cold shock. This protein set, however, is different from that expressed under heat shock conditions and predominantly comprises proteins such as helicases, nucleases, and ribosome-associated components that directly or indirectly interact with the biological information molecules DNA and RNA. Interestingly, in contrast to the heat shock response, to date no cold-specific sigma factor has been identified. Rather, it appears that the cold shock response is organized as a complex stimulon in which post-transcriptional events play an important role. In this review, we present a summary of research results that have been acquired in recent years by examinations of bacterial cold shock responses. Important processes such as cold signal perception, membrane adaptation, and the modification of the translation apparatus are discussed together with many other cold-relevant aspects of bacterial physiology and first attempts are made to dissect the cold shock stimulon into less complex regulatory subunits. Special emphasis is placed on findings concerning the nucleic acid-binding cold shock proteins which play a fundamental role not only during cold shock adaptation but also under optimal growth conditions.