Preservation of membranes in anhydrobiotic organisms: the role of trehalose

Expression of the yeast trehalose-6-phosphate synthase gene in transgenic tobacco plants: pleiotropic phenotypes include drought tolerance

The yeast trehalose-6-phosphate synthase gene (TPS1) was engineered under the control of the cauliflower mosaic virus regulatory sequences (CaMV35S) for expression in plants. Using Agrobacterium-mediated transfer, the gene was incorporated into the genomic DNA and constitutively expressed in Nicotiana tabacum L. plants. Trehalose was determined in the transformants, by anion-exchange chromatography coupled to pulsed amperometric detection. The non-reducing disaccharide accumulated up to 0.17 mg per g fresh weight in leaf extracts of transgenic plants. Trehaloseaccumulating plants exhibited multiple phenotypic alterations, including stunted growth, lancet-shaped leaves, reduced sucrose content and improved drought tolerance. These pleiotropic effects, and the fact that water loss from detached leaves was not significantly affected by trehalose accumulation, suggest that synthesis of this sugar, rather than leading to an osmoprotectant effect, had altered sugar metabolism and regulatory pathways affecting plant development and stress tolerance.

The thermodynamic mechanism of protein stabilization by trehalose

The stabilization of ribonuclease A by alpha-alpha-trehalose was studied by preferential interaction and thermal unfolding. The protein is stabilized by trehalose at pH 2.8 and pH 5.5. Wyman linkage analysis showed increased exclusion of trehalose from the protein domain on denaturation. Preferential interaction measurements were carried out at 52 degrees C at pH 5.5 and 2.8, where the protein is native and unfolded, respectively, and at 20 degrees C where the protein is native at both pH values. At the low temperature, the interaction was preferential exclusion. At 52 degrees C the interaction was that of preferential binding, greater to the native than the unfolded protein, the increment on denaturation being identical to that deduced from the Wyman analysis. The stabilizing effect of trehalose can be fully accounted by the change in transfer free energy on unfolding. The temperature dependence of the preferential interactions of 0.5 M trehalose with ribonuclease A showed that it is the smaller preferential binding to the unfolded protein than to the native one which gives rise to the stabilization. A thermodynamic analysis of the data led to approximate values of the transfer enthalpies and transfer entropies for the trehalose-ribonuclease A system.

The role of trehalose in the physiology of nematodes

The sugar trehalose, an alpha-1-linked non-reducing disaccharide of glucose, is important in the physiology of many micro-organisms as well as in some groups of metazoan organisms, including insects and nematodes. Trehalose is a stress protectant in biological systems as it interacts with and directly protects lipid membranes and proteins from the damage caused by environmental stresses such as desiccation and freezing. Trehalose is present in many nematode species where its concentration often exceeds that of glucose but is usually lower than that of glycogen. In Ascaris suum it is found in all tissues, with highest concentrations in muscle, haemolymph and the female and male reproductive organs. Trehalose acts as an energy reserve in some nematodes and their eggs, and may be important in uptake of glucose; it appears to function as the major circulating blood sugar. Trehalose accumulates in nematodes that can withstand dehydration and may be important in supercooling of nematodes or eggs that can withstand freezing. In many nematodes trehalose is also important in the process of egg hatching. The combined action of 2 enzymes, trehalose 6-phosphate (T6P) synthase and T6P phosphatase, catalyses the synthesis of trehalose in most organisms. Hydrolysis of trehalose glucose is catalysed by trehalase. These enzymes to have been detected in nematodes but the processes regulating their activity are unknown. Trehalose metabolism may provide new molecular targets for attack in nematodes parasitic in mammals.

Characterization of trehalase activities from the thermophilic fungus Scytalidium thermophilum

The thermophilic fungus Scytalidium thermophilum produced large amounts of intracellular and extracellular trehalase activity when grown on starch as the sole carbon source. The specific activity of the purified proteins: 1700 U (mg protein)-1 (extracellular) and 3700 U (mg protein)-1 (intracellular), was many times higher than the values reported for other microbial sources. The apparent molecular mass of the native enzymes was estimated to be 370 kDa (extracellular trehalase) and 398 kDa (intracellular trehalase) by gel-filtration chromatography. Analysis by SDS-PAGE showed unique polypeptide bands of approx. 82 kDa (extracellular trehalase) and 85 kDa (intracellular trehalase), suggesting that the native enzymes were composed of five subunits. The carbohydrate content of extracellular and intracellular trehalases was estimated to be 81% and 51%, respectively. Electrofocusing indicated a pI of 3.7 and 3.4, respectively, for the extracellular and intracellular enzymes. Both trehalases were highly specific for trehalose and were stimulated by calcium and manganese. Calcium and manganese also protected both trehalases from thermoinactivation. Inhibition was observed in the presence of aluminium, mercurium, copper, zinc, EDTA, ADP, and ATP. Apparent Km values, for the extracellular and intracellular trehalases, were 3.58 mM and 2.24 mM, respectively. The optimum of pH for the extracellular and the intracellular trehalase was 6.0, and the optimum of temperature 60 degrees C and 65 degrees C, respectively.

Is trehalose special for preserving dry biomaterials?

Simple sugars, especially disaccharides, stabilize biomaterials of various composition during air-drying or freeze-drying. We and others have provided evidence that direct interaction, an interaction that we believe is essential for the stabilization, between the sugar and polar groups in, for example, proteins and phospholipids occurs in the dry state. Some researchers, however, have suggested that the ability of the sugar to form a glass is the only requirement for stabilization. More recently, we have shown that both glass formation and direct interaction of the sugar and headgroup are often required for stabilization. In the present study, we present a state diagram for trehalose glass and suggest that the efficacy of this sugar for stabilization may be related to its higher glass transition temperatures at all water contents. We also show that trehalose and trehalose:liposome preparations form trehalose dihydrate as well as trehalose glass when rehydrated with water vapor. Formation of the dihydrate sequesters water, which might otherwise participate in lowering the glass transition temperature to below ambient. Because samples remain in the glassy state at ambient temperatures, viscosity is high and fusion between liposomes is prevented.

Purification and biochemical characterization of the ATH1 gene product, vacuolar acid trehalase, from Saccharomyces cerevisiae

The disaccharide trehalose plays a critical role in yeast cell survival during conditions of environmental stress. The vacuole of the yeast Saccharomyces cerevisiae contains an enzyme, acid trehalase (ATH), that is capable of degrading trehalose. Recently, a gene required for ATH activity, ATH1, was cloned and sequenced [Destruelle et al., (1995) Yeast 11, 1015-1025]. The relationship between ATH1 and ATH, however, was not determined. We have purified ATH and shown that it is the ATH1 gene product; peptide sequences from the purified protein correspond to the deduced amino acid sequence of Ath1p. In addition, antiserum to Ath1p specifically recognizes purified ATH.

Arbutin inhibits PLA2 in partially hydrated model systems

Arbutin is a glycosylated hydroquinone found at high concentrations in certain plants capable of surviving extreme and sustained dehydration. In this paper, we examine a potential role of this molecule in anhydrobiosis. We have studied its effects on the physical properties of phospholipids and on preservation of liposomes during drying. Arbutin depresses the gel to liquid crystalline phase transition temperature of dry phospholipids, as measured by differential scanning calorimetry, with a pattern similar to that seen in phospholipids dried with the disaccharide trehalose. Unlike trehalose, however, arbutin does not protect dry liposomes from leaking their contents. Also, using Fourier transform infrared spectroscopy, we found an increase in the vibrational frequency of the phosphate asymmetric stretch in partially hydrated phospholipids in the presence of arbutin. Trehalose, by contrast, depresses the frequency of the phosphate in dry phospholipids, indicating that the modes of interaction of trehalose and arbutin with the bilayer are different. Previously, we have shown that phospholipases can be active in liposomes with surprisingly low water contents. Based on the structural similarity of arbutin to a known inhibitor of phospholipase A2 (PLA2), it appeared possible that arbutin might serve as an inhibitor of phospholipases. Liposomes of varying composition were lyophilized in the presence and absence of phospholipases. When the liposomes were partially rehydrated at 76% relative humidity, arbutin inhibited PLA2, but did not inhibit phospholipases B or C. Accumulation of enzyme product in the liposome membranes was measured by analytical thin layer chromatography, and was taken as a measure of enzyme activity. Arbutin did not inhibit any of the enzymes in the presence of excess water. Based on these data, hypotheses are presented concerning the mechanism of PLA2 inhibition by arbutin in the mostly dehydrated state.

Culture Age, Temperature, and pH Affect the Polyol and Trehalose Contents of Fungal Propagules

The growth and conidial physiology of the entomopathogenic fungi Beauveria bassiana, Metarhizium anisopliae, and Paecilomyces farinosus were studied under different conditions. The effects of culture age (up to 120 days), temperature (5 to 35(deg)C), and pH (2.9 to 11.1) were determined. Growth was optimal at pH 5 to 8 for each isolate and between 20 and 35(deg)C, depending on the isolate. The predominant polyol in conidia was mannitol, with up to 39, 134, and 61 mg g of conidia(sup-1) for B. bassiana, M. anisopliae, and P. farinosus, respectively. Conidia of M. anisopliae contained relatively small amounts of lower-molecular-weight polyols and trehalose (less than 25 mg g(sup-1) in total) in all treatments. Conidia of B. bassiana and P. farinosus contained up to 30, 32, and 25 mg of glycerol, erythritol, and trehalose, respectively, g(sup-1), depending on the treatment. Conidia of P. farinosus contained unusually high amounts of glycerol and erythritol at pH 2.9. The apparent effect of pH on gene expression is discussed in relation to the induction of a water stress response. To our knowledge, this is the first report of polyols and trehalose in fungal propagules produced over a range of temperature or pH. Some conditions and harvesting times were associated with an apparent inhibition of synthesis or accumulation of polyols and trehalose. This shows that culture age and environmental conditions affect the physiological quality of inoculum and can thereby determine its potential for biocontrol.

Deletion of the ATH1 gene in Saccharomyces cerevisiae prevents growth on trehalose

The biological function of the yeast trehalases (EC 3.2.1.28) consists of down-regulation of the concentration of trehalose via glucose formation by trehalose hydrolysis. While it is generally accepted that the cytosolic neutral trehalase (encoded by the NTH1 gene) is responsible for trehalose hydrolysis in intact cells, very little is known about a role of the vacuolar acid trehalase and the product of the recently described neutral trehalase gene YBRO106 (NTH2). We have analyzed the role of the acid trehalase in trehalose hydrolysis using the ATH1 deletion mutant (delta ath1) of Saccharomyces cerevisiae [M. Destruelle et al. (1995) Yeast 11, 1015-10251 deficient in acid trehalase activity under various nutritional conditions. In contrast to wild-type and a mutant deficient in the neutral trehalase (delta nth1), the delta ath1 mutant does not grow on trehalose as a carbon source. Experiments with diploid strains heterozygous for delta ath1 show a gene dosage effect for the ATH1 gene for growth on trehalose. The need for acid trehalase for growth on trehalose is supported by the finding that acid trehalase activity is induced during exponential growth of cells on trehalose while no such induction is measurable during growth on glucose. Our results show that the vacuolar acid trehalase Ath1p is necessary for the phenotype of growth on trehalose, i.e. trehalose utilization, in contrast to cytosolic neutral trehalase Nth1p which is necessary for intracellular degradation of trehalose. For explanation of the need for vacuolar acid trehalase and not cytosolic neutral trehalase for growth on trehalose, the participation of endocytosis for uptake of trehalose from medium to the vacuoles is discussed.

Kinetics and energetics of trehalose transport in Saccharomyces cerevisiae

Cells of Saccharomyces cerevisiae are able to transport trehalose against a concentration gradient, without efflux or counterflow of the labeled substrate. Uptake was inhibited by uncouplers, acetic acid, and organic mercury compounds. The addition of trehalose resulted in alkalinization of the medium. The ratio of H+ depletion to trehalose uptake by yeast cells was approximately 1:1, which indicates the existence of a trehalose-H+ symporter in these cells. The optimum pH for this active H+-trehalose symport was 5.0, and both the Km and the Vmax were negatively affected by increasing or decreasing the extracellular pH from its optimum value. Kinetic studies showed the existence of at least two different trehalose transport activities in yeast cells: a high-affinity H+-trehalose symporter (Km = 4 mM), and a low-affinity transport activity (Km > 100 mM) that could be a facilitated diffusion process. The high-affinity H+-trehalose symporter was repressed by glucose, whereas the low-affinity uptake was constitutively expressed in S. cerevisiae.

Evaluation of a new solution containing trehalose for twenty-hour canine lung preservation

We examined the efficacy of two new preservation solutions containing trehalose--an extracellular type (ET-K) of solution and an intracellular type (IT-K) of solution--in relation to that of Euro-Collins (EC) solution in 20-h canine lung preservation. Canine lungs were flushed with one of the three solutions (n = 5 for each solution) after pretreatment with PGE1 (20 micrograms/kg) and were stored for 20 h at 4 degrees C. The left lungs were transplanted and evaluated to 6 h post transplant. In the ET-K group, the arterial oxygen tension after reperfusion was significantly higher than in the IT-K and EC groups. The pulmonary vascular resistance, wet/dry weight ratio, and histological evaluation of each transplanted lung in the ET-K group were also better than in the IT-K and EC groups. This indicates that ET-K solution is useful for 20-h preservation of canine lung grafts.

Long-term cryopreservation can prevent rejection of canine tracheal allografts with preservation of graft viability

We previously reported that cryopreservation of tracheas for 1 month was possible in a canine tracheal autotransplantation model with use of a preservative solution containing trehalose. Realizing that the allogenicity of many organs is decreased by freezing, we examined the possibility of immunosuppressant-free canine tracheal allotransplantation after long-term cryopreservation. Six to 10 rings of the trachea were removed from donor dogs (n = 12), immersed in the preservative solution, and cryopreserved in a deep freezer at -85 degrees C for 285 +/- 28 days (cryopreservation group). Five rings of the mediastinal trachea of recipient dogs were removed. The cryopreserved tracheas were thawed and transplanted to replace the excised mediastinal tracheas. In a control group (n = 6), the graft was preserved in Euro-Collins solution at 10 degrees C for 16 to 17 hours. Allotransplantation of tracheas was done as in the cryopreservation group. The anastomotic site and graft were covered with an omental pedicle in both groups. In the cryopreservation group, every animal, except one that was killed for pathologic examination, survived more than 2 months. All the grafts of this group were viable, and no stenosis or tracheomalacia was observed. In the control group, most of the animals died within 1 month of tracheal stenosis caused by rejection. These findings reveal that immunosuppressant-free canine tracheal allotransplantation was consistently possible after long-term cryopreservation of the graft in a preservative solution containing trehalose. This simple method could solve both donor shortage and immunosuppression problems.

Disruption of the yeast ATH1 gene confers better survival after dehydration, freezing, and ethanol shock: potential commercial applications

The accumulation of trehalose is a critical determinant of stress resistance in the yeast Saccharomyces cerevisiae. We have constructed a yeast strain in which the activity of the trehalose-hydrolyzing enzyme, acid trehalase (ATH), has been abolished. Loss of ATH activity was accomplished by disrupting the ATH1 gene, which is essential for ATH activity. The delta ath1 strain accumulated greater levels of cellular trehalose and grew to a higher cell density than the isogenic wild-type strain. In addition, the elevated levels of trehalose in the delta ath1 strain correlated with increased tolerance to dehydration, freezing, and toxic levels of ethanol. The improved resistance to stress conditions exhibited by the delta ath1 strain may make this strain useful in commercial applications, including baking and brewing.

Is vitrification involved in depression of the phase transition temperature in dry phospholipids?

Recent literature has suggested that the depression of the phase transition temperature (Tm) in dry phospholipids by sugars may be ascribed to vitrification of the stabilizing solute, rather than by the direct interaction between sugar and phospholipid we have proposed. Koster et al. ((1994) Biochim. Biophys. Acta 1193, 143-150) claim that the only necessity is that the glass transition (Tg) for the sugar exceed Tm for the lipid. Evidence is presented in the present paper that this is not sufficient. Based on the vitrification hypothesis of Koster et al., the predicted order of effectiveness in depressing Tm in dry dipalmitoylphosphatidylcholine (DPPC) is dextran > or = hydroxyethyl starch > stachyose > raffinose > trehalose > sucrose > glucose. In fact, the opposite order was seen. The effect of raffinose, sucrose, or trehalose on Tm in dry DPPC depends on the thermal history of the sample, as we have reported previously. When DPPC dried with trehalose is heated for the first time, Tm is about 55 degrees C, but on the second and subsequent heating scans Tm falls to about 25 degrees C. Koster et al. suggest that this effect is due to heating the sample above Tg rather than to melting the hydrocarbon chains. We present evidence here that all that is required is for the chains to be melted. Further, we show that retention of residual water by DPPC dried with trehalose depends on the drying temperature, but is independent of drying temperature with glucose, a finding that is consistent with direct interaction. We conclude that vitrification is not in itself sufficient to depress Tm in dry phospholipids.

Bacillus subtilis operon under the dual control of the general stress transcription factor sigma B and the sporulation transcription factor sigma H

The sigma B transcription factor of Bacillus subtilis is activated in response to a variety of environmental stresses, including those imposed by entry into the stationary-growth phase, and by heat, salt or ethanol challenge to logarithmically growing cells. Although sigma B is thought to control a general stress regulon, the range of cellular functions it directs remains largely unknown. Our approach to understand the physiological role of sigma B is to characterize genes that require this factor for all or part of their expression, i.e. the csb genes. In this study, we report that the transposon insertion csb40::Tn917lac identifies an operon with three open reading frames, the second of which resembles plant proteins induced by desiccation stress. Primer-extension and operon-fusion experiments showed that the csb40 operon has a sigma B-dependent promoter which is strongly induced by the addition of salt to logarithmically growing cells. The csb40 operon also has a second, sigma H-dependent promoter that is unaffected by salt addition. These results provide support for the hypothesis that sigma B controls a general stress regulon, and indicate that the sigma B and sigma H regulons partly overlap. We suggest that in addition to its acknowledged role in the sporulation process, sigma H is also involved in controlling a subclass of genes that are broadly involved in a general stress response.

Stability of dry liposomes in sugar glasses

Sugars, particularly trehalose and sucrose, are used to stabilize liposomes during hydration (freeze-drying and air-drying). As a result, dry liposomes are trapped in a sugar glass, a supersaturated and thermodynamically unstable solid solution. We investigated the effects of the glassy state on liposome fusion and solute retention in the dry state. Solute leakage from dry liposomes was extremely slow at temperatures below the glass transition temperature (Tg); however, it increased exponentially as temperature increased to near or above the Tg, indicating that the glassy state had to be maintained for dry liposomes to retain trapped solutes. The leakage of solutes from dry liposomes followed the law of first-order kinetics and was correlated linearly with liposome fusion. The kinetics of solute leakage showed an excellent fit with the Arrhenius equation at temperatures both above and below the Tg, with a transitional break near the Tg. The activation energy of solute leakage was 1320 kJ/mol at temperatures above the Tg, but increased to 1991 kJ/mol at temperatures below the Tg. The stabilization effect of sugar glass on dry liposomes may be associated with the elevated energy barrier for liposome fusion and the physical separation of dry liposomes in the glassy state. The half-life of solute retention in dry liposomes may be prolonged by storing dry liposomes at temperatures below the Tg and by increasing the Tg of the dry liposome preparation.

ET-Kyoto solution for 48-hour canine lung preservation

BACKGROUND

ET-Kyoto (ET-K) solution, proven safe for 20-hour lung preservation, was modified to achieve longer preservation: ET-K2 solution with more buffer capacity and ET-K3 with less potassium.

METHODS

Lungs were preserved with one of the three solutions (with prostaglandin E1 at 4 degrees C for 48 hours (n = 5 for each). Left lung transplantation was performed and evaluated for 6 hours.

RESULTS

Each solution became acidic after preservation (p < 0.01), though the change was lowest in the ET-K2 solution. All animals in the ET-K and ET-K3 groups survived for 6 hours after reperfusion, but only 1 survived in the ET-K2 group (p < 0.05). In all groups, partial pressure of oxygen in arterial blood decreased gradually after reperfusion. Pulmonary vascular resistance after reperfusion was significantly lower in the ET-K group than in the ET-K3 group (p < 0.01). Scanning electron microscopic examination showed that endothelial cell swelling and disruption were milder in the ET-K group (with the solution containing potassium of 44 mEq/L) than in the ET-K3 group.

CONCLUSION

Lung preservation can be achieved for 48 hours in ET-K and ET-K3 solutions. Enhancement of buffer capacity provides no advantage. Potassium at 44 mEq/L does not cause deterioration of endothelial cells.

Trehalose-containing solutions enhance preservation of cultured endothelial cells

BACKGROUND AND METHODS

We have developed two types of preservation solutions containing trehalose. ET-Kyoto solution (ET-K) is an extracellular type and IT-Kyoto solution (IT-K) is an intracellular type. In the present study we examined with in vitro assays the ability of ET-K, IT-K, Euro-Collins (EC), and University of Wisconsin (UW) solutions to preserve a murine endothelial cell line. The viability of cells stored in the solutions at 4 degrees C was determined by trypan blue exclusion and MTT assay.

RESULTS

Trypan blue exclusion showed the viability after 48 hours of cold storage to be 49.5 +/- 4.7% (mean +/- standard error) in ET-K, 59.5 +/- 0.7% in IT-K, 29.2 +/- 2.5% in EC, and 55.3 +/- 7.6% in UW (ET-K or UW versus EC, p < 0.05; IT-K versus EC, p < 0.01). MTT assay absorbance values for cells after 48 hours of cold storage were 0.366 +/- 0.0066 (mean +/- standard error) in ET-K, 0.358 +/- 0.0044 in IT-K, 0.336 +/- 0.011 in EC, and 0.362 +/- 0.0019 in UW (ET-K or UW versus EC, p < 0.05). After 120 hours, absorbance values for cells were 0.303 +/- 0.0038 in ET-K, 0.269 +/- 0.0034 in IT-K, 0.186 +/- 0.011 in EC, and 0.265 +/- 0.0066 in UW (ET-K versus UW, p < 0.05; ET-K versus IT-K, p < 0.01; ET-K, IT-K or UW versus EC, p < 0.01).

CONCLUSIONS

As far as the ability to preserve a murine endothelial cell line at a low temperature was concerned, the ET-K solution was superior to the UW solution, the IT-K solution and UW solution were equal, and the ET-K and IT-K solutions were superior to the EC solution.

Effects of glucose and its oligomers on the stability of freeze-dried liposomes

The effects of glucose and its oligomers (maltodextrins) on the stability of sonicated liposomes during freeze-drying were studied by monitoring the retention of the fluorescent dye, Calcein, entrapped in the liposomal inner aqueous phase and by the use of differential scanning calorimetry (DSC). Glucose showed weak cryoprotective effects on dioleoylphosphatidylcholine (DOPC) or egg yolk phosphatidylcholine (eggPC) liposomes, while it had a relatively high cryoprotective effect on dipalmitoylphosphatidylcholine (DPPC) liposomes. Maltose and maltotriose showed high cryoprotective effects on eggPC liposomes, while other maltodextrin, longer oligomers, showed low cryoprotective effects. No saccharide was effective to protect DOPC liposomes. The fluidity and/or packing of lipid membranes had considerable influences on the stability of liposomes during the lyophilization. Maltodextrins showed relatively high cryoprotective effects on DPPC liposomes at low saccharide/lipid molar ratios, although the cryoprotective effects decreased with the increase in the molar ratios. Size measurements suggested that glucose and maltose completely prevented the aggregation and/or fusion of liposomes during lyophilization, and that other maltodextrins induced them due to their weak hydrophobic properties.

Reliable cryopreservation of trachea for one month in a new trehalose solution

We previously reported that trehalose, a reduced disaccharide, was effective in the preservation of lungs. In this study, we investigated the possibility of prolonged cryopreservation of tracheas in a preservative solution containing trehalose. Five rings of cervical trachea were removed and immersed in the preservative solution. The harvested tracheas were then cryopreserved and stored in a deep freezer at -85 degrees C. One month later, five rings of mediastinal trachea were removed. The cryopreserved cervical tracheas were thawed and autotransplanted in place of the excised mediastinal trachea (n = 6). The anastomotic site and graft were then covered with an omental pedicle. All six animals survived for more than 6 months. All grafts survived without any evidence of atrophy or stenosis. Microscopic examination of the grafts showed that the integrity of the tracheal tissues was maintained. Our findings show that consistent cryopreservation of the trachea for 1 month is possible in a preservative solution containing trehalose.

Phospholipase A2 activity in dehydrated systems: effect of the physical state of the substrate

In the presence of excess water, enzymatic activity of phospholipase A2 (PLA2) depends on the physical state of the lipid substrate. In order to determine if this also holds true in dehydrated systems, the physical parameters of charge, hydration state, and head group spacing of liposome membranes and their effects on PLA2 lipid hydrolysis were studied. Liposomes of varying composition were freeze-dried in the presence of PLA2 and partially rehydrated at controlled relative humidities. Accumulation of free fatty acids in the liposomal membranes was used as a measure of PLA2 activity. We found that PLA2, which was not activated during lyophilization, was most active during partial rehydration of the liposomes. The hydration state, charge and headgroup spacing of the membrane were all important in determining PLA2 activity in the dehydrated system.

Global changes in protein synthesis during adaptation of the yeast Saccharomyces cerevisiae to 0.7 M NaCl

Exponentially growing Saccharomyces cerevisiae was challenged to increased salinity by transfer to 0.7 M NaCl medium, and changes in protein synthesis were examined during the 1st h of adaptation by use of two-dimensional gel electrophoresis coupled to computerized quantification. An impressive number of proteins displayed changes in the relative rate of synthesis, with most differences from nonstressed cells being found at between 20 and 40 min. During this period, 18 proteins exhibited more than eightfold increases in their rates of synthesis and were classified as highly NaCl responsive. Only two proteins were repressed to the same level. Most of these highly NaCl-responsive proteins seemed to constitute gene products not earlier reported to respond to dehydration. Applying a selection criterion to subsequent samples of a twofold change in the relative rate of synthesis, 14 different regulatory patterns were discerned. Most identified glycolytic enzymes exhibited a delayed response, and their rates of synthesis did not change until the middle phase of adaptation, with only a minor decrease in the rate of production. A slight salt-stimulated response was observed for some members of the HSP70 gene family. Overall, the data presented indicate complex intracellular signalling as well as involvement of diverse regulatory mechanisms during the period of adaptation to NaCl.

Manipulation of intracellular glycerol and erythritol enhances germination of conidia at low water availability

The insect pathogens Beauveria bassiana, Metarhizium anisopliae and Paecilomyces farinosus can be effective biocontrol agents when relative humidity (RH) is close to 100%. At reduced water availability, germination of propagules, and therefore host infection, cannot occur. Cultures of B. bassiana, M. anisopliae and P. farinosus were grown under different conditions to obtain conidia with a modified polyol and trehalose content. Conidia with higher intracellular concentrations of glycerol and erythritol germinated both more quickly and at lower water activity (aw) than those from other treatments. In contrast, conidia containing up to 235.7 mg trehalose g-1 germinated significantly (P < 0.05) more slowly than those with an equivalent polyol content but less trehalose, regardless of water availability. Conidia from control treatments did not germinate below 0.951-0.935 aw (identical to 95.1-93.5% RH). In contrast, conidia containing up to 164.6 mg glycerol plus erythritol g-1 germinated down to 0.887 aw (identical to 88.7% RH). These conidia germinated below the water availability at which mycelial growth ceases (0.930-0.920 aw). Germ tube extension rates reflected the percentage germination of conidia, so the most rapid germ tube growth occurred after treatments which produced conidia containing the most glycerol and erythritol. This study shows for the first time that manipulating polyol content can extend the range of water availability over which fungal propagules can germinate. Physiological manipulation of conidia may improve biological control of insect pests in the field.

Effect of the kinetics of temperature variation on Saccharomyces cerevisiae viability and permeability

The variation rate of the temperature increase was found to have a great effect on the viability of Saccharomyces cerevisiae subjected to heat perturbations between 25 degrees C and 50 degrees C. A low intensity of the increase rate of temperature could maintain an important viability of the cells (about 34% of the initial population) with regard to the corresponding viability (about 1%) observed after a sudden step change for the same final temperature level of 50 degrees C. A cell volume reduction more important (22% of the initial volume) has been observed in cells submitted to a heat shock than for the cells which have been submitted to a slow kinetic of temperature increase (9%). Such an observation allowed to propose a relation between the membrane permeability and the kinetics of temperature variation.

Comments on the physics and chemistry of trehalose as a storage medium for hemoglobin-based blood substitutes: "from Kramers Theory to the Battlefield"

A glass of the naturally-occurring sugar trehalose may be a suitable medium for the storage of hemoglobin-based blood substitutes. Trehalose has many or possibly all of the properties required for this purpose, including solubilization of hemoglobin to a very high concentration, lack of toxicity, slowing of oxidation to the non-oxygen binding methemoglobin, stability at room temperature and above, and ease of transport. It should also be possible to prepare hemoglobin extremely rapidly for injection into the circulation in situations where blood replacement is required immediately, as in a domestic emergency room or on the battlefield. These practical considerations are briefly discussed, as well as the theoretical reasons for slowing of chemical reactions in the glassy state.

Differential importance of trehalose in stress resistance in fermenting and nonfermenting Saccharomyces cerevisiae cells

The trehalose content in laboratory and industrial baker's yeast is widely believed to be a major determinant of stress resistance. Fresh and dried baker's yeast is cultured to obtain a trehalose content of more than 10% of the dry weight. Initiation of fermentation, e.g., during dough preparation, is associated with a rapid loss of stress resistance and a rapid mobilization of trehalose. Using specific Saccharomyces cerevisiae mutants affected in trehalose metabolism, we confirm the correlation between trehalose content and stress resistance but only in the absence of fermentation. We demonstrate that both phenomena can be dissociated clearly once the cells initiate fermentation. This was accomplished both for cells with moderate trehalose levels grown under laboratory conditions and for cells with trehalose contents higher than 10% obtained under pilot-scale conditions. Retention of a high trehalose level during fermentation also does not prevent the loss of fermentation capacity during preparation of frozen doughs. Although higher trehalose levels are always correlated with higher stress resistance before the addition of fermentable sugar, our results show that the initiation of fermentation causes the disappearance of any other factor(s) required for the maintenance of stress resistance, even in the presence of a high trehalose content.

Origins of the parasitic habit in the nematoda

Circumstances that probably attended and influenced the adoption and development of the parasitic habit amongst the Nematoda are examined. Features that allowed early terrestrial nematodes to exploit discontinuous habitats such as decomposing organic matter, are considered to have been advantageous to microbivorous Secernentea that became parasites of animals and plants. This development followed the appearance of a land flora and that the Amphibia were the first vertebrate hosts of nematodes. Life cycles involving intermediate hosts were essential in drier environments and in a aquatic ones where intermediate hosts preserve the infective stages; keeps them "in circulation", and makes them attractive to predators. It is concluded that the parasitic habit was adopted repeatedly in both Secernentea and Adenophorea, though the latter did not diversify as much. Convergence is a common feature of nematode evolution, and the typical life history pattern of 5 stadia separated by 4 moults is often greatly modified by suppression, extension and diversification of stages and their roles. There is a need to examine the nematodes, especially of invertebrates in the remaining rain forests of Gondwanaland before they disappear.

Trehalose-6-phosphate hydrolase of Escherichia coli

The disaccharide trehalose acts as an osmoprotectant as well as a carbon source in Escherichia coli. At high osmolarity of the growth medium, the cells synthesize large amounts of trehalose internally as an osmoprotectant. However, they can also degrade trehalose as the sole source of carbon under both high- and low-osmolarity growth conditions. The modes of trehalose utilization are different under the two conditions and have to be well regulated (W. Boos, U. Ehmann, H. Forkl, W. Klein, M. Rimmele, and P. Postma, J. Bacteriol. 172:3450-3461, 1990). At low osmolarity, trehalose is transported via a trehalose-specific enzyme II of the phosphotransferase system, encoded by treB. The trehalose-6-phosphate formed internally is hydrolyzed to glucose and glucose 6-phosphate by the key enzyme of the system, trehalose-6-phosphate hydrolase, encoded by treC. We have cloned treC, contained in an operon with treB as the promoter-proximal gene. We have overproduced and purified the treC gene product and identified it as a protein consisting of a single polypeptide with an apparent molecular weight of 62,000 as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The enzyme hydrolyzes trehalose-6-phosphate with a Km of 6 mM and a Vmax of at least 5.5 mumol of trehalose-6-phosphate hydrolyzed per min per mg of protein. The enzyme also very effectively hydrolyzes p-nitrophenyl-alpha-D-glucopyranoside, but it does not recognize trehalose, sucrose, maltose, isomaltose, or maltodextrins. treC was sequenced and found to encode a polypeptide with a calculated molecular weight of 63,781. The amino acid sequence deduced from the DNA sequence shows homology (50% identity) with those of oligo-1,6-glucosidases (sucrase-isomaltases) of Bacillus spp. but not with those of other disaccharide phosphate hydrolases. This report corrects our previous view on the function of the treC gene product as an amylotrehalase, which was based on the analysis of the metabolic products of trehalose metabolism in whole cells.

Heat-shock response in a yeast tps1 mutant deficient in trehalose synthesis

Exponential cells of the Saccharomyces cerevisiae tps1 mutant underwent a rapid loss of viability upon a non-lethal heat exposure (from 28 to 42 degrees C). However, a further more severe heat stress (52.5 degrees C 5 min) induced an increase in the fraction of viable cells. This mutant can not synthesize trehalose either at 28 degrees C or at 42 degrees C due to the lack of a functional trehalose-6P synthase complex. In control experiments carried out with the wild-type W303-1B, heat-stressed exponential phase cultures grown on YPgal at 28 degrees C acquired thermotolerance to a higher extent than identical cultures grown on YPD, although in both cultures the level of stored trehalose was negligible. These data suggest that the bulk of trehalose accumulated in yeast upon mild heat treatments is not sufficient to account for the acquisition of thermotolerance.

Use of Yarrowia lipolytica hexokinase for the quantitative determination of trehalose 6-phosphate

This paper describes a procedure for the quantitative determination of trehalose 6-phosphate (T6P) based on its ability to inhibit hexokinase from Yarrowia lipolytica. The assay is linear between 1 nmol and at least 8 nmol. The concentration of T6P in wild-type Saccharomyces cerevisiae (0.15 mM) and in ras2 mutants (0.25 mM) remained unchanged in the exponential or stationary phase of growth or after heat shock. A tps1 mutant affected in T6P synthase did not show detectable T6P. Heat shock increased the concentration of T6P in Schizosaccharomyces pombe from 0.43 to 0.75 mM.

Interactions between soluble sugars and POPC (1-palmitoyl-2-oleoylphosphatidylcholine) during dehydration: vitrification of sugars alters the phase behavior of the phospholipid

The phase behavior of 1-palmitoyl-2-oleoylphosphatidylcholine (POPC) was characterized as a function of hydration in the presence of combinations of sugars representative of sugars found in seed embryos having differing degrees of desiccation tolerance. The tendency of the sugar mixes to vitrify was also monitored as a function of hydration. Using differential scanning calorimetry, it was found that all sugars diminished the increase in the gel-to-fluid phase transition temperature (Tm) of POPC that occurred upon dehydration of the pure lipid. These results are analyzed in terms of the osmotic and volumetric properties of sugars. Also, it was found that in those samples for which the glass transition temperature (Tg) was greater than the Tm of POPC, Tm was lowered by approx. 20 C degrees from the value for the fully hydrated lipid. X-ray diffraction data confirmed that acyl chain freezing was deferred to a lower temperature during cooling of vitrified samples. The significance of these results is discussed in terms of the ability of many organisms to tolerate desiccation.

Differential changes in the activity of cytosolic and vacuolar trehalases along the growth cycle of Saccharomyces cerevisiae

Saccharomyces cerevisiae cells contain two intracellular and soluble trehalases with distinct subcellular location (cytosol and vacuoles, respectively). Both enzymes showed an opposite pattern of activity along the growth cycle. Activity of the cytosolic trehalase was high in cells growing exponentially on fermentable sugars (glucose, mannose or galactose) and sharply decayed as the cultures enter stationary phase coinciding with the beginning of trehalose biosynthesis. By contrast, vacuolar trehalase was only detectable in glucose-grown resting cells or in cultures growing on respiratory substrates (glycerol or ethanol). This enzyme was partially derepressed in the mutant hex2, which is deficient in glucose repression. Addition of fresh YPD medium to stationary-phase cultures induced the sudden reactivation of cytosolic trehalase with the concomitant slower inactivation of vacuolar trehalase. However, addition of glucose or various nitrogen sources alone had only a minor effect on both activities. The presence of cycloheximide had no effect on cytosolic trehalase, whereas completely blocked the appearance of vacuolar trehalase suggesting the requirement of protein synthesis 'de novo'.

In vivo nuclear magnetic resonance study of the osmoregulation of phosphocholine-substituted beta-1,3;1,6 cyclic glucan and its associated carbon metabolism in Bradyrhizobium japonicum USDA 110

A phosphocholine-substituted beta-1,3;1,6 cyclic glucan (PCCG), an unusual cyclic oligosaccharide, has been isolated from Bradyrhizobium japonicum USDA 110 (D. B. Rolin, P. E. Pfeffer, S. F. Osman, B. S. Swergold, F. Kappler, and A. J. Benesi, Biochim. Biophys. Acta 1116:215-225, 1992). Data presented here suggest that PCCG synthesis is dependent on the carbon metabolism and that osmotic regulation of its biosynthesis parallels regulation of membrane-derived oligosaccharide biosynthesis observed in Escherichia coli (E. P. Kennedy, M. K. Rumley, H. Schulman, and L. M. G. van Golde, J. Biol. Chem. 251:4208-4213, 1976) and Agrobacterium tumefaciens (G. A. Cangelosi, G. Martinetti, and E. W. Nester, J. Bacteriol. 172:2172-2174, 1990). Growth of B. japonicum USDA 110 cells in the reference medium at relatively low osmotic pressures (LO) (65 mosmol/kg of H2O) caused a large accumulation of PCCG and unsubstituted beta-1,3;1,6 cyclic glucans (CG). Sucrose and polyethylene glycol, nonionic osmotica, reduce all growth rates and inhibit almost completely the production of PCCG at high osmotic pressures (HO) above 650 and 400 mosmol/kg of H2O), respectively. We used in vivo 13C nuclear magnetic resonance spectroscopy to identify the active osmolytes implicated in the osmoregulation process. The level of alpha,alpha-trehalose in B. japonicum cells grown in autoclaved or filter-sterilized solutions remained constant in HO (0.3 M sucrose or 250 g of polyethylene glycol 6000 per liter) medium. Significant amounts of glycogen and extracellular polysaccharides were produced only when glucose was present in the autoclaved HO 0.3 M sucrose media. The results of hypo- and hyperosmotic shocking of B. japonicum USDA 110 cells were monitored by using in vivo 31P and 13C nuclear magnetic resonance spectroscopy. The first observed osmoregulatory response of glycogen-containing cells undergoing hypoosmotic shock was release of P(i) into the medium. Within 7 h, reabsorption of P(i) was complete and production of PCCG was initiated. After 12 h, the PCCG content had increased by a factor of 7. Following the same treatment, cells containing little or no glycogen released trehalose and failed to produce PCCG. Thus the production of PCCG/CG in response to hypoosmotic shocking of stationary-phase cells was found to be directly linked to the interconversion of stored glycogen. Hyperosmotic shocking of LO-grown stationary-phase cells with sucrose had no effect on the content of previously synthesized CG/PCCG. The PCCG/CG content and its osmotically induced biosynthesis are discussed in terms of carbon metabolism and a possible role in hypoosmotic adaptation in B. japonicum USDA 110.