Thermotolerance in Saccharomyces cerevisiae: the Yin and Yang of trehalose

Interaction of the sugars trehalose, maltose and glucose with a phospholipid bilayer: a comparative molecular dynamics study

Molecular dynamics simulations are used to investigate the interaction of the sugars trehalose, maltose, and glucose with a phospholipid bilayer at atomic resolution. Simulations of the bilayer in the absence or in the presence of sugar (2 molal concentration for the disaccharides, 4 molal for the monosaccharide) are carried out at 325 and 475 K. At 325 K, the three sugars are found to interact directly with the lipid headgroups through hydrogen bonds, replacing water at about one-fifth to one-quarter of the hydrogen-bonding sites provided by the membrane. Because of its small size and of the reduced topological constraints imposed on the hydroxyl group locations and orientations, glucose interacts more tightly (at identical effective hydroxyl group concentration) with the lipid headgroups when compared to the disaccharides. At high temperature, the three sugars are able to prevent the thermal disruption of the bilayer. This protective effect is correlated with a significant increase in the number of sugar-headgroups hydrogen bonds. For the disaccharides, this change is predominantly due to an increase in the number of sugar molecules bridging three or more lipid molecules. For glucose, it is primarily due to an increase in the number of sugar molecules bound to one or bridging two lipid molecules.

Saccharomyces cerevisiae strains from traditional fermentations of Brazilian cachaça: trehalose metabolism, heat and ethanol resistance

Nine indigenous cachaça Saccharomyces cerevisiae strains and one wine strain were compared for their trehalose metabolism characteristics under non-lethal (40 degrees C) and lethal (52 degrees C) heat shock, ethanol shock and combined heat and ethanol stresses. The yeast protection mechanism was studied through trehalose concentration, neutral trehalase activity and expression of heat shock proteins Hsp70 and Hsp104. All isolates were able to accumulate trehalose and activate neutral trehalase under stress conditions. No correlation was found between trehalose levels and neutral trehalase activity under heat or ethanol shock. However, when these stresses were combined, a positive relationship was found. After pre-treatment at 40 degrees C for 60 min, and heat shock at 52 degrees C for 8 min, eight strains maintained their trehalose levels and nine strains improved their resistance against lethal heat shock. Among the investigated stresses, heat treatment induced the highest level of trehalose and combined heat and ethanol stresses activated the neutral trehalase most effectively. Hsp70 and Hsp104 were expressed by all strains at 40 degrees C and all of them survived this temperature although a decrease in cell viability was observed at 52 degrees C. The stress imposed by more than 5% ethanol (v/v) represented the best condition to differentiate strains based on trehalose levels and neutral trehalase activity. The investigated S. cerevisiae strains exhibited different characteristics of trehalose metabolism, which could be an important tool to select strains for the cachaça fermentation process.

Trehalose As a “Chemical Chaperone”

Trehalose is a disaccharide of glucose that is found at high concentrations in a wide variety of organisms that naturally survive drying in nature. Many years ago we reported that this molecule has the remarkable ability to stabilize membranes and proteins in the dry state. A mechanism for the stabilization rapidly emerged, and it was sufficiently attractive that a myth grew up about trehalose as a universal protectant and chemical chaperone. Many of the claims in this regard can be explained by what is now known about the physical properties of this interesting sugar. It is emerging that these properties may make it unusually useful in stabilizing intact cells in the dry state.

Combined NMR and quantum chemical studies on the interaction between trehalose and dienes relevant to the antioxidant function of trehalose

In a previous study (Oku, K.; Watanabe, H.; Kubota, M.; Fukuda, S.; Kurimoto, M.; Tujisaka, Y.; Komori, M.; Inoue, Y.; Sakurai, M. J. Am. Chem. Soc. 2003, 125, 12739), we investigated the mechanism of the antioxidant function of trehalose against unsaturated fatty acids (UFAs) and revealed that the key factor relevant to the function is the formation of OH...pi and CH...O hydrogen bonds between trehalose and the cis double bonds of the UFA. Here, we investigate whether such intriguing interactions also occur between this sugar and cis double bonds in other unsaturated compounds. For this purpose, we selected various diene compounds (1,3-butadiene, 1,3-pentadiene, 1,4-pentadiene, and 2,5-heptadiene) as interaction partners. All NMR experiments performed, including 1H-1H NOESY measurements, indicated that trehalose selectively interacts with the cis-olefin proton pair in the above diene with a 1:1 stoichiometry, and the C-3 (C-3') and C-6' (C-6) sites of the sugar are responsible for the interaction. Similar interactions were not observed for the mixtures of the diene and other saccharides (neotrehalose, kojibiose, nigerose, maltose, isomaltose, sucrose, maltitol, and sorbitol). Quantum chemical calculations revealed that the OH-3 and OH-6 groups bind to the olefin double bonds of the diene through OH...pi and CH...O types of hydrogen bonds, respectively, and the stabilization energy of the resulting complex is 5-6 kcal mol(-1). These results strongly support the above NMR results. Finally, the activation energies were calculated for the hydrogen abstraction reactions from the activated methylene group of heptadiene. In particular, when the reaction was initiated by a methyl radical, the activation energy was only 10 kcal mol(-1) for the free heptadiene, but on complexation with trehalose it drastically increased to ca. 40 kcal mol(-1). This indicates that trehalose has a significant depression effect on the oxidation of the diene compounds. These results strongly support the antioxidant mechanism deduced in the previous study and indicate that the formation of unique multiple hydrogen bonds between trehalose and cis-olefin bonds is rather a general event not confined to the case of UFA.

Toluene-induced accumulation of trehalose by Pseudomonas sp. BCNU 106 through the expression of otsA and otsB homologues

AIM

The objective of this study was to investigate toluene-induced accumulation mechanism of trehalose in a toluene-tolerant bacterium Pseudomonas sp. BCNU 106.

METHODS AND RESULTS

The accumulation of trehalose by a toluene-tolerant bacterium Pseudomonas sp. BCNU 106 was examined at various cultivation time by measuring the total intracellular trehalose content, trehalase activity and mRNA levels of the trehalose-biosynthetic genes. The pattern of trehalose accumulation corresponded to the mRNA expression pattern of the trehalose-biosynthetic genes with the maximum level at 12 h or 4 h of cultivation with 10% (v/v) toluene, respectively. The trehalose-biosynthetic genes were also cloned and sequenced. Furthermore, the effects of toluene addition on the intracellular osmotic pressure and pH were investigated. It was shown that homeostasis was maintained in the bacterial cells.

CONCLUSIONS

In a toluene-tolerant bacterium Pseudomonas sp. BCNU 106, a significant amount of trehalose was accumulated through the toluene-induced expression of the trehalose-biosynthetic genes after the exposure to toluene.

SIGNIFICANCE AND IMPACT OF THE STUDY

The accumulation of the high level of intracellular trehalose was preceded by the expression of otsA/B genes in toluene-tolerant bacteria, contributing to the elucidation of the tolerance mechanism.

Construction of a recombinant thermostable beta-amylase-trehalose synthase bifunctional enzyme for facilitating the conversion of starch to trehalose

A fusion gene that encoded a polypeptide of 1495 amino acids was constructed from the beta-amylase (BA) gene of Clostridium thermosulfurogenes and trehalose synthase (TS) gene of Thermus thermophilus. The fused gene was overexpressed in Escherichia coli, and a recombinant bifunctional fusion protein with BA at the N-terminal (BATS) or C-terminal (TSBA) of TS having both beta-amylase and trehalose synthase activities with an apparent molecular mass of 164 kDa was obtained. BATS or TSBA catalyzes the sequential reaction in which maltose is formed from starch and then is converted into trehalose. The Km values of the BATS and TSBA fusion enzymes for the reaction from starch to trehalose were smaller than those of an equimolar mixture of BA and TS (BA/TS). On the other hand, the kcat value of BATS approximated that of the BA/TS mixture, but that of TSBA exceeded it. TSBA showed much higher sequential catalytic efficiency than the separately expressed BA/TS mixture. The catalytic efficiency of TSBA or BATS was 3.4 or 2.4 times higher, respectively, than that of a mixture of individual enzymes, showing the kinetic advantage of the fusion enzyme. The thermal stability readings of the recombinant fusion enzymes BATS and TSBA were better than that of the mixture of individual recombinant enzymes. These results apparently demonstrate that fusion enzymes catalyzing sequential reactions have kinetic advantages over a mixture of both enzymes.

Cold response in Saccharomyces cerevisiae: new functions for old mechanisms

The response of yeast cells to sudden temperature downshifts has received little attention compared with other stress conditions. Like other organisms, both prokaryotes and eukaryotes, in Saccharomyces cerevisiae a decrease in temperature induces the expression of many genes involved in transcription and translation, some of which display a cold-sensitivity phenotype. However, little is known about the role played by many cold-responsive genes, the sensing and regulatory mechanisms that control this response or the biochemical adaptations at or near 0 degrees C. This review focuses on the physiological significance of cold-shock responses, emphasizing the molecular mechanisms that generate and transmit cold signals. There is now enough experimental evidence to conclude that exposure to low temperature protects yeast cells against freeze injury through the cold-induced accumulation of trehalose, glycerol and heat-shock proteins. Recent results also show that changes in membrane fluidity are the primary signal triggering the cold-shock response. Notably, this signal is transduced and regulated through classical stress pathways and transcriptional factors, the high-osmolarity glycerol mitogen-activated protein kinase pathway and Msn2/4p. Alternative cold-stress generators and transducers will also be presented and discussed.

The solubility of recombinant proteins expressed in Escherichia coli is increased by otsA and otsB co-transformation

The osmolyte trehalose strongly limits protein aggregation both in vitro and in vivo. The addition of trehalose to the culture medium reduced the aggregation of recombinant proteins expressed in Escherichia coli in a concentration-dependent manner. Comparable positive effects were obtained when the host bacteria were engineered to overexpress the gene products of otsA and otsB, the two enzymes involved in trehalose synthesis. Apparently, the osmolyte preserves protein monodispersion rather than directly facilitating protein folding. However, the stabilization of the protein folding intermediate(s) resulted in higher yields of native proteins and aggregates of lower complexity. Other osmolytes have been tested in vitro in comparison with trehalose. Di-myo-inositol1,1'-phosphate (DIP) seems to be a good candidate to test in in vivo applications, although the opportunity of using otsA/B overexpressing cells is simpler and less expensive.

Erratum to "Diapause-associated metabolic traits reiterated in long-lived daf-2 mutants in the nematode Caenorhabditis elegans" [Mech. Ageing Dev. 127 (5) (2006) 458-472]

The longevity of the Caenorhabditis elegans diapausal dauer larva greatly exceeds that of the adult. Dauer formation and adult ageing are both regulated by insulin/IGF-1 signalling (IIS). Reduced IIS, e.g. by mutation of the daf-2 insulin/IGF-1 receptor gene, increases adult lifespan. This may reflect mis-expression in the adult of dauer longevity-assurance processes. Since IIS plays a central role in the regulation of metabolism, metabolic alterations shared by dauer larvae and daf-2 adults represent candidate mechanisms for lifespan determination. We have conducted a detailed comparison of transcript profile data from dauers and daf-2 mutant adults, focusing on expression of metabolic pathway genes. Our results imply up-regulation in both dauers and daf-2 mutant adults of gluconeogenesis, glyoxylate pathway activity, and trehalose biosynthesis. Down-regulation of the citric acid cycle and mitochondrial respiratory chain occurs in dauers, but not daf-2 adults. However, the F1 ATPase inhibitor was up-regulated in both, implying enhanced homeostasis in conditions where mitochondria are stressed. Overall, the data implies increased conversion of fat to carbohydrate, and conservation of ATP stocks in daf-2 mutant adults, suggesting a state of increased energy availability. We postulate that this fuels increased somatic maintenance activity, as suggested by the disposable soma theory.

Can the different heat shock response thresholds found in fermenting and respiring yeast cells be attributed to their differential redox states?

In this study we used a heat-shock (HS) reporter gene to demonstrate that respiring cells are intrinsically less sensitive (by 5 degrees C) than their fermenting counterparts to a sublethal heat shock. We also used an oxidant-sensitive fluorescent probe to demonstrate that this correlates with lower levels of sublethal reactive oxygen species (ROS) accumulation in heat-stressed respiring cells. Moreover, this relationship between HS induction of the reporter gene and ROS accumulation extends to respiring cells that have had their ROS levels modified by treatment with the anti-oxidant ascorbic acid and the pro-oxidant H(2)O(2). Thus, by demonstrating that the ROS/HSR correlation previously demonstrated in fermenting cells also holds for respiring cells (despite their greater HS insensitivity and higher level of intrinsic thermotolerance), we provide evidence that the intracellular redox state may influence both the sensitivity of the heat-shock response (HSR) and stress tolerance in the yeast Saccharomyces cerevisiae.

Insights on the evolution of trehalose biosynthesis

Background

The compatible solute trehalose is a non-reducing disaccharide, which accumulates upon heat, cold or osmotic stress. It was commonly accepted that trehalose is only present in extremophiles or cryptobiotic organisms. However, in recent years it has been shown that although higher plants do not accumulate trehalose at significant levels they have actively transcribed genes encoding the corresponding biosynthetic enzymes.

Results

In this study we show that trehalose biosynthesis ability is present in eubacteria, archaea, plants, fungi and animals. In bacteria there are five different biosynthetic routes, whereas in fungi, plants and animals there is only one. We present phylogenetic analyses of the trehalose-6-phosphate synthase (TPS) and trehalose-phosphatase (TPP) domains and show that there is a close evolutionary relationship between these domains in proteins from diverse organisms. In bacteria TPS and TPP genes are clustered, whereas in eukaryotes these domains are fused in a single protein.

Conclusion

We have demonstrated that trehalose biosynthesis pathways are widely distributed in nature. Interestingly, several eubacterial species have multiple pathways, while eukaryotes have only the TPS/TPP pathway. Vertebrates lack trehalose biosynthetic capacity but can catabolise it. TPS and TPP domains have evolved mainly in parallel and it is likely that they have experienced several instances of gene duplication and lateral gene transfer.

The natural osmolyte trehalose is a positive regulator of the heat-induced activity of yeast heat shock transcription factor

In Saccharomyces cerevisiae, the intracellular concentration of trehalose increases rapidly in response to many environmental stresses, including heat shock. These high trehalose levels have been correlated with tolerance to adverse conditions and led to the model that trehalose functions as a chemical cochaperone. Here, we show that the transcriptional activity of Hsf1 during the heat shock response depends on trehalose. Strains with low levels of trehalose have a diminished transcriptional response to heat shock, while strains with high levels of trehalose have an enhanced transcriptional response to heat shock. The enhanced transcriptional response does not require the other heat-responsive transcription factors Msn2/4 but is dependent upon heat and Hsf1. In addition, the phosphorylation levels of Hsf1 correlate with both transcriptional activity and the presence of trehalose. These in vivo results support a new role for trehalose, where trehalose directly modifies the dynamic range of Hsf1 activity and therefore influences heat shock protein mRNA levels in response to stress.

Trehalose metabolism is important for heat stress tolerance and spore germination of Botrytis cinerea

To analyse the role of trehalose as stress protectant and carbon storage compound in the grey mould fungus Botrytis cinerea, mutants defective in trehalose-6-phosphate synthase (TPS1) and neutral trehalase (TRE1) were constructed. The Deltatps1 mutant was unable to synthesize trehalose, whereas the Deltatre1 mutant showed elevated trehalose levels compared to the wild-type and was unable to mobilize trehalose during conidial germination. Both mutants showed normal vegetative growth and were not affected in plant pathogenicity. Growth of the Deltatps1 mutant was more heat sensitive compared to the wild-type. Similarly, Deltatps1 conidia showed a shorter survival under heat stress, and their viability at moderate temperatures was strongly reduced. In germinating wild-type conidia, rapid trehalose degradation occurred only when germination was induced in the presence of nutrients. In contrast, little trehalose breakdown was observed during germination on hydrophobic surfaces in water. Here, addition of cAMP to conidia induced trehalose mobilization and accelerated the germination process, probably by activation of TRE1. In accordance with these data, both mutants showed germination defects only in the presence of sugars but not on hydrophobic surfaces in the absence of nutrients. The data indicate that in B. cinerea trehalose serves as a stress protectant, and also as a significant but not essential carbon source for germination when external nutrients are low. In addition, evidence was obtained that trehalose 6-phosphate plays a role as a regulator of glycolysis during germination.

The effect of some osmolytes on the activity and stability of mushroom tyrosinase

The thermodynamical stability and remained activity of mushroom tyrosinase (MT) from Agaricus bisporus in 10 mM phosphate buffer, pH 6.8, stored at two temperatures of 4 and 40 degrees C were investigated in the presence of three different amino acids (His, Phe and Asp) and also trehalose as osmolytes, for comparing with the results obtained in the absence of any additive. Kinetics of inactivation obey the first order law. Inactivation rate constant (kinact) value is the best parameter describing effect of osmolytes on kinetic stability of the enzyme. Trehalose and His have the smallest value of kinact (0.7x10(-4) s-1) in comparison with their absence (2.5x10(-4) s-1). Moreover, to obtain effect of these four osmolytes on thermodynamical stability of the enzyme, protein denaturation by dodecyl trimethylammonium bromide (DTAB) and thermal scanning was investigated. Sigmoidal denaturation curves were analysed according to the two states model of Pace theory to find the Gibbs free energy change of denaturation process in aqueous solution at room temperature, as a very good thermodynamic criterion indicating stability of the protein. Although His, Phe and Asp induced constriction of MT tertiary structure, its secondary structure had not any change and the result was a chemical and thermal stabilization of MT. The enzyme shows a proper coincidence of thermodynamic and structural changes with the presence of trehalose. Thus, among the four osmolytes, trehalose is an exceptional protein stabilizer.

Role of trehalose and heat in the structure of the C-terminal activation domain of the heat shock transcription factor

The heat shock transcription factor (HSF) is the primary transcriptional regulator of the heat shock response in eukaryotes. Saccharomyces cerevisiae HSF1 has two functional transcriptional activation domains, located N- and C-terminal to the central core of the protein. These activation domains have a low level of transcriptional activity prior to stress, but they acquire a high level of transcriptional activity in response to stresses such as heat. Previous studies on the N-terminal activation domain have shown that it can be completely disordered. In contrast, we show that the C-terminal activation domain of S. cerevisiae HSF1 does contain a certain amount of secondary structure as measured by circular dichroism (CD) and protease resistance. The alpha-helical content of the domain can be increased by the addition of the disaccharide trehalose but not by sucrose. Trehalose, but not sucrose, causes a blue shift in the fluorescence emission spectra, which is suggestive of an increase in tertiary structure. Trehalose, which is known to be a chemical chaperone, also increases proteases' resistance and promotes heat-induced increases in alpha-helicity. The latter is particularly intriguing because of the physiological role of trehalose in yeast. Trehalose levels are increased dramatically after heat shock, and this is thought to protect protein structure prior to the increase of heat shock protein levels. Our results suggest that the dramatic changes in S. cerevisiae HSF1 transcriptional activity in response to stress might be linked to the combined effects of trehalose and elevated temperatures in modifying the overall structure of HSF1's C-terminal activation domain.

Use of physiological constraints to identify quantitative design principles for gene expression in yeast adaptation to heat shock

Background

Understanding the relationship between gene expression changes, enzyme activity shifts, and the corresponding physiological adaptive response of organisms to environmental cues is crucial in explaining how cells cope with stress. For example, adaptation of yeast to heat shock involves a characteristic profile of changes to the expression levels of genes coding for enzymes of the glycolytic pathway and some of its branches. The experimental determination of changes in gene expression profiles provides a descriptive picture of the adaptive response to stress. However, it does not explain why a particular profile is selected for any given response.

Results

We used mathematical models and analysis of in silico gene expression profiles (GEPs) to understand how changes in gene expression correlate to an efficient response of yeast cells to heat shock. An exhaustive set of GEPs, matched with the corresponding set of enzyme activities, was simulated and analyzed. The effectiveness of each profile in the response to heat shock was evaluated according to relevant physiological and functional criteria. The small subset of GEPs that lead to effective physiological responses after heat shock was identified as the result of the tuning of several evolutionary criteria. The experimentally observed transcriptional changes in response to heat shock belong to this set and can be explained by quantitative design principles at the physiological level that ultimately constrain changes in gene expression.

Conclusion

Our theoretical approach suggests a method for understanding the combined effect of changes in the expression of multiple genes on the activity of metabolic pathways, and consequently on the adaptation of cellular metabolism to heat shock. This method identifies quantitative design principles that facilitate understating the response of the cell to stress.

Indole-3-acetic acid improves Escherichia coli’s defences to stress

Indole-3-acetic acid (IAA) is a ubiquitous molecule playing regulatory roles in many living organisms. To elucidate the physiological changes induced by IAA treatment, we used Escherichia coli K-12 as a model system. By microarray analysis we found that 16 genes showed an altered expression level in IAA-treated cells. One-third of these genes encode cell envelope components, or proteins involved in bacterial adaptation to unfavourable environmental conditions. We thus investigated the effect of IAA treatment on some of the structural components of the envelope that may be involved in cellular response to stresses. This showed that IAA-treated cells had increased the production of trehalose, lipopolysaccharide (LPS), exopolysaccharide (EPS) and biofilm. We demonstrated further that IAA triggers an increased tolerance to several stress conditions (heat and cold shock, UV-irradiation, osmotic and acid shock and oxidative stress) and different toxic compounds (antibiotics, detergents and dyes) and this correlates with higher levels of the heat shock protein DnaK. We suggest that IAA triggers an increased level of alert and protection against external adverse conditions by coordinately enhancing different cellular defence systems.

Diapause-associated metabolic traits reiterated in long-lived daf-2 mutants in the nematode Caenorhabditis elegans

The longevity of the Caenorhabditis elegans diapausal dauer larva greatly exceeds that of the adult. Dauer formation and adult ageing are both regulated by insulin/IGF-1 signaling (IIS). Reduced IIS, e.g. by mutation of the daf-2 insulin/IGF-1 receptor gene, increases adult lifespan. This may reflect mis-expression in the adult of dauer longevity-assurance processes. Since IIS plays a central role in the regulation of metabolism, metabolic alterations shared by dauer larvae and daf-2 adults represent candidate mechanisms for lifespan determination. We have conducted a detailed comparison of transcript profile data from dauers and daf-2 mutant adults, focusing on expression of metabolic pathway genes. Our results imply up-regulation in both dauers and daf-2 mutant adults of gluconeogenesis, glyoxylate pathway activity, and trehalose biosynthesis. Down-regulation of the citric acid cycle and mitochondrial respiratory chain occurs in dauers, but not daf-2 adults. However, the F(1) ATPase inhibitor was up-regulated in both, implying enhanced homeostasis in conditions where mitochondria are stressed. Overall, the data implies increased conversion of fat to carbohydrate, and conservation of ATP stocks in daf-2 mutant adults, suggesting a state of increased energy availability. We postulate that this fuels increased somatic maintenance activity, as suggested by the disposable soma theory.

Trehalose protects Saccharomyces cerevisiae from lipid peroxidation during oxidative stress

Aiming to focus the protective role of the sugar trehalose under oxidative conditions, two sets of Saccharomyces cerevisiae strains, having different profiles of trehalose synthesis, were used. Cells were treated either with a 10% trehalose solution or with a heat treatment (which leads to trehalose accumulation) and then exposed either to menadione (a source of superoxide) or to tert-butylhydroperoxide (TBOOH). According to our results, trehalose markedly increased viability upon exposure to menadione stress, which seems to be correlated with decrease in lipid peroxidation levels. The protective effect of trehalose against oxidative damage produced by menadione was especially efficient under SOD1 deficiency. On the other hand, this sugar does not seem to participate of the mechanism of acquisition of tolerance against TBOOH, since trehalose pretreatment (addition of external trehalose) was not capable of increase cell survival. Therefore, trehalose plays a role in protecting cells, especially membranes, from oxidative injuries. However, this mechanism of defense is dependent on the type of oxidative stress to which cells are submitted.

Survival of the biocontrol yeast Pichia anomala after long-term storage in liquid formulations at different temperatures, assessed by flow cytometry

AIMS

Investigate the survival of liquid formulations of the biocontrol yeast Pichia anomala J121 at different temperatures, and develop a system for comparative studies of different storage conditions and formulations.

METHODS AND RESULTS

The survival of P. anomala in liquid formulations with lactose, starch and trehalose amendments was measured during prolonged storage at temperatures ranging from -20 to +30 degrees C. The relative survival of the stored cells was rapidly estimated by flow cytometry. After 4 weeks incubation at 4 and 10 degrees C, 75-90% of the cells were viable, with no significant differences between the various formulations. Supplementing the storage buffer with lactose or trehalose increased the survival after longer incubations (8 and 12 weeks) at all temperatures (-20 to 30 degrees C). Trehalose was the most effective protectant at 20 and 30 degrees C (>20% viable cells after 12 weeks at 20 degrees C). The biocontrol activity was maintained after formulation and prolonged storage of P. anomala.

CONCLUSIONS

The storage potential of liquid formulated P. anomala cells can be increased by supplementation with lactose or trehalose. The combination of a custom made incubation chamber and flow cytometry was suitable to evaluate stability of P. anomala formulations.

SIGNIFICANCE AND IMPACT OF THE STUDY

Liquid formulated P. anomala have a long shelf life. The developed test system can be used to study different formulations of other biocontrol agents.

Both heat-shock and cold-shock influence trehalose metabolism in an entomopathogenic nematode

Heat-shock response is highly conserved in animals and microorganisms, and it results in the synthesis of heat-shock proteins. In yeast, heat-shock response has also been reported to induce trehalose accumulation. We explored the relationship between heat- (35 C) or cold-shock (1 and 10 C) and trehalose metabolism in the entomopathogenic nematode, Heterorhabditis bacteriophora. Because both heat- and cold-shocks may precede desiccation stress in natural soil environments, we hypothesized that nematodes may accumulate a general desiccation protectant, trehalose, under both situations. Indeed, both heat- and cold-shocks influenced trehalose accumulation and activities of enzymes of trehalose metabolism in H. bacteriophora. Trehalose increased by 5- and 6-fold in heat- and cold-shocked infective juveniles, respectively, within 3 hr of exposure, compared with the nematodes maintained at 25 C (culture temperature). The activity of trehalose-6-phosphate synthase (T6PS), an enzyme involved in the synthesis of trehalose, also significantly increased in both heat- and cold-shocked nematodes during the first 3 hr of exposure. Generally, the trehalose levels and activities of T6PS declined to their original levels within 3 hr when nematodes were transferred back to 25 C. In both heat- and cold-shocked nematodes, trehalase activity decreased significantly within the first 3 hr and generally returned to the original levels within 3 hr when these nematodes were transferred back to 25 C. The results demonstrate that the trehalose concentrations in H. bacteriophora are influenced by both heat- and cold-shocks and are regulated by the action of 2 trehalose-metabolizing enzymes, T6PS and trehalase. The accumulated trehalose may enhance survival of nematodes under both cold and warm conditions, but it may also provide simultaneous protection against desiccation that may result from subsequent evaporation or freezing. This is the first report of the relationship between trehalose metabolism and heat-shock for the Nematoda.

Sphingoid base is required for translation initiation during heat stress in Saccharomyces cerevisiae

Sphingolipids are required for many cellular functions including response to heat shock. We analyzed the yeast lcb1-100 mutant, which is conditionally impaired in the first step of sphingolipid biosynthesis and shows a strong decrease in heat shock protein synthesis and viability. Transcription and nuclear export of heat shock protein mRNAs is not affected. However, lcb1-100 cells exhibited a strong decrease in protein synthesis caused by a defect in translation initiation under heat stress conditions. The essential lipid is sphingoid base, not ceramide or sphingoid base phosphates. Deletion of the eIF4E-binding protein Eap1p in lcb-100 cells restored translation of heat shock proteins and increased viability. The translation defect during heat stress in lcb1-100 was due at least partially to a reduced function of the sphingoid base-activated PKH1/2 protein kinases. In addition, depletion of the translation initiation factor eIF4G was observed in lcb1-100 cells and ubiquitin overexpression allowed partial recovery of translation after heat stress. Taken together, we have shown a requirement for sphingoid bases during the recovery from heat shock and suggest that this reflects a direct lipid-dependent signal to the cap-dependent translation initiation apparatus.

Genome-wide expression analysis of yeast response during exposure to 4 degrees C

Adaptation to temperature fluctuation is essential for the survival of all living organisms. Although extensive research has been done on heat and cold shock responses, there have been no reports on global responses to cold shock below 10 degrees C or near-freezing. We examined the genome-wide expression in Saccharomyces cerevisiae, following exposure to 4 degrees C. Hierarchical cluster analysis showed that the gene expression profile following 4 degrees C exposure from 6 to 48 h was different from that at continuous 4 degrees C culture. Under 4 degrees C exposure, the genes involved in trehalose and glycogen synthesis were induced, suggesting that biosynthesis and accumulation of those reserve carbohydrates might be necessary for cold tolerance and energy preservation. The observed increased expression of phospholipids, mannoproteins, and cold shock proteins (e.g., TIP1) is consistent with membrane maintenance and increased permeability of the cell wall at 4 degrees C. The induction of heat shock proteins and glutathione at 4 degrees C may be required for revitalization of enzyme activity, and for detoxification of active oxygen species, respectively. The genes with these functions may provide the ability of cold tolerance and adaptation to yeast cells.

Gene expression and molecular characterization of a thermostable trehalose phosphorylase from Thermoanaerobacter tengcongensis

A gene encoding the trehalose phosphorylase (TreP), which reversibly catalyzes trehalose degradation and synthesis from alpha-glucose-1-phosphate (alpha-Glc-1-P) and glucose, was cloned from Thermoanaerobacter tengcongensis and successfully expressed in Escherichia coli. The overexpressed TreP, with a molecular mass of approximately 90 kDa, was determined by SDS-PAGE. It catalyzes trehalose synthesis and degradation optimally at 70 degrees C (for 30 min), with the optimum pHs at 6.0 and 7.0, respectively. It is highly thermostable, with a 77% residual activity after incubation at 50 degrees C for 7 h. Under the optimum reaction conditions, 50 microg crude enzyme of the TreP is able to catalyze the synthesis of trehalose up to 11.6 mmol/L from 25 mmol/L alpha-Glc-1-P and 125 mmol/L glucose within 30 min, while only 1.5 mmol/L out of 250 mmol/L trehalose is degraded within the same time period. Dot blotting revealed that the treP gene in T. tengcongensis was upregulated in response to salt stress but downregulated when trehalose was supplied. Both results indicate that the dominant function of the T. tengcongensis TreP is catalyzing trehalose synthesis but not degradation. Thus it might provide a novel route for industrial production of trehalose.

Organic osmolytes as compatible, metabolic and counteracting cytoprotectants in high osmolarity and other stresses

Organic osmolytes are small solutes used by cells of numerous water-stressed organisms and tissues to maintain cell volume. Similar compounds are accumulated by some organisms in anhydrobiotic, thermal and possibly pressure stresses. These solutes are amino acids and derivatives,polyols and sugars, methylamines, methylsulfonium compounds and urea. Except for urea, they are often called `compatible solutes', a term indicating lack of perturbing effects on cellular macromolecules and implying interchangeability. However, these features may not always exist, for three reasons. First, some of these solutes may have unique protective metabolic roles, such as acting as antioxidants (e.g. polyols, taurine, hypotaurine),providing redox balance (e.g. glycerol) and detoxifying sulfide (hypotaurine in animals at hydrothermal vents and seeps). Second, some of these solutes stabilize macromolecules and counteract perturbants in non-interchangeable ways. Methylamines [e.g. trimethylamine N-oxide (TMAO)] can enhance protein folding and ligand binding and counteract perturbations by urea (e.g. in elasmobranchs and mammalian kidney), inorganic ions, and hydrostatic pressure in deep-sea animals. Trehalose and proline in overwintering insects stabilize membranes at subzero temperatures. Trehalose in insects and yeast,and anionic polyols in microorganisms around hydrothermal vents, can protect proteins from denaturation by high temperatures. Third, stabilizing solutes appear to be used in nature only to counteract perturbants of macromolecules,perhaps because stabilization is detrimental in the absence of perturbation. Some of these solutes have applications in biotechnology, agriculture and medicine, including in vitro rescue of the misfolded protein of cystic fibrosis. However, caution is warranted if high levels cause overstabilization of proteins.

How does yeast respond to pressure?

The brewing and baking yeast Saccharomyces cerevisiae has been used as a model for stress response studies of eukaryotic cells. In this review we focus on the effect of high hydrostatic pressure (HHP) on S. cerevisiae. HHP exerts a broad effect on yeast cells characteristic of common stresses, mainly associated with protein alteration and lipid bilayer phase transition. Like most stresses, pressure induces cell cycle arrest. Below 50 MPa (500 atm) yeast cell morphology is unaffected whereas above 220 MPa wild-type cells are killed. S. cerevisiae cells can acquire barotolerance if they are pretreated with a sublethal stress due to temperature, ethanol, hydrogen peroxide, or pressure. Nevertheless, pressure only leads to protection against severe stress if, after pressure pretreatment, the cells are also re-incubated at room pressure. We attribute this effect to the inhibition of the protein synthesis apparatus under HHP. The global genome expression analysis of S. cerevisiae cells submitted to HHP revealed a stress response profile. The majority of the up-regulated genes are involved in stress defense and carbohydrate metabolism while most repressed genes belong to the cell cycle progression and protein synthesis categories. However, the signaling pathway involved in the pressure response is still to be elucidated. Nitric oxide, a signaling molecule involved in the regulation of a large number of cellular functions, confers baroprotection. Furthermore, S. cerevisiae cells in the early exponential phase submitted to 50-MPa pressure show induction of the expression level of the nitric oxide synthase inducible isoform. As pressure becomes an important biotechnological tool, studies concerning this kind of stress in microorganisms are imperative.

Impacts of fever on locust life-history traits: costs or benefits?

Fever, like other mechanisms for defence against pathogens, may have positive and negative consequences for host fitness. In ectotherms, fever can be attained through modified behavioural thermoregulation. Here we examine potential costs of behavioural fever by holding adult, gregarious desert locusts at elevated temperatures simulating a range of fever intensities. We found no effect of fever temperatures on primary fitness correlates of survival and fecundity. However, flight capacity and mate competition were reduced, although there was no relation between time spent at fever temperatures and magnitude of the response. While these effects could indicate a direct cost of fever, they are also consistent with a shift towards the solitaria phase state that, in a field context, could be considered an adaptive life-history response to limit the impact of disease. These conflicting interpretations highlight the importance of considering complex defence mechanisms and trade-offs in an appropriate ecological context.

Progressive elimination of microinjected trehalose during mouse embryonic development

Recently, sugars such as trehalose have been introduced into mammalian cells by overcoming the permeability barrier of cell membranes, and have provided improved tolerance against stresses associated with freezing and drying. However, the fate of the intracellular sugars has remained an open question. To address this issue, mouse oocytes were microinjected with 0.1 mol/l trehalose, and intracellular trehalose and glucose concentrations were determined during embryonic development using a high performance liquid chromatography and pulsed amperometric detection protocol. Trehalose was not detected in non-injected controls at any stage of development. In the microinjection group, the amount of intracellular trehalose progressively decreased as embryos developed. There was a corresponding increase in intracellular glucose concentration at the two-cell stage, suggesting cleavage of trehalose to two glucose molecules. In summary, this study presents a simple, highly sensitive protocol to determine intracellular sugars. The data reveal rapid elimination of microinjected trehalose during embryonic development. These findings have implications for designing osmolarity-optimized culture media for sugar-injected oocytes.

Cell wall integrity signaling in Saccharomyces cerevisiae

The yeast cell wall is a highly dynamic structure that is responsible for protecting the cell from rapid changes in external osmotic potential. The wall is also critical for cell expansion during growth and morphogenesis. This review discusses recent advances in understanding the various signal transduction pathways that allow cells to monitor the state of the cell wall and respond to environmental challenges to this structure. The cell wall integrity signaling pathway controlled by the small G-protein Rho1 is principally responsible for orchestrating changes to the cell wall periodically through the cell cycle and in response to various forms of cell wall stress. This signaling pathway acts through direct control of wall biosynthetic enzymes, transcriptional regulation of cell wall-related genes, and polarization of the actin cytoskeleton. However, additional signaling pathways interface both with the cell wall integrity signaling pathway and with the actin cytoskeleton to coordinate polarized secretion with cell wall expansion. These include Ca(2+) signaling, phosphatidylinositide signaling at the plasma membrane, sphingoid base signaling through the Pkh1 and -2 protein kinases, Tor kinase signaling, and pathways controlled by the Rho3, Rho4, and Cdc42 G-proteins.

Starvation response of Saccharomyces cerevisiae grown in anaerobic nitrogen- or carbon-limited chemostat cultures

Anaerobic starvation conditions are frequent in industrial fermentation and can affect the performance of the cells. In this study, the anaerobic carbon or nitrogen starvation response of Saccharomyces cerevisiae was investigated for cells grown in anaerobic carbon or nitrogen-limited chemostat cultures at a dilution rate of 0.1 h(-1) at pH 3.25 or 5. Lactic or benzoic acid was present in the growth medium at different concentrations, resulting in 16 different growth conditions. At steady state, cells were harvested and then starved for either carbon or nitrogen for 24 h under anaerobic conditions. We measured fermentative capacity, glucose uptake capacity, intracellular ATP content, and reserve carbohydrates and found that the carbon, but not the nitrogen, starvation response was dependent upon the previous growth conditions. All cells subjected to nitrogen starvation retained a large portion of their initial fermentative capacity, independently of previous growth conditions. However, nitrogen-limited cells that were starved for carbon lost almost all their fermentative capacity, while carbon-limited cells managed to preserve a larger portion of their fermentative capacity during carbon starvation. There was a positive correlation between the amount of glycogen before carbon starvation and the fermentative capacity and ATP content of the cells after carbon starvation. Fermentative capacity and glucose uptake capacity were not correlated under any of the conditions tested. Thus, the successful adaptation to sudden carbon starvation requires energy and, under anaerobic conditions, fermentable endogenous resources. In an industrial setting, carbon starvation in anaerobic fermentations should be avoided to maintain a productive yeast population.

Crystal structure of maltooligosyltrehalose trehalohydrolase from Deinococcus radiodurans in complex with disaccharides

Trehalose (alpha-D-glucopyranosyl-1,1-alpha-D-glucopyranose) is a non-reducing diglucoside found in various organisms that serves as a carbohydrate reserve and as an agent that protects against a variety of physical and chemical stresses. Deinococcus radiodurans possesses an alternative biosynthesis pathway for the synthesis of trehalose from maltooligosaccharides. This reaction is mediated by two enzymes: maltooligosyltrehalose synthase (MTSase) and maltooligosyltrehalose trehalohydrolase (MTHase). Here, we present the 1.1A resolution crystal structure of MTHase. It consists of three major domains: two beta-sheet domains and a conserved glycosidase (beta/alpha)8 barrel catalytic domain. Three subdomains consisting of short insertions were identified within the catalytic domain. Subsequently, structures of MTHase in complex with maltose and trehalose were obtained at 1.2 A and 1.5 A resolution, respectively. These structures reveal the importance of the three inserted subdomains in providing the key residues required for substrate recognition. Trehalose is recognised specifically in the +1 and +2 binding subsites by an extensive hydrogen-bonding network and a strong hydrophobic stacking interaction in between two aromatic residues. Moreover, upon binding to maltose, which mimics the substrate sugar chain, a major concerted conformational change traps the sugar chain in the active site. The presence of magnesium in the active site of the MTHase-maltose complex suggests that MTHase activity may be regulated by divalent cations.

Stress tolerance in fungi — to kill a spoilage yeast

The fungal spoilage of ingredients of food manufacture is an economic problem, often causes product loss and may constitute a health hazard. To effectively combat fungal food spoilage, a mechanistic understanding of tolerance for, and adaptation to, the preservation method used is crucial. Both are dependent on the genetic make-up and growth history of the organism. In the post-genomic era we are arriving at a situation in which, in the model organism Saccharomyces cerevisiae, physiological data, classical molecular biology and whole-genome responses can be combined to obtain explanatory and predictive models for growth. For food spoilage fungi we have not yet reached such a level of understanding, but we may use the knowledge gained for S. cerevisiae for the prevention of spoilage.

Evolutionary engineering of multiple-stress resistant

Various selection procedures in chemostats and batch cultures were systematically tested for their efficiency to select for a multiple-stress resistance phenotype in Saccharomyces cerevisiae. To determine the relative stress resistance phenotypes, mutant populations harvested at different time points and randomly chosen clones from selected populations were grown in batch cultures and exposed to oxidative, freezing-thawing, high-temperature and ethanol stress. For this purpose, we developed a high-throughput procedure in 96-well plates combined with a most-probable-number assay. Among all chemostat and batch selection strategies tested, the best selection strategy to obtain highly improved multiple-stress-resistant yeast was found to be batch selection for freezing-thawing stress. The final mutant populations selected for this particular stress were not only significantly improved in freezing-thawing stress resistance, but also in other stress resistances. The best isolated clone from these populations exhibited 102-, 89-, 62-, and 1429-fold increased resistance to freezing-thawing, temperature, ethanol, and oxidative stress, respectively. General selection guidelines for improving multiple-stress resistance in S. cerevisiae are presented and discussed.

Gts1p stabilizes oscillations in energy metabolism by activating the transcription of TPS1 encoding trehalose-6-phosphate synthase 1 in the yeast Saccharomyces cerevisiae

We reported previously that Gts1p regulates oscillations of heat resistance in concert with those of energy metabolism in continuous cultures of the yeast Saccharomyces cerevisiae by inducing fluctuations in the levels of trehalose, but not in those of Hsp104 (heat shock protein 104). Further, the expression of TPS1, encoding trehalose-6-phosphate synthase 1, and HSP104 was activated by Gts1p in combination with Snf1 kinase, a transcriptional activator of glucose-repressible genes, in batch cultures under derepressed conditions. Here we show that, in continuous cultures, the mRNA level of TPS1 increased 6-fold in the early respiro-fermentative phase, while that of HSP104 did not change. The expression of SUC2, a representative glucose-repressible gene encoding invertase, also fluctuated, suggesting the involvement of the Snf1 kinase in the periodic activation of these genes. However, this possibility was proven to be unlikely, since the oscillations in both TPS1 and SUC2 mRNA expression were reduced by approx. 3-fold during the transient oscillation in gts1Delta (GTS1-deleted) cells, in which the energy state determined by extracellular glucose and intracellular adenine nucleotide levels was comparable with that in wild-type cells. Furthermore, neither the mRNA level nor the phosphorylation status of Snf1p changed significantly during the oscillation. Thus we suggest that Gts1p plays a major role in the oscillatory expression of TPS1 and SUC2 in continuous cultures of Saccharomyces cerevisiae, and hypothesized that Gts1p stabilizes oscillations in energy metabolism by activating trehalose synthesis to facilitate glycolysis at the shift from the respiratory to the respiro-fermentative phase.

Longer lifespan, altered metabolism, and stress resistance in Drosophila from ablation of cells making insulin-like ligands

The insulin/insulin-like growth factor-like signaling pathway, present in all multicellular organisms, regulates diverse functions including growth, development, fecundity, metabolic homeostasis, and lifespan. In flies, ligands of the insulin/insulin-like growth factor-like signaling pathway, the Drosophila insulin-like peptides, regulate growth and hemolymph carbohydrate homeostasis during development and are expressed in a stage- and tissue-specific manner. Here, we show that ablation of Drosophila insulin-like peptide-producing median neurosecretory cells in the brain leads to increased fasting glucose levels in the hemolymph of adults similar to that found in diabetic mammals. They also exhibit increased storage of lipid and carbohydrate, reduced fecundity, and reduced tolerance of heat and cold. However, the ablated flies show an extension of median and maximal lifespan and increased resistance to oxidative stress and starvation.

Opposing effects of two osmolytes ? trehalose and glycerol ? on thermal inactivation of rabbit muscle 6-phosphofructo-1-kinase

Trehalose and glycerol are known as good stabilizers of function and structure of several macromolecules against stress conditions. We previously reported that they have comparable effectiveness on protecting two yeast cytosolic enzymes against thermal inactivation. However, enzyme protection has always been associated to a decrease in catalytic activity at the stabilizing conditions i.e., the presence of the protective molecule. In the present study we tested trehalose and glycerol on thermal protection of the mammalian cytosolic enzyme phosphofructokinase. Here we found that trehalose was able to protect phosphofructokinase against thermal inactivation as well as to promote an activation of its catalytic activity. The enzyme incubated in the presence of 1 M trehalose did not present any significant inactivation within 2 h of incubation at 50 degrees C, contrasting to control experiments where the enzyme was fully inactivated during the same period exhibiting a t0.5 for thermal inactivation of 56+/-5 min. On the other hand, enzyme incubated in the presence of 37.5% (v/v) glycerol was not protected against incubation at 50 degrees C. Indeed, when phosphofructokinase was incubated for 45 min at 50 degrees C in the presence of lower concentrations of glycerol (7.5-25%, v/v), the remaining activity was 2-4 times lower than control. These data show that the compatibility of effects previously shown for trehalose and glycerol with some yeast cytosolic enzymes can not be extended to all globular enzyme system. In the case of phosphofructokinase, we believe that its property of shifting between several different complex oligomers configurations can be influenced by the physicochemical properties of the stabilizing molecules.

Role of reserve carbohydrates in the growth dynamics of Saccharomyces cerevisiae

The purpose of this study was to explore the role of glycogen and trehalose in the ability of Saccharomyces cerevisiae to respond to a sudden rise of the carbon flux. To this end, aerobic glucose-limited continuous cultures were challenged with a sudden increase of the dilution rate from 0.05 to 0.15 h(-1). Under this condition, a rapid mobilization of glycogen and trehalose was observed which coincided with a transient burst of budding and a decrease of cell biomass. Experiments carried out with mutants defective in storage carbohydrates indicated a predominant role of glycogen in the adaptation to this perturbation. However, the real importance of trehalose in this response was veiled by the unexpected phenotypes harboured by the tps1 mutant, chosen for its inability to synthesize trehalose. First, the biomass yield of this mutant was 25% lower than that of the isogenic wild-type strain at dilution rate of 0.05 h(-1), and this difference was annulled when cultures were run at a higher dilution rate of 0.15 h(-1). Second, the tps1 mutant was more effective to sustain the dilution rate shift-up, apparently because it had a faster glycolytic rate and an apparent higher capacity to consume glucose with oxidative phosphorylation than the wild type. Consequently, a tps1gsy1gsy2 mutant was able to adapt to the dilution rate shift-up after a long delay, likely because the detrimental effects from the absence of glycogen was compensated for by the tps1 mutation. Third, a glg1Deltaglg2Delta strain, defective in glycogen synthesis because of the lack of the glycogen initiation protein, recovered glycogen accumulation upon further deletion of TPS1. This recovery, however, required glycogen synthase. Finally, we demonstrated that the rapid breakdown of reserve carbohydrates triggered by the shift-up is merely due to changes in the concentrations of hexose-6-phosphate and UDPglucose, which are the main metabolic effectors of the rate-limiting enzymes of glycogen and trehalose pathways.

Loss of function of KRE5 suppresses temperature sensitivity of mutants lacking mitochondrial anionic lipids

Disruption of PGS1, which encodes the enzyme that catalyzes the committed step of cardiolipin (CL) synthesis, results in loss of the mitochondrial anionic phospholipids phosphatidylglycerol (PG) and CL. The pgs1Delta mutant exhibits severe growth defects at 37 degrees C. To understand the essential functions of mitochondrial anionic lipids at elevated temperatures, we isolated suppressors of pgs1Delta that grew at 37 degrees C. One of the suppressors has a loss of function mutation in KRE5, which is involved in cell wall biogenesis. The cell wall of pgs1Delta contained markedly reduced beta-1,3-glucan, which was restored in the suppressor. Stabilization of the cell wall with osmotic support alleviated the cell wall defects of pgs1Delta and suppressed the temperature sensitivity of all CL-deficient mutants. Evidence is presented suggesting that the previously reported inability of pgs1Delta to grow in the presence of ethidium bromide was due to defective cell wall integrity, not from "petite lethality." These findings demonstrated that mitochondrial anionic lipids are required for cellular functions that are essential in cell wall biogenesis, the maintenance of cell integrity, and survival at elevated temperature.

Inhibition of yeast glutathione reductase by trehalose: possible implications in yeast survival and recovery from stress

Accumulation of trehalose has been implicated in the tolerance of yeast cells to several forms of stress, including heat-shock and high ethanol levels. However, yeast lacking trehalase, the enzyme that degrades trehalose, exhibit poor survival after exposure to stress conditions. This suggests that optimal cell viability also depends on the capacity to rapidly degrade the high levels of trehalose that build up under stress. Here, we initially examined the effects of trehalose on the activity of an important antioxidant enzyme, glutathione reductase (GR), from Saccharomyces cerevisiae. At 25 degrees C, GR was inhibited by trehalose in a dose-dependent manner, with 70% inhibition at 1.5M trehalose. The inhibition was practically abolished at 40 degrees C, a temperature that induces a physiological response of trehalose accumulation in yeast. The inhibition of GR by trehalose was additive to the inhibition caused by ethanol, indicating that enzyme function is drastically affected upon ethanol-induced stress. Moreover, two other yeast enzymes, cytosolic pyrophosphatase and glucose 6-phosphate dehydrogenase, showed temperature dependences on inhibition by trehalose that were similar to the temperature dependence of GR inhibition. These results are discussed in terms of the apparent paradox represented by the induction of enzymes involved in both synthesis and degradation of trehalose under stress, and suggest that the persistence of high levels of trehalose after recovery from stress could lead to the inactivation of important yeast enzymes.

Effect of nitrogen limitation and surplus upon trehalose metabolism in wine yeast

Trehalose metabolism in yeast has been related to stress and could be used as a stress indicator. Winemaking conditions are stressful for yeast and understanding trehalose metabolism under these conditions could be useful for controlling alcoholic fermentation. In this study, we analysed trehalose metabolism of a commercial wine yeast strain during alcoholic fermentation by varying the nitrogen levels from low (below adequate) to high (excess). We determined trehalose, nitrogen, sugar consumption and expression of NTH1, NTH2 and TPS1. Our results show that trehalose metabolism is slightly affected by nitrogen availability and that the main consumption of nitrogen occurs in the first 24 h. After this period, nitrogen is hardly taken up by the yeast cells. Although nitrogen and sugar are still available, no further growth is observed in high concentrations of nitrogen. Increased expression of genes involved in trehalose metabolism occurs mainly at the end of the growth period. This could be related to an adaptive mechanism for fine tuning of glycolysis during alcoholic tumultuous fermentation, as both anabolic and catabolic pathways are affected by such expression.

Biotechnology to improve health in developing countries -- a review

The growing health disparities between the developing and the developed world call for urgent action from the scientific community. Science and technology have in the past played a vital role in improving public health. Today, with the tremendous potential of genomics and other advances in the life sciences, the contribution of science to improve public health and reduce global health disparities is more pertinent than ever before. Yet the benefits of modern medicine still have not reached millions of people in developing countries. It is crucial to recognize that science and technology can be used very effectively in partnership with public health practices in developing countries and can enhance their efficacy. The fight to improve global health needs, in addition to effective public health measures, requires rapid and efficient diagnostic tools; new vaccines and drugs, efficient delivery methods and novel approaches to therapeutics; and low-cost restoration of water, soil and other natural resources. In 2002, the University of Toronto published a report on the "Top 10 Biotechnologies for Improving Health in Developing Countries". Here we review these new and emerging biotechnologies and explore how they can be used to support the goals of developing countries in improving health.