Improvement of tolerance to freeze–thaw stress of baker’s yeast by cultivation with soy peptides.
Izawa, S., Ikeda, K., Takahashi, N. & Inoue, Y. (2007). Applied Microbiology and Biotechnology, 75(3), 533-537.
The tolerance to freeze–thaw stress of yeast cells is critical for frozen-dough technology in the baking industry. In this study, we examined the effects of soy peptides on the freeze–thaw stress tolerance of yeast cells. We found that the cells cultured with soy peptides acquired improved tolerance to freeze–thaw stress and retained high leavening ability in dough after frozen storage for 7 days. The final quality of bread regarding its volume and texture was also improved by using yeast cells cultured with soy peptides. These findings promote the utilization of soy peptides as ingredients of culture media to improve the quality of baker’s yeast.
Starvation resistance and effects of diet on energy reserves in a predatory ground beetle (Merizodus soledadinus; Carabidae) invading the Kerguelen Islands.
Laparie, M., Larvor, V., Frenot, Y. & Renault, D. (2012). Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology, 161(2), 122-129.
The relationship between nutritional requirements and the availability or quality of food is a prime parameter in determining the geographical expansion of invasive insects. At the sub-Antarctic Kerguelen Islands, the invasive ground beetle Merizodus soledadinus becomes the main invertebrate predator when it colonizes new habitats, leading to the local extinction of native fly species. Such changes in the structure of prey communities may alter the energy management (storage and expenditure) of this predator. In this species, we monitored survival and body mass during food deprivation, in addition to evaluating the effects of two distinct diets (maggots versus enchytraeids) on the consumption and restoration of body reserves (sugars and triglycerides). We found that adults can starve for more than 60 days, and feed every 3.76 days on average when food is available. We recorded higher predation rates on maggots, associated with steeper body mass variations, compared to enchytraeids. Sugars and triglycerides were significantly consumed during food deprivation and restored after refeeding, but varied similarly among individuals supplied on the distinct diets. Other parameters may determine the food preferences observed, such as salt content in prey tissues, because M. soledadinus mainly feeds in hypersaline foreshore habitats, and may limit the consumption of osmotic conformers.
Freezing tolerance and low molecular weight cryoprotectants in an invasive parasitic fly, the deer ked (Lipoptena cervi).
Nieminen, P., Paakkonen, T., Eerilä, H., Puukka, K., Riikonen, J., Lehto, V. P. & Mustonen, A. M. (2012). Journal of Experimental Zoology Part A: Ecological Genetics and Physiology, 317(1), 1-8.
Insect cold hardiness is often mediated by low molecular weight cryoprotectants, such as sugars, polyols, and amino acids (AA). While many free-living northern insects must cope with extended periods of freezing ambient temperatures (Ta), the ectoparasitic deer ked Lipoptena cervi imago can encounter subfreezing Ta only during a short autumnal period between hatching and host location. Subsequently, it benefits from the body temperature of the cervid host for survival in winter. This study investigated the cold tolerance of the species by determining its lower lethal temperature (100% mortality, LLT100) during faster and slower cold acclimation, by determining the supercooling point (SCP) and by measuring the concentrations of potential low molecular weight cryoprotectants. The LLT100 of the deer ked was approximately −16°C, which would enable it to survive freezing nighttime Ta not only in its current area of distribution but also further north. The SCP was −7.8°C, clearly higher than the LLT100, indicating that the deer ked displays freezing tolerance. The concentrations of free AA, especially nonessential AA, were higher in the cold-acclimated deer keds similar to several other insects. The concentrations of proline increased together with γ-aminobutyrate, arginine, asparagine, cystine, glutamate, glutamine, hydroxylysine, sarcosine, serine, and taurine. AA could be hypothesized to act as cryoprotectants by, e.g., protecting enzymes and lipid membranes from damage caused by cold.
A novel steamed bread making process using salt‐stressed baker’s yeast.
Yeh, L. T., Wu, M. L., Charles, A. L. & Huang, T. C. (2009). International Journal of Food Science & Technology, 44(12), 2637-2643.
The process of applying salt-stressed baker’s yeast during southern style Chinese steamed bread dough preparation was examined. Baker’s yeast was stressed in 7% salt solution then mixed into dough, which was then evaluated for dough fermentation producing gas, dough expansion, texture profile analysis (TPA), colour, specific volume, spread ratio and sensory analysis. The results of this study pointed out salt-stressed baker’s yeast produced significant amount of gas and dough expansion, particularly after 40 min of salt stressing. The texture of steamed bread was softer (463.08 g) than control (541.35 g) (P < 0.05), greater in specific volume (3.15 cm3 g-1) than control (2.89 cm3 g−1) (P < 0.05), had a lower spread ratio (1.45) than control (1.74) (P < 0.05) and a significantly improved sensory properties for taste (90.6) than control (81.6) (P < 0.05) were obtained.
Differences in cold and drought tolerance of high arctic and sub-arctic populations of Megaphorura arctica Tullberg 1876 (Onychiuridae: Collembola).
Bahrndorff, S., Petersen, S. O., Loeschcke, V., Overgaard, J. & Holmstrup, M. (2007). Cryobiology, 55(3), 315-323.
The springtail Megaphorura arctica (Onychiuridae: Collembola) inhabits the arctic and sub-arctic parts of the northern hemisphere where it on a seasonal basis will be exposed to severe cold and desiccating conditions. In the present study we compared how traits of stress resistance differed between two populations of M. arctica that were collected at a high arctic site (Spitsbergen) and a sub-arctic site (Akureyri, Iceland) with contrasting thermal environments. In addition we investigated how cold and desiccation affected the phospholipid fatty acid composition of M. arctica from Spitsbergen. The springtails from Spitsbergen were the most cold tolerant and this was linked to an almost three times higher level of trehalose accumulation during cryoprotective dehydration (15% and 5% of tissue dry weight in the Spitsbergen and Iceland populations, respectively). Although cryoprotective dehydration is intimately related to desiccation stress it was shown that M. arctica had a higher mortality when dehydrated over ice (−10 or −20°C) than when dehydrated at temperatures above 1°C. Thus, survival was lower after exposure to −10°C than after exposure to a relative humidity of 91.2% RH at +1°C although both treatments led to the same level of dehydration. Exposure to both cold (−10 and −20°C) and desiccation at +1°C caused significant changes in the phospholipid fatty acid composition with some similarities. These changes included a decrease in average chain length of the fatty acids due primarily to an increase in the phospholipid fatty acids 16:0 and a decrease in 18:3 and 20:4ω6.
Trehalose promotes the survival of Saccharomyces cerevisiae during lethal ethanol stress, but does not influence growth under sublethal ethanol stress.
Bandara, A., Fraser, S., Chambers, P. J. & Stanley, G. A. (2009). FEMS Yeast Research, 9(8), 1208-1216.
Trehalose is known to protect cells from various environmental assaults; however, its role in the ethanol tolerance of Saccharomyces cerevisiae remains controversial. Many previous studies report correlations between trehalose levels and ethanol tolerance across a variety of strains, yet variations in genetic background make it difficult to separate the impact of trehalose from other stress response factors. In the current study, investigations were conducted on the ethanol tolerance of S. cerevisiae BY4742 and BY4742 deletion strains, tsl1Δ and nth1Δ, across a range of ethanol concentrations. It was found that trehalose does play a role in ethanol tolerance at lethal ethanol concentrations, but not at sublethal ethanol concentrations; differences of 20–40% in the intracellular trehalose concentration did not provide any growth advantage for cells incubated in the presence of sublethal ethanol concentrations. It was speculated that the ethanol concentration-dependent nature of the trehalose effect supports a mechanism for trehalose in protecting cellular proteins from the damaging effects of ethanol.
Divergent strategies for adaptation to desiccation stress in two Drosophila species of immigrans group.
Parkash, R., Aggarwal, D. D., Ranga, P. & Singh, D. (2012). Journal of Comparative Physiology B, 182(6), 751-769.
Water balance mechanisms have been investigated in desert Drosophila species of the subgenus Drosophila from North America, but changes in mesic species of subgenus Drosophila from other continents have received lesser attention. We found divergent strategies for coping with desiccation stress in two species of immigrans group—D. immigrans and D. nasuta. In contrast to clinal variation for body melanization in D. immigrans, cuticular lipid mass showed a positive cline in D. nasuta across a latitudinal transect (10°46′–31°43′N). Based on isofemale lines variability, body melanization showed positive correlation with desiccation resistance in D. immigrans but not in D. nasuta. The use of organic solvents has supported water proofing role of cuticular lipids in D. nasuta but not in D. immigrans. A comparative analysis of water budget of these two species showed that higher water content, reduced rate of water loss and greater dehydration tolerance confer higher desiccation resistance in D. immigrans while the reduced rate of water loss is the only possible mechanism to enhance desiccation tolerance in D. nasuta. We found that carbohydrates act as metabolic fuel during desiccation stress in both the species, whereas their rates of utilization differ significantly between these two species. Further, acclimation to dehydration stress improved desiccation resistance due to increase in the level of carbohydrates in D. immigrans but not in D. nasuta. Thus, populations of D. immigrans and D. nasuta have evolved different water balance mechanisms under shared environmental conditions. Multiple measures of desiccation resistance in D. immigrans but reduction in water loss in D. nasuta are consistent with their different levels of adaptive responses to wet and dry conditions on the Indian subcontinent.
Sex-specific differences in the physiological basis of water conservation of Drosophila hydei from the western Himalayas.
Parkash, R., Singh, D. & Lambhod, C. (2014). Canadian Journal of Zoology, 92(6), 545-555.
In the cosmopolitan fruit fly Drosophila hydei – Sturtevant 1921 (Diptera: Drosophilidae), the relative abundance of males is significantly higher than females, but the physiological basis of such sex-specific differences are largely unknown. For wild populations of D. hydei, we found seasonal changes (summer versus autumn) in desiccation related traits but in all seasons the desiccation tolerance of males was higher than that of females. For desiccation related traits, we tested whether thermal developmental acclimation at three temperatures (17, 21 and 28°C) matched seasonal changes observed under wild conditions. Male flies showed significantly higher trait values for desiccation resistance, cuticular lipid mass, hemolymph, carbohydrate content and dehydration tolerance as compared with females when reared at lower or higher temperatures despite lack of significant sex-specific differences in the total body water content of flies reared at a particular growth temperature. We observed plastic changes in the amount of cuticular lipids consistent with corresponding differences in the rate of water loss. Treatment of cuticular surface with organic solvent (hexane) supported the role of cuticular lipids in affecting transcuticular water loss. We found significant thermal plastic effects for desiccation related traits of D. hydei but the sexual dimorphism was in the opposite direction i.e. males were more desiccation resistant than females in D. hydei while the reverse is true for many other Drosophila species (Diptera, Drosophilidae). Our results suggest that sex-specific differences in desiccation resistance level of D. hydei are good predictors of relative abundance levels of male and female flies under wild conditions.
Divergent strategy for adaptation to drought stress in two sibling species of montium species subgroup: Drosophila kikkawai and Drosophila leontia.
Ramniwas, S. & Kajla, B. (2012). Journal of Insect Physiology, 58(12), 1525-1533.
Drosophila leontia (warm adapted) has been considered as a sister species of Drosophila kikkawai (sub-cosmopolitan) with a very similar morphology. We found divergent strategies for coping with desiccation stress in these two species of montium subgroup. Interestingly, in contrast to clinal variation for body melanization in D. kikkawai, cuticular lipid mass showed a positive cline in D. leontia across a latitudinal transect. On the basis of isofemale line analysis, within population trait variability in cuticular lipid mass per fly is positively correlated with desiccation resistance and negatively correlated with cuticular water loss in D. leontia. A comparative analysis of water budget of these two species showed that higher abdominal melanization, reduced rate of water loss and greater dehydration tolerance confer higher desiccation resistance in D. kikkawai while the reduced rate of water loss is the only possible mechanism to enhance desiccation tolerance in D. leontia. The use of organic solvents has supported water proofing role of cuticular lipids in D. leontia but not in D. kikkawai. Thus, we may suggest that body melanization and cuticular lipids may represent alternative strategies for coping with dehydration stress in melanic versus non-melanic drosophilids. In both these species, carbohydrates were utilized under desiccation stress but a higher level of stored carbohydrates was evident in D. kikkawai. Further, we found increase desiccation resistance in D. kikkawai through acclimation while D. leontia lacks such a response. Thus, species specific divergence in water balance related traits in these species are consistent with their adaptations to wet and dry habitats.
Rapid effects of humidity acclimation on stress resistance in Drosophila melanogaster.
Aggarwal, D. D., Ranga, P., Kalra, B., Parkash, R., Rashkovetsky, E. & Bantis, L. E. (2013). Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology, 166(1), 81-90.
We tested the hypothesis whether developmental acclimation at ecologically relevant humidity regimes (40% and 75% RH) affects desiccation resistance of pre-adults (3rd instar larvae) and adults of Drosophila melanogaster Meigen (Diptera: Drosophilidae). Additionally, we untangled whether drought (40% RH) acclimation affects cold-tolerance in the adults of D. melanogaster. We observed that low humidity (40% RH) acclimated individuals survived significantly longer (1.6-fold) under lethal levels of desiccation stress (0–5% RH) than their counter-replicates acclimated at 75% RH. In contrast to a faster duration of development of 1st and 2nd instar larvae, 3rd instar larvae showed a delayed development at 40% RH as compared to their counterparts grown at 75% RH. Rearing to low humidity conferred an increase in bulk water, hemolymph content and dehydration tolerance, consistent with increase in desiccation resistance for replicates grown at 40% as compared to their counterparts at 75% RH. Further, we found a trade-off between the levels of carbohydrates and body lipid reserves at 40% and 75% RH. Higher levels of carbohydrates sustained longer survival under desiccation stress for individuals developed at 40% RH than their congeners at 75% RH. However, the rate of carbohydrate utilization did not differ between the individuals reared at these contrasting humidity regimes. Interestingly, our results of accelerated failure time (AFT) models showed substantial decreased death rates at a series of low temperatures (0, −2, or −4°C) for replicates acclimated at 40% RH as compared to their counter-parts at 75% RH. Therefore, our findings indicate that development to low humidity conditions constrained on multiple physiological mechanisms of water-balance, and conferred cross-tolerance towards desiccation and cold stress in D. melanogaster. Finally, we suggest that the ability of generalist Drosophila species to tolerate fluctuations in humidity might aid in their existence and abundance under expected changes in moisture level in course of global climate change.