Adaptation of experimental yeast populations to stressful conditions in relation to population size

The purpose of this experiment was to find out how a population becomes adapted to extremely stressful conditions as its environment deteriorates. We created a deteriorating environment for experimental selection lines of yeast by a stepwise increase in the concentration of salt in the growth medium. After each step, we tested the ability of the lines to grow at a high concentration of salt near the lethal limit for the ancestral strain. We found that mutations enhancing growth in this highly stressful environment began to spread at intermediate salt concentrations. The degree of enhancement was related to effective population size by a power law with a small exponent. The effect size of these mutations also increased with the population size in a similar fashion. From these results, we interpret adaptation to lethal stress as an indirect response to selection for resistance to previous lower levels of stress in a deteriorating environment. This suggests that the pattern of genetic correlation between successively higher levels of stress is an important factor in facilitating evolutionary rescue.     

Genome-wide transcriptional response of Yersinia pestis to stressful conditions simulating phagolysosomal environments

Yersinia pestis is a Gram-negative coccobacillus causing the dangerous disease, plague. Survival of Y. pestis within host macrophages is important in the initial stages of infection. In our present work, DNA microarray was used to determine the expression profiles of Y. pestis strain 201 in response to in vitro simulating conditions of Mg(2+) limitation, polymyxin treatment and oxidative stress that could be found in phagolysosomal environment. It was demonstrated that Y. pestis made appropriate adaptive/protective responses to survive the stressful environments. There are the induced expression of antiphagocytic factors and Mg(2+) transporters under Mg(2+) limitation condition, the stimulation of drug/analogue sensitivity and glycerol assimilation after polymyxin treatment, and the differential expression in genes encoding stress-responsive proteins, components of cell envelope, iron assimilation and regulatory functions in response to both Mg(2+) limitation and polymyxin treatment. Under oxidative stress, Y. pestis uses several mechanisms, especially including the induced expression of detoxification enzymes and DNA repair proteins, to protect from or repair the oxidative cell damages. This microarray analysis would provide the candidates for identifying genes or pathways required for growth and proliferation of Y. pestis in macrophages.     

The magnitude of the T cell response to a clinically significant dose of influenza virus is regulated by TRAIL

An immune response of appropriate magnitude should be robust enough to control pathogen spread but not simultaneously lead to immunopathology. Primary infection with influenza A virus (IAV) results in a localized pulmonary infection and inflammation and elicits an IAV-specific CD8 T cell immune response necessary for viral clearance. Clearance of IAV-infected cells, and recovery from infection, is mediated by perforin/granzyme B- and Fas/FasL-mediated mechanisms. We recently reported that TRAIL is another means by which IAV-specific CD8 T cells can kill IAV-infected cells. The current study examined the role of TRAIL in the pulmonary CD8 T cell response to a clinically significant IAV [A/PR/8/34 (PR8; H1N1)] infection (i.e., leads to observable, but limited, morbidity and mortality in wild-type [WT] mice). Compared with WT mice, IAV-infected Trail(-/-) mice experienced increased morbidity and mortality despite similar rates of viral clearance from the lungs. The increased morbidity and mortality in Trail(-/-) mice correlated with increased pulmonary pathology and inflammatory chemokine production. Analysis of lung-infiltrating lymphocytes revealed increased numbers of IAV-specific CD8 T cells in infected Trail(-/-) mice, which correlated with increased pulmonary cytotoxic activity and increased pulmonary expression of MIG and MIP-1α. In addition, there was decreased apoptosis and increased proliferation of IAV-specific CD8 T cells in the lungs of Trail(-/-) mice compared with WT mice. Together, these data suggest that TRAIL regulates the magnitude of the IAV-specific CD8 T cell response during a clinically significant IAV infection to decrease the chance for infection-induced immunopathology.     

Amino-terminal sequence of a Saccharomyces cerevisiae nuclear protein, NHP6, shows significant identity to bovine HMG1

Several nonhistone chromatin proteins (NHPs) have been isolated from Saccharomyces cerevisiae nuclei. They have molecular masses and amino acid compositions typical of the high mobility group (HMG) proteins from higher eukaryotic cells. Polyclonal antisera raised against two of the NHPs have been used in immunoblots of proteins from subcellular fractions of yeast to show that the NHPs are indeed nuclear. In addition, the amino-terminal amino acid sequences of several of the NHPs were determined. Importantly, the amino-terminal sequence of one of the proteins, NHP6, has significant (60%) identity with a stretch of amino acids in calf thymus HMG1.     

The ontogenetic approach to chlorophyll fluorescence studies of plant photosynthetic apparatus under stressful conditions

Based on the analysis of reasons limiting the application of the method of chlorophyll fluorescence induction for estimating the state of the leaf photosynthetic apparatus under prolonged stress, the necessity of the ontogenetic approach consisting in a more exact determination of leaf age was substantiated. A comparison of the calendar and ontogenetic ways of determination of age of cucumber leaves under controlled conditions revealed essential distinctions in the estimation of plant leaf photosynthetic apparatus by the method of chlorophyll fluorescence induction for two variants distinguishing by the cultivation light regime ("white", 400-700 nm, and "red", 600-700 nm). It was shown that, in the case of prolonged effect of the stress factor on the plant, the unambiguity of the interpretation of chlorophyll fluorescence induction parameters in the estimation of the state of their photosynthetic apparatus depends essentially on the choice of the ontogenetic period of leaves of plants being compared and the accuracy of determination of leaf age.     

Influence of stressful fermentation conditions on neutral lipids of a Saccharomyces cerevisiae brewing strain

The neutral lipid fraction of the aerobically grown starter yeast culture of a Saccharomyces cerevisiae brewing strain, and three-first recycled yeast generations exposed to multiple stress factors during beer fermentation was studied. No pronounced changes in the cellular neutral lipid content between the non-stressed starter and stressed recycled cells were found. However, it was found that recycled yeast generations modulate their neutral lipid composition during fermentation. The ergosterol content was increased at the expense of steryl esters (SEs) and squalene, which resulted in a higher ergosterol/SEs molar ratio and a slightly higher ergosterol/squalene molar ratio. In addition, the proportion of unsaturated fatty acids, mainly palmitoleic acid increased in the neutral lipid fraction of the stressed recycled yeast generations. These results suggest that some specific neutral lipid species and fatty acids stored in the neutral lipid fraction are involved in the adaptive response of the brewer’s yeast to stressful fermentation conditions. The striking finding was a high squalene content in the neutral lipid fraction of both the starter yeast culture and recycled yeast generations (22.4 vs. 19–20%, respectively), implying a possible biotechnological exploitation of this biologically active molecule from the yeast biomass.     

Employment of stressful conditions during culture production to enhance subsequent cold- and acid-tolerance of bifidobacteria

AIMS: This study examined whether exposure of early stationary phase Bifidobacterium longum and B. lactis cells to various combinations of reduced temperature, reduced pH and starvation would enhance the cells' subsequent cold- and/or acid-tolerance. METHODS AND RESULTS: Survival of B. longum in growth medium at 6 degrees C significantly (P < 0.05) increased as a result of starving cells for 30 or 60 min without any simultaneous decrease in temperature or pH. Acid-tolerance of B. lactis (at pH 3.5 in synthetic gastric fluid) increased significantly when the growth medium pH was decreased from 6.0 to 5.2 and cells experienced 30 or 60 min of starvation. Enhanced B. lactis acid-tolerance persisted through 8-11 weeks of -80 degrees C storage in the pH 5.2 growth medium. Upon addition to milk during yogurt manufacture, these cells initially had enhanced acid-tolerance relative to untreated cells but untreated cells became equally acid-tolerant during the first 2.5 h of yogurt manufacture. CONCLUSIONS: The cold- and acid-tolerance of bifidobacteria vary widely, but may be significantly increased by application of sub-lethal stress to early stationary phase cells during culture production. SIGNIFICANCE AND IMPACT OF THE STUDY: The enhancement of B. lactis acid-tolerance observed in this study may be of potential importance in the production of effective ready-to-consume probiotic dietary supplements.     

A laboratory exercise to illustrate increased salivary cortisol in response to three stressful conditions using competitive ELISA

Perceived stress activates the hypothalamus-pituitary-adrenal axis, resulting in the release of glucocorticoids into the systemic circulation. Glucocorticoids cause the elevation of blood glucose, providing the necessary energy for the organism to cope with stress. Here, we outline a laboratory exercise that uses a competitive ELISA kit to illustrate the response of salivary cortisol concentrations to three stressful conditions. Twelve undergraduate students in the General and Comparative Endocrinology course at Iowa State University were subjected to presentation stress, fasting stress, and competition stress to determine their effect on salivary cortisol concentrations. Students had elevated salivary cortisol in response to each of these stresses compared with basal conditions. These results reiterate the importance of glucocorticoids as mediators of the stress response. This study also incorporates the use of the ELISA technique, a modern laboratory tool used to determine the amount of endogenous antigens in plasma or saliva. This laboratory exercise can easily be adapted to fit into already existing physiology and endocrinology curriculums.     

Effect of stressful conditions on the carotenogenic activity of a Colombian strain of Dunaliella salina

The objective was evaluate the carotenogenic activity of Dunaliella salina isolated from the artificial salt flats of municipality of Manaure (Department of La Guajira, Colombia). Two experimental testings were designed, in triplicate, to induce the reversibility of the cell tonality depending on the culture conditions. In the first test (A), to induce the reversibility from green to red tonality in D. salina cells, these were cultured in J/1 medium at a concentration of 4.0 M NaCl, 390 µmol m^?2 s^?1, 0.50 mM KNO₃. In the second test (B), to induce the reversibility from red to green cell tonality, the cultures were maintained in J/1 medium 1 M NaCl, 190 µmol m^?2 s^?1, 5.0 mM KNO₃ and pH 8.2. The population growth was evaluated by cell count and the pigment content was performed by spectrophotometric techniques. It was found that in both tests the culture conditions influenced the population growth and the pigments production of D. salina. There was a significant difference between the mean values of total carotenoids in the test A with 9.67 ± 0.19 μg/ml and second test with 1.54 ± 0.08 μg/ml at a significance level of p < 0.05. It was demonstrated that the culture conditions of test A induce the production of lipophilic antioxidants, among these carotenoids. The knowledge of the stressful conditions for the production of carotenoids from D. salina isolated from artificial saline of Manaure opens a field in implementation of this biotic resource for biotechnological purposes, production of new antibiotics, nutraceuticals and/or biofuels production.     

Linkage analysis of a model quantitative trait in humans: finger ridge count shows significant multivariate linkage to 5q14.1

The finger ridge count (a measure of pattern size) is one of the most heritable complex traits studied in humans and has been considered a model human polygenic trait in quantitative genetic analysis. Here, we report the results of the first genome-wide linkage scan for finger ridge count in a sample of 2,114 offspring from 922 nuclear families. Both univariate linkage to the absolute ridge count (a sum of all the ridge counts on all ten fingers), and multivariate linkage analyses of the counts on individual fingers, were conducted. The multivariate analyses yielded significant linkage to 5q14.1 (Logarithm of odds [LOD] = 3.34, pointwise-empirical p-value = 0.00025) that was predominantly driven by linkage to the ring, index, and middle fingers. The strongest univariate linkage was to 1q42.2 (LOD = 2.04, point-wise p-value = 0.002, genome-wide p-value = 0.29). In summary, the combination of univariate and multivariate results was more informative than simple univariate analyses alone. Patterns of quantitative trait loci factor loadings consistent with developmental fields were observed, and the simple pleiotropic model underlying the absolute ridge count was not sufficient to characterize the interrelationships between the ridge counts of individual fingers.     

Pattern changes associated with the decline of a species in a desert habitat

Summary Estimates were obtained of the patterns exhibited by living and dead stems of Opuntia Bigelovii in a deteriorating desert habitat. The data were interpreted in terms of selective action of a lethal factor, the effect being to reduce the differences in density between high and low density patches of an initially aggregate population, and to result in a trend toward a random distribution of survivors.

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Résumé On a examiné la distribution des tiges vivantes et mortes d'Opuntia Bigelovii dans une communauté du desert. Les données ont revélé une action choisie par l'agent mortel. L'action a reduit les différences de la densité entre les parties de la communauté. Il en résulte que les tiges vivantes assument une dustribution au hasard.

     

Appearance of new hepatic glucocorticoid binding proteins under various stressful conditions: relation to endogenous glucocorticoid secretion

When rats were subjected to the stress of burns, tumors, or partial hepatectomy, a notable new peak of glucocorticoid binding protein appeared on DEAE-cellulose chromatography. This peak accompanied the original peak, which was the only dominant peak in intact rats. The appearance of the new binding protein was concomitant with a high rise in serum corticosterone levels. The new peak was eluted with 0.12-0.14 M NaCl and another, small new peak with 0.02-0.03 M NaCl, while the original peak of intact rats was eluted with 0.05-0.08 M NaCl. In rats adrenalectomized prior to the stress, the new peaks did not appear. To mimic these stressful conditions which provoked a burst of endogenous glucocorticoid, rats were administered with an exogenous high dose of dexamethasone (100 micrograms/100 g B.W.) in vivo. The new peak eluted with 0.12-0.14 M NaCl was again observed and was more dominant in the hormone-treated rats than the stressed rats. These three peaks eluted with 0.02-0.03 M, 0.05-0.08 M, and 0.12-0.14 M NaCl are called here Peak A, B, and C, respectively. This is the first demonstration of the effect of physiological changes in serum levels of glucocorticoid hormone on the nature of glucocorticoid binding protein by DEAE-cellulose chromatography.     

Analysis of a large dataset of mycorrhiza inoculation field trials on potato shows highly significant increases in yield

An increasing human population requires more food production in nutrient-efficient systems in order to simultaneously meet global food needs while reducing the environmental footprint of agriculture. Arbuscular mycorrhizal fungi (AMF) have the potential to enhance crop yield, but their efficiency has yet to be demonstrated in large-scale crop production systems. This study reports an analysis of a dataset consisting of 231 field trials in which the same AMF inoculant (Rhizophagus irregularis DAOM 197198) was applied to potato over a 4-year period in North America and Europe under authentic field conditions. The inoculation was performed using a liquid suspension of AMF spores that was sprayed onto potato seed pieces, yielding a calculated 71 spores per seed piece. Statistical analysis showed a highly significant increase in marketable potato yield (ANOVA, P?<?0.0001) for inoculated fields (42.2 tons/ha) compared with non-inoculated controls (38.3 tons/ha), irrespective of trial year. The average yield increase was 3.9 tons/ha, representing 9.5 % of total crop yield. Inoculation was profitable with a 0.67-tons/ha increase in yield, a threshold reached in almost 79 % of all trials. This finding clearly demonstrates the benefits of mycorrhizal-based inoculation on crop yield, using potato as a case study. Further improvements of these beneficial inoculants will help compensate for crop production deficits, both now and in the future.     

Why is body size more variable in stressful conditions: an analysis of a potential proximate mechanism

Patterns of variability in quantitative traits across environmental gradients have received relatively little attention in evolutionary ecology. A recent meta-analysis showed that relative phenotypic variability in body size tends to decrease with improving environmental conditions. This pattern was explained by introducing the concept of upper threshold size to a general optimality model of individual growth but alternative explanations certainly exist. In particular, it is frequently observed in insects that variability in individual growth rates decreases with improving environmental conditions. Here we explore the effect of this phenomenon on environment-specific variability in adult sizes. A quantitative model shows that relative variability in adult sizes is independent of environmental quality if absolute variability in growth rates remains constant across the gradient of environmental quality. Deviations from this borderline case are definitely realistic in both directions. Both negative and positive relationships between relative variability of body size and environmental quality can thus be predicted to arise as a consequence of environment-specific variability in growth rates. The variability itself can be both genetic or environmental in its nature. We present empirical data which support both the assumptions and conclusions of our model-based analysis, as well as emphasize the advantages of controlled experiments for understanding the proximate sources of phenotypic variance.     

The cosmopolitan maternal heritage of the Thoroughbred racehorse breed shows a significant contribution from British and Irish native mares

The paternal origins of Thoroughbred racehorses trace back to a handful of Middle Eastern stallions, imported to the British Isles during the seventeenth century. Yet, few details of the foundation mares were recorded, in many cases not even their names (several different maternal lineages trace back to 'A Royal Mare'). This has fuelled intense speculation over their origins. We examined mitochondrial DNA from 1929 horses to determine the origin of Thoroughbred foundation mares. There is no evidence to support exclusive Arab maternal origins as some historical records have suggested, or a significant importation of Oriental mares (the term used in historic records to refer to Middle East and western Asian breeds including Arab, Akhal-Teke, Barb and Caspian). Instead, we show that Thoroughbred foundation mares had a cosmopolitan European heritage with a far greater contribution from British and Irish Native mares than previously recognized.     

Factors associated with the catastrophic decline of a cloudforest frog fauna in Guatemala

Comparison of recent and historical surveys of frog populations in cloudforest habitat in Sierra de las Minas, Guatemala, indicated population declines and local extirpation of several species. Pathological exams of diseased tadpoles indicated infection by amphibian chytridiomycosis. The local habitat has been severely altered by recent establishment of large-scale leatherleaf fern production. Analysis of water chemistry at our study site suggested increased nitrogenation associated with the leatherleaf industry.     

Selection of scFv phages on intact cells under low pH conditions leads to a significant loss of insert-free phages

Display of functional antibody fragments on the surface of filamentous bacteriophages allows fast selection of specific phage antibodies against a variety of target antigens. However, enrichment of single chain variable fragment (scFv)-displaying phages is often hampered by the abundance of bacteriophages lacking antibody fragments. Moderate adhesive binding activities and production advantages of these "empty" phages results in their subsequent enrichment during selection on target cells. To date, very limited effort has been made to develop strategies removing nonspecific binding phages during the selection processes. To efficiently reduce insert-free phages when panning on intact cells, we increased the washing stringency by lowering the pH of the buffer with citric acid. Under standard washing procedures (pH 7.4), only approximately 73% of recovered phages were insert-free after three rounds of selection. Using stringent washing procedures (pH 5.0), approximately 12% of recovered phages contained no scFv. Using this protocol, we have cloned an antibody fragment from a mouse/human hybridoma cell line directed against the disialoganglioside GD2. This study confirms that selection of phage antibodies on cells is efficiently enhanced by assays augmenting the stringency to remove nonspecific binding phages.