Characterization of Lactobacillus collinoides response to heat, acid and ethanol treatments

Tolerance to stress and cross-protection in Lactobacillus collinoides were examined after exposure to ethanol, acid or heat shock. Ethanol and heat-adapted cells demonstrate induced homologous␣tolerance and cross-resistance to acid stress. No cross-protection of acid-adapted cells against ethanol and heat stresses was observed. Heat was the only pretreatment leading to cross-protection against the two other stresses. Whole-cell protein extract analysis revealed that each treatment induced a battery of stress proteins; the synthesis of some of these polypeptides being induced by more than one condition. The greatest overlap was observed between ethanol and heat treatments. Ten proteins were found to be common to these stresses. Received: 7 November 1998 / Received revision: 10 February 1999 / Accepted: 12 February 1999     

Induction of barotolerance by heat shock treatment in yeast

In Saccharomyces cerevisiae, heat shock treatment provides protection against subsequent hydrostatic pressure damage. Such an induced hydrostatic pressure resistance (barotolerance) closely resembles the thermotolerance similarly induced by heat shock treatment. The parallel induction of barotolerance and thermotolerance by heat shock suggests that hydrostatic pressure and high temperature effects in yeast may be tightly linked physiologically.     

Water Pumping Activity of the Root System in the Process of Cross-Adaptation of Sunflower Plants to Hyperthermia and Water Deficiency

To elucidate the mechanisms of cross-adaptation, we investigated the effect of heat shock (HS, for 2 h at 45°C) on leaf tolerance to overheating and exudation by roots detached from 25–30-day old sunflower (Helianthus annuus L.) plants. It was demonstrated that preheating enhanced considerably leaf tolerance and activated root exudation, especially under water deficiency produced by plant transfer to the hypertonic NaCl solution (17 mM). Under water deficiency conditions, the roots of HS-treated plants pumped water against the osmotic pressure (OP) gradient between the exudate and the external solution. Therefore, we concluded that this pumping was realized due to a metabolic (non-osmotic) constituent of root pressure. In the roots of plants that were not treated with HS, the OP gradient became positive. This fact implies that the HS-pretreatment of plants retarded the penetration of sodium and chlorine ions into roots. The data obtained demonstrate that HS induced a cross-adaptation of plants to high temperature and water deficiency. Such cross-adaptation involves, as an important component, an acceleration of water metabolism, including an enhanced water pumping activity of root system.     

Heat‐shock proteins and cross‐tolerance in plants

Environmental stresses dramatically affect plant survival and productivity. Because plants are immobile, presumably different strategies are required for protection against transient stresses. Under stress, plants synthesize specific proteins, and their accumulation has a role in protecting the tissue from possible damage. An increasing number of studies show the existence of cross‐tolerance in plants: Exposure of tissue to moderate stress conditions often induces resistance to other stresses. Many varied mechanisms explaining the phenomenon of cross‐tolerance have been proposed, and they often, but not always, suggest that specific proteins are induced by one kind of stress and are involved in the protection against other kinds. Although various cross‐protections have been demonstrated in a number of plants, a common mechanism has not been found. This review discusses heat‐shock proteins and their possible roles in protecting the plant under heat and other stresses.     

Stress‐induced pyruvate accumulation contributes to cross protection in a fungus

It is commonly observed that microorganisms subjected to a mild stress develop tolerance not only to higher doses of the same stress but also to other stresses – a phenomenon called cross protection. The mechanisms for cross protection have not been fully revealed. Here, we report that heat shock induced cross protection against UV, oxidative and osmotic/salt stress conditions in the cosmopolitan fungus Metarhizium robertsii. Similarly, oxidative and osmotic/salt stresses also induced cross protection against multiple other stresses. We found that oxidative and osmotic/salt stresses produce an accumulation of pyruvate that scavenges stress‐induced reactive oxygen species and promotes fungal growth. Thus, stress‐induced pyruvate accumulation contributes to cross protection. RNA‐seq and qRT‐PCR analyses showed that UV, osmotic/salt and oxidative stress conditions decrease the expression level of pyruvate consumption genes in the trichloroacetic acid cycle and fermentation pathways leading to pyruvate accumulation. Our work presents a novel mechanism for cross protection in microorganisms.     

Methylglyoxal detoxification by a DJ-1 family protein provides dual abiotic and biotic stress tolerance in transgenic plants

Methylglyoxal (MG) is a key signaling molecule resulting from glycolysis and other metabolic pathways. During abiotic stress, MG levels accumulate to toxic levels in affected cells. However, MG is routinely detoxified through the action of DJ1/PARK7/Hsp31 proteins that are highly conserved across kingdoms and mutations in such genes are associated with neurodegenerative diseases. Here, we report for the first time that, similar to abiotic stresses, MG levels increase during biotic stresses in plants, likely contributing to enhanced susceptibility to a wide range of stresses. We show that overexpression of yeast Heat shock protein 31 (Hsp31), a DJ-1 homolog with robust MG detoxifying capabilities, confers dual biotic and abiotic stress tolerance in model plant Nicotiana tabacum. Strikingly, overexpression of Hsp31 in tobacco imparts robust stress tolerance against diverse biotic stress inducers such as viruses, bacteria and fungi, in addition to tolerance against a range of abiotic stress inducers. During stress, Hsp31 was targeted to mitochondria and induced expression of key stress-related genes. These results indicate that Hsp31 is a novel attractive tool to engineer plants against both biotic and abiotic stresses.     

Establishment of thermotolerance in maize by exposure to stresses other than a heat shock does not require heat shock protein synthesis

Maize (Zea mays) seedlings were pretreated prior to heat shock with either a progressive water stress of −0.25 megapascal PEG/hour from 0 to −1.25 megapascal over a 6-hour time period, or various concentrations of copper, cadmium, or zinc for 4 days. When the subsequent heat shock of 40 or 45°C was administered for 3 hours, the seedlings showed an induced thermotolerance to these temperatures, which were otherwise lethal to control (water grown) seedlings. Thermotolerance was exhibited by both the root and the shoot of pretreated seedlings, even though the water and heavy metal stresses were applied only to the roots. Neither of these pretreatments had induced the synthesis of detectable levels of heat shock proteins (Hsps) at the time of heat shock. Pretreatment of seedlings with a progressive heat shock of 2°C/hour from 26 to 36°C, which did induce Hsps 18, 70, and 84, resulted in tolerance of a severe water stress of −1.5, −1.75, or −2.0 megapascal for 24 hours. But these seedlings producing Hsps were no better protected against water stress than those pretreated with a progressive water stress which did not produce Hsps. Hsps appear not to act as general stress proteins and their presence is not always required for the establishment of thermotolerance.     

Pyrophosphate is a source of phosphoryl groups for Escherichia coli protein phosphorylation

Abstract Stress tolerance and cross-protection in Enterococcus faecalis ATCC19433 were examined after exposure to bile salts, acid or heat shock. Bile salts and heat adapted cells demonstrated induced homologous tolerance and cross-resistance. No cross-protection of heat adapted cells against acid stress is observed and pretreatment with bile salts even sensitized the cells to this challenge. Whole-cell protein extract analysis revealed that each treatment induced a battery of stress proteins. Some of these polypeptides are induced by more than one treatment. The greatest overlap is observed between bile salts and heat treatments. Eighteen stress proteins, including DnaK and GroEL, are common between these stresses.     

Heat Stress Responses in Cultured Plant Cells : Heat Tolerance Induced by Heat Shock versus Elevated Growing Temperature

Using cultured pear (Pyrus communis cv Bartlett) cells, heat tolerance induced by heat shock was compared to that developed during growth at high temperature. After growth at 22°C, cells exposed to 38°C for 20 minutes (heat shock) showed maximum increased tolerance within 6 hours. Cells grown at 30°C developed maximum heat tolerance after 5 to 6 days; this maximum was well below that induced by heat shock. Heat shock-induced tolerance was fully retained at 22°C for 2 days and was only partly lost after 4 days. However, pear cells acclimated at 30°C lost all acquired heat tolerance 1 to 2 days after transfer to 22°C. In addition, cells which had been heat-acclimated by growth at 30°C showed an additional increase in heat tolerance in response to 39°C heat shock. The most striking difference between heat shock and high growth temperature effects on heat tolerance was revealed when tolerance was determined using viability tests based on different cell functions. Growth at 30°C produced a general hardening, i.e. increased heat tolerance was observed with all three viability tests. In contrast, significantly increased tolerance of heat-shocked cells was observed only with the culture regrowth test. The two types of treatment evoke different mechanisms of heat acclimation.     

Nucleosomal organization of a BPV minichromosome containing a human H4 histone gene

Summary When the body temperature of rats is elevated to 42°C, four heat shock proteins, with the molecular weights of 70000, 71000, 85000, and 100000 (hsp 70, hsp 71, hsp 85, and hsp 100, respectively), are induced in various tissues of rats (Fujio et al., J Biochem 101, 181–187, 1987). Heat shock proteins are induced by various stresses other than heat in varieties of cultured cells, so we studied whether heat shock proteins are induced in intact rats by different treatments. Analysis of the translation products of poly(A) + RNA isolated from the livers of rats recovering from ischemia of the liver showed that mRNAs for hsp 70, hsp 71, and hsp 85 were induced. These hsp-mRNAs were also induced in the livers of rats 6 h after a partial hepatectomy, and had returned to control levels 24 h after the surgery. These results suggested that heat shock proteins have not only the function of protection against various stresses but also physiological functions in the normal growth and development of animals.     

Genome-wide identification of genes involved in tolerance to various environmental stresses inSaccharomyces cerevisiae

During fermentation, yeast cells are exposed to a number of stresses — such as high alcohol concentration, high osmotic pressure, and temperature fluctuation — so some overlap of mechanisms involved in the response to these stresses has been suggested. To identify the genes required for tolerance to alcohol (ethanol, methanol, and 1-propanol), heat, osmotic stress, and oxidative stress, we performed genome-wide screening by using 4828 yeast deletion mutants. Our screens identified 95, 54, 125, 178, 42, and 30 deletion mutants sensitive to ethanol, methanol, 1-propanol, heat, NaCl, and H₂O₂, respectively. These deleted genes were then classified based on their cellular functions, and cross-sensitivities between stresses were determined. A large number of genes involved in vacuolar H⁺-ATPase (V-ATPase) function, cytoskeleton biogenesis, and cell wall integrity, were required for tolerance to alcohol, suggesting their protective role against alcohol stress. Our results revealed a partial overlap between genes required for alcohol tolerance and those required for thermotolerance. Genes involved in cell wall integrity and the actin cytoskeleton are required for both alcohol tolerance and thermotolerance, whereas the RNA polymerase II mediator complex seems to be specific to heat tolerance. However, no significant overlap of genes required for osmotic stress and oxidative stress with those required for other stresses was observed. Interestingly, although mitochondrial function is likely involved in tolerance to several stresses, it was found to be less important for thermotolerance. The genes identified in this study should be helpful for future research into the molecular mechanisms of stress response.     

The stationary-phase sigma factor σS (RpoS) is required for a sustained acid tolerance response in virulent Salmonella typhimurium

The acid tolerance response (ATR) of log-phase Salmonella typhimurium is induced by acid exposures below pH 4.5 and will protect cells against more extreme acid. Two systems are evident: a transiently induced system dependent on the iron regulator Fur that provides a moderate degree of acid tolerance and a more effective sustained ATR that requires the alternate sigma factor σ^S encoded by rpoS. Differences between the acid responses of virulent S. typhimurium and the attenuated laboratory strain LT2 were attributed to disparate levels of RpoS caused by different translational starts. The sustained ATR includes seven newly identified acid shock proteins (ASPs) that are dependent upon σ^S for their synthesis. It is predicted that one or more of these ASPs is essential for the sustained system. The sustained ATR also provided cross-protection to a variety of other environmental stresses (heat, H₂O₂ and osmolarity); however, adaptation to the other stresses did not provide significant acid tolerance. Therefore, in addition to starvation, acid shock serves as an important signal for inducing general stress resistance. Consistent with this model, σ^S proved to be induced by acid shock. Our results also revealed a connection between the transient and sustained ATR systems. Mutations in the regulator atbR are known to cause the overproduction of ten proteins, of which one or more can suppress the acid tolerance defect of an rpoS mutant. One member of the AtbR regulon, designated atrB, was found to be co-regulated by σ^S and AtbR. Both regulators had a negative effect on atrB expression. The results suggest AtrB serves as a link between the sustained and transient ATR systems. When σ^S concentration are low, a compensatory increase in AtrB is required to engage the transiently induced, RpoS-independent system of acid tolerance. Results also suggest different acid-sensitive targets occur in log-phase versus stationary-phase cells.     

Pressure response in the yeast Saccharomyces cerevisiae: from cellular to molecular approaches.

Yeasts are unicellular organisms that are exposed to a highly variable environment, concerning the availability of nutrients, temperature, pH, radiation, access to oxygen and, specially, water activity. Evolution has selected yeasts to tolerate, to a certain extent, these environmental stresses. High hydrostatic pressure (HHP) exerts a broad effect upon yeast cells, interfering with the cell membranes, cellular architecture and in processes ofpolymerisation and denaturation of proteins. Gene expression patterns in response to HHP revealed a stress response profile. The majority of the upregulated genes were involved in stress defence and carbohydrate metabolism while most of the repressed ones were in cell cycle progression and protein synthesis categories. In addition, in the present work it was seen that mild pressure induced cell cycle arrest and protection against severe stresses, such as high temperature, high pressure and ultra cold shock. Nevertheless, this protection was only significant if the cells were incubated at atmospheric pressure after the HHP treatment. Expression of genes that were upregulated by HHP and are related to resistance to this stresses were also analyzed, and, for the majority of them, higher induction was attained after 15 min post-pressurization. Taken together, the results imply an interconnection among stresses.     

Isolation of a New Intermediary Substance Consisting of Colistin Fatty Acid and l-α,δ-Diaminobutyric Acid from Colistin-producing Cells of Bacillus colistinus Koyama

Several saccharides were found to be significantly effective in providing protection against hydrostatic pressure and high temperature damage in the yeast Saccharomyces cerevisiae. The extent of barotolerance and thermotolerance with seven different sugars showed a linear relationship to their mean number of equatorial OH groups. The same linear relatioship is seen when sugars protect protein molecules against elevated temperatures in vitro. Some sugars were more effective in providing protection against hydrostatic pressure nearly a hundred times than high temperature. Pre-heat shock treatment on yeast cells induce various stress tolerances. In this report, pre-heat shocked cells showed potent protection against elevated temperature, but these cells showed faint protection against elevated pressure.

These results suggest that sugars may protect cells against hydrostatic pressure and high temperature in a similar manner, probably by stabilizing the macromolecule(s), and such type of protection may be suited for pressure stress.     

Effect of salicylic acid on the development of induced Thermotolerance and induction of heat shock protein synthesis in the <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis> cell culture

Salicylic acid (SA) could be involved in the development of tolerance to abiotic stresses, to heat shock in particular. Under normal conditions (26°C), treatment with SA improved the tolerance of heterotrophic Arabidopsis thaliana (L.) Heynh culture to severe heat shock (50°C). Under mild heat shock (37°C) inducing the development of thermotolerance, the presence of SA, in contrast, reduced the capability of arabidopsis cells to tolerate high temperature (50°C) and simultaneously suppressed induction of HSP synthesis (Hsp101 and Hsp17.6) important for the development of induced thermotolerance. Since SA suppressed cell respiration and activated the alternative pathway of electron transport, SA is supposed, by modulating mitochondria functions, to be an endogenous regulator of plant stress gene expression.     

Overexpression of Small Heat Shock Protein LimHSP16.45 in Arabidopsis Enhances Tolerance to Abiotic Stresses

Small heat shock proteins (smHSPs) play important and extensive roles in plant defenses against abiotic stresses. We cloned a gene for a smHSP from the David Lily (Lilium davidii (E. H. Wilson) Raffill var. Willmottiae), which we named LimHSP16.45 based on its protein molecular weight. Its expression was induced by many kinds of abiotic stresses in both the lily and transgenic plants of Arabidopsis. Heterologous expression enhanced cell viability of the latter under high temperatures, high salt, and oxidative stress, and heat shock granules (HSGs) formed under heat or salinity treatment. Assays of enzymes showed that LimHSP16.45 overexpression was related to greater activity by superoxide dismutase and catalase in transgenic lines. Therefore, we conclude that heterologous expression can protect plants against abiotic stresses by preventing irreversible protein aggregation, and by scavenging cellular reactive oxygen species.     

Metabolome responses of Enterococcus faecium to acid shock and nitrite stress

Enterococcus faecium is gaining increasing interest due to its virulence and tolerance to a range of stresses (e.g., acid shock and nitrite stress in human stomach). The chemical taxonomy and basic structural features of cellular metabolite can provide us a deeper understanding of bacterial tolerance at molecular level. Here, we used hierarchical classification and molecular composition analysis to investigate the metabolome responses of E. faecium to acid shock and nitrite stress. Our results showed that considerable high biodegradable compounds (e.g., dipeptides) were produced by E. faecium under acid shock, while nitrite stress induced the accumulations of some low biodegradable compounds (e.g., organoheterocyclic compounds and benzenoids). Complete genome analysis and metabolic pathway profiling suggested that E. faecium produced high biodegradable metabolites responsible for the proton-translocation and biofilm formation, which increase its tolerance to acid shock. Yet, the presence of low biodegradable metabolites due to the nitrite exposure could disturb the bacterial productions of surface proteins, and thus inhibiting biofilm formation. Our approach uncovered the hidden interactions between intracellular metabolites and exogenous stress, and will improve the understanding of host-microbe interactions.     

Heat Shock Protein-Mediated Resistance to High Hydrostatic Pressure in Escherichia coli

A random library of Escherichia coli MG1655 genomic fragments fused to a promoterless green fluorescent protein (GFP) gene was constructed and screened by differential fluorescence induction for promoters that are induced after exposure to a sublethal high hydrostatic pressure stress. This screening yielded three promoters of genes belonging to the heat shock regulon (dnaK, lon, clpPX), suggesting a role for heat shock proteins in protection against, and/or repair of, damage caused by high pressure. Several further observations provide additional support for this hypothesis: (i) the expression of rpoH, encoding the heat shock-specific sigma factor σ³², was also induced by high pressure; (ii) heat shock rendered E. coli significantly more resistant to subsequent high-pressure inactivation, and this heat shock-induced pressure resistance followed the same time course as the induction of heat shock genes; (iii) basal expression levels of GFP from heat shock promoters, and expression of several heat shock proteins as determined by two-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis of proteins extracted from pulse-labeled cells, was increased in three previously isolated pressure-resistant mutants of E. coli compared to wild-type levels.     

Role of chlorophylls and carotenoids in seed tolerance to abiotic stressors

It is found that chlorophylls are not fully destructed during seed ripening and can be detected in appreciable quantities in physiologically mature seeds. The elevated content of residual chlorophylls reduces seed tolerance to abiotic stresses. The seed carotenoids were represented mainly by lutein and, in much smaller quantities, by β-carotene. Carotenoids were found to accumulate in seeds during accelerated aging and during seed germination at high temperatures. The ratio of carotenoid to chlorophyll content (Car/Chl) is proposed to be a measure of seed tolerance to stress factors. The seeds with elevated Car/Chl ratio were characterized by higher tolerance to stress treatments. It is supposed that the presence of chlorophylls in seeds enhances oxidative stress induced by abiotic stress factors. Carotenoids are considered as antioxidants protecting the seeds against oxidative stress.