Loss Of Heat Resistance Research Articles

A Saccharomyces cerevisiae G-protein coupled receptor, Gpr1, is specifically required for glucose activation of the cAMP pathway during the transition to growth on glucose.

In the yeast Saccharomyces cerevisiae the accumulation of cAMP is controlled by an elaborate pathway. Only two triggers of the Ras adenylate cyclase pathway are known. Intracellular acidification induces a Ras-mediated long-lasting cAMP increase. Addition of glucose to cells grown on a non-fermentable carbon source or to stationary-phase cells triggers a transient burst in the intracellular cAMP level. This glucose-induced cAMP signal is dependent on the G alpha-protein Gpa2. We show that the G-protein coupled receptor (GPCR) Gpr1 interacts with Gpa2 and is required for stimulation of cAMP synthesis by glucose. Gpr1 displays sequence homology to GPCRs of higher organisms. The absence of Gpr1 is rescued by the constitutively activated Gpa2Val-132 allele. In addition, we isolated a mutant allele of GPR1, named fil2, in a screen for mutants deficient in glucose-induced loss of heat resistance, which is consistent with its lack of glucose-induced cAMP activation. Apparently, Gpr1 together with Gpa2 constitute a glucose-sensing system for activation of the cAMP pathway. Deletion of Gpr1 and/or Gpa2 affected cAPK-controlled features (levels of trehalose, glycogen, heat resistance, expression of STRE-controlled genes and ribosomal protein genes) specifically during the transition to growth on glucose. Hence, an alternative glucose-sensing system must signal glucose availability for the Sch9-dependent pathway during growth on glucose. This appears to be the first example of a GPCR system activated by a nutrient in eukaryotic cells. Hence, a subfamily of GPCRs might be involved in nutrient sensing.

Performance analysis for a real closed regenerated Brayton cycle via methods of finite-time thermodynamics

SYNOPSIS Performance analysis of a real power cycle has been performed using finite-time thermodynamics. The analytical formulae about the relations between power output and pressure ratio, and between efficiency and pressure ratio of a real closed regenerated Brayton cycle coupled to variable-temperature heat reservoirs are derived. In the analysis, the irreversibilities involve the heat resistance losses in the hot- and cold-side heat exchangers and the regenerator, the irreversible (non-isentropic) expansion and compression losses in the turbine and compressor, and the pressure drop loss in the pipe and system. The optimal performance characteristics of the cycle may be obtained by optimising the distribution of heat conductance or heat-transfer surface areas among two heat exchangers and regenerator, and the matching between working fluid and heat reservoirs. For the specified heat reservoir conditions, the power output is dependent on the effectiveness of the regenerator, and there exists an optimal matching among the effectivenesses of the hot- and cold-side heat exchangers and the regenerator. The influences of the effectiveness of the regenerator, the effectiveness of the hot- and cold-side heat exchangers, the efficiencies of the turbine and compressor, the pressure recovery coefficient and the inlet temperature ratio of the heat reservoirs on the power output and efficiency of the cycle are analysed by detailed numerical examples.

Finite Time Thermodynamic Optimization or Entropy Generation Minimization of Energy Systems

The historical background, research development, and the state-of-the-art of finite time thermodynamic theory and applications are reviewed from the point of view of both physics and engineering. The emphasis is on the performance optimization of thermodynamic processes and devices with finite-time and/or finite-size constraints, including heat engines, refrigerators, heat pumps, chemical reactions and some other processes, with respect to the following aspects: the study of Newton's law systems, an analysis of the effect of heat resistance and other irreversible loss models on the performance, an analysis of the effect of heat reservoir models on the performance, as well as the application for real thermodynamic processes and devices. It is pointed out that the generalized thermodynamic optimization theory is the development direction of finite thermodynamics in the future.

Performance analysis for endoreversible closed regenerated Brayton heat pump cycles

Finite-time thermodynamic performance of isentropic closed regenerated Brayton heat pump cycles coupled to constant—and variable—temperature heat reservoirs has been analyzed in this paper. The relations between heating load and pressure ratio and between COP (coefficient of performance) and pressure ratio are derived for the two cases of heat reservoirs. In the analysis, the sole irreversibility is the heat resistance losses in the heat exchangers between the working fluid and the high, and low, temperature heat reservoirs and the regenerator. A numerical example is also given.

Cooling load versus COP characteristics for an irreversible air refrigeration cycle

The effect of heat resistance on the performance of an air refrigeration cycle is analyzed with a finite time heat transfer analysis. The present work extends the recent studies on refrigerator performance by incorporating nonisentropic compression and expansion. Relations between cooling load and pressure ratio and between COP (coefficient of performance) and pressure ratio for the air refrigeration cycle in which the irreversibilities of heat resistance losses in the hot and cold-side heat exchangers and nonisentropic losses in the compression and expansion processes are derived. The results show that there exists a maximum value of COP and that the cooling load has a parabolic dependence on COP, unlike the monotonically decreasing behaviour in the case of an endoreversible air refrigeration cycle.

97/03097 A generalised model of a real heat engine and its performance

The sole irreversibility considered in an endo-reversible Carnot heat-engine model is the loss of heat-resistance between the engine and its surrounding heat reservoirs. This paper presents a new steady-state-flow irreversible Carnot heat-engine model by taking additional account of several internal irreversibilities of the heat engine, such as heat leakage, friction, turbulence and other undesirable irreversibility factors. This is done by means of a constant parameter and a constant coefficient, together with the loss of heat-resistance. Analysis and optimisation of the model were carried out to investigate the effect of the various irreversibilities on the performance of the model. Numerical examples illustrate the effectiveness of the model.

Inhibition by Monoglycerides of l-Alanine-Triggered Bacillus cereus and Clostridium botulinum Spore Germination and Outgrowth

Germination of Bacillus cereus T and Clostridium botulinum 62A spores in l-alanine solutions was totally inhibited by monolaurin (0.182 mM), monomyristin (0.331 mM), monolinolein (0.564 mM), and monolinolenin (0.142 mM). These monoglycerides inhibited the commitment to germinate, possibly by interfering with germinant diffusion to the binding site(s). They also blocked postcommitment to germinate reactions including loss of heat resistance. Outgrowth of fully germinated B. cereus T spores in the presence of l-alanine was inhibited by these monoglycerides.

The 3-phosphoglycerate kinase of the hyperthermophilic archaeum Pyrococcus woesei produced in Escherichia coli: loss of heat resistance due to internal translation initiation and its restoration by site-directed mutagenesis

Heterologous expression of the gene coding for 3-phosphoglycerate kinase (PGK) of the hyperthermophilic archaeum, Pyrococcus woesei (Pw), in Escherichia coli (Ec) yielded only low recovery of recombinant PGK (re-PGK) in heatprecipitated crude extracts. Moreover, we noticed contamination with a 28-kDa protein, from which PGK could hardly be separated, even under stringent conditions after tagging the re-PGK with a His 6-tag. The preparations contaminated with the 28-kDa protein showed an unexpectedly low thermal stability. Under the same conditions (85°C, 30 min), however, the enzyme from the original organism was completely resistant to heat inactivation. As shown by sizeexclusion chromatography, re-PGK forms tight associations with the 28-kDa protein, which was found to represent a C-terminal fragment of PGK and to arise as a product of internal translation initiation within the pgk gene. Mutations changing the internal ribosome-binding site effectively suppressed the production of the 28-kDa protein and restored the thermal stability of the Pw re-PGK.

Inhibition of l-alanine triggered Bacillus cereus T spore germination and outgrowth by fatty acids and glyceryl monododecanoate

Germination of Bacillus cereus T spores in l-alanine solutions was inhibited totally by lauric (0·25 mM) and oleic (0·885 mM) acids and partially by linoleic acid (0·71 mM), linolenic acid (0·36 mM) and glyceryl monododecanoate (0·36 mM). Inhibition of spore germination was reversible. Lauric or oleic acid inhibited commitment to germinate possibly by interference with germinant diffusion to the binding site(s). These two fatty acids also blocked reactions of postcommitment to germinate including loss of heat resistance. All fatty compounds inhibited outgrowth of fully germinated spores. This was accompanied by inhibition of oxygen consumption by glyceryl monododecanoate and linolenic acid.

Inhibition of Bacterial Spore Growth by Fatty Acids and Their Sodium Salts

The antimicrobial activity of 11 fatty acids and their salts was tested on spores of Clostridium botulinum 62A, Clostridium sporogenes PA3679, and Bacillus cereus F4165/75.Linolenic acid was the most inhibitory fatty acid and lauric acid was the most inhibitory of the saturated fatty acids. Minimum inhibitory concentrations ranged from 50–150 μg/ml for lauric acid, ≥150 μg/ml for myristic acid, 30–100 μg/ml for linoleic acid, and 10–75 μg/ml for linolenic acid depending on the strain. Caprylic, capric, palmitic, stearic, arachidic, and erucic acids showed only partial inhibition (44 to 90%) at concentrations as high as 150 μg/ml.Addition of 0.2–0.3% (wt/vol) starch neutralized the inhibitory effect of palmitic, linoleic, and linolenic acids but had no effect on lauric acid even when increased to 1%.Lauric, linoleic, and linolenic acids were shown to inhibit spore germination as measured by loss of spore heat resistance.

Role of spore coats in the germinative response of Bacillus cereus to adenosine and its analogues

Spores of the strain NCIB 8122 of Bacillus cereus have been depleted of coats by treatment with 0.1% sodium dodecyl sulfate--200 mM 2-mercaptoethanol--0.5 M NaCl (pH 9.6). The coat-depleted spores did not show any decrease in viability, heat resistance, refractility, dipicolinic acid content, or specific activities of several protoplastic enzymes. The germinative response of the coat-depleted spores to adenosine and several analogues thereof was found qualitatively similar to that obtained with intact spores. However, germination kinetics appeared to be affected by coat removal, since germination rate measured as loss of refractility was eight times slower even at inducer concentrations 10-fold higher than those required to promote optimal germination response of intact spores. Loss of heat resistance, on the other hand, was hardly affected by coat removal. These results suggest that, even though spore coats are not essential for the triggering reaction, they are required for a rapid evolution of the later events in the germination process.

The possible involvement of trypsin-like enzymes in germination of spores of Bacillus cereus T and Bacillus subtilis 168.

Germination of spores of Bacillus cereus T and Bacillus subtilis 168 was inhibited by the trypsin inhibitors leupeptin and tosyllysine chloromethyl ketone (TLCK) and by the substrates tosylarginine methyl ester (TAME), benzoyl-L-arginine-p-nitroanilide (L-BAPNA) and D-BAPNA. Potencies of these inhibitory compounds were estimated by finding the concentration which inhibited 50% germination (ID50), as measured by events occurring early (loss of heat resistance), at an intermediate stage [dipicolinic acid (DPA) release], and late in germination (decrease in optical density). In B. cereus T, all the compounds inhibited early and late events with the same ID50. In B. subtilis, TAME inhibited early and late events at the same ID50, but all other inhibitors had a lower ID50 for late events than for early events. This suggests that a trypsin-like enzyme activity is involved at two sequential stages in the germination of B. subtilis spores, one occurring at or before the loss of heat resistance and one at or before the decrease in optical density. Different trypsin-like activities were detected in broken dormant spores and germinated spores of B. cereus T and in germinated spores of B. subtilis by means of three chromogenic substrates: benzoyl-L-phenylalanyl-L-valyl-L-arginine-p-nitroanilide (L-PheVA), L-BAPNA and D-BAPNA. Separation of extracts of germinated spores on non-denaturing polyacrylamide gels showed that in both species the substrates were hydrolysed by three distinct enzymes with different electrophoretic mobilities. The three enzymes had different Ki values for the above inhibitors.(ABSTRACT TRUNCATED AT 250 WORDS)

Calmodulin antagonists inhibit germination of Bacillus cereus T spores

The effects of two calmodulin antagonists, trifluoperazine (TFP) and N‐(6‐aminohexyl)‐5‐chloro‐1‐naphthalene sulphonamide hydrochloride (W‐7) on L‐alanine‐induced germination of Bacillus cereus T spores were examined by measuring commitment to germination, decrease in optical density at 660 nm and phase‐contrast microscopy. The kinetics of optical density decrease suggested competitive inhibition of TFP or W‐7 with both L‐alanine and D‐alanine (L‐alanine analogue and germination inhibitor) as determined by Lineweaver‐Burk and Schild plots, respectively. Germination inhibition was pH‐dependent. The I50 values for maximum decreasing rate of optical density in 10 mmol/l L‐alanine plus 5 mmol/l adenosine at pH 6·4 were 0·21 and 0·74 mmol/l for TFP and W‐7, respectively. Much less effect of N‐(6‐aminohexyl)‐l‐naphthalene sulphonamide hydrochloride than W‐7 lends support to the specificity of W‐7. The calmodulin antagonists were effective at a step in germination after commitment and loss of heat resistance. It is postulated that this process is necessary in the germination of B. cereus T spores to convert phase‐bright spores to phase‐dark spores and to cause a decrease in optical density.

Induction of germination in Myxococcus xanthus fruiting body spores

Summary Myxococcus xanthus, when starved on a solid surface, undergoes a multicellular cycle of development that consists of fruiting and sporulation. Myxospore germination has been followed in CTT, a complex medium composed mainly of peptides, by monitoring the sequential disappearance of some characteristic spore properties. Loss of heat resistance, shortly after incubation was initiated, was followed by loss of resistance to SDS and finally, refractility and ovoid shape. Germination of a population of myxospores did not occur synchronously. However, in the presence of calcium, germination was activated, being more rapid and synchronous. Other spore activation treatments tested did not have the same stimulatory effect. We searched for specific nutrients or chemicals capable of inducing germination. Amino acids, unlike other potential carbon and energy sources for M. xanthus, or several sugars tested, were most effective in triggering germination. Continuous incubation in CTT and Casamino acids germinant solutions was not required for induction and completion of germination of a large proportion of spores in a population.

Failure Problems In Composites

AbstractFiber reinforced polymer matrix composites have become very useful in chemical processing systems, in transportation applications such as automobiles, aircraft and boats, in electrical hardware and in sports equipment. Failures in these rarely involve gross cohesive fracture; usually leaks develop, the stiffness decreases, local delamination occurs, the dielectric properties degrade or the strength declines. Almost all of these failures can be traced to local cracking, either at the fiber matrix interface or within the matrix itself. The cracks are generated by mechanical loads, by thermal excursions or by fluid absorption, because the relevant properties of the fiber and the matrix often differ by orders of magnitude. Current technology attempts to avoid the cracks by maximizing the fiber-matrix adhesion and great progress has been made in this area. An alternative interposes a thin compliant layer, rubber, between the two constituents thereby reducing the stress concentrations which exist because of their greatly different properties. Cracking is inhibited, composite strength is increased and its energy absorption also rises; if the rubber layer is thin (a few thousand Angstroms) no loss of stiffness or heat resistance is evident.

Uptake of l-[14C]-alanine by glutaraldehyde-treated and untreated spores ofBacillus subtilis

The effect of glutaraldehyde on the uptake of L-alanine, and subsequent germination, in spores of Bacillus subtilis NCTC 8236 was examined. Germination was induced by single amino acids, D-glucose and phosphate buffer at 37 degrees C. L-alanine was the best germinant of all amino acids tested. Pretreatment of spores with low concentrations of acid and alkaline glutaraldehyde inhibited subsequent germination, complete inhibition being observed at concentrations of 0.1% (w/v). This concentration also prevented the loss of heat resistance of spores placed in germination medium and exposed to 75 degrees C. Radioactive studies indicated that maximum uptake of L-alanine occurred after ca 30 min at 37 degrees C. Only 1.2% of available L-alanine was taken up during germination. Pretreatment of spores with glutaraldehyde did not interfere with L-alanine uptake at aldehyde concentrations up to 0.5% (w/v). However, this was significantly reduced at a glutaraldehyde concentration of 1.0% (w/v). Minimal differences were observed between acid and alkaline forms of the aldehyde. The results are discussed in terms of the mode of action of glutaraldehyde.

Uptake of L-[ 14C]-alanine by glutaraldehyde-treated and untreated spores of Bacillus subtilis

The effect of glutaraldehyde on the uptake of L-alanine, and subsequent germination, in spores of Bacillus subtilis NCTC 8236 was examined. Germination was induced by single amino acids, D-glucose and phosphate buffer at 37°C. L-alanine was the best germinant of all amino acids tested. Pretreatment of spores with low concentrations of acid and alkaline glutaraldehyde inhibited subsequent germination, complete inhibition being observed at concentrations of 0.1% (w/v). This concentration also prevented the loss of heat resistance or spores placed in germination medium and exposed to 75°C. Radioactive studies indicated that maxium uptake of L-alanine occurred after ca. 30 min at 37°C. Only 1.2% of available L-alanine was taken up during germination. Pre-treatment of spores with glutaraldehyde did not interfere with L-alanine uptake at aldehyde concentrations up to 0.5% (w/v). However, this was significantly reduced at a glutaraldehyde concentration of 1.0% (w/v). Minimal differences were observed between acid and alkaline forms of the aldehyde. The results are discussed in terms of the mode of action of glutaraldehyde.

Biochemical Analysis of the Bacillus subtilis 1604 Spore Germination Response

Germination at 37 degrees C of spores of Bacillus subtilis 1604 in the L-alanine and potassium phosphate (ALA) and the glucose, fructose, L-asparagine, potassium chloride (GFAK) germinant systems was triggered following heat activation at 70 degrees C for 1 h. In these conditions, 50% of the spore population became committed to germinate after exposure for 10 min and 14 min to ALA and GFAK, respectively, at which time 38% and 30% losses of OD600 had taken place. Dipicolinic acid (DPA) release, loss of heat resistance and release of soluble hexosamine-containing fragments occurred after commitment and were closely associated with loss of refractility in both the ALA and GFAK pathways. Net ATP synthesis could not be detected until 3-4 min after initiation of germination in both ALA and GFAK, by which time greater than 20% of the spore population was committed to germinate. The ALA and GFAK germination pathways were greater than 99% inhibited by 3 and 1 mM-HgCl2, respectively, as measured by OD600 loss. Reversible post-commitment HgCl2-sensitive sites were present in the ALA and GFAK pathways which were 50% inhibited by 0.125 mM and 0.05 mM-HgCl2, respectively. A pre-commitment HgCl2-sensitive site was identified in the ALA pathway which was 55% inhibited by 6 mM-HgCl2. At 3 mM-HgCl2, 70% of the spore population became committed to germinate in the ALA pathway, whereas less than 5% OD600 loss occurred. In this system, loss of heat resistance was associated with commitment, whereas OD600 loss and DPA release were identified as post-commitment events. The ALA and GFAK pathways were insensitive to a variety of metabolic inhibitors. Protease inhibitors had different effects on the ALA and GFAK pathways: phenylmethanesulphonyl fluoride (PMSF) solely inhibited ALA germination at a pre-commitment site and had little effect on GFAK germination, whereas N alpha-p-tosyl-L-arginine methyl ester (TAME) inhibited both the ALA and GFAK pathways at pre- and post-commitment sites. These results are discussed in relation to a recently proposed model for the triggering of Bacillus megaterium KM spore germination.

Thermal acclimation and tolerance to lethal high temperature in the mountain stream amphipod Paramelita nigroculus (Barnard)

1. 1. Rates of upward and reverse acclimation were studied in Paramelita nigroculus (Barnard) from a mountain stream using a modification of the Critical Thermal Maximum (CTM) method. The upper lethal temperatures were measured using the LT 50 method. 2. 2. Acclimation rates were found to be typical of most crustaceans, with a gain of resistance to high temperature, following transfer from 8.5 to 20°C, being completed in 1–2 days. Loss of heat resistance took slightly longer (3 days). 3. 3. The species is strongly sexually dimorphic, males being significantly smaller than females. Neither sex, body length nor feeding status was found to affect tolerance levels. 4. 4. The LT 50 (min) for animals acclimated to 13.5°C ranged from approximately 300 min at 27°C to 4 min at 31°C. 5. 5. LT 50 values for 20°C-acclimated individuals were significantly higher than those acclimated at 13.5°C at corresponding test temperatures.

The use of inhibitors to identify early events during Bacillus megaterium KM spore germination.

The germination response of spores of Bacillus megaterium KM, as measured by loss of A600, is more than 95% inhibited by 1 mM-HgCl2. Two Hg2+-sensitive sites (referred to as 'sites I and II') have been identified during germination. Site I represents a pre-commitment event and can be protected from HgCl2 by 50 mM-D-alanine, whereas site II represents a post-commitment event and is not D-alanine-protectable. At 1 mM-HgCl2, 25% of the spore population becomes committed to germinate, but an A600 loss of less than 5% occurs. In this system, loss of heat resistance was associated with commitment, whereas selective cortex hydrolysis, release of pyridine-2,6-dicarboxylic acid, Zn2+ and soluble peptidoglycan, as well as loss of refractility, were identified as post-commitment events. The commitment event was reversibly inhibited by several proteinase inhibitors and a membrane bulking agent. A model of spore germination based on these results is presented.