High-pressure studies in cell biology

Recovery and maintenance of live amphipods at a pressure of 580 bars from an ocean depth of 5700 meters

Amphipods were collected from an ocean depth of 5700 meters in a windowed pressure-retaining trap, kept alive in the trap for as long as 9 days aboard ship, and transported to a land laboratory. Observations suggest that the animals can easily tolerate decompressions of 29 percent and briefly of 70 percent of the value of 580 bars, the pressure of their natural habitat. The average pleopod beat frequency was 106 beats per minute. Evidence suggests that food (fish bait) can have at least a 4-day residence time in the gut of these animals.

Permeabilization and inhibition of the germination of spores of Aspergillus niger for gluconic acid production from glucose

In this study, the role of citral to permeabilize the spores of Aspergillus niger and replace sodium azide in the bioconversion medium was studied. Further, characterization of glucose oxidase of spores was carried out by exposing both permeabilized and unpermeabilized spores to different pressures (1, 2, 2.7 kb) and temperatures (60, 70, 80, 90 degrees C). Unpermeabilized spores after exposure to high temperatures were permeabilized by freezing before using as catalyst in the bioconversion reaction. Results showed that citral permeabilized the spores and could inhibit spore germination in the bioconversion medium. Rate of reaction was significantly increased from 1.5 to 4.35 g/Lh which was higher than the commercial glucose oxidase 2g/Lh). Glucose oxidase activity of A. niger was resistant to pressure. However, pressure treatment could not permeabilize them. Behaviour of fresh and permeabilized spores to temperature varied significantly. Glucose oxidase activity of fresh spores exposed to high temperature was unaffected at 70 degrees C till 15 min and 84% of relative activity was retained even after 1h at 70 degrees C while permeabilized spore got inactivated at 70 degrees C for 15 min, which followed the same pattern as commercial glucose oxidase. Cellular membrane integrity was lost due to permeabilization by freezing which resulted in heat-inactivation of glucose oxidase when spores were permeabilized before heat treatment. Thus, glucose oxidase of spore remains heat stable when unpermeabilized and active while permeabilized and its reaction rate is higher than the commercial glucose oxidase.

Inactivation of Colletotrichum gloeosporioides spores by high hydrostatic pressure combined with citral or lemongrass essential oil

Anthracnose, caused by the fungus Colletotrichum gloeosporioides, is the main post-harvest disease of the papaya. Inactivation of the spores of C. gloeosporioides in saline solution by the use of high hydrostatic pressure, citral oil and lemongrass oil, alone and in combination, was studied. C. gloeosporioides spores were efficiently inhibited after a pressure treatment of 350 MPa for 30 min. When C. gloeosporioides was treated with 0.75 mg ml(-1) of citral or lemongrass oil, the pressure needed to achieve the same spore inhibition was 150 MPa. This work suggests the use of high hydrostatic pressure and plant essential oils as an alternative control for fruit diseases.

Induction of baroresistance by hydrogen peroxide, ethanol and cold-shock inSaccharomyces cerevisiae

The acquisition of tolerance to high hydrostatic pressure of 220 MPa (HHP) in response to a 0.4 mM hydrogen peroxide, 6% ethanol and cold-shock (10 degrees C) pretreatment for different lengths of times was studied in the yeast Saccharomyces cerevisiae. The protection conferred by these different treatments was similar ( approximately 3 log cycles) and time-dependent. Analysis of the induction of the most pressure up-regulated genes under these conditions was investigated by RT-PCR. Our results revealed that the cell stress response to HHP shares common features with hydrogen peroxide and ethanol stresses, but differs in some way to cold-shock.

Role of nitric oxide in the response of Saccharomyces cerevisiae cells to heat shock and high hydrostatic pressure

Nitric oxide (NO) is a simple and unique molecule that has diverse functions in organisms, including intracellular and intercellular messenger. The influence of NO on cell growth of Saccharomyces cerevisiae and as a signal molecule in stress response was evaluated. Respiring cells were more sensitive to an increase in intracellular NO concentration than fermentatively growing cells. Low levels of NO demonstrated a cytoprotective effect during stress from heat-shock or high hydrostatic pressure. Induction of NO synthase was isoform-specific and dependent on the metabolic state of the cells and the stress response pathway. These results support the hypothesis that an increase in intracellular NO concentration leads to stress protection.

Effect of hydrostatic pressure on the morphology and ultrastructure of wild-type and trehalose synthase mutant cells of Saccharomyces cerevisiae

AIMS

Saccharomyces cerevisiae was used for studying the physiological effects of hydrostatic pressure.

METHODS AND RESULTS

The effects of hydrostatic pressure on the ultrastructure of wild-type and trehalose-6-phosphate synthase (tps1) mutant cells were investigated by transmission electron microscopy. Pressure induced several morphological changes in wild-type and tps1 cells, the latter showing greater structural alterations. When the cells were submitted to a preheat treatment they both acquired resistance to the pressure treatment.

CONCLUSION

As the tps1 mutant was 1000-fold more barosensitive than its parental strain, it showed greater structural alterations compared with the wild-type. Microscopic images of the yeast cells suggested that hydrostatic pressure induced changes in the cytoskeleton and therefore, on the cell wall and in the dynamics of the organelles.

SIGNIFICANCE AND IMPACT OF THE STUDY

This work presents the effects of hydrostatic pressure on the morphology of yeast cells and confirms the importance of several different factors in the protection of cells against stress.

Effect of hydrostatic pressure of a mutant of Saccharomyces cerevisiae deleted in the trehalose-6-phosphate synthase gene

Mutants Saccharomyces cerevisiae deleted on the trehalose-6-phosphate synthase gene (tps1) and their parental wild-type cells were submitted to hydrostatic pressure in the range of 0-200 MPa. Experimental evidence showed that viability for both strains decreased with increasing pressure and that tps1 mutants, unable to accumulate trehalose, were more sensitive to hydrostatic pressure than the wild-type cells. Additionally, both tps1 and wild-type cells in the stationary phase, when there is an accumulation of endogenous trehalose, were more resistant to pressure than proliferating cells. Under these conditions, mutant cells were also more sensitive to pressure treatment than the wild type. The present work also showed that mild pressure pretreatment did not induce hydrostatic pressure resistance (barotolerance) in yeast cells.

Hydrostatic pressure promotes the acidification of vacuoles in Saccharomyces cerevisiae

Application of hydrostatic pressure caused a delay or cessation of cell growth in Saccharomyces cerevisiae. The yeast vacuole is an acidic organelle involved in cellular ion homeostasis and degradation of proteins. Hydrostatic pressure promoted the acidification of the vacuoles in the strain IFO 2347. A pressure of 40 to 60 MPa reduced the vacuolar pH, defined using 6-carboxyfluorescein, from 6.05 to 5.88, while a pressure of 20 MPa did not affect the pH. Similar results were obtained with the strain X2180. Bafilomycin A1, a specific inhibitor of vacuolar H(+)-ATPase (V-H(+)-ATPase), caused a significant alkalization of vacuoles in the strain X2180. The pHs rose to 7.34 and 6.84 at both atmospheric pressure and a pressure of 40 MPa, respectively. Meanwhile, vacuolar accumulation of the weak base quinacrine was increased by a pressure of 40 MPa, suggesting that uptake of the dye was induced by the increased pH gradient across the vacuolar membrane.

Direct induction of tetraploids or homozygous diploids in the industrial yeast Saccharomyces cerevisiae by hydrostatic pressure

Hydrostatic pressure and a dye plate method were used to investigate the direct induction of tetraploids or homozygous diploids from the industrial diploid or haploid yeast Saccharomyces cerevisiae. Above 200 MPa, hydrostatic pressure greatly inactivated the strains HF399s1 (alpha haploid), P-540 (a/alpha diploid), and P-544 (a/alpha diploid). At the same time, when pressure-treated cells of these strains were spread on a dye plate, some of the visible colonies were stained red/blue or dark blue (variant colonies); the rest stained violet, similar to colonies originating from diploid cells or haploid cells that were not pressure-treated. In addition, above 100 MPa, the formation of variant colonies increased with increasing pressure, and maximized (1 x 10(-1)) at 200 and 250 MPa, respectively. The size of almost all variant cells from P-544, P-540, and HF399s1 was visibly increased compared with that of untreated cells and the measured cellular DNA content of P-540 and HF399s1 was double that of untreated cells. Furthermore, based on random spore analysis and mass-matings, induced variants in the diploid strains were found to be tetraploid with an a/a/alpha/alpha genotype at the mating-type locus or, in the haploid strains, homozygous diploid with an alpha/alpha genotype. From these results we conclude that pressure treatment in combination with a dye plate is a useful method for strain improvement by direct induction of tetraploids or homozygous diploids from industrial strains whether diploid or haploid.

High-pressure freezing for the preservation of biological structure: theory and practice

The two main advantages of cryofixation over chemical fixation methods are the simultaneous stabilization of all cellular components and the much faster rate of fixation. The main drawback pertains to the limited depth (less than 20 microns surface layer) to which samples can be well frozen when freezing is carried out under atmospheric conditions. High-pressure freezing increases the depth close to 0.6 mm to which samples can be frozen without the formation of structurally distorting ice crystals. This review discusses the theory of high-pressure freezing, the design of the first commercial high-pressure freezing apparatus (the Balzers HPM 010), the operation of this instrument, the quality of freezing, and novel structural observations made on high-pressure-frozen cells and tissues.

Effects of isolation and high helium pressure on the nucleolus of sympathetic neurons in the rat superior cervical ganglion

In prokaryotes, unicellular eukaryotes and cell-free systems, pressure is known to exert an inhibitory effect on protein synthesis and RNA metabolism, the mechanism(s) of which remain to be investigated in detail. The purpose of the present in vitro study was to compare ultrastructural and quantitative changes of the nucleolus, which is the site of ribosome biogenesis, in sympathetic neurons of rat superior cervical ganglia (SCG) maintained for 2, 3 and 5 h in NCTC 109 medium and subjected to pressure or not. In control SCG (left) the nucleolus greatly increased in volume (+ 33%) 2 h after excision, in comparison with SCG fixed immediately. This overall enlargement was found to reflect a marked increase in all nucleolar components (from 16 to 87%). After 5 h, volumes of nucleolus, fibrillar centers and vacuolar component returned to control values, whereas dense fibrillar and granular components remained affected. Such early and transient changes are regarded as reflecting basic metabolic changes associated with increased nucleolar RNA that should be of primary concern to experiments using SCG transplanted in culture media. Compression under helium up to 180 atmospheric pressure for 1 h of right SCG maintained for 2 h in culture medium, was shown to induce, on the contrary, a marked decrease in nucleolar volume (-39%) and in volumes of all nucleolar components (from -36 to -51%). When they were kept at constant high pressure for 1 and 3 h a progressive recovery of volumes of nucleoli and nucleolar components was observed. Consequently, compression was shown to exert opposite effects to those of isolation of SCG. Present data are interpreted as an inhibitory effect of pressure on ribosome biogenesis. Such observations on a vertebrate neuron might open a new field in the search for cellular mechanisms underlying the effects of pressure on living organisms and especially on the nervous system.

Axis determination in eggs of Xenopus laevis: a critical period before first cleavage, identified by the common effects of cold, pressure and ultraviolet irradiation

Exposure of eggs of Xenopus laevis to a temperature of 1.0 degree C for 4 min or a pressure of 8000 psi for 5 min in a critical period before first cleavage results in embryos exhibiting a reduction and loss of structures of the body axis. The deficiencies occur in a craniocaudal progression which is dose dependent. In the extreme, totally axis-deficient embryos with radial symmetry are formed. Maximum sensitivity to cold and pressure occurs at 0.6 of the time from fertilization to first cleavage and extends from approximately 0.4 to 0.8, the period between pronuclear contact and mitosis, and the approximate period of gray crescent formation. The effects of cold and pressure resemble those previously reported for uv irradiation in that (1) the types of axis-deficient embryos produced are morphologically indistinguishable; (2) sensitivity in all cases ends before 0.8; (3) cold and uv effects, although not those of pressure, can be prevented by cotreatment with D2O; and (4) impaired eggs can be rescued by oblique orientation. We interpret these results as follows: during the 0.4-0.8 period the egg reorganizes its contents in a manner critical for subsequent development of the embryonic body axis. The reorganization process involves cytoskeletal elements, some of which are sensitive to cold, pressure, and uv, and protected by D2O. Rescue by oblique orientation can be understood as the result of a gravity-driven reorganization of the egg's contents, supplanting the normal mechanochemical process impaired in treated eggs.

Effects of high hydrostatic pressure on normal and neoplastic rat cells in culture

Four types of rat cells in culture were exposed to hydrostatic pressures in the range 1-1,500 bar. Each applied pressure was constant for half an hour. The morphological effects of pressure application were studied by phase contrast microscopy, and mortality was measured by total cell counts and the trypan blue exclusion test. Morphological changes characterized by cell rounding were observed in secondary fetal brain cells and fibroblasts at about 700 bar. In two permanent neoplastic neurogenic cell lines similar changes occurred at 1,000 to 1,100 bar. When approximately 50% of the cells were rounded, mortality began to increase, as compared with controls. This was gradual in secondary cells and comparatively abrupt in the permanent neoplastic lines. Malignant cells in culture may therefore be more resistant to hydrostatic pressure than their normal counterparts.

Mutagenic action of hydrostatic pressure on yeast: a cell cycle analysis

Pressure-treated log growth cultures (14,000 psi equivalent to 966 x 10(5) N/m2 for 4 h) of Saccharomyces cerevisiae were fractionated across a linear Ficoll gradient by zonal rotor centrifugation. This procedure separated the yeast cells on the basis of size and volume into a continuum of cell cycle ages. Cell survival and petite mutation frequency were determined for several zonal fractions. Survival of yeast cells after pressure treatment was maximal in zonal fractions obtained from either the top (single cells in G1) or the botton ("doublets") of the gradient. Intermediate zonal fractions showed more lethality, with minimal survival occurring in zonal fractions containing a large proportion of yeast cells in which buds were just beginning to emerge (initiation of S phase). The petite mutation frequency was minimal in zonal fractions from the top (single cells in G1) and bottom ("doublets") of the gradient. Induction increased to a maximum in those fractions containing cells in S phase.

Structure of wet specimens in electron microscopy. Improved environmental chambers make it possible to examine wet specimens easily

Several recent technological advances have increased the practicality and usefulness of the technique of electron microscopy of wet objects. (i) There have been gains in the effective penetration of high-voltage microscopes, scanning transmission microscopes, and high-voltage scanning microscopes. The extra effective penetration gives more scope for obtaining good images through film windows, gas, and liquid layers. (ii) Improved methods of obtaining contrast are available (especially dark field and inelastic filtering) that often make it possible to obtain sufficient contrast with wet unstained objects. (iii) Improved environmental chamber design makes it possible to insert and examine wet specimens as easily as dry specimens. The ultimate achievable resolution for wet objects in an environmental chamber will gradually become clear experimentally. Resolution is mainly a function of gas path, liquid and wet specimen thickness, specimen stage stability, acceleration voltage, and image mode (fixed or scanning beam) (13). Much depends on the development of the technique for controlling the thickness of extraneous water film around wet objects or the technique for depositing wet objects onto dry, hydrophobic support films. Although some loss of resolution due to water or gas scattering will always occur, an effective gain is anticipated in preserving the shape of individual molecules and preventing the partial collapse that usually occurs on drying or negative staining. The most basic question for biological electron microscopy is probably whether any living functions of cells can be observed so that the capabilities of the phase contrast and interference light microscopes can be extended. Investigators are now rapidly approaching a final answer to this question. The two limiting factors are (i) maintaining cell motility in spread cells immersed in thin layers of media and (ii) reducing beam radiation damage to an acceptable level. The use of sensitive emulsions and image intensifiers can bring the observation dose below that required to stop cell motility. Use of a timed, pulsed deflector system enables sufficiently short exposures to be obtained to eliminate blurring due to Brownian motion. Environmental chambers have enhanced the possibilities of electron diffraction analysis of minute crystals and ordered biological structures. High-resolution electron diffraction patterns (especially kinematic) of protein crystals can only be obtained in a wet environment. Hence, it may now be possible to obtain undistorted images of protein molecules. Moreover, by subjecting diffraction patterns to image-iterative techniques (56), it will be possible to phase the electron diffraction patterns to give a calculated image with a higher resolution than that which can be produced by electron microscope objective lenses. Environmental chambers offer exciting prospects for the determination of water structure and water and ice nucleation (atmospheric science). Nucleation data near the molecular level have been badly needed for some time. The application of environmental chambers in industrial chemistry, for example, in studies of polymerization, catalysis, and corrosion, are awaiting exploration. They offer an unusual approach to measurements of reaction kinetics through images that should be both sensitive and rapid.