Escherichia coli growth under modeled reduced gravity

Bacteria exhibit varying responses to modeled reduced gravity that can be simulated by clino-rotation. When Escherichia coli was subjected to different rotation speeds during clino-rotation, significant differences between modeled reduced gravity and normal gravity controls were observed only at higher speeds (30-50 rpm). There was no apparent affect of removing samples on the results obtained. When E. coli was grown in minimal medium (at 40 rpm), cell size was not affected by modeled reduced gravity and there were few differences in cell numbers. However, in higher nutrient conditions (i.e., dilute nutrient broth), total cell numbers were higher and cells were smaller under reduced gravity compared to normal gravity controls. Overall, the responses to modeled reduced gravity varied with nutrient conditions; larger surface to volume ratios may help compensate for the zone of nutrient depletion around the cells under modeled reduced gravity.     

Physiological Responses of Synechocystis sp. PCC 6803 under Clinorotation

Photosystem efficiency and the characteristic on oxidative stress were examined to elucidate the metabolic responses of Synechocystis sp. PCC 6803 to short-term clinorotation. Results compiled when using clinostat to simulate microgravity for 60?h, showed that clinorotation clearly prohibited the photochemical quantum yield, but promoted the synthesis of chlorophyll and total protein. This may be a compensatory mechanism for the algal cell to maintain its normal metabolism. An increased malondialdehyde (MDA) content of algal cell upon clinorotation, together with an enhanced catalase (CAT) activity was observed during the whole period of clinorotation. One conclusion is that short-term clinorotation acts as a kind of stress, and that these physiological responses may be a special way for an algal cell to adapt itself to a different environment other than earth gravity.     

Clinorotation Effect on Response of Cress Leaves to Red and Far-Red Light

Responses of cress (Lepidium sativum L.) seedling leaves to separate and simultaneous illumination with red (660 nm) and far-red (735 nm) light were studied under fast clinorotation (50 rpm) and usual gravity (1g) conditions. The monochromatic light emitting diodes (LEDs) have been used for illumination of seedlings from above. The growth and spatial orientation of leaves and the location of presumable gravisensors in petioles were analysed. Clinorotation in the dark promoted the radial expansion of leaf lamina and unfolding of leaves. It was shown that clinorotation in red light inhibited significantly the elongation of petioles as compared with that under the action of gravity force. Simultaneous red and far-red illumination promoted the growth of petioles under clinorotation, but did not affect the orientation of laminas, which remained the same as of the 1-g control ones. Red light, applied separately and simultaneously with far-red light, guided the bending of laminas as well as the unfolding of leaf petioles in both usual and clinorotation conditions. Histological and cytological analyses of petioles revealed the presence of movable amyloplasts in endodermic cells in proximal region of petioles. Comparison of intracellular positioning of amyloplasts in petioles of leaves grown under clinorotation and the action of gravity allows a presumption that these plastids may be identified as gravisensors of garden cress leaves. The obtained data imply that clinorotation and exposition to monochromatic red light or simultaneous illumination by red and far-red light affect the elongation of petioles of cress seedling leaves. Spectral components guide the unfolding of laminas in a gravity-independent manner.     

The stress protein level under clinorotation in context of the seedling developmental program and the stress response

Heat-shock proteins (HSP70 and HSP90) are present in plant cells under the normal growth conditions. At the same time, a variety of environmental disruptions results in their rapid synthesis as a substantial part of adaptation. HSP amounts can be indicative of a cellular stress level. Altered gravity (clinorotation) is unnatural for plants, so it may be a kind of stress. The aim of this study was to analyze the influence of horizontal clinorotation on the HSP70 and HSP90 level during seedling development. Pea (Pisum sativum L.) seedlings grown for 3 days from seed imbibitions in stationary control and under slow clinorotation (2 rpm) are used for this investigation. Western blot analysis indicated that HSP70 and HSP90 were abundant in the embryos of dry seeds and their amount decreased significantly during seed germination. But under horizontal clinorotation, their level in seedlings remained higher compared to the control. Furthermore, a comparison of the influence of horizontal and vertical clinorotation on the HSP level was carried out. On the ELISA data, HSP70 and HSP90 amounts in the 3-day old seedlings were higher after horizontal clinorotation than after vertical. The obtained data show an increased HSP70 and HSP90 level in pea seedlings under clinorotation. Both, rotation and change in the cell position relatively to a gravity vector affect the HSP level.     

Effects of Altered Gravity on the Cytoskeleton of Neonatal Rat Cardiocytes

As an intracellular load-bearing structure, the cytoskeleton is hypothesized to play a crucial role in gravity perception of the cell. Recent data show that the cytoskeleton, which includes actin microfilaments and microtubules, is involved in modulating both the electrical and the mechanical activities of the myocardium. The present study employed observation and quantified analyses of fluorescent images of cardiocytes under different gravity conditions. In acute gravitational change (micro- and hypergravity) induced by parabolic flight, we found disassembly of microtubules but enhanced polymerization of microfilaments, with rearrangement from G-actin to F-actin. In ground-based experiments, exposure of cardiocytes to 2×g hypergravity (centrifugation) led to increased width and number of actin fibers from 2 to 48 h, while microtubules showed no significant changes except polarization at 24 and 48 h. In contrast, exposure of cardiocytes to clinorotation led to disassembly of microtubules from 1 to 48 h, while microfilaments showed no significant changes except redistribution, which was accompanied by rounding of the cells (48 h). We assume that the sensitivity of microfilaments to hypergravity and that of microtubules to microgravity might contribute to the specific cytoskeletal changes observed in parabolic flight. These findings indicate different sensitivity and responses of microfilaments and microtubules to different gravitational changes, which might be part of functional adaptations of the cardiocytes to altered gravitational environments.     

Analysis of Statoliths Displacement in <Emphasis Type="Italic">Chara</Emphasis> Rhizoids for Validating the Microgravity-Simulation Quality of Clinorotation Modes

In single-celled rhizoids of the green algae Chara, positively gravitropic growth is governed by statoliths kept in a dynamically stable position 10–25 μ m above the cell tip by a complex interaction of gravity and actomyosin forces. Any deviation of the tube-like cells from the tip-downward orientation causes statoliths to sediment onto the gravisensitive subapical cell flank which initiates a gravitropic curvature response. Microgravity experiments have shown that abolishing the net tip-directed gravity force results in an actomyosin-mediated axial displacement of statoliths away from the cell tip. The present study was performed to critically assess the quality of microgravity simulation provided by different operational modes of a Random Positioning Machine (RPM) running with one axis (2D mode) or two axes (3D mode) and different rotational speeds (2D), speed ranges and directions (3D). The effects of 2D and 3D rotation were compared with data from experiments in real microgravity conditions (MAXUS sounding rocket missions). Rotational speeds in the range of 60–85 rpm in 2D and 3D modes resulted in a similar kinetics of statolith displacement as compared to real microgravity data, while slower clinorotation (2–11 rpm) caused a reduced axial displacement and a more dispersed arrangement of statoliths closer to the cell tip. Increasing the complexity of rotation by adding a second rotation axis in case of 3D clinorotation did not increase the quality of microgravity simulation, however, increased side effects such as the level of vibrations resulting in a more dispersed arrangement of statoliths. In conclusion, fast 2D clinorotation provides the most appropriate microgravity simulation for investigating the graviperception mechanism in Chara rhizoids, whereas slower clinorotation speeds and rotating samples around two axes do not improve the quality of microgravity simulation.     

Comparison Study of Gravity-Dependent Displacement of Amyloplasts in Statocytes of Cress Roots and Hypocotyls

In this study, the kinetics of gravity-dependent movement of amyloplasts (statoliths) along root statocytes and hypocotyls (endodermis cells) has been analyzed and compared in order to testify cytoskeleton involvement in the displacement of statoliths in cress (Lepidium sativum L.) seedling statocytes. After 32 h of growth at 1 g or under a fast clinorotation (50 rpm), the seedlings were treated for 24 min as follows: exposition to clinorotation or 180° inversion and the action of gravitational force in root tip or hypocotyl tip direction. Statolith displacement was studied by light microscopy on semi-thin longitudinal sections of hypocotyls and root caps, measuring the distance between the centre of plastids and morphological cell bottom. Considerable temporal differences have been determined between the kinetics of the longitudinal motion of amyloplasts in root and hypocotyl statocytes of 1-g seedlings upon exposition to fast clinorotation and inversion. In statocytes of both organs of seedlings grown under fast clinorotation, the gravity provoked displacement of statoliths in the direction of its action; however, the displacement was much faster in hypocotyl than in root statocytes. It has been assumed that the gravity-determined longitudinal transport of amyloplasts, both in hypocotyl endodermic cells and root statocytes of cress seedlings, is modulated by the cytoskeleton.     

Distribution of Calcium Ions in Cells of the Root Distal Elongation Zone Under Clinorotation

Currently, calcium ions are known to play a crucial role in the vital activity of plant cells and in stimulus–response coupling for many environmental signals, altered gravity included. The available data on changes in Ca^2?+? distribution and concentration in the cells of different organisms influenced by altered gravity allow to suggest that microgravity affects the calcium messenger system, and provide new insight for the understanding of calcium-and gravity-dependent cellular processes. We have studied with confocal microscopy the distribution and relative content of calcium ions in the Beta vulgaris root distal elongation zone cells grown under slow horizontal clinorotation, reproducing one of the microgravity particularities, namely the absence of an orienting action of the gravity vector, compared to control conditions. We demonstrate that Ca^2?+? relative content is 1.3 times higher in the roots of seedlings grown upwards and 1.2 times higher in the seedlings grown downwards compared to the control. Based on obtained data, taking into account the specific physiological properties of cells in the distal elongation zone, it is supposed that, under clinorotation, enhanced Ca^2?+? relative content affects Ca^2?+?-dependent cytoskeleton reorganization involved in cell gravisensing in altered gravity.     

The effect of simulated microgravity on bacteria from the mir space station

The effects of simulated microgravity on two bacterial isolates, Sphingobacterium thalpophilium and Ralstonia pickettii (formerly Burkholderia pickettii), originally recovered from water systems aboard the Mir space station were examined. These bacteria were inoculated into water, high and low concentrations of nutrient broth and subjected to simulated microgravity conditions. S. thalpophilium (which was motile and had flagella) showed no significant differences between simulated microgravity and the normal gravity control regardless of the method of enumeration and medium. In contrast, for R. pickettii (that was non-motile and lacked flagella), there were significantly higher numbers in high nutrient broth under simulated microgravity compared to normal gravity. Conversely, when R. pikkettii was inoculated into water (i.e., starvation conditions) significantly lower numbers were found under simulated microgravity compared to normal gravity. Responses to microgravity depended on the strain used (e.g., the motile strain exhibited no response to microgravity, while the non-motile strain did), the method of enumeration, and the nutrient concentration of the medium. Under oligotrophic conditions, non-motile cells may remain in geostationary orbit and deplete nutrients in their vicinity, while in high nutrient medium, resources surrounding the cell may be sufficient so that high growth is observed until nutrients becoming limiting.     

Alterations in Protein Expression of Arabidopsis thaliana Cell Cultures During Hyper- and Simulated Micro-Gravity

Callus cell cultures of Arabidopsis thaliana exposed to hypergravity (8×g), 2D clinorotation and random positioning exhibit changes in gene expression (Martzivanou et al., Protoplasma 229:155–162, 2006). In a recent investigation we could show that after 2 h of exposure also the protein complement shows treatment-related changes which are indicative for reactive oxygen species being involved in the perception of/response to changes in the gravitational field. In the present study we have extended these investigations for a period of up to 16 h of exposure. We report on changes in abundance of 28 proteins which have been identified by nano HPLC-ESI-MS/MS, and which were altered in amount after 2 h of treatment. According to changes between 2 and 16 h we could distinguish four groups of proteins which either declined, increased from down-regulated to control levels, showed a transient decline or a transient increase. With regard to function, our data indicate stress relief or adaptation to a new gravitational steady state under prolonged exposure. The latter assumption is supported by the appearance of a new set of 19 proteins which is changed in abundance after 8 h of hypergravity. A comparative analysis of the different treatments showed some similarities in response between 8×g centrifugation and 2D clinorotation, while random positioning showed the least responses.     

Crack significance evaluation with special reference to welded structures

Fracture mechanics parameters (stress intensity factorK _I and its critical valueK _Ic , crack opening displacement, and the contourJ integral) are originally defined for static and quasistatic loading conditions. On the basis of theoretical background, standard test methods for the experimental determination of their specific values were developed. Structural integrity analysis requires the extension of application of these parameters to other types of loading. We propose new parameters for stress corrosion (stress corrosion cracking thresholdK _1sco ), for cyclic loading (stress intensity factor range ΔK and fatigue threshold ΔK _th), and for creeping at elevated temperatures (C ^* andC _t integrals). The structural integrity of welded structures is mainly affected by cracks in welded joints. We demonstrate the practical application of fracture mechanics parameters to the evaluation of structural integrity under the above-mentioned loading conditions. Faculty of Technology and Metallurgy, University of Belgrade, Yugoslavia. Faculty of Mechanical Engineering, University of Belgrade, Yugoslavia. Published in Fizyko-Khimichna Mekhanika Materialiv, Vol. 32, No. 2, pp. 107–118, March–April, 1996.     

Non-uniform temperature gradients and thermal stresses produced by a moving heat flux applied on a hollow sphere

This work presents numerical analyses of transient temperature and thermally-induced stress distributions in a hollow steel sphere heated by a moving uniform heat source applied on a certain zenithal segment (the heated zenithal segment, Θ _H ) of its outer surface (the processed surface) under stagnant ambient conditions. Along the process, the moving heat source (MHS) moves angularly from the first zenithal segment to the last zenithal segment on the processed surface with a constant angular speed, ω, and then returns backward to the first zenithal segment with the same speed. It is assumed that the inner surface is heat-isolated and that the outer surface except the heated segment is under stagnant ambient conditions. The numerical calculations are performed individually for a wide range of thermal conductivity, λ, of steel and for the different Θ _H s. The maximum effective thermal stress ratio calculated as per the heat flux intensity (q ₀) can be reduced in considerable amounts. By increasing λ(∼75%) and ω(∼63%) the maximum effective thermal stress ratio calculated can be significantly reduced.     

The Metal-Halide Lamp Under Varying Gravity Conditions Measured by Emission and Laser Absorption Spectroscopy

Diffusive and convective processes in the metal-halide lamp cause an unwanted axial colour segregation. Convection is induced by gravity. To understand the flow phenomena in the arc discharge lamp it has been investigated under normal laboratory conditions, micro-gravity (ISS and parabolic flights) and hyper-gravity (parabolic flights 2g, centrifuge 1g–10g). The measurement techniques are webcam imaging, and emission and laser absorption spectroscopy. This paper aims to give an overview of the effect of different artificial gravity conditions on the lamp and compares the results from the three measurement techniques.     

Tension of an elastoplastic disk. Part 2. Edge crack

Within the framework of the model of plasticity strips, we study the elastoplastic problem of fracture mechanics concerning the development of these strips near the tips of an edge crack in a circular disk. We assume that plastic deformations near the crack tip are localized along three plasticity strips (L ₁,L ₂,L ₃) under the conditions of plane stressed state and along two plasticity strips (L ₁,L ₂) under the conditions of plane deformation. One of these strips (L ₃) is modeled by a line of discontinuity of normal and tangential displacements and the remaining two strips (L ₁,L ₂) are modeled by the lines of discontinuity of tangential displacements. Their lengths and orientations are determined as a result of numerical solution of the problem by the method of singular integral equations. We also present the values of the crack-tip opening displacements. Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 36, No. 1, pp. 17–22, January–February, 2000.     

Weibull analysis for normal/accelerated and fatigue random vibration test

In this paper, the formula to estimate the sample size n to perform a random vibration test is derived only from the desired reliability (R(t)). Then, the addressed n value is used to design the ISO16750‐3 random vibration test IV for both normal and accelerated conditions. For the normal case, the applied random vibration stress (S) is modeled by using the Weibull stress distribution [W(s)]. Similarly, for the testing time (t), the Weibull time distribution [W(t)] is used to model its random behavior. For the accelerated case, by using the over‐stress factor fitted from the W(t) and W(s) distributions, four accelerated scenarios are formulated with their corresponding testing's profiles. Additionally, from the W(s) analysis, the stress formulation to perform the fatigue and Mohr stress analysis is given. Since the given Weibull/fatigue formulation is general, then the formulas to determine the W(s) parameters, which correspond to any principal stresses values and/or vice versa, are given. Although the application is performed to demonstrate R(t) = 0.97 by testing only n₂ = 6 parts, the guidelines to use the values given in columns n, S, and t of the Weibull analysis table to generate several accelerated testing plans are given.     

Fatigue behavior of aluminum alloys under biaxial loading

The biaxiality effect, especially the effect of non-singular stress cycling, on the fatigue behavior was studied, employing cruciform specimens of aluminum alloys 1100-H14 and 7075-T651. The specimens, containing a transverse or a 45^o inclined center notch, were subjected to in-phase (IP) or 100% out-of-phase (hereinafter referred to as “out-of-phase or OP”) loading of stress ratio 0.1 in air. The biaxiality ratio λ ranged from 0 to 1.5, and 3 levels of stress were applied. It was observed that: (1) at a given λ, a lower longitudinal stress induced a longer fatigue life under IP and OP loading, and the fatigue life was longer under IP loading, (2) the fatigue crack path profile was influenced by λ, phase angle (0^o or 180^o), and initial center notch (transverse or 45^o inclined); (3) the fatigue crack path profiles, predicted analytically and determined experimentally, had similar features for the specimens with a transverse center notch under IP loading; and (4) the fatigue crack growth rate was lower and the fatigue life longer for a greater λ under IP loading, whereas it changed little with change in λ under OP loading. These results demonstrate that non-singular stress cycling affects the biaxial fatigue behavior of aluminum alloys 1100-H14 and 7065-T651under IP and OP loading.