Force and velocity of mycoplasma mobile gliding

The effects of temperature and force on the gliding speed of Mycoplasma mobile were examined. Gliding speed increased linearly as a function of temperature from 0.46 microm/s at 11.5 degrees C to 4.0 microm/s at 36.5 degrees C. A polystyrene bead was attached to the tail of M. mobile using a polyclonal antibody raised against whole M. mobile cells. Cells attached to beads glided at the same speed as cells without beads. When liquid flow was applied in a flow chamber, cells reoriented and moved upstream with reduced speeds. Forces generated by cells at various gliding speeds were calculated by multiplying their estimated frictional drag coefficients with their velocities relative to the liquid. The gliding speed decreased linearly with force. At zero speed, the force measurements extrapolated to 26 pN at 22.5 and 27.5 degrees C. At zero force, the speed extrapolated to 2.3 and 3.3 microm/s at 22.5 and 27.5 degrees C, respectively--the same speeds as those observed for free gliding cells. Cells attached to beads were also trapped by an optical tweezer, and the stall force was measured to be 26 to 28 pN (17.5 to 27.5 degrees C). The gliding speed depended on temperature, but the maximum force did not, suggesting that the mechanism is composed of at least two steps, one that generates force and another that allows displacement. Other implications of these results are discussed.     

Temperature dependence of the repulsive pressure between phosphatidylcholine bilayers.

Bilayer structure and interbilayer repulsive pressure were measured from 5 to 50 degrees C by the osmotic stress/x-ray diffraction method for both gel and liquid crystalline phase lipid bilayers. For gel phase dibehenoylphosphatidylcholine (DBPC) the bilayer thickness and pressure-distance relations were nearly temperature-independent, and at full hydration the equilibrium fluid spacing increased approximately 1 A, from 10 A at 5 degrees C to 11 A at 50 degrees C. In contrast, for liquid crystalline phase egg phosphatidylcholine (EPC), the bilayer thickness, equilibrium fluid spacing, and pressure-distance relation were all markedly temperature-dependent. As the temperature was increased from 5 to 50 degrees C the EPC bilayer thickness decreased approximately 4 A, and the equilibrium fluid spacing increased from 14 to 21 A. Over this temperature range there was little change in the pressure-distance relation for fluid spacings less than approximately 10 A, but a substantial increase in the total pressure for fluid spacings greater than 10 A. These data show that for both gel and liquid crystalline bilayers there is a short-range repulsive pressure that is nearly temperature-independent, whereas for liquid crystalline bilayers there is also a longer-range pressure that increases with temperature. From analysis of the energetics of dehydration we argue that the temperature-independent short-range pressure is consistent with a hydration pressure due to polarization or electrostriction of water molecules by the phosphorylcholine moiety. For the liquid crystalline phase, the 7 A increase in equilibrium fluid spacing with increasing temperature can be predicted by an increase in the undulation pressure as a consequence of a temperature-dependent decrease in bilayer bending modulus.     

Low-temperature growth of Shewanella oneidensis MR-1

Shewanella oneidensis MR-1 is a mesophilic bacterium with a maximum growth temperature of approximately 35 degrees C but the ability to grow over a wide range of temperatures, including temperatures near zero. At room temperature ( approximately 22 degrees C) MR-1 grows with a doubling time of about 40 min, but when moved from 22 degrees C to 3 degrees C, MR-1 cells display a very long lag phase of more than 100 h followed by very slow growth, with a doubling time of approximately 67 h. In comparison to cells grown at 22 degrees C, the cold-grown cells formed long, motile filaments, showed many spheroplast-like structures, produced an array of proteins not seen at higher temperature, and synthesized a different pattern of cellular lipids. Frequent pilus-like structures were observed during the transition from 3 to 22 degrees C.     

Fast pyrolysis of soybean cake: product yields and compositions

This study was an investigation of the role of important parameters influencing pyrolysis yields from soybean cake. Experiments were carried out at temperatures ranging from 400 to 700 degrees C, for various nitrogen flow rates, heating rates and particle sizes. The maximum liquid yield was 42.83% at a pyrolysis temperature of 550 degrees C with a sweeping gas rate of 200 cm3 min(-1) and heating rate of 700 degrees C min(-1) for a soybean cake sample having 0.425 < D(p) < 0.85 mm particle size. The various characteristics of liquid product were identified. Thus, the aliphatic sub-fraction of the bio-oil was analysed by GC-MS and further structural analyses of bio-oil and aromatic and polar sub-fractions were conducted using FT-IR and 1H-NMR. The H/C ratios and the structural analysis of the fractions obtained from the biocrudes showed that the fractions were quite similar to currently utilised transport fuels.     

Ultrasound Velocity Measurement in a Liquid Metal Electrode

A growing number of electrochemical technologies depend on fluid flow, and often that fluid is opaque. Measuring the flow of an opaque fluid is inherently more difficult than measuring the flow of a transparent fluid, since optical methods are not applicable. Ultrasound can be used to measure the velocity of an opaque fluid, not only at isolated points, but at hundreds or thousands of points arrayed along lines, with good temporal resolution. When applied to a liquid metal electrode, ultrasound velocimetry involves additional challenges: high temperature, chemical activity, and electrical conductivity. Here we describe the experimental apparatus and methods that overcome these challenges and allow the measurement of flow in a liquid metal electrode, as it conducts current, at operating temperature. Temperature is regulated within ±2 °C using a Proportional-Integral-Derivative (PID) controller that powers a custom-built furnace. Chemical activity is managed by choosing vessel materials carefully and enclosing the experimental setup in an argon-filled glovebox. Finally, unintended electrical paths are carefully prevented. An automated system logs control settings and experimental measurements, using hardware trigger signals to synchronize devices. This apparatus and these methods can produce measurements that are impossible with other techniques, and allow optimization and control of electrochemical technologies like liquid metal batteries.     

Olive bagasse (Olea europea L.) pyrolysis

Olive bagasse (Olea europea L.) was pyrolysed in a fixed-bed reactor. The effects of pyrolysis temperature, heating rate, particle size and sweep gas flow rates on the yields of the products were investigated. Pyrolysis runs were performed using pyrolysis temperatures between 350 and 550 degrees C with heating rates of 10 and 50 degrees C min(-1). The particle size and sweep gas flow rate varied in the ranges 0.224-1.8mm and 50-200 cm3 min(-1), respectively. The bio-oil obtained at 500 degrees C was analysed and at this temperature the liquid product yield was the maximum. The various characteristics of bio-oil obtained under these conditions were identified on the basis of standard test methods. The empirical formula of the bio-oil with heating value of 31.8 MJ kg(-1) was established as CH(1.65)O(0.25)N(0.03). The chemical characterization showed that the bio-oil obtained from olive bagasse may be potentially valuable as a fuel and chemical feedstock.     

Influence of cooling rates and plunging temperatures in an interrupted slow-freezing procedure for semen of the African catfish, Clarias gariepinus

The objective of this study was to optimize interrupted slow-freezing protocols for African catfish semen. Semen diluted with methanol and extender was frozen in 1-ml vials in a programmable freezer. The temperatures of the freezer (T(chamber)) and of the semen (T(semen)) were measured simultaneously. We first tested two-step freezing protocols with different cooling rates (-2, -5, and -10 degrees C/min) and different temperatures at plunging into liquid N2. The difference between T(semen) and T(chamber) increased with faster cooling rates. In all programs, survival of spermatozoa, expressed as hatching rates, increased from near zero when T(semen) at plunging was higher than -30 degrees C to values equal to those of control when T(semen) at plunging was equal to or lower than -38 degrees C. The inclusion of an isothermal holding period before plunging into liquid N2 (three-step freezing protocols) resulted in an equilibration between T(semen) and T(chamber) and improved semen survival. Semen could be plunged at temperatures as high as -36 degrees C when cooled at -5 or -10 degrees C/min, without compromising postthaw semen survival. Cooling at -2 degrees C/min in combination with a 5-min holding period reduced postthaw survival. We conclude that with slow cooling rates of -2 to -5 degrees C/min, hatching rates can be maximized by plunging as soon as T(semen) reaches -38 degrees C. The isothermal holding period is beneficial when faster rates are used. A simple and efficient protocol for freezing African catfish semen can be obtained by cooling at a rate of -5 to -10 degrees C/min combined with a 5-min holding period in the freezer, at -40 degrees C.     

Amylose crystallization from concentrated aqueous solution

Maize amylose, separated from granular starch by means of an aqueous leaching process, was used to investigate spherulite formation from concentrated mixtures of starch in water. Amylose (10-20%, w/w) was found to form a spherulitic semicrystalline morphology over a wide range of cooling rates (1-250 degrees C/min), provided it was first heated to >170 degrees C. This is explained through the effect of temperature on chain conformation. A maximum quench temperature of approximately 70 degrees C was required to produce spherulitic morphology. Quench temperatures between 70 and 110 degrees C produced a gel-like morphology. This is explained on the basis of the relative kinetics of liquid-liquid phase separation vis-à-vis crystallization. The possibility of the presence of a liquid crystalline phase affecting the process of spherulite formation is discussed.     

Dry air-induced constriction in lung periphery: a canine model of exercise-induced asthma

We studied the effects of the flow of dry air on collateral tone in the lung periphery. A bronchoscope was wedged in sublobar segments of anesthetized dogs, and measurements of collateral resistance (Rcs) were recorded before and after flow was increased from 200 to 2,000 ml/min for a 5-min period. Five minutes after exposure was completed, Rcs increased by an average of 117 +/- 25.2% (SE) over control. Maximum Rcs occurred 5 min after the challenge was concluded and required 48 +/- 10.5 min to return to base line. When flow rate was held constant and exposure period varied, Rcs increased with increased stimulus duration. With exposure times held constant, the response of the collateral system was positively associated with changes in stimulus strength (flow rate). No refractory period was observed with repetitive challenges. Finally, when dry air (delivered at 22 degrees C) and conditioned air (i.e., delivered at 28 degrees C; relative humidity = 80%) challenges were alternated in the same wedged segment, dry air produced a mean increase in Rcs of 93.2%, whereas challenge with warm moist air increased Rcs only 33.5%. Regardless of which challenge was presented first, dry air consistently produced a greater constrictor response. This response is similar to that observed in cold air- and exercise-induced asthma and indicates that the lung periphery in dogs, like larger airways in asthmatic subjects, has the potential to increase tone when exposed to dry air. Peripheral airways in dogs thus constitute a model that can be used for the investigation of exercise-induced asthma.     

松毛虫狭颊寄蝇实验种群生态学研究

松毛虫狭颊寄蝇(Carcelia matsukarehae)是松毛虫重要的寄生天敌之一。在控制松毛虫自然种群增长中起重要的作用。本文在15℃、18℃、22℃、25℃、29℃、32℃6个恒温。相对湿度为70％～85％,光照为12：12(L：D)的条件下研究了松毛虫狭颊寄蝇的生态学特性。结果表明,松毛虫狭颊寄蝇的世代发育起点温度是5．23℃。积温为523．73日·度。成虫寿命在没有补充营养的条件下为1．3～8．06d,喂以30％蜜糖水。寿命可以从9．63d延长到36．42d。成虫产卵的最适温度为236℃,每雌最大产量为86粒．种群增长最适温度22～25℃．以近似方法计算22℃和25℃下实验种群繁殖特征生命表参数。在22℃,R0、T0、rc和A值分别为24．89、37．33、0．086和1．089。在25℃时分别为20．01、32．38、0．09和1．10．22℃时种群最大LxMx出现在成虫羽化后第33～38天。25℃时的LxMx最大值出现在成虫羽化后第29～34天。     

Kinetics and modeling of temperature effects on batch xanthan gum fermentation

Batch fermentation kinetics of xanthan gum production from glucose by Xanthomonas campestris at temperatures between 22 degrees C and 35 degrees C were studied to evaluate temperature effects on cell growth and xanthan formation. These batch xanthan fermentations were modeled by the logistic equation for cell growth, the Luedeking-Piret equation for xanthan production, and a modified Luedeking-Piret equation for glucose consumption. Temperature dependence of the parameters in this model was evaluated. Growth-associated rate constants increased to a maximum at approximately 30 degrees C and then decreased to zero at approximately 35 degrees C. This temperature effect can be modeled using a square-root model. On the contrary, non-growth-associated rate constants increased with increasing temperature, following the Arrhenius relationship, in the entire temperature range studied. The model developed in this work fits the experimental data very well and can be used in a simulation study. However, due to the empirical nature of the model, the parameter values need to be reevaluated if the model is to be applied to different growth conditions.     

A gas-flow cryostat for use in freeze-quench studies: design and application to discontinuous pre-steady-state spectral analyses

A design for an improved freeze-quench apparatus is presented. A freeze-quench apparatus has two main parts: the apparatus which mixes the reactants and after a set time sprays the reacting mixture into the quencher, and the quenching apparatus itself. The quenching apparatus is the novel feature of our design and it comprises a gas-flow cryostat mounted directly onto a liquid nitrogen storage Dewar. The gas flow maintains the temperature of a small volume of isopentane, which acts as the freeze-quench agent, at -140 degrees C. (The apparatus can maintain the quenching temperature over the range -190 degrees C to room temperature.) Because of the small size of the cryostat and the much reduced volume of solvent used by this method it is more convenient to use than its predecessors, can be used in the open laboratory, and is safer. Our apparatus is designed for application to electron paramagnetic resonance studies but could be easily modified for use with other spectroscopic techniques.     

Thermoresistance in Saccharomyces cerevisiae yeasts

Under natural conditions, yeast Saccharomyces cerevisiae reproduce, as a rule, on the surface of solid or liquid medium. Thus, life cycle of yeast populations is substantially influenced by diurnal changes in ambient temperature. The pattern in the response of unrestricted yeast S. cerevisiae culture to changes in the temperature of cultivation is revealed experimentally. Yeast population, in the absence of environmental constraints on the functioning of cell chemosmotic bioenergetic system, demonstrates the ability of thermoresistance when the temperature of cultivation switches from the range of 12-36 degrees C to 37.5-40 degrees C. During the transient period that is associated with the temperature switching and lasts from 1 to 4 turnover cycles, yeast reproduction rate remains 1.5-2 times higher than under stationary conditions. This is due to evolutionary acquired adaptive activity of cell chemosmotic system. After the adaptive resources exhausting, yeast thermoresistance fully recovers at the temperature range of 12-36 degrees C within one generation time under conditions of both restricted and unrestricted nourishment. Adaptive significance of such thermoresistance seems obvious enough--it allows maintaining high reproduction rate in yeast when ambient temperature is reaching a brief maximum shortly after noon.     

Vitrification in plants as a natural form of cryoprotection

A small group of woody plants from the far northern hemisphere can, while in the dormant state, tolerate freezing and thawing to and from any subzero temperature at rates less than 30 degrees C/hr. In addition, the hardiest of them can tolerate cooling and warming between -20 degrees C and any colder temperature at virtually any combination of rates subsequent to cooling to -20 degrees C at rates less than 5 degrees C/hr. We term this latter capability "quench hardiness." I and my colleagues have shown that the limits of this quench hardiness can be closely correlated to the stability of intracellular glasses formed during the slow cooling of hardy tissues in the presence of extracellular ice. In this paper, I briefly review the evidence for intracellular glass formation and present data indicating that major components of the glass forming solutions are raffinose and stachyose. Evidence from differential scanning calorimetry that sugar-binding soluble proteins are also important is presented. Finally, I correlate data from our work with that of other workers to make the case that, even when most of a cytoplasmic solution is vitrified, fluid microdomains remain which can lead to long-term biodegradation during storage at high subzero temperatures.     

Maximum rates of cooling by three programmable freezers, and the potential relevance to sperm cryopreservation

Maximum rates of cooling for the Asymptote EF 100 and the Cryologic CL8800 temperature controller with either a standard or fast chamber were determined and viewed in the context of sperm cryopreservation. All three systems use liquid nitrogen to cool the plate or chamber which would hold the sample, opposed by a variable amount of heat from an internal heater. Maximum rates of cooling for all systems were a function of the temperature gradient between the liquid nitrogen and the plate/chamber and at a plate/chamber temperature of 15 degrees C were 16.5 degrees C/min, 13.3 degrees C/min and 8.0 degrees C/min for the Asymptote EF100, Cryologic fast and slow chambers respectively. These machines are not suited to the freezing of sperm from species requiring rapid rates of cooling, an important consideration when planning to purchase a piece of equipment for this application, and scientists are advised to discuss specifically their requirements with prospective suppliers.     

Relationship of growth temperature and thermotropic lipid phase changes in cytoplasmic and outer membranes from Escherichia coli K12.

Purified cytoplasmic and outer membranes isolated from cells of wild type Escherichia coli grown at 12, 20, 37 and 43 degrees C were labelled with the fatty acid spin probe 5-doxyl stearate. Electron spin resonance spectroscopy revealed broad thermotropic phase changes. The inherent viscosity of both membranes was found to increase as a function of elevated growth temperature. The lipid order to disorder transition in the outer membrane but not the cytoplasmic membrane was dramatically affected by the temperature of growth. As a result, the cytoplasmic membrane presumably existed in a gel + liquid crystalline state during cellular growth at 12 and 20 degrees C, but in a liquid crystalline state when cells were grown at 37 and 43 degrees C. In contrast, the outer membrane apparently existed in a gel + liquid crystalline state at all incubation temperatures. Data presented here indicate that the temperature range over which the cell can maintain the outer membrane phospholipids in a mixed (presumedly gel + liquid crystalline) state correlates with the temperature range over which growth occurs.     

Elevation of the heat resistance of Salmonella typhimurium by sublethal heat shock

The survival of Salmonella typhimurium after a standard heat challenge at 55 degrees C for 25 min increased by several orders of magnitude when cells grown at 37 degrees C were pre-incubated at 42 degrees, 45 degrees or 48 degrees C before heating at the higher temperature. Heat resistance increased rapidly after the temperature shift, reaching near maximum levels within 30 min. Elevated heat resistance persisted for at least 10 h. Pre-incubation of cells at 48 degrees C for 30 min increased their resistance to subsequent heating at 50 degrees, 52 degrees, 55 degrees, 57 degrees or 59 degrees C. Survival curves of resistant cells were curvilinear. Estimated times for a '7D' inactivation increased by 2.6- to 20-fold compared with cells not pre-incubated before heat challenge.     

Studies on cephalopod rhodopsin: photoisomerization of the chromophore.

Photoisomerization of the chromophore of squid rhodopsin is dependent upon the irradiation temperature. Above 0 degrees C, only 11-cis in equilibrium all-trans reaction proceeds and the all-trans leads to 9-cis reaction is limited to extremely low efficiency. At liquid nitrogen temperature, 11 cis in equilibrium all-trans in equilibrium 9-cis reaction takes place. At intermediary low temperatures (-80 degrees C to -15 degrees C) another isomer of retinal may be produced by the irradiation, which forms a pigment having an absorbance maximum at 465 nm (P-465). The formation of P-465 decreases remarkably in the narrow temperature range from -30 degrees C to 0 degrees C where mesorhodopsin converts to metarhodopsin. Medsorhodopsin is quite different from metarhodopsin in the photoisomerization of the chromophore because P-465 is produced from the former but not from the latter. No P-465 is produced both at liquid nitrogen temperature and above 0 degrees C. P-465 is more labile than any of the other photoproducts so far known, that is isorhodopsin, alkaline and acid metarhodopsins. P-465 is converted to metarhodopsin by irradiation.     

Temperature dependence of the kinetics of the urea-induced dissociation of human plasma alpha 2-macroglobulin into half-molecules. A minimum rate at 15 degrees C indicates hydrophobic interaction between the subunits.

The kinetics of the urea-induced dissociation of human plasma alpha 2-macroglobulin to half-molecules has been studied as a function of temperature by using small-angle scattering of X-rays and neutrons. The most striking result of the present investigation is that there is a minimum in reaction rate at about 15 degrees C, and that the rate increases when the temperature is lowered, or raised, from that value. By analyzing the first-order rate constants in terms of transition-state theory it was found that the dissociation is associated with a large and positive change in heat capacity between the activated complex and native alpha 2-macroglobulin (delta CP is in the range 5 to 6 kJ mol-1 K-1). In analogy with pure thermodynamic investigations, where a large change in heat capacity normally is interpreted as a melting of hydrophobic interaction, we therefore propose that hydrophobic interaction is involved in the so-called non-covalent interactions between the subunits of alpha 2-macroglobulin. As a result of the present investigation, it also follows that the free energy of activation delta G has a maximum at about 32 degrees C, whereas the enthalpy of activation delta H and the entropy of activation delta S are zero at about 15 degrees C and 32 degrees C, respectively. These temperatures are slightly dependent upon the concentration of urea and upon whether the reaction is run in a 1H or a 2H medium. Furthermore, from the kinetic point of view, at low temperature the reaction can be characterized as enthalpy driven, whereas at high temperature, it can be characterized as entropy driven.     

Temperature regulation during centrifugal elutriation and its effect on cell separation

Centrifugal elutriation appears to be a promising method for cell separation. The quality of the separation may be limited by the control of temperature within the separation chamber, which affects the fluid viscosity and rotor speed. The factors affecting the temperature regulations have been re-examined. At flow rates between 10 and 40 mL/min the temperature within the chamber was primarily dependent on the temperature of the fluid flowing into the rotor. Increases in the temperature of the fluid while it flowed through the rotor were observed and were greater at higher rotor speeds and lower flow rates. This heating, caused by friction at the rotating seal, could raise the fluid temperature within the chamber by as much as 6 degrees C. Fluctuations in the temperature of the centrifuge produced temperature variations of only 0.3 degrees C in the fluid in the elutriation chamber. Small increases in the rate of elutriation of cells, concomitant with centrifuge cooling and speed fluctuations, were detected by optical density measurements. However, neither the modal volume nor coefficient of variation of the collected cells were affected.