Acidophilic xylanase from Aureobasidium pullulans: efficient expression and secretion in Pichia pastoris and mutational analysis

A yeast-like fungus Aureobasidium pullulans var. melanigenum strain ATCC 20524 produces an extracellular acidophilic endo-1,4-beta-xylanase with an optimum pH of 2.0 [Ohta et al., J. Biosci. Bioeng., 92, 262-270 (2001)]. The xynI cDNA encoding the precursor protein (XynI) was expressed in the methylotrophic yeast Pichia pastoris under the control of the alcohol oxidase I gene promoter. The 34 amino acid prepro-signal peptide of the A. pullulans XynI directed the efficient secretion of 178 mg of active xylanase per liter of the culture medium. The secretion level of the xylanase with its own signal peptide was comparable to that of the mature protein fused to the prepro leader from Saccharomyces cerevisiae alpha-mating factor and twofold higher than that of the mature protein fused to the pre-type signal peptide from P. pastoris acid phosphatase. The N-terminal amino acid sequence and the apparent M(r) of 24 kDa of the secreted recombinant protein indicated the native-like processing of the A. pullulans XynI signal sequence in P. pastoris. The three-dimensional model and mutational analysis of the xynI gene product showed that Asp-73 and Glu-157 residues located at the upper and lower edges of the active site cleft, respectively, play a significant role in its low pH optimum.     

Resonator filters using shear horizontal-type leaky surface acoustic wave consisting of heavy-metal electrode and quartz substrate

The authors have succeeded in exciting a new type of leaky surface acoustic wave (LSAW) having only a shear horizontal (SH) component that has a large electromechanical coupling factor, a large reflection coefficient, and excellent temperature stability, by combining interdigital transducers (IDTs) and reflectors made of heavy-metal films such as gold (Au), tantalum (Ta), and tungsten (W) on the ST-cut 90/spl deg/ X propagation (direction perpendicular to the X-axis) quartz substrate. This LSAW does not have a propagation decay. The square of the electromechanical coupling factor is 2.1-2.7 times larger than, the reflection coefficient is 30 times larger than, and the temperature characteristic is the same as those of a Rayleigh wave on an ST-cut X propagation quartz substrate. The authors applied this SH LSAW to resonators and resonator filters. As a result, we succeeded in developing the low loss and very small-sized resonators and resonator filters (1/5-1/4 of conventional device sizes) with IDTs with a small number of finger pairs and very small reflectors, for the first time.     

Ultrafast deposition of microcrystalline silicon films using high-density microwave plasma

For fast deposition of microcrystalline silicon (μc-Si:H) films, a microwave-induced high-density plasma source is developed. By using this plasma source, highly crystallized μc-Si:H films can be deposited from SiH₄+He plasma without even using H₂ dilution and substrate heating. A systematic deposition study shows that the film deposition rate increases with increase in the input microwave power and the SiH₄ flow rate. The film crystallinity also improves with power but degrades with increase in the SiH₄ flux. After optimizing the plasma conditions, the deposition of a highly crystallized μc-Si film has been realized at an ultrafast deposition rate higher than 700 nm/s.     

Transmission electron microscopy observation of vitrinite from Liddell bituminous coal treated with tetralin

To assess the suitability of transmission electron microscopy (TEM) for investigating the detailed process of coal/solvent interaction, TEM observations have been made of small blocks of Liddell vitrinite that had been treated with tetralin in an autoclave at 320 and 350 °C. In vitrinite treated at 320 °C cell cavity fillings became porous, while the walls between cell cavities remained uniform and showed no internal texture. In vitrinite particles treated with tetralin at 350 °C two zones were recognizable at the edges of the particles: a more electron-dense inner zone and a less electron-dense outer zone. Also present in these specimens were plastospheres consisting of two different materials, primary vitroplast (a more electron-dense core) and secondary vitroplast (a less electron-dense crust). Such detailed texture has not been observed with incident light microscopy, and TEM techniques provide useful information not previously obtainable.     

Numerical simulation of GaN single-crystal growth process in ammonothermal autoclave – Effects of baffle shape

The numerical simulation of an ammonothermal process for growing GaN bulk single crystals has been performed by using the SC/Tetra computational fluid dynamics software. The autoclave is assumed to be axisymmetric. Heat transfer by natural convection is discussed in the case of flat and funnel-shaped baffles. Simulation results show that the optimum baffle angle is approximately 20°. This result is identical to that obtained in our previous study on the hydrothermal ZnO crystal growth process.     

Asymmetric electric double layer capacitors using carbon electrodes with different pore size distributions

Asymmetric capacitors composed of carbon electrodes with different pore size distributions (PSD) were constructed in order to study the fundamental relationship between the PSD of positive and negative carbon electrodes and the performance of electric double layer capacitors. The performance of asymmetric capacitors in a non-aqueous electrolyte solution (TEMA·BF₄/PC) was found to be governed by the PSD of the carbon used in the negative electrode. Capacitance depends on the BET surface area of the negative electrode and the rate performance depends on its mesoporous surface area. These results were explained by the fact that it is more difficult to adsorb large solvated cations (TEMA⁺) in micropores (less than 2 nm wide) than in mesopores (2-50 nm wide), and that this is more difficult with a higher rate of charge-discharge.     

Concrete — moisture

Engineer research associate Hiroshi Hashida of the Tokyo Institute of Technology and co-authors Kyouji Tanaka and Michio Koike present test results on moisture redistribution in concrete which will help practitioners to understand and overcome the problems this causes in applied finishes.     

Corrosion evaluation of Au-Cu-Pd ternary alloys

The corrosion resistivity of single-phase Au-Cu-11 at% Pd alloys was evaluated by using a parameterQ which represented the total amount of anodic reaction in a potentiostatic polarization test. The result was compared with those for binary Au-Cu, ternary Au-Cu-11 at % Ag and some commercial alloys. The validity of usingQ as a corrosion parameter was confirmed by the good agreement between the analysed and calculated values of copper ion dissolved into the test solution. By replacing a part of the copper in Au-Cu alloys with palladium the corrosion resistivity can be greatly improved, but silver has no such significant effect. The value ofQ decreased by both treatments of homogenization and grain refinement of the alloy. One of the advantages of the alloy having a single-phase structure is that inhomogeneity in the distribution of the constituents is small even in the as-cast state, which results in a small galvanic effect.     

Pressure carbonization of pitch/phenolic resin mixtures

Phenolic resins and the benzene-soluble fraction of a coal tar pitch were mixed in a solvent (pyridine) and carbonized at 600° C in a gold tube under a pressure of 30 MPa. Yields, optical textures and graphitizabilities of the carbons were studied. Large carbon yields (>80%) were obtained from sealed tubes under pressure (closed system). In open tubes under pressure (open system), only slight improvements in carbon yields were observed. As the resin content in the starting mixtures increased, the optical texture of the resultant carbons decreased from coarse mosaic to isotropic through intermediates with a gradual decrease in size of mosaic units. These intermediate optical textures occurred with a wider range of resin content under pressure than under atmospheric pressure, especially from closed systems. Changes in structural parameters of the carbons after the 2800° C treatment corresponded to the changes in optical texture with resin content.