Koichi Igarashi

Light intensity distribution in the externally illuminated cylindrical photo-bioreactor and its application to hydrogen production by Rhodobacter capsulatus

The light distribution in the externally illuminated cylindrical photo-bioreactor for production of hydrogen by a photosynthetic bacterium Rhodobacter capsulatus ST-410 was estimated. The estimation was performed on the basis of the Matsuura and Smiths diffuse model [1]. In the diffuse model, the incident light rays are assumed to proceed in every direction and the local intensity is calculated as the sum of the intensities of light. Since Lambert-Beers law, extensively used in photometry, was not useful for explaining the decrease in the intensity of light by the biomass, an empirical expression was used. The measurement of the intensities from every direction was conducted in an externally illuminated cylindrical photo-bioreactor having an inner diameter of 60mm and a working volume of 550ml. The obtained results confirmed our estimation. The light distribution was applied to estimate the hydrogen production by R. capsulatus ST-410 using the same photo-bioreactor. The overall hydrogen-production rate was successfully estimated.

The initial stage of crystallization of lysozyme: a differential scanning calorimetric (DSC) study

The initial stage of crystallization of hen-egg-white lysozyme was investigated. Lysozyme molecules formed a structure just after the supersaturated solution was prepared. The structure could be understood as changes in solution three-dimensional structure induced by attractive interactions or aggregates with an average size of 6.5 nm. The structure formation, however, did not immediately link to crystal growth. An induction period was needed before the start of crystal growth. DSC analysis of the supersaturated solution revealed that the structure thus formed at the beginning of crystallization is transformed just before the end of the induction period. DSC analysis also revealed that the driving force of the transformation is the formation of hydrophobic bonds between lysozyme molecules. Our understanding of the behavior of lysozyme molecules before crystal growth was furthered by measurement of the ζ-potential of the aggregates. Based on the present results, a possible model of the early stage of crystal growth of lysozyme was proposed.

Production of large crystals with a narrow crystal size distribution by a novel WWDJ batch crystallizer

A novel WWDJ (Wall Wetter/double-deck jacket) batch crystallizer has been developed and used for the crystallization of L-aspartic acid, resulting in large product crystals with a narrow crystal size distribution. The batch crystallizer was equipped with a slurry sprinkler fixed on the shaft of an impeller, and a double-deck jacket. The slurry sprinkler, known as Wall Wetter, is specially designed for agitating the slurry and sprinkling it on the wall of the crystallizer headspace which is covered by the upper jacket. It was expected that by setting the upper jacket temperature at an appropriate high temperature, fine crystals could be dissolved during the fall of slurry along the wall, and consequently the crystal size distribution would shift to the large side. L-aspartic acid was chosen as an example to demonstrate this process. L-aspartic acid was crystallized at an initial supersaturation ratio (C/C s ) of 1.7 with no seeds. The classification exponent n and characteristic size D e of product crystals, which were evaluated by the Rosin Rammler Sperling Bennet (RRSB) distribution function, were 3.9 and 302 μm, respectively, compared with 2.2 and 237 μm, respectively, in a control crystallization experiment not using the Wall Wetter.

Relationship between Cell Morphology and Intracellular Potassium Concentration in Candida albicans

Previously we reported that valinomycin inhibited hyphal growth and induced growth as a chain of yeast cells under hyphal growth induction conditions in Candida albicans. To elucidate the hyphal growth inhibition by valinomycin, we examined the effect of various chemicals on the morphology and found that miconazole inhibited hyphal growth as well as valinomycin: both compounds promoted the leakage of potassium from cells. Analysis of intracellular potassium suggested that hyphal cells contain potassium at high concentrations in comparison with yeast cells. Hyphal growth inhibition by valinomycin was obstructed by the addition of serum. Potassium measurement showed that the addition of serum causes an increase in intracellular potassium, suggesting that the obstruction by serum might be due to an increase in intracellular potassium. The above-mentioned results strongly suggest that the addition of valinomycin and miconazole decreased interacellular potassium and this decrease inhibited hyphal transition.

Control of solvent-mediated transformation of crystal polymorphs using a newly developed batch crystallizer (WWDJ-crystallizer)

Abstract Using a newly developed batch crystallizer (WWDJ-crystallizer) equipped with a slurry sprinkler named Wall Wetter and a double-deck jacket, a suppression of the solvent-mediated transformation of the metastable polymorphic crystals was attempted. Crystallization of l -glutamic acid was carried out to show an example of the suppression. The target polymorphic crystals, namely the metastable α-form crystals were exclusively obtained from the aqueous solution without transformation to the stable β-form polymorph even at a temperature where the transformation could not be avoided if a conventional batch crystallizer was used. The characteristic size of crystals obtained by WWDJ-crystallizer was large and their size distribution was narrow, comparing with those obtained by a conventional crystallizer.

Analysis of Chitin at the Hyphal Tip of Candida albicans Using Calcofluor White

Staining with calcofluor white (CFW), which is known to bind chitin-rich areas of the cell wall, revealed a difference in the fluorescence intensity at the hyphal tip between Candida albicans hyphal cells that were grown in modified Lee (M-Lee) and SPG media. The fluorescence intensity at the tip increased with the addition of salts and sugar to SPG. The chitin levels per dry cell weight in cells grown in modified Lee and SPG with 1.0 M NaCl were also higher than in SPG. These results suggest that chitin synthesis at the tip of C. albicans might be activated by the addition of salts and sugar to a medium.

Dissolution kinetics of crystals in suspension and its application to l-aspartic acid crystals

Abstract The kinetics of the dissolution of l -aspartic acid crystals under the gentle and vigorous agitation was investigated. A dissolution rate equation was derived by assuming two steps: the disintegration of molecules from the surface of crystals and the mass transfer of disintegrated molecules into the bulk solution. An intrinsic expression of the relationship between the solute concentration of the bulk solution and the dissolution time was also derived. The dissolution process of monodisperse and polydisperse crystals of l -aspartic acid was well estimated, and the change of crystal size distribution of polydisperse crystals during dissolution was simulated with good accuracy.

Characterization of a Saccharomyces cerevisiae mutant with pseudohyphae and cloning of a gene complementing the mutation

Screening for morphological mutants of a haploid strain of Saccharomyces cerevisiae was done on the basis of their cell-shape on a solid medium containing isoamyl alcohol, which causes cell elongation, to obtain information on the morphogenesis. Mutant J19, which had pseudohyphae in liquid medium even in the absence of isoamyl alcohol, had many elongated cells. Few reports exist of haploid cells growing as pseudohyphae in liquid culture. Cell-wall analysis showed that J19 had ordinary amounts of alkali-insoluble glucan and chitin, but that isoamyl alcohol in the medium caused structural changes in the cell wall. Addition of a DNA fragment that included the wild-type SCL1 gene to J19 complemented its morphological phenotype. Sequencing of J19 SCL1 showed that the glycine at position 226 in the Scl1 protein had been replaced by asparatic acid, suggesting that this mutation in the protein, a subunit of proteasomes, may be involved in the morphological change.

Synthesis and degradation of acyl peptide using enzyme from Pseudomonas aeruginosa

The detailed properties of the enzyme from Pseudomonas aeruginosa, which catalyzes the N-acyl linkage between myristic acid and the N-terminal glycine residue of the octapeptide GNAAAARR-NH(2) (PKA) in aqueous solution without ATP and CoA, were studied. The substrate specificity for the acyl peptide in the synthetic reaction was examined, and it was found that at least eight amino acid residues are required for the reaction and that the N-terminal glycine residue is not absolutely essential for the reaction because the activity was detected using the octapeptide that has an N-terminal alanine. The activity was also strongly affected by the amino acid sequence because the activity was very weak in the reaction using GARASVLS-NH(2) (HIV-1p17(gag)). The substrate specificity for fatty acids was also examined. In the reactions using lauric acid and decanoic acid, only slight activities were detected; however, those activities were very small compared with the activity in the reaction using myristic acid. In addition, the degradation of myristoyl PKA by the enzyme was detected, although there are only a few reports on demyristoylation. The optimum pH and temperature of the degradation reaction were consistent with those of the synthetic reaction. The degradation reaction was inhibited by divalent cations.