Jun Ichi Koizumi

Factors Affecting the Activity of a Protein Bioflocculant Produced by Nocardia amarae

Abstract Flocculating activities of the cell surface substances (FIX-fractions a, b and c) of Nocardia amarae were studied at their minimal concentrations. One of the three substances (FIX-fraction b) proved to exhibit flocculating activity when its concentration was moderately low. The activity was affected by the buffer concentration of the test suspension. Sufficient flocculation was not observed in 1 mM sodium phosphate buffer (pH 6.8), while flocculation occurred in 10 mM and 50 mM buffer. The effects of various salts were also studied. Salts (NaCl, CaCl2, Al2(SO4)3, and FeCl3) stimulated the activity of the flocculant; however, an excessive addition of FeCl3 inhibited flocculation.

Synthesis of non-competitive inhibitors of sphingomyelinases with significant activity.

A series of short-chain analogues of N-palmitoylsphingosine-1-phosphate, modified by replacement of the phosphate and the long alkenyl side chain with hydrolytically stable difluoromethylene phosphonate and phenyl, respectively, were prepared to study the structure-activity relationship for inhibition of sphingomyelinase. The study revealed that inhibition is highly dependent upon the stereochemistry of the asymmetric centers of the acylamino moiety, and resulted in identification of a non-competitive inhibitor with the same level of inhibitory activity of schyphostatin, the most potent of the few known small molecular inhibitors of sphingomyelinase.

Significance of the estimation light-absorption rate in the analysis of growth of - Rhodopseudomonas spheroides

SummaryRhodopseudomonas spheroides S was cultured anaerobically and batchwise in light. The light-absorption rate of the cells was assessed by solving numerically an integro-differential equation (Boltzmanns equation) using end Monte Carlo method.For light-limited growth, the specific growth rate of the cells was correlated linearly with the specific light-absorption rate.The Lambert-Beer law could not be used to assess correctly the light absorption by the bacterial cells in the culture medium, because the scattering of light by the cells could not be neglected. The correlation between the light-absorption rate and the cell concentration in the medium is discussed in relation to the scale-up of bio-photoreactors.

Biosynthesis of poly(3-hydroxybutyrate-Co-3-hydroxyvalerate) by a mutant of Sphaerotilus natans

The copolyester of 3-hydroxybutyrate and 3- hydroxyvalerate was synthesized from the combined carbon sources of glucose and sodium propionate by a filamentaion-defective mutant of Sphaerotilus natans, which is a typical filamentous bacterium often found in activated sludge. The 3-hydroxyvalerate content in the produced polymer increased with increasing concentrations of propionate. Cell growth and polyester synthesis were observed even when 0.6% sodium propionate was added to the medium, when the 3-hydroxyvalerate content in the polymer produced was about 60 mol%. The monomer composition of the copolymer was also varied by aeration conditions, time of propionate feeding, and cultivation time. This strain flocculated in accordance with cell growth, allowing rapid and convenient separation of the biomass from the culture fluid.

A kinetic assessment of substantial oxidation by Sulfolobus acidocaldarius in pyrite dissolution

Abstract The relative contributions of biological and chemical reactions to the total rate of pyrite oxidation in the presence of Sulfolobus acidocaldarius were studied on the basis of experimental work coupled with mathematical modeling. Kinetic constants for the individual reactions were determined in independent experiments. The specific growth rate of cells on the pyrite surface, which is the only unknown parameter, was assumed to be ( μ s = 0.1 h −1 ) and justified by the agreement of the simulated results of a proposed model and the experimental results. The model includes: reversible adsorption, biological dissolution of pyrite by the adsorbed cells, chemical dissolution of pyrite accompanied by the reduction of ferric ions to ferrous ions, biochemical oxidation of ferrous ions to ferric ions by free cells, and change of the surface area of pyrite particles. It is suggested that the contributions of direct (biological) and indirect (chemical) reactions to the total rate of pyrite oxidation were in a ratio of 2:1.