Diffusion of oxygen in alginate gels related to the kinetics of methanol oxidation by immobilized Hansenula polymorpha cells

Abstract

In the yeast Hansenula polymorpha an oxygen-requiring enzyme, alcohol oxidase, catalyzes the conversion of methanol into formaldehyde. After growth on methanol cells of the organism were harvested and entrapped in barium-alginate gels. The diffusion of oxygen towards these cells is seriously hindered by the polymer network. This caused significant changes in the kinetics of methanol oxidation by the immobilized cells as compared to that observed with cells free in suspension. The apparent K~(O2) of the immobilized cells was dependent upon the density of the cells in the alginate beads and the bead radius. Using a well-known theoretical model, originally developed to describe the kinetics of oxygen diffusion in mold pellets, the diffusion coefficient for oxygen in barium-alginate gels was estimated. This coefficient was only 25% of that in water. The model also allowed an adequate simulation of the observed kinetics of methanol oxidation by the immobilized cells.List of Symbols C, local oxygen concentration inside the alginate bead; tool -cm-3; C, external oxygen concentration; tool -cm -3" D(O:)~g, diffusion constant for oxygen in a barium-alginate matrix; era 2 9 s-l; Ks(O2) , Michaelis-Menten constant for oxygen at excess (200 raM) methanol; raM; p, ratio of D(Oz)alg over O(O2)water; Qo2, rate of oxygen consumption by free cells (at C = C); tool 9 s -1 , g-1 cells; 002, rate of oxygen consumption by the alginate beads; tool. s -t. g-i cells; Q(32 rate of oxygen consumption by immobilized cells (at C = C); tool 9 s -1 -g 1 cells; Q'o2 maximum rate of oxygen consumption; tool 9 s t . g-1 cells; R, radius of an alginate bead; cm; r, radial distancc; x, dimensionless radius (r/R); y, dimensionless oxygen concentration (C/s ct, Thiele modulus given by Eq. 5; fl, dimensionless Micbaelis-Mxnten constant for oxygen [Ks(02)/O ] ; l,~, cell density of an alginate bead; g cells, cm -3 alginate beads; r] effectiveness factor given by Eq. 7 Offprint requests to: W. Harder containing per dm 3 of deionized water: (NH02SO4, 2.5g; MgSO4.7 H20 , 0.2g; NaI-IzPO4, 3,0 g; K2HPO4, 0.7 g; yeast extract, 0.5 g; trace elements solution (Vishniac and Santer 1957),

Comparison of fermentation properties and specific enzyme activities of free and calcium-alginate-entrapped Saccharomyces cerevisiae

“…As determined by several authors (Beunink et al 1989;Rehm 1986, 1988;Hiemstra et al 1983) the 0 2 supply can be diminished up to 25% in a gel matrix. The more than tenfold higher specific phosphofructokinase activities in entrapped cells in comparison to free cells are apparently not caused by their better protection against oxygen by the alginate, because all fermentations were carried out under anaerobic conditions.…”

Oxygen diffusivity in gel beads containing viable cells

“…A microphotograph of a section of gel bead is shown in Figure 4. 19 Recalculated value with a diffusivity in water of 2.56 X m'/s. Microphotograph of growing immobilized Asp.…”

Determination of the effective diffusion coefficient of oxygen in gel materials in relation to gel concentration

“…At 30 *C they found a value of 1.94"10 -9 m2s -1 (70% of that in pure water). Hiemstra et al (1983) calculated the diffusion coefficient in 2% barium alginate containing yeast cells, which was 0.7"10 -9 m2s -1 at a temperature of 37 *C (25% of that in pure water). Adlercreutz (1986) found a val'ue of 2.11"10 -9 m2s -1 for the diffusion coefficient of oxygen in 2% calcium alginate (77% of that in pure water).…”