DIFFUSION IN IMMOBILIZED-CELL AGAR LAYERS - INFLUENCE OF MICROBIAL BURDEN AND CELL MORPHOLOGY ON THE DIFFUSION-COEFFICIENTS OF L-MALIC ACID AND GLUCOSE

The diffusivities of l-malic acid and glucose in an agar membrane entrapping small amounts of Escherichia coli or Rhodospirillum rubrum whole cells were measured using time lag (TL) and steady state (SS) methods. Diffusivities were overestimated by the SS method. For concentrations of immobilized R. rubrum cells ranging between 104 and 109 organisms cm-3 agar (20 ng-2 mg dry weight cm-3 agar), the diffusion coefficient of l-malic acid, determined by both methods, was related to the logarithm of the membrane cell content by a decreasing linear relationship. The diffusion coefficient of glucose obtained by TL analysis was not significantly affected by the presence in the membrane of 3 ng-0.3 mg dry wt. E. coli cm-3 agar. However, values arising from the SS method decreased linearly as a function of the amount of immobilized organisms. Membranes containing R. rubrum cells offered higher diffusional resistance to l-malic acid and glucose than those loaded with the same amount of E. coli cells. © 1990 Springer-Verlag.