THE EFFECTIVE DIFFUSIVE PERMEABILITY OF A NONREACTING SOLUTE IN MICROBIAL CELL AGGREGATES

Aggregates of Escherichia coli confined within hollow-fiber reactors were either formed in place by culturing cells within the reactors, or were prepared by injecting a cell suspension that had been concentrated by centrifugation. The effective diffusive permeability of an uncharged nonreacting tracer, nitrous oxide within the cell aggregates was calculated from measurements of the tracer flux through the aggregates. Estimates of the hydraulic permeability were also obtained for the aggregates that were grown in place. The effective diffusive permeability was found to decrease with increasing cell volume fraction to a value, for aggregates comprising 95% cells, of ca. 30% that obtained for cell-free buffer solution. The dependence on the cell volume fraction was described adequately by the well-known Hashin-Shtrikman bounds for a two-phase medium. The transport properties of aggregates cultivated in place were not significantly different from those of aggregates prepared by centrifugation.