SPATIAL-DISTRIBUTION OF VIABLE CELLS IMMOBILIZED IN AGAR MEMBRANES

The biocatalytic structures obtained by immobilizing microorganisms in planar gel slabs have been studied and modeled to better understand t he dynamics of systems controlled by diffusion-reaction-growth couplin gs. The theoretical results give two kinds of information : the time e volution of the extra-membrane system due to the intra-membrane reacti ons which can easily be compared to experiments, and the intra-membran e behaviour which is mainly characterized by the concentration profile s. The steady state cell concentration profile is one of the most impo rtant elements of a system's behaviour. In addition to photographs tak en at different depths in the membrane, we have developed an original, simple and reproducible technique for the experimental determination of the intra-membrane cell concentration profiles. The technique uses a home-made microtome to obtain gel slices, in which the cell concentr ation is determined using visible spectroscopy. By using this techniqu e, we have shown a good agreement between the theoretical predictions and the experimental profiles, which validates the modeling.