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 the dynamics of systems controlled by diffusion-reaction-growth couplings. The theoretical results give two kinds of information: the time evolution of the extra-membrane system due to the intra-membrane reactions which can easily be compared to experiments, and the intra-membrane behaviour which is mainly characterized by the concentration profiles. The steady state cell concentration profile is one of the most important elements of a system's behaviour. In addition to photographs taken 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 concentration is determined using visible spectroscopy. By using this technique, we have shown a good agreement between the theoretical predictions and the experimental profiles, which validates the modeling.