Pattern of growth and respiratory activity of Saccharomyces cerevisiae (baker's yeast) cells growing entrapped in an insolubilised gelatin gel

Yeast cells immobilized by entrapment in an insolubilized gelatine gel have been investigated with regard to their pattern of growth and respiratory activity. Mass-transfer resistance offered by the matrix and growth of the entrapped cells determine a gradient of nutrients throughout the gel which is responsible for both a lower specific growth rate of immobilized cells with respect to that of free ones, and a heterogeneous biomass distribution, which progressively increased cellular density from the inside to the outside of the matrix. The spatial organization of the growing cells leads to the formation of a biofilm perfectly adherent to the surface of the matrix. Measurements of the oxygen-uptake rate of the immobilized cells, after having been released from the matrix by tripsin digestion, and confocal microscopy of cells stained with Rhodamine 123 demonstrate the occurrence of a gradient of respiratory activity throughout the immobilized culture.