Effects of immobilization on growth, fermentation properties, and macromolecular composition of Saccharomyces cerevisiae attached to gelatin

The kinetic properties of Saccharomyces cerevisiae immobilized on crosslinked gelatin were found to be substantially different from those of the suspended yeast. Batch fermentation experiments conducted in a gradientless reaction system allowed comparison of immobilized cell and suspended cell performance. The specific rate of ethanol production by the immobilized cells was 40-50% greater than for the suspended yeast. The immobilized cells consumed glucose twice as fast as the suspended cells, but their specific growth rate was reduced by 45%. Yields of biomass from the immobilized cell population were lower at one-third the value for the suspended cells. Cellular composition was also affected by mobilization. Measurements of intracellular poly-saccharide levels showed that the immobilized yeast stored larger quantities of reserve carbohydrates and contained more structural polysaccharide than did suspended cells. Flow cytometry was used to obtain DNA, RNA, and protein frequency functions for immobilized and suspended cell populations. These data showed that the immobilized cells have higher ploidy than cells in suspension. The observed changes in immobilized cell metabolism and composition may have arisen from disturbance to the yeast cell cycle by cell attachment, causing alterations in the normal pattern of yeast bud development, DNA replication, and synthesis of cell wall components.