Publisher Summary This chapter discusses immobilized living cells, their advantages, and their applications in industry. Over the past two decades, there have been rapid developments in the use of enzymes as catalysts for industrial, analytical, and medical purposes and a new field of research called enzyme technology. Current and industrial applications of continuous single-enzyme reactions are carried out using immobilized microbial cells. Immobilized living cells should be preferred to immobilized enzymes for degradative and synthetic reactions in industry; another major advantage of immobilized cells is that the operational stability of the immobilized living cells may often be greatly enhanced by the regeneration of the enzyme activities of the immobilized cells. The use of immobilized cells enables greater control throughout the reaction. The applications of immobilized living cells are not limited to the production of chemical fermentation products but have been extended to the production of viral particles or synchronous cells, the chromatographic separation of special cells, the culturing of animal tissue, and, more recently, the immobilization and use of plant cells in the production of alkaloids.

Immobilized Living Cells and Their Applications

Methods of cell immobilization roughly parallel those of enzyme immobilization and can best be classified by the nature of the mode of attachment, that is, as mechanical, chemical or ionic. In mechanical immobilization, the cells are localized by means of physical barriers. In chemical immobilization, covalent bonds are formed among cells or to a solid phase. In ionic immobilization, electrostatic, van der Waal’s or London forces of attraction are present. Cells can also attach themselves to solid supports in the course of natural growth, using a combination of these means. This classification is obviously not clear-cut but does serve the purpose of organizing the diverse methods of immobilization available. In Table 2.1, examples of cell immobilization are classified by mode of attachment.

Methods of Cell Immobilization

Three basic types of immobilization (i.e. without carrier, entrapment and immobilization on the carrier surface) of microbial cells, nonmicrobial cell populations and subcellular organelles are reviewed. These are further developed into a number of combined and less frequently used techniques of immobilization and application of cell biocatalysts for industrial biotransformations in pharmacy, food industry and agriculture, including novel approached and some unpublished authors’ results.

Immobilized Cells

Yeasts cells (Saccharomyces cerevisiae) were immobilized by occlusion in pectin gel, no significant changes in their biological activity being observed. The ethanol production rate was found to be negatively affected by the diameter of the beads when the cell concentration in them was high. The fermentative activity was only slightly modified by pectin concentration. Cells maintained their growth capacity and the beads could be reutilized several times in succesive batch fermentations. After freeze-drying and storage at room temperature the beads retained both their morphological and mechanical characteristics as well as 93% of their initial fermentative activity.

Production of ethanol by yeasts immobilized in pectin

Whole cells of a killer strain of Saccharomyces cerevisiae have been covalently linked to the modified hydroxyalkyl methacrylate gel Separon H-1000 E. The occurence of cell division and the killer phenomenon were observed when immobilized cells were incubated in nutrient medium.

Immobilization of yeast cells with retention of cell division and extracellular production of macromolecules

The potential of hydroxyalkyl methacrylate gel as a support for yeast cell immobilization by covalent attachment was investigated with respect to the length of spacer used and the manner of its activation. Saccharomyces paradoxus cells were immobilized successfully onto glutaraldehyde activated glycyl-, β-alanyl-and e-aminocaproyl-derivatives of the above mentioned gel modified with hexamethylenediamine. Results suggest that covalent attachment via spacer is strongly influenced by cell surface characteristics.

J. Čoupek

Papers

Immobilization of yeast cells onto hydroxyalkyl methacrylate gels modified by spacers of different lengths