Coimmobilization of cells and/or enzymes is performed for three main reasons: first, to enable cells to use other, nonmetabolizable substrates than the natural ones of the corresponding strain (1 ,2 ); second, to enlarge the product spectrum by utilization of the catalytic capabilities of the coimmobilized enzyme or cell (3 ); and third, to simplify conventional two- or more step processes. A simplification of multiple-step processes can also be obtained by using recombinant strains containing the genes of the needed additional enzymes (4 ).
