Chapter 17 - Use of Immobilized Cell Systems to Prepare Fine Chemicals

Abstract

This chapter discusses various applications of immobilized cell systems for preparation of fine chemicals. Microbial enzymes are classified into two forms—extracellular enzyme and intracellular enzyme. If whole microbial cells can be immobilized directly without extracting enzyme, the immobilized cells can be used as a solid catalyst. In such immobilized microbial cells, the procedure for extraction of enzyme can be omitted, and loss of enzyme activity is expected to be kept to a minimum. In addition, if the microbial cells having multienzyme systems are immobilized and can be used as a solid catalyst, the possibility exists that the fermentative methods involving multienzyme reactions may be replaced by the continuous enzyme reaction using immobilized cells. The methods for immobilization of microbial cells can be classified into three categories analogous to the immobilization of enzymes, that is, carrier-binding, cross-linking, and entrapping methods. Continuous enzyme processing by the immobilized microbial cells is advantageous in the following cases—(1) when the enzymes are intracellular, (2) when the enzymes extracted from microbial cells are unstable, (3) when the enzymes are unstable during and after immobilization, (4) when the microorganism contains no other enzymes that catalyze interfering side reactions or when those interfering enzymes can be readily inactivated or removed, and (5) when the substrates and products are not high molecular compounds. For the unit production of a desired compound, the volume of fermentation broth is much smaller in the case of the continuous method using immobilized cells than in the case of conventional batch fermentative methods.