Bioconversion using immobilized recombinant flocculent yeast cells carrying a fused enzyme gene in an 'intelligent' bioreactor

Immobilized recombinant cells of the flocculent yeast Saccharomyces diastaticus carrying an expression plasmid for a fused enzyme between rat cytochrome P4501A1 and yeast NADPH-cytochrome P450 reductase were used in the bioconversion reaction from acetanilide (AA) to p-acetaminophene (p-AAP). Immobilization of the strain within reticulated polyurethane foam biomass support particles (BSPs) was effected passively in situ in a fluidized-bed bioreactor using 'draw and fill' operation. In repeated batch reactions both the final product concentration and the production rate were notably improved compared with the results obtained using freely suspended cells without BSPs. Cells immobilized within BSPs exhibited a significantly high level of expression of the fused enzyme. In addition, a high proportion of plasmid-carrying cells was maintained among the immobilized cells, in contrast to a much lower proportion among freely suspended cells released from the BSPs. Since the bioreactor became packed with highly expressing cells immobilized within BSPs as a consequence of spontaneous screening, it was termed an 'intelligent' bioreactor, and is believed to offer significant potential for the further development of efficient production processes. (C) 1998 Elsevier Science S.A. All rights reserved.