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

Immobilized recombinant cells of the flocculent yeast Saccharomyces diastat icus carrying an expression plasmid for a fused enzyme between rat cytochro me P4501A1 and yeast NADPH-cytochrome P450 reductase were used in the bioco nversion reaction from acetanilide (AA) to p-acetaminophene (p-AAP). Immobi lization of the strain within reticulated polyurethane foam biomass support particles (BSPs) was effected passively in situ in a fluidized-bed bioreac tor using 'draw and fill' operation. In repeated batch reactions both the f inal product concentration and the production rate were notably improved co mpared with the results obtained using freely suspended cells without BSPs. Cells immobilized within BSPs exhibited a significantly high level of expr ession of the fused enzyme. In addition, a high proportion of plasmid-carry ing cells was maintained among the immobilized cells, in contrast to a much lower proportion among freely suspended cells released from the BSPs. Sinc e the bioreactor became packed with highly expressing cells immobilized wit hin BSPs as a consequence of spontaneous screening, it was termed an 'intel ligent' bioreactor, and is believed to offer significant potential for the further development of efficient production processes. (C) 1998 Elsevier Sc ience S.A. All rights reserved.