PLANT-CELL BIOREACTOR FOR THE PRODUCTION OF PROTOBERBERINE ALKALOIDS FROM IMMOBILIZED THALICTRUM-RUGOSUM CULTURES

Cultured Thalictrum rugosum cells were immobilized using a glass fiber substratum previously shown to provide optimum immobilization efficiency based on spontaneous adhesion mechanisms. When cultivated in shake flasks, immobilized cells exhibited decreased growth and protoberberine alkaloid production rates in comparison to freely suspended cells. Since alkaloid production is growth associated in T. rugosum, the decreased specific production rate was a function of the slower growth rate. Cells immobilized on glass fiber mats appear to be amenable for extended culture periods. Maximum biomass and protoberberine alkaloid levels were maintained for at least 14 days in immobilized cultures. In contrast, fresh weight, dry weight, and total alkaloid content decreased in suspension cultures following the linear growth phase. Glass fiber mats were incorporated into a 4.5-L plant cell bioreactor as horizontal disks supported on a central rod. Mixing in the reactor was provided by the combined actions of a magnetic impeller and a cylindrical sparging column. The entire inoculum biomass of T. rugosum, introduced as a suspension, was spontaneously immobilized within 8 h. During linear phase, the growth rate of bioreactor-cultivated immobilized cells (mu = 0.06 day-1) was 50% that of immobilized cells cultivated in shake flasks (mu = 0.12 day-1). Percentage of cell viability in both systems was determined to be similar. The growing biomass in the bioreactor was completely retained by the glass fiber substratum during a 28-day culture period. The increase in specific production of protoberberine alkaloids was initially similar in bioreactor- and shake-flask-cultivated immobilized cells. However, the maximum specific production of bioreactor-grown cultures was lower. The scaleup potential of an immobilization strategy based on the spontaneous adhesion of cultured plant cells to glass fibers is demonstrated.