APPLICATION OF MEMBRANE TUBING AERATION AND PERFLUOROCARBON TO IMPROVE OXYGEN DELIVERY TO HAIRY ROOT CULTURES

Growth and atropine production by Atropa belladonna hairy roots were s tudied in bioreactor cultures using porous polypropylene membrane tubi ng as a supplementary aeration device and with FC-43 perfluorocarbon e mulsion added to the medium. Both these treatments were applied to imp rove oxygen transfer to the roots. Membrane tubing aeration allowed di rect delivery of oxygen within the root clump, thus overcoming mass tr ansfer resistances associated with poor intraclump penetration of liqu id convective currents. Combined air sparging and membrane tubing aera tion in a gas-driven bioreactor supported biomass levels 32-65% higher than sparging only of air or oxygen-enriched air at the same total ga s flow rate. The optimal air flow rate ratio between the sparger and m embrane tubing giving the maximum final biomass concentration was 0.2: 0.4 L min(-1). Intraclump dissolved oxygen tensions at high biomass de nsities were generally greater using air delivered by combined sparger -membrane tubing aeration than with sparging only of air or oxygen-enr iched air. Specific atropine levels were not significantly affected by membrane tubing aeration. Indicators of anaerobic metabolism, such as lactic acid, ethanol, and ADH activity levels, were not significantly different in sparged and membrane-aerated systems; A. belladonna hair y roots also did not produce aerenchyma in response to oxygen limitati ons. Addition of perfluorocarbon emulsion to Murashige and Skoog mediu m in sparged stirred tank bioreactors did not improve growth, even whe n the emulsion was continuously recycled for re-aeration in an externa l vessel. Perfluorocarbons are associated with enhancement of gas-liqu id oxygen transfer, so their ineffectiveness in this work most likely reflects the dominance of liquid-solid transfer resistances in hairy r oot cultures. The results of this investigation highlight the importan ce of developing new approaches for site-directed aeration of hairy ro ot cultures, targeting oxygen delivery into the zones of highest root density.