K. Kanokwaree et Pm. Doran, APPLICATION OF MEMBRANE TUBING AERATION AND PERFLUOROCARBON TO IMPROVE OXYGEN DELIVERY TO HAIRY ROOT CULTURES, Biotechnology progress, 14(3), 1998, pp. 479-486
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.