CHARACTERIZATION OF FLUID-FLOW RESISTANCE IN ROOT CULTURES WITH A CONVECTIVE FLOW TUBULAR BIOREACTOR

Agrobacterium transformed root cultures of Hyoscyamus muticus were gro wn in a recirculating 2 L tubular bioreactor system. Performance of th is convective flow reactor (CFR) was compared to a bubble column (BC) reactor of the same geometry: replicated CFR experiments produced an a verage tissue concentration of 556 +/- 4 grams fresh weight per liter in 30 d whereas the bubble column produced only 328 +/- 5 grams per li ter corresponding to 25.3 +/- 0.0 and 14.3 +/- 0.5 grams dry weight pe r liter, respectively. Because media nutrient levels were maintained s ufficiently high to saturate growth rate, the improved performance of the CFR is attributed to enhanced convective mass transfer. The pressu re drops observed for flow through roots grown within the reactors wer e more than an order of magnitude higher than previously obtained by p lacing roots grown in shake culture into defined geometries. The exper imentally observed flow resistance was much higher than would be predi cted from correlations using the root diameter as the characteristic d iameter for flow resistance. Several lines of evidence suggest that ro ot hairs are a substantial contributor to the observed high flow resis tance in these transformed root cultures. Pressure drop increased nonl inearly with velocity which could not be adequately described by a mod ified form of the Ergun equation. Kyan et at's (1970) equation, althou gh predicting such curvature, relies almost exclusively on an empirica l packing deflection term to describe the hydrodynamic behavior. Impli cations of these results to the design of submerged reactor systems fo r root culture are discussed. (C) 1998 John Wiley & Sons, Inc.