BIOREACTORS FOR SURFACE-IMMOBILIZED CELLS

Surface immobilization of plant cells avoids the problem of hydrodynam ic or shear stress, which tends to be characteristic of suspended cell s cultured in typical, mechanically agitated bioreactor systems. Surfa ce immobilization also promotes the natural tendency for plant cells t o aggregate, which may improve the synthesis and accumulation of secon dary metabolites. In addition, exchange of medium is made simple in su rface-immobilized systems, and extracellular secondary products are ea sily recovered on a continuous basis. However, problems related to reg ulation of the thickness of the immobilized cell layer, maintenance of the biomass in a productive condition, and vacuolar retention of seco ndary products have yet to be resolved satisfactorily. This review foc usses on two surface-immobilization technologies, differing primarily in the nature and the configuration of the inert support. Prototypes o f these designs have been applied to a variety of plant cell systems a t bioreactor volumes up to 20 litres. Results obtained with several al ternative technologies are also summarized.